Scientists arguing that global warming is primarily caused by natural processes
Attribution of climate change, based on Meehl et al. (2004), which represents the consensus view
1979ÔÇô2009: Over the past 3 decades, temperature has not correlated with sunspot trends. The top plot is of sunspots, while below is the global atmospheric temperature trend. El Chich??n and Pinatubo were volcanoes, while El Ni??o is part of ocean variability. The effect of greenhouse gas emissions is on top of those fluctuations.
1860ÔÇô1980: In contrast, earlier there was apparent similarity between trends in terrestrial sea surface temperatures and sunspots (related to solar magnetic activity: TSI varies slightly while UV and indirectly cosmic rays vary somewhat more).Both consensus and non-consensus scientific views involve multiple climate change influences including solar variability and internal forcings, plus human influences such as greenhouse gas emissions and land use change.[15] However, they differ on issues such as how sensitive they think the climate system is to increases in greenhouse gases.[15][16]Scientists in this section have made comments that the observed warming is more likely attributable to natural causes than to human activities. Their views on climate change are usually described in more detail in their biographical articles.
Khabibullo Abdusamatov, mathematician and astronomer at Pulkovo Observatory of the Russian Academy of Sciences said in a 2007 news agency interview: "Global warming results not from the emission of greenhouse gases into the atmosphere, but from an unusually high level of solar radiation and a lengthy ÔÇô almost throughout the last century ÔÇô growth in its intensity."[17]
Sallie Baliunas, astronomer, Harvard-Smithsonian Center for Astrophysics said in a 2002 lecture for The Heritage Foundation: "Most of the increase in the air's concentration of greenhouse gases from human activitiesÔÇöover 80 percentÔÇöoccurred after the 1940s. That means that the strong early 20th century warming must be largely, if not entirely, natural."[18]"The coincident changes in the sun's changing energy output and temperature records on earth tend to argue that the sun has driven a major portion of the 20th century temperature change."[18] "[T]he recent warming trend in the surface temperature record cannot be caused by the increase of human-made greenhouse gases in the air."[19][not in citation given]
Ian Clark, hydrogeologist, professor, Department of Earth Sciences, University of Ottawa said in a 2004 newspaper letter:"That portion of the scientific community that attributes climate warming to CO2 relies on the hypothesis that increasing CO2, which is in fact a minor greenhouse gas, triggers a much larger water vapour response to warm the atmosphere. This mechanism has never been tested scientifically beyond the mathematical models that predict extensive warming, and are confounded by the complexity of cloud formation ÔÇô which has a cooling effect. ... We know that [the sun] was responsible for climate change in the past, and so is clearly going to play the lead role in present and future climate change. And interestingly... solar activity has recently begun a downward cycle."[20]
Chris de Freitas, Associate Professor, School of Geography, Geology and Environmental Science, University of Auckland said in a 2006 newspaper article: "There is evidence of global warming. ... But warming does not confirm that carbon dioxide is causing it. Climate is always warming or cooling. There are natural variability theories of warming. To support the argument that carbon dioxide is causing it, the evidence would have to distinguish between human-caused and natural warming. This has not been done."[21]
David Douglass, solid-state physicist, professor, Department of Physics and Astronomy, University of Rochester was reported to have said in a 2007 paper in the International Journal of Climatology: "The observed pattern of warming, comparing surface and atmospheric temperature trends, does not show the characteristic fingerprint associated with greenhouse warming. The inescapable conclusion is that the human contribution is not significant and that observed increases in carbon dioxide and other greenhouse gases make only a negligible contribution to climate warming."[22]
Don Easterbrook, emeritus professor of geology, Western Washington University said in a 2006 presentation to the Geological Society of America: "Glaciers advanced from about 1890ÔÇô1920, retreated rapidly from ~1925 to ~1945, readvanced from ~1945 to ~1977, and have been retreating since the present warm cycle began in 1977. ... Because the warming periods in these oscillations occurred well before atmospheric CO2 began to rise rapidly in the 1940s, they could not have been caused by increased atmospheric CO2, and global warming since 1900 could well have happened without any effect of CO2. If the cycles continue as in the past, the current warm cycle should end soon and global temperatures should cool slightly until about 2035, then warm about 0.5 ??C from ~2035 to ~2065, and cool slightly until 2100."[23]
