Why Anthropogenic Global Warming

Why Anthropogenic Global Warming

Posted by Ed Leaver 10 October 2012. Last update 5 May 2013.

We know the earth is warming because we can measure it. We know mankind is causing the warming because we can measure his fingerprint. National scientific organizations confirm the reality of anthropogenic global warming and human-induced climate change. We excerpt the general policy statements issued by the American Geophysical Union and the American Institute of Physics, and provide links to comprehensive resources. Our aim here is brevity: we briefly discuss three specific climate change signatures that together provide irrefutable evidence of man’s involvement in global warming, reference commentary on the 2009 Climate Research Unit emails controversy, and cite the skeptically independent Berkeley Earth Surface Temperature study that subsequently confirmed results of previous ”main-stream” studies of global warming. References are provided to primary and secondary sources.

Once upon a time a long time ago in a land not far removed from CU Boulder’s Geology Department, I perused in idyllic innocence a course in Physical Geology. And it so happened our instructor chose a fine spring day to spring upon us the concept of Continental Drift, which as concepts go, had been around since the late 16th century but – Alfred Wegener’s heroic efforts and a plethora of supporting geological evidence notwithstanding – had not gained widespread acceptance for want of physical mechanism to explain its widespread wide-spreading.

Until the mid 1960’s when detailed magnetic mappings forced even the most calcified static-earther to reconsider the errors of his ways. Still, the whole idea of the entire Indian Subcontinent being untimely ripped from the arms of Mother Africa and driven into South Asia with aught but the Himalaya to show for it, was rediculous on its face: ”You don’t actually believe that?” one wag asked facetiously.

Prof. Larson’s cheerful rejoinder is the title aphorism for today’s article.

1 Overview and Summary

Many will be satisfied with the professional society policy statements. These are provided first, followed by a list of specific sources providing progressively more scientific detail. Of particular note are Spencer Weart’s The Discovery of Global Warming history and science site at the American Institute of Physics, RealClimate: Climate science from climate scientists with its comprehensive resources, and the Berkeley Earth Surface Temperature project noted for directly addressing issues raised by climate skeptics in the wake of the ”Climategate” controversy. Subsequent sections introduce specific aspects of climate study, and illustrate specific indicator fingerprints of man’s contribution (and cause) of Earth’s warming climate.

The first is a section on Earth’s Atmosphere, how earth’s surface temperature is measured, and how we know anthropogenic greenhouse gases – notably carbon dioxide – are responsible for warming. The fingerprint section looks, as a specific example, at the simultaneous warming of the troposphere and cooling of the stratosphere. This is a differential measurement that largely rejects common mode effects such as varying albedo and solar irradiance.

A Matter of Heat introduces some concepts of radiative transfer and radiative forcing. The section on Anthropogenic Forcing links several papers discussing the predominant role of greenhouse gases in Earth’s current energy imbalance. References are provided showing just how small the forcing from solar variations is relative to human greenhouse gas contributions. Set in the context of the Maunder Sunspot Minimum during the 17th century Little Ice Age, these show a miraculously cooler sun will not free us from our dilemma. Nor will the relatively feeble irradiance forcings from orbital perturbations (Milankovitch Cycles).

As most of earth’s surface heat energy resides in her oceans, we provide a few references that describe how ocean temperatures are measured, and link the results obtained from the modern Argo free-floating system of sounding buoys with those of the pioneering Challenger survey one hundred forty years ago. We introduce Attribution Analysis and cite model studies that link ocean warming patterns to the distribution of anthropogenic greenhouse gases. Models that included only solar variations could not reproduce the fingerprint observed in the Challenger/Argo record.

Most of today’s climate skepticism was generated by the so-called ”Climategate” disinformation campaign running up to the 2009 Copenhagen Climate Conference. We provide a few references to the ensuing witch-hunt before moving on to one beneficial result: the independent review of global warming data and conclusions by Prof. Richard Muller’s Berkeley Earth Surface Temperature project, which found remarkably close agreement between their analysis and those of the major climate research groups.

Mankind’s influence on climate is not limited to anthropogenic greenhouse gases. We conclude with a short section on contributions from soot.

Contents

List of Figures

1.1 Statement of the American Geophysical Union

From the American Geophysical Union’s 2012 Position Statement (pdf):

”The scientific evidence for human activity impacting climate is strong and widely accepted within the scientific community. Given the significant current and potential impacts of climate change, scientists have a unique responsibility to educate the public and public policy makers on this topic.

”The Earth’s climate is now clearly out of balance and is warming. Many components of the climate system – including the temperatures of the atmosphere, land and ocean, the extent of sea ice and mountain glaciers, the sea level, the distribution of precipitation, and the length of seasons – are now changing at rates and in patterns that are not natural and are best explained by the increased atmospheric abundances of greenhouse gases and aerosols generated by human activity during the 20th century. Global average surface temperatures increased on average by about 0.6C over the period 1956 – 2006. As of 2006, eleven of the previous twelve years were warmer than any others since 1850. The observed rapid retreat of Arctic sea ice is expected to continue and lead to the disappearance of summertime ice within this century...”

Continued at AGU Position Statement, Human Impacts on Climate (html).

1.2 Statement of the American Physical Society

From the American Physical Society’s National Policy Statement:

07.1 CLIMATE CHANGE (Adopted by Council on November 18, 2007)

”Emissions of greenhouse gases from human activities are changing the atmosphere in ways that affect the Earth’s climate. Greenhouse gases include carbon dioxide as well as methane, nitrous oxide and other gases. They are emitted from fossil fuel combustion and a range of industrial and agricultural processes.

”The evidence is incontrovertible: Global warming is occurring.

”If no mitigating actions are taken, significant disruptions in the Earths physical and ecological systems, social systems, security and human health are likely to occur. We must reduce emissions of greenhouse gases beginning now.

”Because the complexity of the climate makes accurate prediction difficult, the APS urges an enhanced effort to understand the effects of human activity on the Earths climate, and to provide the technological options for meeting the climate challenge in the near and longer terms. The APS also urges governments, universities, national laboratories and its membership to support policies and actions that will reduce the emission of greenhouse gases. ”

From the 2010 Commentary:

”The evidence for global temperature rise over the last century is compelling. However, the word ”incontrovertible” in the first sentence of the second paragraph of the 2007 APS statement is rarely used in science because by its very nature science questions prevailing ideas. The observational data indicate a global surface warming of 0.74 C (+/- 0.18 C) since the late 19th century.”

Continued at National Policy Statement 07.1 Climate Change.

 

2 Specific Resources

 

2.1 NOAA

National Oceanic and Atmospheric Administration.

NOAA: National Climate Data Center.
NOAA: Global Warming Frequently Asked Questions. (General Audience)
NOAA: The State of the Climate 2009 Highlights. (General Audience)
NOAA: How Do We Know The World Has Warmed (pdf). (General Audience)
NOAA: The State of the Climate 2009. (Scientific)
NOAA: Past Decade Warmest on Record According to Scientists in 48 Countries:

The 2009 State of the Climate report draws on data for 10 key climate indicators that all point to the same finding: the scientific evidence that our world is warming is unmistakable. More than 300 scientists from 160 research groups in 48 countries contributed to the report, which confirms that the past decade was the warmest on record and that the Earth has been growing warmer over the last 50 years...


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Figure 1: Ten Climatic Indicators
Source: The State of the Climate 2009.

”Despite the variability caused by short-term changes, the analysis conducted for this report illustrates why we are so confident the world is warming. When we look at air temperature and other indicators of climate, we see highs and lows in the data from year to year because of natural variability. Understanding climate change requires looking at the longer-term record. When we follow decade-to-decade trends using multiple data sets and independent analyses from around the world, we see clear and unmistakable signs of a warming world.” -Peter Stott, head of Climate Monitoring and Attribution, UK Met Office Hadley Centre.

NOAA: The State of the Climate 2011 report is not just a rehash of 2009, and has different organization.

