The Case for Blaming Humans for Global Warming

Written by Roger W. Cohen, PhD

If 20th century warming was indeed exceptional, then previous warming episodes and all natural
variations must have been smaller. Interestingly, in the first IPCC report of 1990, we saw this graphic (above)  of global temperature since about the year 1000.

There is a strong Medieval Warming Period, a deep Little Ice Age, and a sporadic warming trend since around 1700.

But when we get to the 2001 Report, we are presented with the Hockey Stick. It was based on various proxy “thermometers” such as tree rings. It seems to show that the earth purrs along merrily and constantly until the 20th century, when rapid warming takes off.

The hockey stick became the poster child of global warming, the most celebrated graph since
Descartes invented the idea of graphs. We saw it in Gore’s movie. It appeared over and over again in the IPCC report. Let me read from that report, “The rate and duration of warming of the 20th century has been much greater than in any of the previous nine centuries.

Similarly, it is likely that the 1990s have been the warmest decade and 1998 the warmest year of the millennium.” End of argument? No.

We now know that this statement is baseless; it rests on work laden with technical errors and outright finagling. Climategate told us about the behind-the-scenes manipulations to promote and defend the stick, and to prevent criticisms from being published. But even before Climategate, the work of Steve McIntyre, Ross McKitrick, Hans Von Storch, and others had disposed of it from a science perspective.

There are many documented serious problems with the stick. The early statistical methods were found to be flawed; they would produce an upward “blade” even from bogie proxies with no trend.

Other research indicated that the method itself inherently underestimates past temperature changes by a factor of two or more. There is deliberate cherry-picking: the consistent and repeated inclusion of certain favorable proxies, while excluding many others from nearby locations that don’t show stick behavior.

There is the addition of fictional data to create the appearance of warming when the real data don’t show any. There is even an example of contrary data entered upside down so as to contribute to stick behavior.

The most notorious issue involves a widely publicized e-mail string that has scientists discussing a socalled “trick” to “hide the decline.” They were talking about how to deal with a problem in showing how tree ring proxies stack up to the actual temperature record.

The problem is that tree rings showed a decline in their inferred temperature after around 1960-1980, while the actual temperature is believed to have increased. This is called the “divergence problem.”

At issue is whether tree rings can be trusted as proxy “thermometers” going back 1,000 years or more if they can’t reproduce the last 40 years.

The divergence problem was known before the revelations. What is new is that we now know
there was deliberate deception to mask the discrepancies. So in this graph from IPCC 2001, you see four proxy reconstructions wiggling along pretty flat for centuries, then starting up, but if you look close, they mysteriously end around 1960 or soon after.

The actual instrumental record is spliced on to the proxies to create an upward sweeping blade, and the eye loses track of the proxies. In fact proxy data disappear. The part left out for one proxy is shown in the lower right.

It decreases while the instrumental temperature goes up; in fact it drops all the way down to the baseline level of all proxies over the last 400 years.

In the UN WMO Anniversary Report, the trick is complete. We are shown continuous proxy curves as if there are real data after 1960. No one can tell that the last forty years are really instrumental data grafted on because the proxies don’t work.

As a touch of irony, the Forward to that report reads in part, “The WMO stands ready to maintain its role as the authoritative international scientific voice on weather and climate.”

Then there is the revelation that much raw data used to construct the thermometer temperature
record itself from stations around the world have been lost or deleted. It means that other scientists
cannot check basic calculations appearing to show a long-term rise in temperature over the past 150 years.

Destroying data is scientific unacceptable, made doubly damning because of the importance of
the instrumental record and its role in climate modeling – more on this later.

We may never know with certainty how 20th century warming stacks up against the Medieval. The
2006 Wegman Report to Congress concluded that the data just aren’t good enough. But it is a fact
that by latest count, 56 proxy studies – shown below in purple — have the Medieval Period warmer
than today, while only 9 – shown here in blue — have it cooler.

And those nine are not independent.

They are produced by the same researchers, reviewed by the same incestuous set of reviewers, who
use a core of a few proxies again and again to get the hockey stick result. The weight of evidence from proxy studies is that the 20th century was not exceptionally warm after all.

