Twentieth Century warming was nothing unusual. Climate is cyclic, and there are cycles within cycles. The graph below, based on reconstruction from the geologic record, shows that there have been several cycles of warming and cooling since the end of the last glacial epoch. The temperature during the Holocene Climate Optimum was 3ºF to 10ºF warmer than today in many areas.
Evidence for these cycles is found in the ice cores from Greenland and Antarctica, in fossil pollen records, in cores of sediments taken beneath lakes and the ocean, in the distribution of glacial deposits, in the analysis of stalagmites in caves, and in the historic record. These records also show that the cycles were global events.
It is still unclear why these cycles occur at the intervals they do. Some researchers say it’s a combination of solar cycles which periodically reinforce each other both positively and negatively.
For most of the history of this planet, atmospheric carbon dioxide levels were more than 10 times the current level. For most of the last 250 million years carbon dioxide levels were more than three times the current level.
Climate alarmist claims that our carbon dioxide emissions could trigger runaway global warming is pure nonsense. It if could happen, it would have happened already. Run-away warming cannot happen on this planet because Earth is a water world. Warming increases evaporation. Water vapor, and its latent heat, is carried aloft by convection. Heat is lost to space when the water vapor condenses. The condensation also produces clouds which reflect incoming solar radiation. That is Earth’s negative feedback mechanism to prevent run-away warming.
Dansgaard, W. , et al., 1969, One Thousand Centuries of Climatic Record from Camp Century on the Greenland Ice Sheet, Science 17 Vol. 166. no. 3903.
Friis-Christensen, E. And Lassen, K., 1999, Length of Solar Cycle: An Indicator of Solar Activity Closely Associated with Climate, Science 254.
Hu, F.S. et al., 2003, cyclic Variation and Solar Forcing of Holocene Climate in the Alaskan Subarctic, Science 301.
Niggerman, S., et al., 2003, A Paleoclimate Record of the last 17,000 Years in Stalagmites from the B7 Cave, Sauerland, Germany, Quaternary Science Reviews 22.
Pisias, N.G. et al., 1973, Spectral analysis of Late Pleistocene-Holocene Sediments, Quaternary Research, March 1973.
Schönwiese, Christian, 1995, Klimaänderungenaten, Analysen, Prognosen.-224 S.ISBN: 978-3-540-59096-5.
Viau, A.E. et al., 2002, Widespread Evidence of 1,500-yr Climate Variability in North America during the Past 14,000 Years, Geology 30.