 

2.2 American Institute of Physics

The Discovery of Global Warming: A hypertext history of how scientists came to (partly) understand what people are doing to cause climate change. (December 2011, periodically updated.) For those interested in historical and geophysical details, Spencer R. Weart (former Director of the Center for History of Physics of the American Institute of Physics) has intended this informative little project to be a one-stop shop for climate change at several levels. Recommended.

 

2.3 Intergovernmental Panel on Climate Change

”The Intergovernmental Panel on Climate Change (IPCC) is a scientific intergovernmental body, set up at the request of member governments. It was first established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), and later endorsed by the United Nations General Assembly through Resolution 43/53. Its mission is to provide comprehensive scientific assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and socio-economic consequences, and possible options for adapting to these consequences or mitigating the effects...

”The IPCC does not carry out its own original research, nor does it do the work of monitoring climate or related phenomena itself... (it) bases its assessments mainly on peer reviewed and published scientific literature.”

IPCC: Home Page.
IPCC: Publications and Data Reports.
IPCC: Assessment Reports.

 

2.4 Center for Climate and Energy Solutions

”Launched in November 2011, C2ES is the successor to the Pew Center on Global Climate Change. C2ES believes that ensuring safe, reliable, affordable energy for all – while protecting the global climate – is a paramount challenge of the 21st century.” This is actually a pretty large and comprehensive site; not lending itself to sound-bite synopsis. Here are a select-pew links:

C2ES: Home Page.
C2ES: Science Impacts.
C2ES: Global Warming Facts and Figures
C2ES: The Candidates on Climate and Energy: A Guide to the Key Policy Positions of President Obama and Governor Romney

 

2.5 National Academy of Science

NAS: Home Page
NAS: Publications
NAS: America’s Climate Choices Final Report. 2011. Comprehensive Policy Statement and Recommendations.
NAS: What You Need to Know About Energy. 2008. Informative basic overview.
SkS: Video on Climate Change Lines of Evidence by the National Academy of Science.

 

2.6 RealClimate

RealClimate: Climate science from climate scientists maintains another, more comprehensive one-stop directory of links to climate change information. It includes Spencer Weart’s The Discovery of Global Warming site referenced above, as well as links to information provided by NCAR, NASA, National Academy of Science, SUNY Suffolk, UK Government, IPCC, New Scientist, UK Met Office, and more. (Much more. Global Circulation and Radiative Transport Codes. Data. Visualization. Sigh.) Highly recommended.

 

2.7 SkepticalScience

Skeptical Science gets skeptical about global warming skepticism. Explaining climate change science & rebutting global warming misinformation:

”Scientific skepticism is healthy. Scientists should always challenge themselves to improve their understanding. Yet this isn’t what happens with climate change denial. Skeptics vigorously criticise any evidence that supports man-made global warming and yet embrace any argument, op-ed, blog or study that purports to refute global warming. This website gets skeptical about global warming skepticism. Do their arguments have any scientific basis? What does the peer reviewed scientific literature say?”

Edited and largely written by climate and journalism professionals, a comprehensive resource for up-to-date information on misinformation. Plenty of good climate science, too. Recommended.

ailyClimate

2.8 The Daily Climate

The Daily Climate is, of course, weather. It is also rather more variable and eclectic in the variety of its topics than some other sites.

2.9 Global Warming, Man or Myth?

Global Warming, Man or Myth?. Scott A. Mandia is Professor of Earth and Space Sciences and Assistant Chair of the Physical Sciences Department at Suffolk County Community College, Long Island, New York, USA. From his introduction:

”Climate change has been extensively researched and the overwhelming majority of climate scientists agree that the observed modern day global warming is unprecedented and is very likely caused by humans. Although there is strong consensus among climate experts, many in the general public still think that these scientists are unsure about climate change and the role that humans have played in modern day global warming. The real science is primarily represented in peer-reviewed science journals but there are some good sources listed in Suggested Reading. Science journals are typically not accessible to the general public and are also highly mathematical. Global warming misinformation is primarily published on Web pages, blogs, television shows, radio, and other forms of mass media, all of which are much more accessible to the general public than scientific journals. The result is that the misinformation is reaching more people than the real science. This Website tries to bridge the knowledge gap by summarizing some of the key research that has led scientists to their overwhelming consensus while also addressing some of the unfounded claims by climate change denialists.”

 

2.10 Berkeley Earth

The Berkeley Earth Surface Temperature Study (BEST) was initiated by Physics Prof. Richard Muller with the aim of independently verifying the climate research inaccuracies alleged by skeptics following the 2009 theft and selective dissemination of emails between East Anglica’s Climatic Research Unit Director Phil Jones and other members of the climate community. The BEST study group consisted of physicists and mathematicians not otherwise associated with climate research. Their results confirmed that the accepted ”main stream” temperature data was valid and

”...the average temperature of the Earth’s land has risen by 1.5C over the past 250 years. The good match between the new temperature record and historical carbon dioxide records suggests that the most straightforward explanation for this warming is human greenhouse gas emissions.”

In a 30 July 2012 New York Times column, Prof. Muller wrote:

”Four of our papers have undergone extensive scrutiny by the scientific community, and the newest, a paper with the analysis of the human component, is now posted, along with the data and computer programs used. Such transparency is the heart of the scientific method; if you find our conclusions implausible, tell us of any errors of data or analysis.”

”What about the future? As carbon dioxide emissions increase, the temperature should continue to rise. I expect the rate of warming to proceed at a steady pace, about one and a half degrees over land in the next 50 years, less if the oceans are included. But if China continues its rapid economic growth (it has averaged 10 percent per year over the last 20 years) and its vast use of coal (it typically adds one new gigawatt per month), then that same warming could take place in less than 20 years.”

Also see Berkeley Earth below.

 

2.11 Other

Other comprehensive references as I find them:

 

3 Earth’s Atmosphere

Earth’s atmospheric temperature and pressure both smoothly vary with altitude. Pressure decreases, but temperature both decreases in some regions and increases in others. Atmospheric scientists divide the atmosphere into four such regions – Troposphere, Stratosphere, Mesosphere, and Thermosphere – separated by boundaries where temperature stops decreasing with with altitude and begins increasing (tropopause and mesopause), or alternatively stops increasing with altitude and and begins decreasing again (stratopause). A fifth region, the Exosphere, is the very top-most region of the atmosphere whose lower boundary is loosely defined as that altitude above which molecular collisions are rare and upward-moving gas molecules follow essentially ballistic trajectories, being brought back to earth only by the attraction of earth’s gravity. Extending roughly half the distance to the moon, the exosphere is the transitional zone between Earth’s atmosphere and interplanetary space. These atmospheric layers are illustrated in Fig. 2. Radiation penetration depths and layer properties are respectively diagrammed in Figs. 3 and 4.


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Figure 2: Endeavour Silhouette
Space Shuttle Endeavour appears to straddle the stratosphere and mesosphere in this photo. The orange layer is the Troposphere, where all of the weather and clouds which we typically watch and experience are generated and contained. This orange layer gives way to the whitish Stratosphere and then into the Mesosphere.
Source: spaceflight.nasa.gov/gallery/images/shuttle/sts-130/html/iss022e062672.html.


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Figure 3: Depths of Solar Radiation Penetration into the Atmosphere
Source: www.theozonehole.com/atmosphere.htm.