There are other problems with the assertion that 20th century warming was exceptional. One stems
from the fact that it occurred in two bursts – one from about 1910 through about 1940 and one from about 1970 to 2000.

Those two bursts are shown below in separate graphs of global average temperature versus time over a 51-year period – one is from 1895 through 1946; the other is from 1957 through 2008.

The scales are the same for both graphs. The earlier one is ascribed to natural causes because human emissions then were insignificant compared to later in the century. The later one is blamed on us.

The problem is that the first burst was just as fast as the second. Quiz: which is which? Answer: The one blamed on us is on the left. If the first was natural, why is the second unnatural?

Another problem is that there is now serious discomfort with the surface instrumental data

For example, we observe a steady divergence of satellite data from land-based data since the satellite measurement era began in 1979. The graph below is from a recent publication plots the
difference between land data from the National Climate Data Center and the satellite data sets from
the University of Alabama at Huntsville and the Remote Sensing Systems company.

We expect the track indicated by the purple. The expanding difference points to highly exaggerated warming trends in land-based data, by about 1½ degrees Celsius per century. This instrumental difference is much more than the entire 20th century warming trend.

Quiz Number 2: Which data streams are not in the IPCC reports?

We now know that published land temperature trends are highly correlated with socioeconomic
variables such as urban heat island effects, land use, and preferential cool-station drop out, so much so that the published trend may be exaggerated by a factor of two.

And then there is the constant back-correcting of past trends. These corrections consistently make
the past look cooler, whereas unbiased corrections should equally favor warming and cooling.

When you see a published graph of temperature trend, the odds are good that it is steeper than it was a few years ago – because past data have been adjusted to make it look steeper. The problem of data quality and integrity is huge and is just beginning to be unraveled, thanks to the Climategate disclosures and information becoming available in this country through the Freedom of Information Act.

The real backbone of the case is the climate models. These very complex computer models are first
calibrated against the observed warming of the 20th century and then used to forecast climate for
future emissions scenarios.

This calibrating or “hindcasting” is where the exaggeration of past trends gets to be important. The steeper the warming, the harder to account for it with just natural variations.

Indeed, models cannot reproduce past warming with just natural variations, so it is assumed it was caused mostly by greenhouse gases, mainly CO2.

Using the models, the IPCC says that doubling of atmospheric CO2 relative to the preindustrial era – the mid 1800s — will warm the earth on average by 2 to 4 ½ degrees C, with a most likely value of 3 degrees.

That doubling should occur sometime in the second half of the century. But the whole edifice rests on whether those natural variations and the so called “feedbacks” in the climate system are modeled correctly.

Feedbacks are physical and chemical changes in the climate that add to or subtract from the warming effect of CO2 just by itself. They are very hard to get right, and it is not a matter of raw computing power.

Without any feedbacks, the effect of doubling atmospheric CO2 is only about 1 degree. To get serious global warming, there must be large amplifying feedbacks to turbocharge the warming.

In Slide 10, my one equation says that the global warming we get for doubling of atmospheric CO2 is that naked one degree for CO2 all by itself, divided by (1-f). f is called the feedback factor. If all the feedbacks add up to zero, global warming is 1 degree C.

But at one extreme is large positive reinforcing feedback, when f equals 1. Then climate is unstable: adding a single molecule of CO2 would set off runaway warming. To see this, insert for example f=0.99 in the equation, then global warming would be 100 degrees.

But f could also be less than 0, corresponding to negative feedback. Then global warming would be less than 1 degree for doubling. The climate models on which the IPCC relies say that feedback is strongly positive; f is between about 0.5 and 0.8, creating the serious warming they warn us about.

This large positive feedback is itself troubling, because the geological history of the earth suggests that the climate is inherently stable.

The most important feedback is called the cloud-water vapor feedback. Add a little more CO2 in the
air, and the earth will warm slightly. Surface evaporation will increase, giving more water vapor – the daddy of all greenhouse gases. Water vapor forms clouds, and much depends on the clouds.

