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Disinformation about Global Warming


David Morrison

Volume 34.2, March / April 2010

For the past decade I have followed the growing evidence for climate change and global warming, talking to colleagues who are atmospheric scientists and at­tend­ing presentations by leading scientists at professional meetings such as the American Association for the Advance­ment of Science (AAAS) and the American Geophysical Union (AGU). Rarely in that time did I meet anyone who seriously disagreed with the growing consensus about global warming and the threats it imposes. This past October, however, I found these ideas disputed by both fellow skeptics and some in the audience we were speaking to. This was a shock, and it made me look again at the claims of the warming dissenters. I would like to share some of what I learned.

There is a lot of misinformation and disinformation about global warming on the Internet, driven in part by political and economic issues. These political and economic aspects are complex, and relatively few scientists understand them in detail. It is important to remember that climate is long term by definition; trends in climate require at least a decade to reveal themselves. Thus we can understand the climate trends in the 1990s pretty well but not yet in the 2000s.

One of the goals of the deniers seems to be to sow confusion and give the impression that the science behind global warming is weak. This disinformation campaign is at least partly successful; polls (for example, the 2009 Pew/AAAS poll, SI, November/December 2009) show that about half the people in the United States think there is substantial disagreement among scientists, when actually there has been a consensus on this topic for about a decade. The scientific case becomes stronger all the time, but public acceptance is lagging. Most of the counterarguments  don’t make scientific sense, or else they are based on information that is obsolete. It is fine to be skeptical, but we need to be concerned when skepticism drifts into denial.

This is not the place to make the case for global warming; that is done very well in the reports of the Intergovernmental Panel on Climate Change. See especially the IPCC Summary for Policymakers and Frequently Asked Questions posted at Instead, I list below (in bold) some “red-flag” arguments from global warming deniers that can help you spot disinformation.

