Thread: Guess what people? The Earth's warming, and we've played a part.

Now, for sake of reading, I've devided this post into three sections. Section 1 deals with proving that the Earth is warming. If your alread believe the Earth is warming, then go ahead and skip to section 2. And Section 3 is the references.

So, without further ado, let's get this **** started:

SECTION I: Arguements against Global warming and debunking them.

An ice age was predicted in the 1970's.

What was the scientific consensus in the 1970s regarding future climate? The most cited example of 1970s cooling predictions is a 1975 Newsweek article "The Cooling World" that suggested cooling "may portend a drastic decline for food production."

"Meteorologists disagree about the cause and extent of the cooling trend… But they are almost unanimous in the view that the trend will reduce agricultural productivity for the rest of the century."

A 1974 Time magazine article Another Ice Age? painted a similarly bleak picture:

"When meteorologists take an average of temperatures around the globe, they find that the atmosphere has been growing gradually cooler for the past three decades. The trend shows no indication of reversing. Climatological Cassandras are becoming increasingly apprehensive, for the weather aberrations they are studying may be the harbinger of another ice age."

Peer-Reviewed Literature

However, these are media articles, not scientific studies. A survey of peer reviewed scientific papers from 1965 to 1979 show that few papers predicted global cooling (7 in total). Significantly more papers (42 in total) predicted global warming (Peterson 2008). The large majority of climate research in the 1970s predicted the Earth would warm as a consequence of CO2. Rather than 1970s scientists predicting cooling, the opposite is the case.
Figure 1: Number of papers classified as predicting global cooling (blue) or warming (red). In no year were there more cooling papers than warming papers (Peterson 2008).Scientific Consensus

In the 1970s, the most comprehensive study on climate change (and the closest thing to a scientific consensus at the time) was the 1975 US National Academy of Sciences/National Research Council Report. Their basic conclusion was "…we do not have a good quantitative understanding of our climate machine and what determines its course. Without the fundamental understanding, it does not seem possible to predict climate…"This is in strong contrast with the current position of the US National Academy of Sciences: "...there is now strong evidence that significant global warming is occurring... It is likely that most of the warming in recent decades can be attributed to human activities... The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action." This is in a joint staetment with the Academies of Science from Brazil, France, Canada, China, Germany, India, Italy, Japan, Russia and the United Kingdom.In contrast to the 1970s, there are now a number of scientific bodies that have released statements affirming man-made global warming. Here's some other sites:

• National Oceanic and Atmospheric Administration
• Environmental Protection Agency
• NASA's Goddard Institute of Space Studies
• American Geophysical Union
• American Institute of Physics
• National Center for Atmospheric Research
• American Meteorological Society
• The Royal Society of the UK
• Canadian Meteorological and Oceanographic Society
• American Association for the Advancement of Science

Reasoning Behind Cooling Predictions

Quite often, the justification for the few global cooling predictions in the 1970s is overlooked. Probably the most famous such prediction was Rasool and Schneider (1971):

"An increase by only a factor of 4 in global aerosol background concentration may be sufficient to reduce the surface temperature by as much as 3.5°K."

Yes, their global cooling projection was based on a quadrupling of atmospheric aerosol concentration. This wasn't an entirely unrealistic scenario - after all, sulfur dioxide (SO2) emissions were accelerating quite rapidly up until the early 1970s (Figure 2). These emissions caused various environmental problems, and as a result, a number of countries, including the USA, enacted SO2 limits through Clean Air Acts. As a result, not only did atmospheric aerosol concentrations not quadruple, they declined starting in the late 1970s:

Figure 2: Global sulfur dioxide emissions by source (PNNL)Similarly, if we now limit CO2 emissions, we can also eventually get global warming under control.

Summary:

So global cooling predictions in the 70s amounted to media and a handful of peer reviewed studies. The small number of papers predicting cooling were outweighed by a much greater number of papers predicting global warming due to the warming effect of rising CO2. Today, an avalanche of peer reviewed studies and overwhelming scientific consensus endorse man-made global warming. To compare cooling predictions in the 70s to the current situation is both inappropriate and misleading. Additionally, we reduced the SO2 emissions which were causing global cooling. The question remains whether we will reduce the CO2 emissions causing global warming.