William M. Gray, Professor Emeritus and head of The Tropical Meteorology Project, Department of Atmospheric Science, Colorado State University said in a 2006 newspaper interview: "I am of the opinion that [global warming] is one of the greatest hoaxes ever perpetrated on the American people."[24]
William Happer, physicist specializing in optics and spectroscopy, Princeton University said in a 2006 newspaper interview: "All the evidence I see is that the current warming of the climate is just like past warmings. In fact, it's not as much as past warmings yet, and it probably has little to do with carbon dioxide, just like past warmings had little to do with carbon dioxide"[25]
William Kininmonth, meteorologist, former Australian delegate to World Meteorological Organization Commission for Climatology wrote in a 2004 article and book: "There has been a real climate change over the late nineteenth and twentieth centuries that can be attributed to natural phenomena. Natural variability of the climate system has been underestimated by IPCC and has, to now, dominated human influences."[26]
David Legates, associate professor of geography and director of the Center for Climatic Research, University of Delaware wrote in a 2006 article for the National Center for Policy Analysis: "About half of the warming during the 20th century occurred prior to the 1940s, and natural variability accounts for all or nearly all of the warming."[27]
Tad Murty, oceanographer; adjunct professor, Departments of Civil Engineering and Earth Sciences, University of Ottawa said in 2005: Global warming "is the biggest scientific hoax being perpetrated on humanity. There is no global warming due to human anthropogenic activities. The atmosphere hasnÔÇÖt changed much in 280 million years, and there have always been cycles of warming and cooling. The Cretaceous period was the warmest on earth. You could have grown tomatoes at the North Pole"[28]
Tim Patterson, paleoclimatologist and Professor of Geology at Carleton University in Canada said in a 2007 newspaper article: "There is no meaningful correlation between CO2 levels and Earth's temperature over this [geologic] time frame. In fact, when CO2 levels were over ten times higher than they are now, about 450 million years ago, the planet was in the depths of the absolute coldest period in the last half billion years. On the basis of this evidence, how could anyone still believe that the recent relatively small increase in CO2 levels would be the major cause of the past century's modest warming?"[29][30]
Ian Plimer, Professor emeritus of Mining Geology, The University of Adelaide said in a 2002 television debate: "Natural climate changes occur unrelated to carbon dioxide contents. We've had many, many times in the recent past where we've rapidly gone into a greenhouse and the carbon dioxide content has been far, far lower than the current carbon dioxide content... It looks as if carbon dioxide actually follows climate change rather than drives it".[31]
Nicola Scafetta, research scientist in the physics department at Duke University said in a 2010 article originally written for the Italian magazine La Chimica e lÔÇÖIndustria (Chemistry and Industry): "At least 60% of the warming of the Earth observed since 1970 appears to be induced by natural cycles which are present in the solar system. A climatic stabilization or cooling until 2030ÔÇô2040 is forecast by the phenomenological model."[32][33]
Tom Segalstad, head of the Geology Museum at the University of Oslo said in a 2007 presentation to the 9th International Symposium on Mining in the Arctic: "The IPCC's temperature curve (the so-called 'hockey stick' curve) must be in error, because the Medieval warm period (the "Climate Optimum") and the Little Ice Age both are absent from their curve, on which the IPCC bases its future projections and recommended mitigation. All measurements of solar luminosity and 14C isotopes show that there is at present an increasing solar radiation which gives a warmer climate (Willson, R.C & Hudson, H.S. 1991: The Sun's luminosity over a complete solar cycle. Nature 351, 42ÔÇô44; and Coffey, H.E., Erwin, E.H. & Hanchett, C.D.: Solar databases for global change models.
www.ngdc.noaa.gov/stp/SOLAR/solarda3.html). Warmer climate was previously perceived as an optimum climate and not catastrophic. ... On a wet basis the Earth's atmosphere consists by mass of ~73.5% nitrogen, ~22.5% oxygen, ~2.7% water, and ~1.25% argon. CO2 in air is in minimal amount, ~0.05% by mass, and with minimal capacity (~2%) to influence the "Greenhouse Effect" compared to water vapor"[34]