There are well documented problems with the way the climate models deal with clouds. Colorado State Distinguished Professor of Atmospheric Science Graeme Stephens writes in an extensive review of the cloud feedback issue that, “Different assumptions … produce very different conclusions about the magnitude and sign of feedbacks.” And further, “The lack of maturity of feedback analysis methods also suggests that progress in understanding climate feedback will require development of alternative methods of analysis.”

In addition to theoretical problems, there are major observational issues. Recent empirical studies by Richard Lindzen of MIT, Roy Spencer of the University of Alabama, Stephen Schwartz of Brookhaven National Labs and others provide evidence that the feedback factor is in fact small and may even be net negative so as to dampen global warming.

There is also a large body of work that strongly implicates natural variations such as solar variability and unforced changes in ocean cycles in 20th century warming.

Indeed, the weight of empirical evidence points to a global temperature rise of only about 1 degree C for doubling of CO2, with about half of it already in the bank because of past emissions.

The links provided allow access to a number of papers, reports, and reviews indicating low feedback and therefore a warming of only around a degree. Whatever the problems with models, real science predicts real things that really happen. The most fundamental tenet of science is the notion that it must be tested by prediction.

If it is successful, we keep it around tentatively; if not, we show it the door. The climate models have failed to predict the course of global temperature or to identify an observed greenhouse gas fingerprint. The temperature projections in earlier IPCC reports have greatly overstated subsequent measured temperature trends.

The graph below compares the central projections of global average temperature from each of the four IPCC reports to the actual temperature trend, starting in each report year. The models keep calling for a rate of warming that just doesn’t happen.

Indeed, counter to model predictions and despite steady increases in atmospheric CO2, there has been no statistically significant global warming since around 1995, and the oceans down to a depth of 700 meters have actually cooled slightly since 2004 when the Project Argo deep diving buoys were deployed.

That is the case for attribution of global warming to human emissions. It rests on the climate models and the hockey stick, neither of which holds up well to hardnosed scientific scrutiny. So what about that appeal to authority, “All scientific societies agree… ” It is the show stopper to engaging any lay person on the issue.

Indeed the societies have become yet more important as IPCC credibility has declined, and National Academy of Sciences leadership has announced its intention to provide science advocacy for what it thinks is needed societal change.

So a small group of physicists set out in early 2009 to try to moderate the 2007 Policy Statement of the American Physical Society, the world’s second largest society of physicists. The key point of concern has been the excerpt from the Statement shown below.

The passage is laden with problems: Nothing in science is incontrovertible; Global warming is not
occurring, at least for more than ten years; but worst of all is the simple fact that none of this is based on a scientific assessment undertaken by the Society itself. It simply parrots the posture of the IPCC and its derivatives. It has angered many members.

Even those unfamiliar with the science disliked its definitiveness, its successive non sequiturs, and its alarmist nature.

With Climategate and other disclosures casting doubt over the integrity of climate science and eroding public trust invested in science and scientists, we petitioned the Society to conduct an independent and objective study of the global warming issue.

So far 265 physicists have endorsed the call for a new look at the science, and as you can see from the samples below, some highly experienced and distinguished physicists think we need that look.

The signatories come from diverse academic, government, and industrial backgrounds. There are 100 Fellows and members of the National Academies of Sciences and Engineering. Many have authored important books on various physics topics, and many have won significant prizes and awards, including a Nobel.

A number have published major research on the global warming issue, authored books on it, or worked in contiguous areas of meteorology and climate. Nearly all have backgrounds in key science
areas that underlie the global warming issue.

But backing off does not come easily or happily to large organizations that are invested in a position, especially one strongly conducive to continued research funding. To date, the APS Statement remains intact, but a long explanatory note has been added; the original 157 word Statement is retained but appended with 827 words of explanation.

There is a problem when you need a group of physics monks to expend more than 5 times the number of words to explain what the original words meant.

But grudging progress is being made. The Society is still considering a study. But we are not waiting
around. I want to use this occasion to announce our plans to start a Forum on Climate Physics within the APS, under terms specified in the Society Constitution.

It will be a way for physicists with all points of view to meet, learn about and debate the science, and present research insights independent of the posture of the physics monks. Every scientist, climate expert or no, has a dog in this fight that is literally to preserve the scientific method, so painfully assembled over the past 400 years.