The Earth has warmed before!

If there's one thing that all sides of the climate debate can agree on, it's that climate has changed naturally in the past. Long before industrial times, the planet underwent many warming and cooling periods. This has led some to conclude that if global temperatures changed naturally in the past, long before SUVs and plasma TVs, nature must be the cause of current global warming. This conclusion is the opposite of peer-reviewed science has found.
Our climate is governed by the following principle: when you add more heat to our climate, global temperatures rise. Conversely, when the climate loses heat, temperatures fall. Say the planet is in positive energy imbalance. More energy is coming in than radiating back out to space. This is known as radiative forcing, the change in net energy flow at the top of the atmosphere. When the Earth experiences positive radiative forcing, our climate accumulates heat and global temperature rises (not monotonically, of course, internal viability. will add noise to the signal).
How much does temperature change for a given radiative forcing? This is determined by the planet's climate sensitivity. The more sensitive our climate, the greater the change in temperature. The most common way of describing climate sensitivity is the change in global temperature if atmospheric CO2 is doubled. What does this mean? The amount of energy absorbed by CO2 can be calculated using line-by-line radiative transfer codes. These results have been expirementall confirmed by satellite and surface mesurments. The radiative forcing from a doubling of CO2 is 3.7 Watts per square metre (W/m²) (IPCC AR4 Section 2.3.1).

So when we talk about climate sensitivity to doubled CO2, we're talking about the change in global temperatures from a radiative forcing of 3.7 Wm^-2. This forcing doesn't necessarily have to come from CO2. It can come from any factor that causes an energy imbalance.
How much does it warm if CO2 is doubled? If we lived in a climate with no feedbacks, global temperatures would rise 1.2°C (Lorius 1990). However, our climate has feedbacks, both positive and negative. The strongest positive feedback is water vapour. As temperature rises, so too does the amount of water vapour in the atmosphere. However, water vapour is a greenhouse gas which causes more warming which leads to more water vapour and so on. There are also negative feedbacks - more water vapour causes more clouds which can have both a cooling and warming effect.
What is the net feedback? Climate sensitivity can be calculated from empirical observations. One needs to find a period where we have temperature records and measurements of the various forcings that drove the climate change. Once you have the change in temperature and radiative forcing, climate sensitivity can be calculated. Figure 1 shows a summary of the peer-reviewed studies that have determined climate sensitivity from past periods (Knutti & Hegerl 2008).
Figure 1: Distributions and ranges for climate sensitivity from different lines of evidence. The circle indicates the most likely value. The thick coloured bars indicate likely value (more than 66% probability). The thin coloured bars indicate most likely values (more than 90% probability). Dashed lines indicate no robust constraint on an upper bound. The IPCC likely range (2 to 4.5°C) and most likely value (3°C) are indicated by the vertical grey bar and black line, respectively.
There have been many estimates of climate sensitivity based on the instrumental record (the past 150 years). Several studies used the observed surface and ocean warming over the twentieth century and an estimate of the radiative forcing. A variety of methods have been employed - simple or intermediate-complexity models, statistical models or energy balance calculations. Satellite data for the radiation budget have also been analyzed to infer climate sensitivity.
Some recent analyses used the well-observed forcing and response to major volcanic eruptions during the twentieth century. A few studies examined palaeoclimate reconstructions from the past millennium or the period around 12,000 years ago when the planet came out of a global ice age (Last Glacial Maximum).
What can we conclude from this? We have a number of independent studies covering a range of periods, studying different aspects of climate and employing various methods of analysis. They all yield a broadly consistent range of climate sensitivity with a most likely value of 3°C for a doubling of CO2.
The combined evidence indicates that the net feedback to radiative forcing is significantly positive. There is no credible line of evidence that yields very high or very low climate sensitivity as a best estimate.
CO2 has caused an accumulation of heat in our climate. The radiative forcing from CO2 is known with high understanding and confirmed with empirical observation. The climate response to this heat build-up is determined by climate sensitivity.
Ironically, when skeptics cite past climate change, they're in fact invoking evidence for strong climate sensitivity and net positive feedback. Higher climate sensitivity means a larger climate response to CO2 forcing. Past climate change actually provides evidence that humans can affect climate now.