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Figure 4: Atmospheric Layers
The atmosphere is divided into five layers. It is thickest near the surface and thins out with height until it eventually merges with space. The lowest three layers are homogeneous, all gaseous components are equally mixed, save for water which precipitates from the troposphere. The thermosphere and exosphere are extremely rarified, with density too low to support mixing or sound. Here atmospheric gases separate by molecular weight; there is very little carbon dioxide above the mesosphere.
  1. The troposphere is the first layer above the surface and contains half of the Earth’s atmosphere and nearly all atmospheric water vapor. Weather occurs in this layer. The troposphere is largely opaque to infrared radiation; nearly all solar energy that converts to heat at the surface is absorbed in the lower troposphere and re-radiated as illustrated in Fig. 6.1 As it rises, this warm lower air cools by quasi-adiabatic expansion. Cooling is further enhanced by upward thermal radiation by water vapor from the upper troposphere.2 The result is the familiar decrease in temperature with tropospheric altitude.
  2. Ultraviolet-C radiation is almost entirely absorbed (blocked) in the upper stratosphere by ozone and oxygen (which UV converts to ozone). This absorption of UV energy causes an increase in temperature with stratospheric altitude. The resulting temperature inversion makes the stratosphere very stable, and smooth flying for jet aircraft.
  3. The air is thin enough in the mesosphere that carbon dioxide can more readily radiate heat energy directly into space with increasing altitude. This allows radiative cooling to dominate over UV absorption, causing the mesophere to once again grow colder with altitude.
  4. The thermosphere is thin enough that molecular collisions become too infrequent to support homogeneous mixing; lighter oxygen and nitrogen begin to predominate over CO2. Their ionization by extreme ultraviolet radiation marks the beginning of the ionosphere, the layer with auroras that also reflects many radio waves. Ionization makes the gas extremely hot, but the gas is too rarefied to transfer appreciable heat to spacecraft.
  5. The atmosphere merges into space in the extremely thin exosphere. This is the upper limit of our atmosphere.

Source: TheOzoneHole.com.


 

3.1 Taking earth’s temperature

As with most geophysical measurements, taking an accurate reading of earth’s mean global surface air temperature is a bit harder than it looks. For example, one must define what one means by ”surface air”, as sunlight-warmed ground can heat the air in its closest proximity by direct convection. Sources of information:

”Widespread, reliable instrumental records are available only for the last 150 years or so. To study how climatic conditions varied prior to the time of the Industrial Revolution, paleoclimatologists rely on proxy evidence such as tree rings, corals, ocean and lake sediments, cave deposits, fossils, ice cores, borehole temperatures, glacier length records, and documentary evidence. For example, records of Alpine glacier length, some of which are derived from paintings and other documentary evidence, have been used to reconstruct the time series of surface temperature variations in south-central Europe for the last several centuries. Until recently, most reconstructions of climate variations over the last few thousand years focused on specific locations or regions. Starting in the 1990s, researchers began to combine proxy records from different geographic regions, often using a variety of different types of records, in an effort to document large-scale climate changes over the last few millennia. Most of these large-scale surface temperature reconstructions have focused on hemispheric average or global average surface temperatures over the last few hundred to few thousand years... ” (ibid.)

An overview of temperature determination with periodic updates is at GISS Surface Temperature Analysis (GISTEMP). A cited scientific reference explaining the NASA/GISS approach is Hansen et al. (2010) Global Surface Temperature Change (pdf).

 

3.2 Taking man’s fingerprint

Beginning at the turn of the last century with the work of Swedish chemist Svante Arrhenius, geoscientists eventually obtained two seminal results:

To repeat: (1) Increasing carbon dioxide and water vapor at the earth’s surface results in an expanded and warmer lower atmosphere (troposphere) and cooler stratosphere, as opposed to (2) increasing solar radiation which results in warming at all levels.8,9

Of course, atmospheric heating is a bit more complicated than this qualitatitive one dimensional radiation transport argument. Meaningful quantitative results require coupling radiative transport to at least a simple atmospheric circulation model to account for convection and water vapor transport.10

Accurate stratospheric temperatures have been available the past 50 years, and clearly display the tell-tale tropospheric heating / stratospheric cooling signature expected of low-altitude heating from greenhouse gases. This is illustrated by the following figure from The State of the Climate 2009:


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Figure 5: Eleven key global warming indicators from State of the Climate 2009.
Note inverted troposphere/stratosphere temperature trend in the right hand column, a distinctive fingerprint of increasing greenhouse gases in the troposphere.

Of further interest from Wikipedia’s Instrumental temperature record:

”The preliminary results of an assessment carried out by the Berkeley Earth Surface Temperature group and made public in October 2011, found that over the past 50 years the land surface warmed by (about 0.9 C), and their results mirrors those obtained from earlier studies carried out by the NOAA, the Hadley Centre, and NASA’s GISS. The study addressed concerns raised by skeptics including urban heat island effect, ‘poor’ station quality, and the ‘issue of data selection bias’ and found that these effects did not bias the results obtained from these earlier studies.”

See Berkeley Earth below. As compelling as they may be, atmospheric temperature profiles and land surface temperatures are not quite the entire story: some mention might also be made of near-surface sea temperature and heat content. Man’s fingerprints may be found on those as well.

 

4 A Matter of Heat

Early 19th century natural scentists – particularly those in Europe – were fascinated with field observations that suggested much greater glacial extent in the perhaps not-too-distant geological past, and a coincident cooler climate. They were also beginning to get a handle on heat. We introduce the solar constant as a measure both of the solar radiation incident upon earth, and the power the earth must reflect or radiate to maintain constant temperature. This allows us to define radiative forcing as a measure of the imbalance in atmospheric energy flow introduced by increasing (or decreasing) atmospheric greenhouse gases, atmospheric aerosols, or surface reflectivity (albedo). We then look at man’s contribution to Earth’s present heat imbalance. In subsequent subsections we look at studies of the effect of possible variations in the solar constant as exemplified during the Little Ice Age, and the effects variations in Earth’s orbital parameters had (or may have had) on climate during the Pleistocene Ice Age. We see these solar and orbital effects are dwarfed by modern anthropogenic greenhouse forcing.

The Solar Constant (total solar irradiance, total solar insolation) is defined as the quantity of solar energy at normal incidence outside the atmosphere at the mean sun-earth distance. The luminousity of the Sun, its total energy output, is L 3.86 × 1026 Watts. Earth’s mean distance from the sun, 1 AU (astronomical unit) is r 1.5 × 1011meters. The power per unit area at 1 AU is the solar constant: L(4πr2) 1366Wm2. (DJ Jeffery Lecture 8: The Sun.)

”Solar output is nearly, but not quite, constant. It includes all types of solar radiation, not just visible light. Variations in total solar irradiance were too small to detect with technology available before the satellite era. Total solar output is now measured to vary (over the last three 11-year sunspot cycles) by approximately 0.1%.11 The Earth receives a total amount of radiation determined by its circular cross section (πRE2), but as it rotates this energy is distributed across the entire surface area (4πRE2). Hence the average incoming solar radiation, taking into account the angle at which the rays strike and that at any one moment half the planet does not receive any solar radiation, is one-fourth the solar constant (approximately 340 Wm2). At any given moment, the amount of solar radiation received at a location on the Earth’s surface depends on the state of the atmosphere, the location’s latitude, and the time of day.”12

The Earth’s mean radius RE = 6,371km, and its surface area 5.1006 × 1014m2. 340 Watts is the average amount of power received by each square meter of the Earth’s surface. Ignoring the (relatively) small amount of energy contributed by cooling of the earth’s core,13 340 watts is also the amount of power each square meter must either reflect or radiate, on average, when the earth’s temperature is at equilibrium. About 48% of this (163 watts) is actually absorbed by the earth’s surface, the remainder is reflected or directly absorbed by the atmosphere as illustrated in Fig. 6:


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Figure 6:
On average, 340 watts per square meter of solar energy arrives at the top of the atmosphere. Earth returns an equal amount of energy back to space by reflecting some incoming light and by radiating heat (thermal infrared energy). Most solar energy is absorbed at the surface, while most heat is radiated back to space by the atmosphere. Earth’s average surface temperature is maintained by two large, opposing energy fluxes between the atmosphere and the ground (right) – the greenhouse effect. (NASA illustration by Robert Simmon, adapted from Trenberth et al. 2009, using CERES flux estimates provided by Norman Loeb.) Source: The Atmosphere’s Energy Budget.

4.1 Radiative Forcing

”Radiative Forcing” has several similar but not quite identical definitions. From Wikipedia:

”In simple terms, radiative forcing is ”...the rate of energy change per unit area of the globe as measured at the top of the atmosphere.”[4] In the context of climate change, the term ”forcing” is restricted to changes in the radiation balance of the surface-troposphere system imposed by external factors, with no changes in stratospheric dynamics, no surface and tropospheric feedbacks in operation (i.e., no secondary effects induced because of changes in tropospheric motions or its thermodynamic state), and no dynamically induced changes in the amount and distribution of atmospheric water (vapour, liquid, and solid forms).”