We come now to the, “It doesn’t matter,” response. The Precautionary Principle warns that no matter how small the risk, we have to drive it as close to zero as we can. Not so fast. We need to include economic risk in the equation as well as risk of environmental damage. And when we do, things get more complicated.

Here I will put on my strategic planning hat. I spent a good part of my career sorting out the economic benefits, costs, and risks of various technology policies and specific technologies.

First understand that in any serious emissions reduction scenario, we are talking about diverting huge amounts of capital from the economy. Marty Hoffert of NYU and colleagues and Tom Wigley of NCAR and his colleagues have independently calculated how much new emissionless energy the world will need to deploy in order to stabilize the atmosphere at various levels of CO2.

They estimated that by 2050, 10 to 30 trillion watts of emissionless primary energy production would be needed to stabilize at twice the pre-industrial level. With renewables costing about $5-$10 per average watt above and beyond hydrocarbon- based energy, the additional capital could easily exceed $50 trillion over 40 years.

Even in this era of mega spending and hyper deficits, this is real money. Such a capital investment would be equivalent to devoting the entire current U.S. private nonresidential capital investment over 40 years to the extra cost of emissionless energy. It would suck capital from all other investments that would otherwise go to advancing the quality of life for everyone on earth, with the
most severe impact on the poorest people in the less developed world.

But we can say more about the economic impact besides its huge magnitude. Using models,
environmental economists have explored the benefits and costs of various policy options. An
integrated assessment model is the mother of all models. Think of it as a carbon cycle model, climate model, and economic model ganged together.

A leading practitioner of such models is Economics Professor William Nordhaus, Sterling Professor of Economics at Yale University. He is a Fellow of the American Academy of Arts and Sciences.

He serves on the Congressional Budget Office Panel of Economic Experts. In 2005, the Association of Environmental and Resource Economists presented him with the Publication of Enduring Quality Award.

This is considered the “Nobel” of environmental economics, and Nordhaus is generally believed to be on the short list for the actual Nobel. Here is an excerpt of results from his 2008 book. Slide 16 lists ratios of the present value of benefits from avoided climate change damage to the present value of the costs for various policies – assuming the IPCC’s most likely value of climate sensitivity: 3 degrees C for doubling of CO2.

There are some interesting things here. First, the optimum policy under this scenario is a gradually implemented carbon tax.

It returns a benefit of nearly 2½ times costs. But a 50-year delay before doing anything is very close to optimal. It affords time for economies to grow so they can better afford the costs of abatement.

A strengthened Kyoto – which stresses cap-and-trade – just about breaks even. Constraining global temperature rise to 2 degrees C, a favorite for EU flag waving, gets us into negative return territory. And the truly draconian Gore proposal returns only 50 cents on the dollar.

Interestingly, the model says that if IPCC is right, we are going to endure a large percentage of damage no matter what we do, and the more aggressively we try to avoid it, the less attractive the investment becomes.

But now the real punch line: From what we know, the IPCC’s value of 3 degrees C for doubling is almost certainly much too high, so these benefit to cost ratios and the climate damage are also too high.

So the Precautionary Principle is hazardous to our future economic health. The science and the
economics are coupled, and it makes a great deal of difference whether we follow the IPCC case or the body of empirical evidence.

Indeed following the Precautionary Principle would logically lead us to spend trillions on other improbable events such as the next large asteroid collision, and we know that will happen someday.
One purpose of science is to reduce uncertainty so as to facilitate wise decisions to promote human

The Precautionary Principle claims that one special brand of uncertainty is itself a reason to make decisive economic changes. But the science simply does not support any kind of economic
intervention. Beware of the “It doesn’t matter” response. It does matter, and it matters a great deal.

To wrap up, I want to talk a little about the anger response: “You denier! How dare you tell me there won’t be a catastrophe.”

Here I rely largely on my son Geoff, the academic social psychologist in the family. As contrary evidence has accumulated, proponents of global warming have shown signs of cognitive dissonance.