For sake of viewing, will continue in later posts.

I doubt there's any question about whether or not climate is currently in a warming trend. The question is, are humans causing it by their actions, or is it a natural cycle, or a combination of both? Either way, I remain skeptical, as I really doubt humans have a causative effect.

Originally Posted by lizzie

I doubt there's any question about whether or not climate is currently in a warming trend. The question is, are humans causing it by their actions, or is it a natural cycle, or a combination of both? Either way, I remain skeptical, as I really doubt humans have a causative effect.

Well, some do question whether the warming trend is real. Reasons for the questions range from "it's a staggeringly large and competent global conspiracy" to "temperature sensors are too close to cities and therefore are having the readings thrown off."

Microsite influences and the urban heat island effect have been researched rather thoroughly. The NWS and NASA want good data, after all. Paradoxically, some of the research showed a (very slight) bias in the record towards cooling, not warming, when some of the allegations were checked out.

What in particular makes you doubt human influence? I guess you could go with which step in the process do you question:

1) That an increase in carbon dioxide levels would cause a temperature change
2) That an increase in carbon dioxide levels would cause a temperature change of the observed magnitude
3) That humans are raising carbon dioxide levels
4) Other, please specify

Editor's note: While "carbon dioxide" is referenced, assume that any greenhouse gas is also in the consideration

SECTION II

There's no scientific consensus!

Scientists need to back up their opinions with research and data that survive the peer-review process. A survey of all peer-reviewed abstracts on the subject 'global climate change' published between 1993 and 2003 shows that not a single paper rejected the consensus position that global warming is man caused (Oreskes 2004). 75% of the papers agreed with the consensus position while 25% made no comment either way (focused on methods or paleoclimate analysis).

Subsequent research has confirmed this result. A survey of 3146 earth scientists asked the question "Do you think human activity is a significant contributing factor in changing mean global temperatures?" (Doran 2009). More than 90% of participants had Ph.D.s, and 7% had master’s degrees. Overall, 82% of the scientists answered yes. However, what are most interesting are responses compared to the level of expertise in climate science. Of scientists who were non-climatologists and didn't publish research, 77% answered yes. In contrast, 97.5% of climatologists who actively publish research on climate change responded yes. As the level of active research and specialization in climate science increases, so does agreement that humans are significantly changing global temperatures.

poll_scientists.gif

Figure 1: Response to the survey question "Do you think human activity is a significant contributing factor in changing mean global temperatures?" (Doran 2009) General public data come from a 2008 Gallup poll.

Most striking is the divide between expert climate scientists (97.4%) and the general public (58%). The paper concludes:

"It seems that the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes. The challenge, rather, appears to be how to effectively communicate this fact to policy makers and to a public that continues to mistakenly perceive debate among scientists."

This overwhelming consensus among climate experts is confirmed by an independent study that surveys all climate scientists who have publicly signed declarations supporting or rejecting the consensus. They find between 97% to 98% of climate experts support the consensus (Anderegg 2010). Moreover, they examine the number of publications by each scientist as a measure of expertise in climate science. They find the average number of publications by unconvinced scientists (eg - skeptics) is around half the number by scientists convinced by the evidence. Not only is there a vast difference in the number of convinced versus unconvinced scientists, there is also a considerable gap in expertise between the two groups.