The IPCC uses the following specific definition:

”The ‘radiative forcing’ of the surface-troposphere system due to the perturbation in or the introduction of an agent (say, a change in greenhouse gas concentrations) is the change in net (down minus up) irradiance (solar plus long-wave; in Wm2) at the tropopause AFTER allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values.[2]”

This second, more restricted definition allows climate scientists to speak of the relative forcing contribution of water vapor independent of that of carbon dioxide, even though the actual amount of water vapor in the atmosphere depends strongly upon temperature, and is therefore sensitive to the amount of carbon dioxide. The tropopause is the boundary between the troposphere and stratosphere, the nominal elevation at which temperature stops decreasing with altitude in the turbulent troposphere, and begins its gradual increase with altitude in the calm stratosphere where heating is driven by oxygen and ozone absorption of ultraviolet radiation. See Troposphere, Stratosphere, and Idealized Greenhouse Model.

 

4.2 Anthropogenic Forcing

In Anthropogenic and natural warming inferred from changes in Earths energy balance,14 Markus Huber and Reto Knutti describe an extensive study comparing fifty years of observational geothermal and energy data with extensive modeling of natural and anthropogenic forcing factors to provide a natural/anthropogenic attribution estimate independent of spatial warming patterns and dependent only on known changes to Earth’s net energy balance and in radiative forcing. They found that ”since the mid-twentieth century, greenhouse gases contributed 0.85C of warming (5 - 95% uncertainty: 0.6 - 1.1C), about half of which was offset by the cooling effects of aerosols, with a total observed change in global temperature of about 0.56C.” Forcings modeled included CO2, Methane, N2O, Halocarbons and Montreal gases, Stratospheric ozone, tropospheric ozone, direct and indirect aerosols, black and organic carbon, stratospheric water vapour, volcanic ash, gases, and aerosols, and solar. Using the SRES A2 projected emissions scenario (considered most likely), the authors calculate ”the historic cumulative forcing would be doubled in the next 33 (28-38) years and tripled in 52 (45-60) years.”

Huber and Knutti estimate a net positive forcing of 0.54 (0.36-0.76)Wm2. See New approach to determining human impact on climate gives same answer for further commentary.

These results are corroborated in a contemporary research briefing by Hansen et al. Earth’s Energy Imbalance:

”Deployment of an international array of Argo floats, measuring ocean heat content to a depth of 2000 m, was completed during the past decade, allowing the best assessment so far of Earth’s energy imbalance. The observed planetary energy gain during the recent strong solar minimum reveals that the solar forcing of climate, although significant, is overwhelmed by a much larger net human-made climate forcing. The measured imbalance confirms that, if other climate forcings are fixed, atmospheric CO2 must be reduced to about 350 ppm or less to stop global warming. In our recently published paper (Hansen et al., 2011), we also show that climate forcing by human-made aerosols (fine particles in the air) is larger than usually assumed, implying an urgent need for accurate global aerosol measurements to help interpret continuing climate change...

”We used other measurements to estimate the energy going into the deeper ocean, into the continents, and into melting of ice worldwide in the period 2005-2010. We found a total Earth energy imbalance of + 0.58 ± 0.15Wm2...

The role of the Sun:

”The measured positive imbalance in 2005-2010 is particularly important because it occurred during the deepest solar minimum in the period of accurate solar monitoring (Fig. 7). If the Sun were the only climate forcing or the dominant climate forcing, then the planet would gain energy during the solar maxima, but lose energy during solar minima. The fact that Earth gained energy at a rate 0.58Wm2 during a deep prolonged solar minimum reveals that there is a strong positive forcing overwhelming the negative forcing by below-average solar irradiance. That result is not a surprise, given knowledge of other forcings, but it provides unequivocal refutation of assertions that the Sun is the dominant climate forcing...

To repeat: the Earth’s current net energy imbalance is 0.58 ± 0.15Wm2 positive, at the deepest solar minimum yet recorded.(Modern minimum; see Fig. 7 and ”Solar Variations” below.) The negative solar forcing due to the present (2011-2012) solar minimum is utterly overwhelmed by positive anthropogenic greenhouse gas forcing, even when all other negative forcings are considered. The Hansen group concludes ”(T)he Earth’s energy imbalance confirms an earlier estimate on other grounds that CO2 must be reduced to about 350 ppm or less to stabilize climate...”

Such CO2 reduction is, of course, simply not possible. The toothpaste is out of the tube.

 

4.3 Solar Variations and the Little Ice Age

The sun is not quite constant, and it has long been speculated the 600 year Little Ice Age commencing about 1300 A.D. may have been result of solar variation, as evidenced by the 17th century Maunder Sun-Spot Minimum.15 The possible degree of solar forcing during that period is quantified and compared with that of greenhouse gases by George Fuelner,16 who shows the TSI (total solar irradiance) at the Maunder Minimum differed from that of the 2008 minimum by less than 1Wm2 (negative), and possibly as little as 0 - 0.3 Wm2. Modern GHG forcing is about 3 Wm2, and aerosol cooling at about -1.5 Wm2, both of which are considerably larger than any possible solar forcings during the Little Ice Age and preceding Medieval Warm Period. Feulner concludes

Although Delaygue and Bard come to a reasonably agreeable 1Wm2 estimate from Be10 ice core data,17 Feulner’s conclusion that ”Solar activity was not the dominant driver for the Little Ice Age” is supported by a recent study suggesting vulcanism to be the trigger.18

The 2008 solar minimum was at about 1365.24 Wm219 Spencer Weart concludes Changing Sun, Changing Climate? with:

”Some of the scientists who reported evidence of past connections between solar and climate changes warned explicitly that their data did not show that the current global warming was natural – it only showed the extreme sensitivity of the climate system to small perturbations. Back in 1994 a U.S. National Academy of Sciences panel had estimated that if solar radiation were to weaken as much as it had during the 17th-century Maunder Minimum, the entire effect would be offset by another two decades of accumulation of greenhouse gases. A 2010 study reported that by the late 21st century a Maunder-Minimum solar effect would be offset with barely a single decade of emissions. As one expert explained, the Little Ice Age ”was a mere ’blip’ compared with expected future climatic change.”

Emphasis added. Additional Solar Variability references are collected at NOAA Paleoclimatology Climate Forcing Data.


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Figure 7:
Total solar irradiance (energy received from the Sun) as observed directly by satellites. Left scale is the energy passing through an area perpendicular to Sun-Earth line. Averaged over Earth’s surface the absorbed solar energy is 240Wm2. From the low to high point of a sunspot cycle, the change in ”radiative forcing” (roughly speaking, change in energy transferred to our planet) is 0.25Wm2, and is roughly equivalent to the interference in radiation passing through the atmosphere caused by 15 years of human emissions of carbon dioxide at the 2010 rate. Monthly surface temperature means are plotted in Figure 14 for the same time period. Image source: NASA-GISS.

 

4.4 Orbital Variations and Major Glaciations

Facination with Ice Ages and their possible cause was the original driver of the science of climatology. By the end of the twentieth century the idea that, given a suitable global distribution of land mass, glacial periods could be triggered by subtle interactions between orbit variations (Milankovitch Cycles) and carbon dioxide forcings, had gained wide acceptance and remains an area of active research.20 Here we discuss results of detailed modeling that show the great Pleistocene Glacial Periods (”ice ages”) cannnot recur during the current era of orbital variations and land mass distributions, at our present levels of CO2.

For an Ice Age to occur, continents must be distributed such that there is sufficient land near the poles to support glacial ice caps, and a continuous landlink between the polar regions to direct ocean currents to transfer heat between them. These requirements are met today by the locations of Greenland, Canada, northern Europe and Siberia in the north, Antarctica in the south, and the North-South American continental link between them. The last was completed with the raising of the Panama Isthmus and closing of the Central American Seaway about 5 million years ago.21 Estimated global temperatures during this modern epoch are shown in the right half of Fig. 8, CO2 in Fig. 9:


[Picture]


Figure 8:
”Earth as we know it” began with the closing of the Central American Seaway about 5 mybpe, and subsequent establishment of northern river drainages to the Arctic. Note abrupt onset of Antarctic glaciation with opening of the Drake Passage about 35 mybpe. Source: Temperature of Planet Earth.