The idea is that when presented with information that is dissonant from long held beliefs or strong beliefs that people have invested in, the easiest way to deal with it is to ignore it, refuse to accept it, or simply avoid that type of information.

This helps explain why people can be resistant to new information that on a rational basis should be good news. Why would you get angry if someone tells you, “There won’t be a climate catastrophe.”

More than a half century ago, Leon Festinger developed the concept of cognitive dissonance and
conducted early studies referred to even today. One study looked at people who bought bomb
shelters during the Cold War.

It found that they tended to exaggerate the threat of nuclear war and to discount prospects for tension-reducing proposals, almost as if they were invested in nuclear war.

Festinger’s book, When Prophecy Fails, tells of a doomsday cult that predicted the end of the world on a particular date. When the day came and went, paradoxically the believers became even more
determined they were right.

They became louder and proselytized even more aggressively. So we can expect ever more strident, extreme, and opaque defenses from proponents. Here for example is an excerpt from a recent letter signed by National Academy of Sciences members:

“Many recent assaults on climate science and, more disturbingly, on climate scientists by climate change deniers, are typically driven by special interests or dogma, not by an honest effort to provide an alternative theory that credibly satisfies the evidence.”

We are told that warming is accelerating when there has been none. Bizarre warnings of completely speculative “tipping points” abound. We are told that even cooling is consistent with global warming, and indeed global warming has morphed into Climate Change, allowing it to embrace anything that happens, much like astrology.

The global warming issue will limp on, and evidence against a serious human contribution will continue to mount. So as our elected representatives consider burdensome regulations and legislation, they should know that it will not make a whit of difference to the climate and will cause unnecessary economic hardship for all of us, especially the world’s poorest who might otherwise aspire to finally make great strides this century.

Links to a Sampling of Scientific Literature, Reports, Presentations, and Other Material

Hockey Stick/Climategate
E. J. Wegman et al, Ad Hoc Committee Report on the “Hockey Stick” Global Climate Reconstruction, Committee
on Energy and Commerce, US House of Representatives, Washington, DC (2006)
A. W. Montford, The Yamal Implosion, 09-30-09
A. W. Montford, Climate Cuttings 33, 11-20-09
A. W. Montford, The Hockey Stick Illusion: Climategate and the Corruption of Science, (Independent Minds,
S. McIntyre, Memorandum to Parliament (CRU 32) (2010),,
with figures:
C. D. Idso et al, Medieval Warming Project, Center for the Study of Carbon Dioxide and Global Change