Consensus_publications.jpg

Figure 2: Distribution of the number of researchers convinced by the evidence of anthropogenic climate change and unconvinced by the evidence with a given number of total climate publications (Anderegg 2010).
Scientific organizations endorsing the consensus

The following scientific organizations endorse the consensus position that "most of the global warming in recent decades can be attributed to human activities":

American Association for the Advancement of Science
American Astronomical Society
American Chemical Society
American Geophysical Union
American Institute of Physics
American Meteorological Society
American Physical Society
Australian Meteorological and Oceanographic Society
Australian Bureau of Meteorology and the CSIRO
British Antarctic Survey
Canadian Foundation for Climate and Atmospheric Sciences
Canadian Meteorological and Oceanographic Society
Environmental Protection Agency
European Federation of Geologists
European Geosciences Union
European Physical Society
Federation of American Scientists
Federation of Australian Scientific and Technological Societies
Geological Society of America
Geological Society of Australia
International Union for Quaternary Research (INQUA)
International Union of Geodesy and Geophysics
National Center for Atmospheric Research
National Oceanic and Atmospheric Administration
Royal Meteorological Society
Royal Society of the UK

The Academies of Science from 19 different countries all endorse the consensus. 11 countries have signed a joint statement endorsing the consensus position:

Academia Brasiliera de Ciencias (Brazil)
Royal Society of Canada
Chinese Academy of Sciences
Academie des Sciences (France)
Deutsche Akademie der Naturforscher Leopoldina (Germany)
Indian National Science Academy
Accademia dei Lincei (Italy)
Science Council of Japan
Russian Academy of Sciences
Royal Society (United Kingdom)
National Academy of Sciences (USA) (12 Mar 2009 news release)

A letter from 18 scientific organizations to US Congress states:

"Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research demonstrates that the greenhouse gases emitted by human activities are the primary driver. These conclusions are based on multiple independent lines of evidence, and contrary assertions are inconsistent with an objective assessment of the vast body of peer-reviewed science."

The consensus is also endorsed by a Joint statement by the Network of African Science Academies (NASAC), including the following bodies:

African Academy of Sciences
Cameroon Academy of Sciences
Ghana Academy of Arts and Sciences
Kenya National Academy of Sciences
Madagascar's National Academy of Arts, Letters and Sciences
Nigerian Academy of Sciences
l'Académie des Sciences et Techniques du Sénégal
Uganda National Academy of Sciences
Academy of Science of South Africa
Tanzania Academy of Sciences
Zimbabwe Academy of Sciences
Zambia Academy of Sciences
Sudan Academy of Sciences

Two other Academies of Sciences that endorse the consensus:

Royal Society of New Zealand
Polish Academy of Sciences


But please, Continue to tell me how that one sentence you read from half of a part of an article COMPLETELY refutes all I just posted.

The earth is warming. So what?

So this:

Humans aren't having an impact.

Back in 1988, NASA's James Hansen made some of the first projections of future global warming with a global climate model. He created 3 scenarios which he called Scenarios A, B, and C which used various possible future greenhouse gas emissions levels. Scenario A used a model with accelerating greenhouse gas emissions, Scenario B had linearly increasing emissions, and Scenario C had emissions leveling off after the year 2000. None of these models ended up matching greenhouse gas emissions exactly right, but the radiative forcing (energy imbalance) in Scenario B was closest, too high by about 10% as of 2009. Additionally, the climate sensitivity in Hansen's 1988 model (4.2°C global warming for a doubling of atmospheric CO2) was a bit higher than today's best estimate (3°C warming for CO2 doubling).

Hansen's Scenario B projected a global warming trend from 1984-2009 of 0.26°C per decade. The actual trend as measured by surface temperature stations over that period was about 0.2°C per decade. When corrected for the 10% smaller radiative forcing than Scenario B and the higher climate sensitivity in Hansen's models, his study projected the global warming over the ensuing 25 years almost perfectly.

Meehl et al. (2004) took a different approach. Instead of projecting future surface temperature change, they used climate models to attempt to attribute past temperature changes in a method known as 'hindcasting' (as opposed to forecasting). In their study, Meehl et al. show that natural forcings cannot account for the increase in global temperatures in the second half of the 20th century, and that models using both natural and anthropogenic forcings model the temperature change over the 20th century most accurately.



Stott et al. (2003) took yet another approach, examining surface temperature changes region-by-region across the planet and comparing them to how climate models predicted they should have changed. Stott found that regional temperature changes could also be traced back to anthropogenic global warming.