[Picture]


Figure 9: Atmospheric C02 during the Pleistocene Ice Age.
Here increasing Carbon dioxide probably leads the temperature rise of Fig. 8 at the onset of Pleistocene interglacial warm periods by a short interval ( < 1ky), as has been shown for the most recent episode.22 This may be consistent with initial CO2 release from ocean or permafrost triggered by orbital variations, long-term stochastic feedback processes effecting during a period of delicately-balanced land distribution, ocean circulation, and CO2, or a combination of both. After initiation, subsequent warming would follow the usual CO2-temperature-water vapor positive feedback forcing, perhaps aided by increasing solar insolation. Image source: Timescale Matters: 800,000 years of CO2 (NOAA video).


[Picture]


Figure 10: Same as 9, scale relative to two IPCC emission scenarios.
Image Source: Climate Bomb.

During the recent Pleistocene Ice Age carbon dioxide concentrations fluctuated between a low of about 160-180 ppm during glacial periods, and maximum of about 280 ppm during interglacials, as shown in Fig. 9. The 110 ppm difference between our current post-industrial CO2 level of 390 ppm and the interglacial maximum already exceeds the entire 100 ppm CO2 fluctuation range during that Ice Age. Detailed models that couple climate with glaciation show that with today’s orbital configuration and expected future variances, another glacial period cannot occur until CO2 concentrations again dip beneath 240-280 ppm. Even if we were to stop all greenhouse gas emission today - an impossibility - CO2 concentrations could not drop to such pre-industial levels for tens of thousands of years.23

”No glacial inception is projected to occur at the current atmospheric CO2 concentrations of 390 ppmv (ref. 1). Indeed, model experiments suggest that in the current orbital configuration - which is characterized by a weak minimum in summer insolation - glacial inception would require CO2 concentrations below preindustrial levels of 280 ppmv (refs 2, 3, 4)...”24

Increasing carbon dioxide concentrations will not stop – cannot stop – at today’s 390 ppm. Indeed, greenhouse gases are unlikely to stabilize even beneath 650 ppm CO2 equivalent, well over twice the Pleistocene maximum.25 Developed and developing world economies are all powered by cheap, reliable electricity. For homes, for offices, for farms, and particularly for industry.26 The cheaper and more reliable its electric power, the better off a country’s people, and the more competitive they are with respect to their neighbors and the world economy at large. Coal is cheap to mine, cheap to transport short distances, and coal-fired power plants are cheap to build and get reliably operational without a large amount of additional infrastructure. A nationwide power grid is not required. Coal is ubiquitous and cheap. Cheap as dirt.

The economics of coal are so compelling it is estimated the electric power needs of growing economies in Asia and the subcontinent will be limited not by the abundance of coal, but by the availability of water for mining and transport, and to cool the generators. Only then can they turn to more expensive energy options.27

The Holocene is history. Warmly welcome the Anthrocene!28

5 Climate Modeling: Fingerprint by Attribution Analysis

One powerful technique used by climate modellers to distinguish and estimate the extent of human contributions to climate change is to run two ensembles of climate models, one with only natural aerosol and green house gas forcings, the second with both natural and man-made forcings, and compare the two ensemble means with the observed temperature trend taken from field measurements. The numerical experiment might be phrased something like

Question:
”Can the observed climate trend be adequately fit with known natural greenhouse gas concentration time histories, natural aerosol concentration time histories, and known or proxied solar irradiance time history, OR must one also include known anthropogenic GHG and aerosol contributions as well? How good are the fits obtained each way, and by what measure(s)? What is the significance of their difference, and by what measures? How do uncertainties propagate?”

Such a numerical experiment is termed an ”attribution analysis”, as it attempts to attribute different contributions of the observed trend to different input components of the models. An example is provided by NCAR, reproduced here as figure 11:

”The simulations that include only natural variability, including changes in the Sun and eruptions of volcanoes, show that we should have seen a decrease in the global average temperature in the last several decades.

”The simulations that most closely resemble the observed record are the ones that take the cooling effect of air pollution and the warming effect of greenhouse gases into account.”

Image source: Meehl, G.A., W.M. Washington, C.M. Ammann, J.M. Arblaster, T.M.L. Wigley and C. Tebaldi, 2004: Combinations of Natural and Anthropogenic Forcings in Twentieth-Century Climate. J. Climate, 17, 3721-3727. Similar results using more recent models are in Solar and Greenhouse Gas Forcing and Climate Response in the Twentieth Century . J. Climate, 16, 426-444.


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Figure 11: Attribution Analysis of Global Warming 1: Surface Temperature
  • The black line plots human observations of Earth’s temperature.
  • The blue line summarizes simulations performed using only natural influences on climate (volcanoes and solar variations).
  • The red line, from a set of simulations that includes sulfate aerosol pollution and greenhouse gases.
  • Shading in pale blue and pale pink shows the range of results (the model uncertainty) for each group of simulations, or ensemble.

6 Ocean Temperature and Heat Content: Challenger and Argo

Although ocean temperatures have spatial and temporal variations of their own, their heat capacity and slow mixing rates relative to the atmosphere allow long-term oceanic temperature trends to complement the land surface temperature record, and in some sense smooth the rapid variations seen in land measurements. We link modeling results that show measured oceanic spatial and temporal thermal variations cannot be explained by models of solar variation alone, but fit remarkably well to models incorporating anthropogenically distributed surface-level greenhouse gas.

”Changing temperature throughout the oceans is a key indicator of climate change. Since the 1960s about 90% of the excess heat added to the Earths climate system has been stored in the oceans. The oceans dominant role over the atmosphere, land, or cryosphere comes from its high heat capacity and ability to remove heat from the sea surface by currents and mixing. The longest interval over which instrumental records of subsurface global-scale temperature can be compared is the 135 years between the voyage of HMS Challenger (1872 - 1876) and the modern data set of the Argo Programme (2004 - 2010).”29

In 1872 HMS Challenger commenced an historic three and a half year oceanographic survey, sounding the depths, collecting sediment samples, and recording temperature profiles in nearly 300 locations in the Atlantic and Pacific basins. She discovered the submerged mountains of the Mid-Atlantic Ridge, and the oceans’ stratification by temperature.

The 21st century dawned with deployment of Argo, a global array of over 3,000 free-drifting profiling floats that measure the temperature and salinity of the upper 2000 m of the ocean. This allows, for the first time, continuous monitoring of the temperature, salinity, and velocity of the upper ocean... Deployments began in 2000 and continue today at the rate of about 800 per year.

From Researchers match modern ocean temperature records to those of the 1870s:

”For each of 273 Challenger temperature profiles from the Atlantic and Pacific Oceans, researchers interpolated Argo measurements from the same location, depth, and time of year. Modern surface ocean temperatures (averaged over 2004-2010) were higher at 211 of those points. On average, the surface of the Atlantic is about 1C warmer – 0.4C for the Pacific. The authors write, ”As Challenger’s sampling was more intensive in the Atlantic and the warming may be greater in that ocean, we estimate the global difference as the area-weighted mean of the Atlantic and Pacific values, 0.59C ± 0.12.

”As you’d expect, that difference diminishes with depth. At 366 meters (200 fathoms), the area-weighted ”global” average today is 0.39C ± 0.18. At 914 meters (500 fathoms), its down to 0.12C ± 0.07, and the difference disappears by about 1,500 meters depth.”

Source Article: Nature Climate Change 2, 425-428 (2012) 135 years of global ocean warming between the Challenger expedition and the Argo Programme. DOI: 10.1038/NCLIMATE1461

XBT was an earlier United States Navy float system not originally intended for scientific application. But it was what was available, and Argo data has been beneficial in reducing uncertainties in XBT. Figuring out how fast the ocean is warming concludes ”the oceans have warmed at a rate of 0.64 ± 0.11Wm2 for the entire 16-year period”, consistent with the above 0.59C ± 0.12.