  1. We should not worry about carbon dioxide since the main greenhouse gas is water vapor. This statement misrepresents the heating process. It is the carbon dioxide (and methane) that controls the thermal structure of the atmosphere. Water vapor content is highly variable and essentially follows the carbon dioxide, providing a positive feedback that amplifies the effects of carbon dioxide.
  2. What we are seeing are “natural variations” caused primarily by variations in solar output. This is false; we have been monitoring solar energy for a quarter century, and the variations are taken into account in all the climate models. Most of the temperature variations up to the beginning of the twentieth century can be traced to small changes in solar output, plus long-term cyclical changes in Earth’s orbit and short-term cooling associated with large volcanic eruptions. There are also heating and cooling events associated with El Nino and other shifts in the circulation of the ocean and atmosphere. Since mid-century, however, the rapid heating from carbon dioxide in the atmosphere is overwhelming these “natural” cycles.
  3. The apparent increase in temperature is an artifact caused by the fact that much of the data are from cities, which are warmer than their surroundings. This is also wrong; the “heat island” effect has been corrected in plots of global temperatures. A great deal of scientific effort is going into understanding and combining the various measurements of temperature to produce a consistent data set, combining direct measurements on the ground and from space with indirect “proxy” information, for example from isotopic measurements that track temperature very closely. Also, of course, there are large-scale effects of rising temperature that are easily seen, such as retreat of glaciers, melting on the Greenland and Antarctic icecaps, and loss of sea ice in the Arctic.
  4. While temperatures seem to have been rising in the lower atmosphere (the troposphere), they are dropping in the stratosphere. People who say this don’t realize that this is the expected signature of greenhouse warming (because greenhouse gases in the troposphere impede the flow of radiant heat from Earth’s surface to the stratosphere). If there were an external cause, such as increased energy from the Sun, both troposphere and stratosphere would be heating. Today’s computational models allow greenhouse warming to be distinguished from other causes and reveal the primacy of greenhouse warming over the past several decades.
  5. Human activity and volcanic eruptions both add to the cloud cover and cause more sunlight to be reflected from the atmosphere. This largely counteracts any heating from the greenhouse effect. Atmospheric pollution, both natural (from volcanoes) and human-caused (from smoke and other aerosols), does influence temperature, reflecting sunlight and reducing the warming we would have from increased greenhouse effect alone. Without these contributions to cooling, the added greenhouse heating would be significantly greater than what we measure. There are also temperature increases caused by darkening of the surface, because more sunlight is absorbed. As the ice melts in the Arctic Ocean, the dark water absorbs a great deal more sunlight, an effect that will accelerate future global warming.
  6. IPCC-2007
  7. The warming trend during the 1990s is no big deal; temperatures are actually lower than they were in the medieval warm period. This is wrong; over at least the past few thousand years, temperatures have never been as high as they are today. By the middle of the twentieth century the temperature passed the record highs from about a thousand years ago, and they have been rising ever since, taking us into unknown climate territory.
  8. IPCC-2007
  9. While there was warming in the 1990s, this has stopped and the world is now beginning what may be a long-term cooling cycle. This is a misinterpretation of the temperature measurements. There are always short-term fluctuations in global temperature superimposed on the the overall warming trend. Those who say the temperature has plateaued or is cooling over the past decade start with the anomalously high temperature in 1998, reflecting a major El Nino event that year. If you adopt such a high temperature excursion as your baseline, of course the values tend to be lower for the next several years (called the regression to the mean). But putting aside the temperature spike in 1998, temperatures during the past decade have continued the warming trend of the 1990s.
  10. More carbon dioxide is good, since it makes plants grow better. This might be true if we could increase carbon dioxide without greenhouse heating, but high temperatures are not good for most plants. In addition, the increase in carbon dioxide acidifies the oceans, which can destroy coral reefs or have deleterious effects on zooplankton, on which much ocean life depends. Over much of the Earth, localized long-term droughts caused by global warming will have a major negative effect on plants.
  11. There is no consensus; many scientists disagree about global warming. This is not true at all. Dissenters have published hardly any peer-reviewed scientific papers in the past decade. The dissenters are mostly not climate scientists, and they have offered no alternative models to explain the data. The national academies of science in all of the industrialized countries have endorsed the findings of the Intergovernmental Panel on Climate Change (IPCC), which represents a strong scientific agreement on both the reality of global warming and the challenges it implies.
  12. How can we trust climate scientists when numerous e-mails from the U.K. climate scientists show that they have distorted their data and actively suppressed dissenting opinions? These stolen e-mails from a British climate center reveal how real scientists work, warts and all. People write things in personal e-mails that they would never want published. There is no evidence, however, of fudging or suppressing the climate data. There appear to have been efforts to influence editors of scientific journals not to publish papers by global-warming deniers. At one level this is exactly what scientists normally do: vet papers through the peer-review process to weed out poor science. If the actions go further and represent impropriety, that will be revealed by the current investigation. But there is nothing in this controversy that undercuts the overwhelming scientific consensus about human-caused global warming.

Finally, let me comment on the role of the skeptic. (See also Stuart Jordan, “The Global Warming Debate: Science and Scientists in a Democracy,” SI, November/December 2007, and Jordan’s response to several global warming disputers in “Response to ‘Assessing the Credibility of CFI’s Credibility Project,’” SI, January/February 2010.) Note that I have said nothing about future warming trends, rises in sea level, or warming-induced increases in the severity of storms. As the saying goes, it is difficult to make predictions, especially about the future. It is certain that warming will continue since temperatures are dominated by the increasing carbon dioxide in the atmosphere. In spite of promises, there has been no reduction in the rate of CO2 production, and even if governments take drastic action we will continue to pump out lots of greenhouse gases at least through the middle of this century. In addition, the climate system itself has inertia, and the warming lags the CO2 concentration by ten to fifteen years. There are also major uncertainties about feedback effects, especially from warming in the polar regions, which might accelerate melting ice and contribute to release of CO2 and methane from the tundra. Scientists have tried to model these processes, and their simulations agree for the next ten to twenty years. Beyond that, the models diverge, however, due both to uncertainties in the computations and to differences in the assumptions made. It is reasonable to be skeptical about specific predictions, especially after 2030, but that should not blind us to what is happening to our planet now.


The IPCC reports and the peer-reviewed articles they reference are the basic resources for this article. In addition to the IPCC materials, I recommend two reliable Web sites: RealClimate—Climate Science from Climate Scientists, available at, and SkepticalScience—Examining the Sci­ence of Global Warm­ing Skepticism, available at

David Morrison

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David Morrison is a long-time NASA senior scientist and Committee for Skeptical Inquiry fellow. He now divides his time between the SETI Institute and the NASA Lunar Science Institute. He hosts the "Ask an Astrobiologist" column at NASA's website.