"The causes of twentieth century temperature change in six separate land areas of the Earth have been determined by carrying out a series of optimal detection analyses. The warming effects of increasing greenhouse gas concentrations have been detected in all the regions examined, including North America and Europe….Our results show significant anthropogenic warming trends in all the continental regions analyzed. In all these regions, greenhouse gases are estimated to have caused generally increasing warming as the century progressed, balanced to a greater or lesser degree, depending on the region, by cooling from sulfate aerosols in the middle of the century."



Climate models predict that as a consequence of anthropogenic global warming, the planet should warm more at night than during the day. Braganza et al. (2004) investigated the changes in DTR over the past 50 years and concluded as follows:

"Observed DTR over land shows a large negative trend of ~0.4°C over the last 50 years that is very unlikely to have occurred due to internal variability. This trend is due to larger increases in minimum temperatures (~0.9°C) than maximum temperatures (~0.6°C) over the same period. Analysis of trends in DTR over the last century from five coupled climate models shows that simulated trends in DTR due to anthropogenic forcing are much smaller than observed. This difference is attributable to larger than observed changes in maximum temperatures in four of the five models analysed here, a result consistent with previous modelling studies."

Essentially Braganza et al. found that that while DTR is decreasing as expected by climate models, it’s decreasing more than they predicted because daytime temperatures are increasing less than they predict, possibly because the models omit changes in the Earth’s reflectivity from factors like cloudcover and land use change. Here you can see the observed changes in maximum, minimum, mean global temperature, and DTR vs. predictions by the four climate models used in the study.


As the lower atmosphere warms due to an enhanced greenhouse effect, the upper atmosphere is expected to cool as a consequence. The simple way to think about this is that greenhouse gases are trapping heat in the lower atmosphere. Since less heat is released into the upper atmosphere (starting with the stratosphere), it cools.

Jones et al. (2003) investigated the changes in temperature over the past 4 decades at both the near surface (troposphere) and stratosphere layers, and compare them to changes predicted by a coupled atmosphere/ocean general circulation model, HadCM3. They concluded as follows.

"Our results strengthen the case for an anthropogenic influence on climate. Unlike previous studies we attribute observed decadal-mean temperature changes both to anthropogenic emissions, and changes in stratospheric volcanic aerosols. The temperature response to change in solar irradiance is also detected but with a lower confidence than the other forcings."

The layers above the stratosphere are expected to cool as a result of global warming as well, for similar reasons (less heat reaching higher levels as it’s trapped in the lower atmosphere). Jarvis et al. (1998) investigated changes in the thermosphere and ionosphere in 1998 and concluded as follows.

"The estimated long-term decrease in altitude is of a similar order of magnitude to that which has been predicted to result in the thermosphere from anthropogenic change related to greenhouse gases."

Laštovička et al. (2006) arrived at a similar conclusion.

"The upper atmosphere is generally cooling and contracting, and related changes in chemical composition are affecting the ionosphere. The dominant driver of these trends is increasing greenhouse forcing, although there may be contributions from anthropogenic changes of the ozone layer and long-term increase of geomagnetic activity throughout the 20th century. Thus, the anthropogenic emissions of greenhouse gases influence the atmosphere at nearly all altitudes between ground and space, affecting not only life on the surface but also the space-based technological systems on which we increasingly rely."


800.jpg

Figure 6: Atmospheric temperature and Ionospheric electron density vs. Altitude (Laštovička 2006)
Ocean Heat Content

Ocean heat content has increased significantly over the past 40 years. In fact, approximately 84% of the total heating of the Earth system over that period has gone into warming the oceans. Barnett et al. (2005) investigated the cause of this warming signal, and concluded as follows.

"[the increase in ocean heat content] cannot be explained by natural internal climate variability or solar and volcanic forcing, but is well simulated by two anthropogenically forced climate models. We conclude that it is of human origin, a conclusion robust to observational sampling and model differences. Changes in advection combine with surface forcing to give the overall warming pattern. The implications of this study suggest that society needs to seriously consider model predictions of future climate change."