Finally, from The Computer Models Vindicated (1990s-2000s):

”A final nail... came in 2005... natural fluctuations had kept air temperatures roughly the same since the late 1990s; the significant question was whether the oceans were continuing to warm. The team(s) found that over many decades the planet’s content of heat-energy had been rising, and was rising still (this continued steadily after 2005 as well). There was only one remotely plausible source of the colossal addition of energy: the Earth must be taking in more energy from sunlight than it was radiating back into space. Simple physics calculated that to heat all that sea water required nearly an extra watt per square meter, averaged over the planet’s entire surface, year after year. The number was just what the elaborate greenhouse effect computations had been predicting for decades. James Hansen, leader of one of the studies, called the visible increase of the planet’s heat content a ”smoking gun” proof of greenhouse effect warming (see graph). Moreover, in each separate ocean basin there was a close match between the pattern of rising temperatures measured at each location and depth and detailed model calculations of where the greenhouse effect warming should appear. Warming from other sources, for example a change in the Sun’s output, could not produce these patterns.”30,31

The aforementioned solar and internal ocean variations warming patterns are reproduced here as Fig. 12, GHG patterns as Fig. 13:


[Picture]


Figure 12: Attribution Analysis of Global Warming 2: Natural Ocean Forcings
Multiple realizations from the Parallel Climate Model (PCM) control run allowed estimation of the probability distribution of signal strength associated with natural internal variability. The hatched region represents the 90% confidence limits of the natural internal variability signal strength. The observed signal strength (red dots) bears little resemblance to that expected from natural internal variability. The ensemble-averaged strength of the warming signal in four runs forced by observed solar and volcanic variability (green triangles) is also shown. There is no agreement between the two. The solar plus volcanic signals are generally indistinguishable from those expected from natural internal variability alone on the time and space scales used in this study. (This and Fig 13 reproduced from Barnett, Tim P., et al. Science 309: 284-87 (2005) ”Penetration of Human-Induced Warming into the World’s Oceans.” Source: http://www.sciencemag.org/content/309/5732/284/F2.large.jpg)


[Picture]


Figure 13: Attribution Analysis of Global Warming 3: Natural + Anthropgenic Ocean Forcings
Anthropogenic forcing signal strength (green hatched region) compared to that obtained from the observations (red dots). There is excellent agreement at most depths in all oceans. The hatched region shows the range of the signal strength estimates from five different realizations of identically forced simulation with the PCM, whereas the smaller green dots within the region are the individual realizations. (Reproduced from Barnett, Tim P., et al. Science 309: 284-87 (2005) ”Penetration of Human-Induced Warming into the World’s Oceans.” Source: http://www.sciencemag.org/content/309/5732/284/F3.large.jpg)

7 Climategate and Berkeley Earth Surface Temperature Study

In November 2009 unknown parties with unknown agenda stole what had been considered private emails between widely – though not uniformly – respected East Anglica Climate Research Unit (CRU) Director Phil Jones and other members of the climate research community. These created a minor sensation when selectively published out of context on the internet, and there were indignant calls for Jones’ resignation.

Seven University, Parliamentary, and a National Science Foundation investigation later, no scientific misconduct was uncovered and Jones retained his position without reprimand, albeit with the understanding that England’s Freedom of Information Act should be respected regardless of the perceived trollish origins of a particular request, and that the climate community as a whole might better serve the public by being more open with its data. See Additional Climategate Commentary, and Wikipedia’s Climatic Research Unit email controversy.

Such has been done, with one positive outcome being Prof. Richard Muller’s Project Berkeley Earth.

The Berkeley Earth Surface Temperature Study

From The Guardian: Can a group of scientists in California end the war on climate change? .

”We are bringing the spirit of science back to a subject that has become too argumentative and too contentious,” says Richard Muller, Berkeley Earth’s Principal Investigator. ”We are an independent, non-political, non-partisan group. We will gather the data, do the analysis, present the results and make all of it available. There will be no spin, whatever we find.” Why does Muller feel compelled to shake up the world of climate change? ”We are doing this because it is the most important project in the world today. Nothing else comes close.”

So, what did The Berkeley Earth Surface Temperature Study find? Essentially, they reproduced the results previously obtained by the ”Big Three” – NASA GISS, NOAA/NCDC, and Hadley/CRU – with remarkable precision. In addition, the Berkeley group pushed the temperature record back another century, to 1750 AD (land coverage 5%). From their Web Page:

”Berkeley Earth has just released analysis of land-surface temperature records going back 250 years, about 100 years further than previous studies. The analysis shows that the rise in average world land temperature globe is approximately 1.5 degrees C in the past 250 years, and about 0.9 degrees in the past 50 years.

”Berkeley Earth also has carefully studied issues raised by skeptics, such as possible biases from urban heating, data selection, poor station quality, and data adjustment. We have demonstrated that these do not unduly bias the results.

”Many of the changes in land-surface temperature can be explained by a combination of volcanoes and a proxy for human greenhouse gas emissions. Solar variation does not seem to impact the temperature trend...

”I was not expecting this.” -Richard Muller,

”The Berkeley Earth team values the simplicity of its analysis, which does not depend on the large complex global climate models that have been criticized by climate skeptics for their hidden assumptions and adjustable parameters. The conclusion that the warming is due to humans is based simply on the close agreement between the shape of the observed temperature rise and the known greenhouse gas increase.”

More information is available at www.BerkeleyEarth.org.

Additional commentary:

Climate skeptics perform independent analysis. John Timmer - Oct 24 2011.

Berkeley Earth project is back to re-re-confirm Earth is warming. John Timmer - July 30 2012.

Koch-Funded Study Finds ‘Global Warming Is Real’, ‘On The High End’, and ‘Essentially All’ Due To Carbon Pollution. Joe Romm - Jul 28 2012.

The Conversion of a Climate-Change Skeptic. Richard A. Muller - July 28 2012.


The Escalator
[Picture]


Figure 14: The Escalator
Berkeley Earth Surface Temperature (BEST) land-only surface temperature data. Average of NASA GISS, NOAA NCDC, and UK Royal Met Office Hadley Centre HadCRUT4 monthly global surface temperature anomalies from January 1970 through August 2012 (green) with linear trends applied to the timeframes Jan ’70 - Oct ’77, May ’77 - Dec ’85, Jan ’86 - June ’94, Nov ’94 - Dec ’00, Jan ’01 - Aug ’12. (blue), and 1973 - 2010 (red). Total Solar Irradiance for the same time period is shown in Figure 7. Blog posts explaining the graphic are:

Image Source: Global Surface Temperature: Going Down the Up Escalator, Figure 1.


8 Albedo and Soot

Speaking of forcings, one would be remiss not to at least mention the climate impact of anthropogenic soot: carbon black created during the incomplete combustion of most hydrocarbons but principally coal, wood, and diesel. Soot might contribute as much – or even more – to global warming as anthropogenic carbon dioxide, and is in principle much easier to control and eliminate from the Earth’s atmosphere and surface. That is, provided we address the problem while there is still sufficient snowfall to re-cover glaciers and ice packs:

Relatively easy (relative to reduction, capture, and sequestration of CO2) solutions include replacement of old diesel engines, coal power plants, and traditional wood and coal-burning cooking stoves with more modern, cleaner-burning alternatives – even those using the same fuels. Education must play a central role: much of the third world (and first) does not know how to get best cleanliness and efficiency from the internal combustion engines they have. And bombing ”them” into oblivion with new cook-stoves won’t do any good if ”they” are left uninformed about how to cleanly burn wood, grass, or coal, and why it is important to do so:

Soot warming ’maybe bigger than greenhouse gases’ - NASA.
Soot Ranks Second After CO2 in Arctic Ice Melt Warming Contribution.
Sulfates plus black carbon a nasty combo for warming.

We make passing mention to atmospheric aerosols. These are mostly short-lived. Wind-blown Dust and volcanic ash fall out by gravity within a few years of injection. The other major atmospheric reflectors are sulfates, mostly SO2 and SO3. These readily react with water vapor and precipitate as acid rain. Apart from some very delicately balanced (CO2, glaciers, sea-ice) eras such as occured during the Little Ice Age, which apparently was ending even before man’s intervention, it would seem aerosols can have no long-term climate effect without frequent or continuous re-injection.