Bias in Land Temperatures
R. R. McKitrick and P. J. Michaels, Quantifying the Influence of Anthropogenic Surface Processes and Inhomogeneities on Gridded Global Climate Data, Journal of Geophysical Research 112, D24S09, doi:10.1029/2007JD008465, (2007)
J. D’Aleo and A. Watts, Surface Temperature Records: Policy Driven Deception?, Science and Public Policy Institute (2010)
Feedbacks, Natural Variations, and Climate Sensitivity
G. L. Stevens, Cloud Feedbacks in the Climate System: A Critical Review, J. Climate 18, 237-273 (2005)
D. H. Douglass and J. R. Christy, Limits on CO2 Climate Forcing from Recent Temperature Data of Earth, Energy and Environment, 20 (2009)
D. H. Douglass and R. S. Knox, Ocean Heat Content and Earth’s Radiation Imbalance, Physics Letters A 373, 3296–3300 (2009)
D. H. Douglass et al, A Comparison of Tropical Temperature Trends With Model Predictions, International Journal of Climatology (2007)
R. S. Lindzen, Global Warming – Sensibilities and Science Third International Conference on Climate Change, 06- 22-2009
R. S. Lindzen, Deconstructing Global Warming, Presentation to the Competitive Enterprise Institute, 10-26-2009
R. S. Lindzen and Y-S Choi, On the Determination of Climate Feedbacks from ERBE Data, Geophysical Research Letters, 36, L16705, doi:10.1029/2009GL039628 (2009)
N. Scafetta and B.J. West, Phenomenological Reconstructions of the Solar Signature in the Northern Hemisphere Surface Temperature Records Since 1600, Journal of Geophysical Research 112, D24S03, doi:10.1029/2007JD008437 (2007) %201600.pdf
N. Scafetta, Climate Change and Its Causes, Science and Public Policy Institute (2010)
N. J. Shaviv, Using the Oceans as a Calorimeter to Quantify the Solar Radiative Forcing, Journal of Geophysical Research 113, A11101, doi:10.1029/2007JA012989 (2008)
S. E. Schwartz, Heat Capacity, Time Constant, and Sensitivity of Earth’s Climate System. Journal of Geophysical Research, 112, D24S05, doi:10.1029/2007JD008746 (2007)
R. W. Spencer et al, Cloud and Radiation Budget Changes Associated with Tropical Intraseasonal Oscillations, Geophysical Research Letters, 34 L15707, doi:10.1029/2007/GL029698, (2007)
R. W. Spencer, Satellite Evidence Against Global Warming Being Caused by Increasing CO2, Search and Discovery Article #110117 (2009)
R. W. Spencer, The Great Global Warming Blunder: How Mother Nature Fooled the World’s Top Climate Scientists, (Encounter Books, 2010)  A.A. Tsonis et al, A New Dynamical Mechanism for Major Climate Shifts, Geophysical Research Letters, 34, L13705, doi:10.1029/2007GL030288 (2007)
J. Scott Armstrong et al, Global Warming Alarm Based on Faulty Forecasting Procedures: Comments on the United States Department of State’s U.S. Climate Action Report 2010, 5th ed. May 5, 2010,
S. F. Singer, Nature, Not Human Activity, Rules the Climate (Heartland, 2008)
C. D. Idso, S. F. Singer et al, Climate Change Reconsidered (Heartland, 2009)
Role of the National Academy of Sciences and the American Physical Society
Martin Rees (President, Royal Society) and Ralph J. Cicerone (President, U.S. National Academy of Sciences),
Letter to the Financial Times, April 9, 2010
Open Letter, Climate Change and the Integrity of Science, Science 05-10-10
American Physical Society Policy Statement (2007) and Addendum (2010),
American Physical Society Petition: Signatories, Comments, and Other Information

Energy and Atmospheric Carbon Dioxide
M. H. Hoffert et al, Energy Implications of Future Stabilization of Atmospheric CO2 Content, Nature, 395, 881-884
T. L. Wigley et al, Economic and Environmental Choices in the Stabilization of Atmospheric CO2 Content, Nature 240, 240-243 (1996)

Economic Impact and Cognitive Dissonance
W. D. Nordhaus, A Question of Balance: Weighing the Options on Global Warming Policies (Yale University Press,
G. C. Álvarez et al, Study of the Effects on Employment of Public Aid to Renewable Energy Sources, Universidad Rey Juan Carlos (2009)
L. Festinger et al, When Prophecy Fails: A Social and Psychological Study of A Modern Group that Predicted the Destruction of the World (University of Minnesota Press, 1956)
F. K. Berrien et al, The Fallout-Shelter Owners: A Study of Attitude Formation, The Public Opinion Quarterly 27, No. 2, 206-216 (Oxford University Press, 1963) (subscription required)

[Editor’s note: the above was first published as ‘Understand Climate Science Before Making Climate Policy‘  George C. Marshall Institute, by Roger W. Cohen, May 14, 2010]

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Comments (3)

  • Avatar

    Al Shelton


    Much too long of an article.
    Also, CO2 has been debunked as a cause of global warming.
    Going on, and on, and on, about CO2 and AGW is much like the old Ptolemaic proponents of the claim that the earth is the center of the universe and planetary motions explained with epicycles. IMO.

    • Avatar

      Terry Shipman


      Yes. Even the threat of the Inquisition and torture could not stop the eventual acceptance of the heliocentric model of the solar system. It took very brave people to go against the “consensus.”

  • Avatar

    Iván Moreira B.


    This article was published into October 19th, 2019 and originally was written in 2010, by this reason this one mention that Mr. William Nordhaus is candidate to the Nobel prize that finally get, he won Nobel Prize of Economy in 2018 with Paul Romer.

Comments are closed