6d8f10fe_Barnett+2007.jpg

Figure 7: Modeled vs. Observed Ocean Temperature Changes
Sea Level Pressure

Gillett et al. (2003) compared observed changes in sea level pressure with those predicted by four coupled ocean–atmosphere climate models and concluded as follows.

"Here we detect an influence of anthropogenic greenhouse gases and sulphate aerosols in observations of winter sea-level pressure (December to February), using combined simulations from four climate models. We find increases in sea-level pressure over the subtropical North Atlantic Ocean, southern Europe and North Africa, and decreases in the polar regions and the North Pacific Ocean, in response to human influence….Overall, we find that anthropogenic greenhouse gases and sulphate aerosols have had a detectable influence on sea-level pressure over the second half of the twentieth century: this represents evidence of human influence on climate independent of measurements of temperature change."



Zhang et al. (2007) showed that models using natural + anthropogenic forcings do a much better job of matching observed precipitation trends than either natural or anthropogenic alone. The correlation with natural forcings alone is extremely weak - only 0.02. With anthropogenic alone is 0.69, and with both combined is 0.83 over the past 75 years.

"We show that anthropogenic forcing has had a detectable influence on observed changes in average precipitation within latitudinal bands, and that these changes cannot be explained by internal climate variability or natural forcing. We estimate that anthropogenic forcing contributed significantly to observed increases in precipitation in the Northern Hemisphere mid-latitudes, drying in the Northern Hemisphere subtropics and tropics, and moistening in the Southern Hemisphere subtropics and deep tropics. The observed changes, which are larger than estimated from model simulations, may have already had significant effects on ecosystems, agriculture and human health in regions that are sensitive to changes in precipitation"


Anthropogenic global warming is caused by an increase in the amount of downward longwave infrared radiation coming from greenhouse gases in the atmosphere. Philipona et al. (2004) measured the changes and trends of radiative fluxes at the surface and their relation to greenhouse gas increases and temperature and humidity changes measured from 1995 to 2002 at eight stations of the Alpine Surface Radiation Budget (ASRB) network. They concluded as follows.

"The resulting uniform increase of longwave downward radiation manifests radiative forcing that is induced by greenhouse gas concentrations and water vapor feedback, and proves the "theory" of greenhouse warming with direct observations."

Evans et al. (2006) took it a step further, performing an analysis of high resolution specral data which allowed them to quantitatively attribute the increase in downward radiation to each of several greenhouse gases. The study went as far as to conclude,

"This experimental data should effectively end the argument by skeptics that no experimental evidence exists for the connection between greenhouse gas increases in the atmosphere and global warming."


As the concentration of greenhouse gases in the atmosphere increases, we expect to see less infrared radiation escaping at the top of the atmosphere. Satellite observations have confirmed that the decrease in upward longwave radiation matches well with model predictions, including in Harries 2001, Griggs 2004, and Chen 2007, the latter of which concluded:

"Changing spectral signatures in CH4, CO2, and H2O are observed, with the difference signal in the CO2 matching well between observations and modelled spectra."



Increased_Greenhouse_Effect.jpg

Figure 8: Increased greenhouse effect from 1970 to 2006. Black line is satellite observations. Red line is modeled results (Chen 2007)


This increase in downward and decrease in upward infrared radiation is expected to create an enery imbalance. Trenberth et al. (2009) used satellite data to measure the Earth's energy balance at the top of the atmosphere (TOA) and found that the net imbalance was 0.9 Watts per square meter. (Wm-2) This figure is consistent with the calculations in Hansen et al. 2005 using ocean heat data.

"The predicted energy imbalance due to increasing greenhouse gases has grown to 0.85 ± 0.15 W/m2"

Hansen 2005.jpg

1000x800px-a07b92e8_Hansen+2005.jpg

Figure 9: TOA Radiation (Trenberth 2009)

Murphy et al. (2009) obtained a similar result.

"About 20% of the integrated positive forcing by greenhouse gases and solar radiation since 1950 has been radiated to space. Only about 10% of the positive forcing (about 1/3 of the net forcing) has gone into heating the Earth, almost all into the oceans. About 20% of the positive forcing has been balanced by volcanic aerosols, and the remaining 50% is mainly attributable to tropospheric aerosols. After accounting for the measured terms, the residual forcing between 1970 and 2000 due to direct and indirect forcing by aerosols as well as semidirect forcing from greenhouse gases and any unknown mechanism can be estimated as 1.1 ± 0.4 Wm-2."