 

9 Conclusions

We provided excerpts from AGU and AIP policy papers and provided links to comprehensive climate and global warming resources. We then made cursory introduction to basic ideas of atmospheric layers, heat, and radiation transport.

We discussed three signature fingerprints of man’s responsibility for global warming:

We cite studies that show that if the Little Ice Age was caused by decreased solar flux, the negative forcing of that decrease was no more than half the current positive greenhouse forcing. Likewise, if the major Pleistocene glacial periods were triggered by orbital variations, at 390ppm current CO2 levels are at least 100ppm too high for such glaciation to recur. Neither the sun, the moon, nor the planets will relieve us from responsibility for human-induced global warming.

We touched upon the economics of coal and electric power, and the bottom line bears repeating: global greenhouse gas emissions will continue to rise – and probably accellerate – unless we develop and deploy a reliable emissions-free electric power technology that is cheaper to install and become operational, than coal.

We have focused on carbon dioxide and water vapor as the predominant greenhouse gases in this thin overview. They are not the only ones of course, and the role of methane in particular may will significantly increase in the not-too-distant future. An 80% reduction in all greenhouse gas emissions would be necessary to stabilize future greenhouse radiative forcing to 2010 levels. Even if that were possible, the planet will continue to warm until its energy balance again becomes neutral32:

”It is found that the time required to absorb anthropogenic CO2 strongly depends on the total amount of emissions; for emissions similar to known fossil fuel reserves, the time to absorb 50% of the CO2 is more than 2000 yr. The long-term climate response appears to be independent of the rate at which CO2 is emitted over the next few centuries. (Ed: it depends on the total amount of CO2 emitted, not its rate.) Results further suggest that the lifetime of the surface air temperature anomaly might be as much as 60% longer than the lifetime of anthropogenic CO2 and that two-thirds of the maximum temperature anomaly will persist for longer than 10,000 yr. This suggests that the consequences of anthropogenic CO2 emissions will persist for many millennia.” (From Lifetime of Anthropogenic Climate Change: Millennial Time Scales of Potential CO2 and Surface Temperature Perturbations. DOI: 10.1175/2008JCLI2554.1)

A similar study

...examines whether empirical estimates of greenhouse gas emissions between 2000 and 2008, a period typically modelled within scenario studies, combined with short-term extrapolations of current emissions trends, significantly constrains the 2000-2100 emission pathways. The paper concludes that it is increasingly unlikely any global agreement will deliver the radical reversal in emission trends required for stabilization at 450 ppmv carbon dioxide equivalent (CO2e). Similarly, the current framing of climate change cannot be reconciled with the rates of mitigation necessary to stabilize at 550 ppmv CO2e and even an optimistic interpretation suggests stabilization much below 650 ppmv CO2e is improbable. (From Reframing the climate change challenge in light of post-2000 emission trends)

Finally, correlation of future CO2 concentrations with past, current, and projected fossil fuel carbon release is discusssed in Future Climate Change, and illustrated by Fig 17:


[Picture] [Picture]

Figure 15: Emissions of main greenhouse gases across the RCPs 2000 - 2100
Figure 16: Trends in concentrations of greenhouse gases 2000 - 2100

Grey area indicates the 98th and 90th percentiles (light/dark grey) of the literature...The dotted lines indicate four of the SRES marker scenarios. Note that the literature values are not harmonized. From van Vuuren et.al. 2011, and Clarke et al. 2010. Source: G.P. Wayne The Beginner’s Guide to Representative Concentration Pathways Figures 8 and 9.

Figure 17: Carbon Consumption and CO2 Concentrations for 4 Emissions Scenarios


[Picture]


Figure 18: Corresponding Temperature Trends for 3 Emissions Scenarios
Based on different emission scenarios, the Intergovernmental Panel on Climate Change (IPCC) estimates that Earth will warm between two and six degrees Celsius over the next century. The orange line provides an estimate of what global temperatures would be if greenhouse gases stay at year 2000 levels. Image source: NASA Earth Observatory, based on IPCC Fourth Assessment Report (2007), available at Climate History & the Cryosphere.

For more information see Energy Realities Infographics, which includes population projections, and its CO2 Emissions Scenarios.

Continued Reading

As the glaciers of ignorance slowly recede, the terminal morass of climatology advances apace:

  1. Nature 484, 228-232 (12 April 2012) Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability. doi:10.1038/nature10946
    ”Our findings suggest that anthropogenic aerosol emissions influenced a range of societally important historical climate events such as peaks in hurricane activity and Sahel drought. Decadal-scale model predictions of regional Atlantic climate will probably be improved by incorporating aerosol – cloud microphysical interactions and estimates of future concentrations of aerosols, emissions of which are directly addressable by policy actions.”
  2. Skeptical Science has a nice video that shows the effect on the recent (35-year) temperature trend of removing the contributions to volcanoes (such as Pinatubo and El Chinchon), solar actrivity (minor) and El Nino / La Nina. Evens out some natural variations in the upward trend, which is seen to be maintaining apace.

1Early on, at the turn of the twentieth century, the troposphere was thought to be entirely opaque to infrared radiation, and therefore adding more atmospheric carbon dioxide could not raise the earth’s temperature. Later, more detailed spectroscopic studies showed significant tropspheric transmission of infrared. But relative tropospheric infrared opacity didn’t matter: adding additional carbon dioxide would result in a warmer planet regardless. See A Fundamentally Stable System? and following.

2Carbon dioxide also radiates upward, of course. But as there is so much more carbon dioxide above the troposphere than there is water vapor, most of the troposphere’s upward carbon dioxide radiation is reflected back downward as part of the radiative transfer process. The upper atmosphere is more transparent to upward radiation from tropospheric water vapor, which thus has more immediate effect on upper tropospheric cooling than does carbon dioxide.

3From The CO2 Greenhouse Effect Demonstrated (1950-1967):

”The (solution) was to follow how the radiation passed up layer by layer. Consider a layer of the atmosphere so high and thin that heat radiation from lower down would slip through. Add more gas, and the layer would absorb some of the rays. Therefore the place from which heat energy finally left the Earth would shift to a higher layer. That would be a colder layer, unable to radiate heat so efficiently. The imbalance would cause all the lower levels to get warmer, until the high levels became hot enough to radiate as much energy back out as the planet received.”

4Not entirely dry, of course. For example, nocilucent clouds are formed from ice crystals high in the mesophere. From Simple Models of Climate Change:

”It was no simple matter to calculate how changing the level of CO2 would alter radiation and thus surface temperature, and how that would in turn affect the level of water vapor, and how that would bring a further cascade of changes until the atmosphere reached a new equilibrium. The numerical computations cost Arrhenius month after month of laborious pencil work as he estimated the energy balance for each zone of latitude.”

5From Radiation Math: In 1956 Gilbert Plass explained clearly, for the first time, that the water vapor absorption lines did not block the quite different CO2 absorption spectrum, adding that there was scarcely any water in the upper atmosphere anyway. He further explained that although some of the CO2 band itself was truly saturated, there were many lines to the side where adding more of the gas would increase the absorption of radiation. His arguments and calculations showed convincingly that adding or subtracting CO2 could seriously affect the radiation balance, layer by layer through the atmosphere, altering the temperature by a degree or more down to ground level.

6Hegerl, Gabriele C.; et al.. ”Understanding and Attributing Climate Change” (PDF). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change. p. 675. Retrieved 2008-02-01.

7”The Relative Roles of Ozone and Other Greenhouse Gases in Climate Change in the Stratosphere”. Geophysical Fluid Dynamics Laboratory. 2007-02-29.

