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Professor Ian D. Clark's prepared testimony to the Senate committee - 15/12/11

The earth has experienced global warming for most of the 20th century, raising global temperatures about 0.6°C. This shift to warmer conditions ended a 400 year cold period known as the little ice age during which glaciers globally had extended to maximal positions and which was characterized by failures in agriculture documented in Europe and most notably in the Danish Greenland colonies. The 20th century rise in global temperature has been accompanied by large-scale retreat of glaciers and expansion of agriculture.

The rise in temperature is characterized by a steady increase up to 1940, a decrease through to the mid 1970s, a second steady increase through the 1980s and 1990s, and a decade of essentially flat temperature to today.

Twentieth century warming has also been accompanied by an increase in atmospheric CO2 by some 100 ppm or some 36% due to a combination of land clearing for agriculture, warming of the oceans and the burning of fossil fuels. However, unlike the temperature curve, CO2 has been steadily rising, with an increase in rate during the cold 1950s and 1960s.

The early 20th century rise in temperature is recognized by both sides of the debate to have been essentially natural. Only the rise in temperature of the 1980s to 1990s is attributed by the IPCC to anthropogenic CO2.

The flat trend for temperatures over the past decade contrasts with the IPCC predictions, based on General Circulation Models, of a 0.2°C per decade rise in temperatures.

The 20th century warming trend is not unusual. A similar warm period, the 200 year Medieval climate optimum at the turn of the 10th century is well documented by expansion of the Vikings across an ice-free North Atlantic to Greenland and Labrador and by grape growing in England as examples. Further back in the Holocene interglacial period we see multiple examples of climate optima characterized by warming and documented by numerous paleoclimate records from lake and bog sediments. During this period, atmospheric CO2 had little fluctuation, and therefore played no role in the changing climate.

Through the ice ages of the past million years, global temperature has varied more significantly, and is well documented by deep ice core records from the Antarctic ice sheet. This archive of temperature has also produced a very robust record of atmospheric CO2, which on initial inspection, correlates remarkably well with temperature and suggested by many as playing a role in forcing climate through the ice ages. Closer inspection requires a greater understanding of gas-ice relationships in glaciers, but indisputably shows that increases in atmospheric CO2 clearly lag temperature by on average some 800 years. This record shows that CO2 has played no role in the dramatic climate change of the ice ages.

We can look further back in time and see that even over the past 500 million years CO2 has played no role in the changes in global temperature documented by Dr. Jan Veizer.  Rather, we see that despite atmospheric CO2 being over 10 times higher than today, we had global ice ages. In fact, the CO2 levels we have today (including our anthropogenic contributions) are near the lowest during the history of life on earth.

How then does the IPCC attribute so much global warming to the recent increases in CO2. Modellers recognize that CO2 is a very minor greenhouse gas and is not on its own responsible for the observed warming. Water vapour and low altitude clouds, i.e. the water cycle, is by far the major greenhouse agent, and is responsible for maintaining our planet at a comfortable 14°C. Models amplify the very minor CO2 effect with a much stronger water vapour feedback to achieve the warming trends predicted for the 21st century.

The models have been proven wrong by careful measurement of atmospheric temperature trends over the past 40 years. The models predict strong greenhouse warming in the troposphere as a signal of CO2-driven warming. However, the measured temperature record shows no such warming. Climate scientists’ statements in emails leaked from the CRU document their great concern with this discrepancy and their recognition that “the models are wrong.”

So what is driving 20th century warming? New scientific evidence developed over the past two decades is increasingly demonstrating an enhanced role for solar forcing. A recent paper published in Nature (Solanki et al. 2004) shows that the sun has been more active in the past 100 years than in the past 11,000 years. Further, they show that global temperature over this period is strongly correlated with radioisotopes that are well-recognized as proxies of solar activity.

On a regional basis, for the Arctic region, measurements of solar activity have been highly correlated with surface temperatures. The warming in the Arctic has also been shown to be unrelated to the so-called arctic amplification of greenhouse warming, but rather is due to changes in vertical temperature profiles that were not predicted by the models.

In summary, we can say:

There is no geological evidence that CO2 has behaved in the past as a significant forcing mechanism for climate.

CO2 remains at the lowest range observed over geological time.

CO2 is more than a benign gas. It is an essential nutrient for plants, and within reasonable limits has only beneficial effects for life.

Our efforts to limit the use of fossil carbon-based energy has solved no environmental problems, yet has created many more, including the accelerated production of ethanol and the conversion of tropical rainforest to tropical palm oil production.

It is time to address real, tangible environmental issues.