464x290px-LL-3e04a637_Murphy+2009.jpg

Figure 10: Cumulative energy budget for the Earth since 1950 (Murphy 2009)

This is an impressively wide variety of global and regional climate change observations strongly matching the changes predicted by climate models and providing clear fingerprints of human-caused climate change.

Originally Posted by Fletch

The earth is warming. So what?

Various negative things are expected from this. People tend to focus on the magnitude of temperature changes, but really rate of change is probably more important. Yes, the earth has been hotter than this, and it has been colder than this. Changing faster than this, on the other hand is unusual and when climate does change this quickly, we see serious repercussions in the fossil records. Animals and plants only adapt so quickly, the ones that can't keep up don't survive. Seeing as how we eat animals and plants, this may be of some concern to us.

The overall impact on crop yields is expected to be negative, and other social and economic damage stems from increased frequency of severe weather events, rising sea levels, loss of biodiversity, etc.

Not to mention the fact that our oil dependence is a national security risk that we should work harder to fix.

I personally hate this one.

Mars is cooling.

The primary empirical evidence for long term, global warming on Mars comes from Fenton 2007. Fenton compared a composite snapshot of Mars from 1977 taken by the Viking spacecraft to a 1999 image compiled by the Mars Global Surveyor (referencing work from Geissler 2005). The 1977 snapshot showed a brighter planet. In 1999, the planet had a lower albedo, with prominent darker regions in the southern mid and high latitudes. Using the albedo changes in a general circulation model, Fenton calculated a 22 year global warming trend of 0.65°C.

mars_snapshots.jpg

Figure 1: Snapshots of Mars 1977 (top) and 1999 (bottom). Image courtesy of Geissler 2005.

Fenton attributed the warming to surface dust causing a change in the planet's albedo. Martian dust plays a major role in the planet's climate (Kahn 1992). Solar variations are not the main driver of Martian climate. Nevertheless, an important question remains: is the interpretation of long term global warming on Mars correct?

A broader view of Martian climate change
To put these results in proper perspective, an understanding of what drives Martian climate is required. Global dust storms increase the surface albedo by settling brighter dust on dark surfaces. Within a year after a dust storm, various wind systems remove the dust and Mars returns to a normal, lower albedo.

The 1977 snapshot was taken after a global dust storm had deposited dust over the southern latitudes, lightening the planet surface. Before the storm, the planet had albedo comparable to recent measurements (Szwast 2006).

Fenton drew conclusions about long term climate by comparing two end points. This led to the classic error of mistaking weather for climate (similar to the recent global cooling argument). When you look at the broader data, there is no discernable long term trend in albedo:


mars_albedo_mosaics.gif

Figure 2: Comparison of data sampling by Fenton 2007 (left, comparing 2 end points) and the full sample of data (courtesy Mark Richardson).

The apparent long-term warming between the 1970's and 1990's is largely a consequence of the timing of the two snapshots used. The "brighter" 1977 snapshot was immediately after a global dust storm when the planet was temporarily lighter. The "darker" 1999 snapshot was of the planet in it's usual state. There is little evidence that Mars is undergoing decadal-scale, long term global warming. In fact, following the 2001 global dust storm, the southern hemisphere was brighter than in 1977 (Szwast 2006).

Conclusion
The empirical evidence isn't conclusive on whether global warming is happening on Mars. However, to answer the question on whether the sun is causing Earth's global warming, there is plentiful data on solar activity and Earth's climate. Many papers have examined this data, concluding the correlation between sun and climate ended in the 70's when the modern global warming trend began.

So the argument that Martian warming disproves anthropogenic global warming fails on two points - there is little empirical evidence that Mars is warming and Mars' climate is primarily driven by dust and albedo, not solar variations.

I'm an ignorant little prick!

Sounds like a personal problem.