8From Simple Models vs. Skeptics (1990s-2000s):

”Other climate changes that could be deduced easily from an enhanced greenhouse effect, but that would not follow from other influences, would likewise show up unambiguously in the early years of the 21st century. For example, if extra greenhouse gases in the lower atmosphere were indeed absorbing radiation coming up from the surface, that should cause a cooling of the stratosphere above these layers. A greenhouse-effect stratospheric cooling was not only plausible on elementary grounds but was calculated in 1967 by the first widely accepted global computer model, and all the more elaborate subsequent models. On the other hand, if the observed surface warming was due to a more active Sun, or many other possible causes, the atmosphere ought to warm up more uniformly. By the mid 2000s a stratospheric cooling was unequivocally observed: an unmistakable fingerprint of greenhouse-effect warming.(105a)

”No less persuasive, Arrhenius and everyone since had calculated that the Arctic must warm more than other parts of the globe. The main reason was that even a little warming would melt some of the snow and ice, exposing dark soil and water that would absorb sunlight. Enhanced Arctic warming was a solid feature of models from the simplest hand-waving to the most sophisticated computer studies.(106*) And in fact, it was in places like the Arctic Ocean, Scandinavia, and Siberia that global warming became most noticeable in the 1990s.”

9From The Sun vs. Greenhouse Gases (2000s): ”The most advanced computer modeling groups did manage to reproduce the faint influence of the sunspot cycle on climate. Their calculations showed that since the 1970s that influence had been overtaken by the rising effects of greenhouse gases. The modelers got a good match to maps of the climate changes observed over the past century, but only if they included the effects of the gases, and not if they tried to attribute it all to the Sun. For example, if they put in only an increase of solar activity, the results showed a warmer stratosphere. Adding in the greenhouse effect made for stratospheric cooling (since the gases trapped heat closer to the surface). And cooling was what the observations showed.(57*)”

10From The CO2 Greenhouse Effect Demonstrated (1950-1967):

”In the numbers printed out for Manabe’s model in 1964, some of the general characteristics, although by no means all, looked rather like the real atmosphere.(16) By 1967, after further improvements in collaboration with Richard Wetherald, Manabe was ready to see what might result from raising the level of CO2. The result was the first somewhat convincing calculation of greenhouse effect global warming. The movement of heat through convection kept the temperature from running away to the extremes Möller had seen. Overall, the new model predicted that if the amount of CO2 doubled, temperature would rise a plausible 2C.(17*) In the view of many experts, this widely noted calculation (to be precise: the Manabe-Wetherald one-dimensional radiative-convective model) gave the first reasonably solid evidence that greenhouse warming really could happen.”

11From Wikipedia: Solar Variation.

12From Wikipedia: Solar Constant.

13The earth’s core and residual radioactivity contribute a flux of about 0.075 Wm2 at the surface. This is about 0.046% of the 163 Wm2 provided to Earth’s surface by the sun, about 5% of the approximate 1.5 Wm2 estimated for anthropogenic forcing, and 14% of the 0.54 Wm2 net heat imbalance estimated by Hansen et al.

14Nature Geoscience 5, 31-36 (2012). DOI:10.1038/NGEO1327.

15See Changing Sun, Changing Climate.

16 Are the most recent estimates for Maunder Minimum solar irradiance in agreement with temperature reconstructions? . Geophysical Research Letters, 38, L16706, 4 PP., 2011 doi:10.1029/2011GL048529

17 An Antarctic view of Beryllium-10 and solar activity for the past millennium. Climate Dynamics, Published online 1 April 2010. DOI: 10.1007/s00382-010-0795-1.

18”...Intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium. A transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times, and that cold summers can be maintained by sea-ice/ocean feedbacks long after volcanic aerosols are removed. Our results suggest that the onset of the LIA can be linked to an unusual 50-year-long episode with four large sulfur-rich explosive eruptions, each with global sulfate loading > 60 Tg. The persistence of cold summers is best explained by consequent sea-ice/ocean feedbacks during a hemispheric summer insolation minimum; large changes in solar irradiance are not required.”

Miller said the Little Ice Age likely would have occurred without decreased summer solar radiation at the time. ”Estimates of the sun’s variability over time are getting smaller; it’s now thought by some scientists to have varied little more in the last millennium than during a standard 11-year solar cycle.” (Ed: 0.25Wm2.)

Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks. G.H. Miller et al. Geophysical Research Letters, 39, L02708, 5 PP., 2012. doi:10.1029/2011GL050168.

19 Deep Solar Minimum. (NASA 1 April 2009) ”This is the quietest sun we’ve seen in almost a century,” agrees sunspot expert David Hathaway of the Marshall Space Flight Center.

20See Astronomical Theory of Climate Change.

21See ”How the Isthmus of Panama Put Ice in the Arctic: Drifting continents open and close gateways between oceans and shift Earth’s climate.” For illustrations of past land mass distributions and continental drift, visit Paleomap Project.

22Nature 484, 49-54 (05 April 2012) Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation. doi:10.1038/nature10915
”...temperature is correlated with and generally lags CO2 during the most recent deglaciation. Differences between the respective temperature changes of the Northern Hemisphere and Southern Hemisphere parallel variations in the strength of the Atlantic meridional overturning circulation recorded in marine sediments. These observations... support the conclusion that an antiphased hemispheric temperature response to ocean circulation changes superimposed on globally in-phase warming driven by increasing CO2 concentrations is an explanation for much of the temperature change at the end of the most recent ice age.”

23This is simplistic. In How long will global warming last?, Prof. David Archer writes

”My model indicates that about 7% of carbon released today will still be in the atmosphere in 100,000 years [7]. I calculate a mean lifetime, from the sum of all the processes, of about 30,000 years. That’s a deceptive number, because it is so strongly influenced by the immense longevity of that long tail. If one is forced to simplify reality into a single number for popular discussion, several hundred years is a sensible number to choose, because it tells three-quarters of the story, and the part of the story which applies to our own lifetimes.

”However, the long tail is a lot of baby to throw out in the name of bath-time simplicity. Major ice sheets, in particular in Greenland [8], ocean methane clathrate deposits [9], and future evolution of glacial/interglacial cycles [10] might be affected by that long tail. A better shorthand for public discussion might be that CO2 sticks around for hundreds of years, plus 25% that sticks around forever.”

Also see Parameters for tuning a simple carbon cycle model, and Global warming feedbacks on terrestrial carbon uptake under the Intergovernmental Panel on Climate Change (IPCC) emission scenarios.

24 Determining the natural length of the current interglacial. Nature Geoscience 5, 138 - 141 (2012) P. C. Tzedakis, J. E. T. Channell, D. A. Hodell, H. F. Kleiven & L. C. Skinner doi:10.1038/ngeo1358. Additional commentary at Carbon emissions ’will defer Ice Age’.

25 Reframing the climate change challenge in light of post-2000 emission trends

26See The Fake Fire Brigade Revisited #3 - The Biggest Part of Business As Usual - Electricity: ”You don’t have to be rich to have stable electricity, but your country needs stable electricity to become (or stay) rich.”

27 Asia Risks Water Scarcity Amid Coal-Fired Power Embrace. Also at The Oil Drum. Note that natural gas is both cheaper to transport long distances than coal and — for reasons partially related to the amount of water used in coal mining and transportation — requires but a third the amount of water for a given output than does coal. Gas also produces half the amount of CO2 per btu as coal, which doesn’t really help the agw problem if one then builds thrice as many plants. Conventional nuclear consumes even more water than coal, but as it’s usually more expensive as well, nuclear is not a consideration where coal or gas is available. The problem is illustrated by Can an Economy Learn to Live with Increasingly High Oil Prices?, Figure 5.

28Not to be confused with the entirely unrelated Anthracene, Anthrocene derives from the Latin Anthropocene – ”age of man” – and Anthracite, the purest grade of coal. Anthrocene is, literally, ”age of man’s coal.”

29Nature Climate Change, 2012. 135 years of global ocean warming between the Challenger expedition and the Argo Programme. DOI: 10.1038/NCLIMATE1461

30Barnett, Tim P., et al. Science 309: 284-87 (2005) ”Penetration of Human-Induced Warming into the World’s Oceans.”

31Hansen, James E., et al. Science 308: 1431-35. (2005). ”Earth’s Energy Imbalance: Confirmation and Implications.”

32 When it comes to greenhouse gases carbon dioxide isnt the only culprit.