Kienast, F., Tarasov, P., Schirrmeister, L., Grosse, G. and Andreev, A.A. 2008. Continental climate in the East Siberian Arctic during the last interglacial: Implications from palaeobotanical records. Global and Planetary Change 60: 535-562.
In an attempt to portray earth's current temperature as being extremely high and, therefore, extremely dangerous (as well as CO2-induced), Hansen et al. (2006) have claimed the earth "is approximately as warm now as at the Holocene maximum and within ~1°C of the maximum temperature of the past million years.
What was done
In a study that provides evidence that is pertinent to this claim, Kienast et al. studied plant macrofossils found in permafrost deposits on Bol'shoy Lyakhovsky Island (73°N, 141°30'E) of the New Siberian Archipelago on the coast of the Dimitrii Laptev Strait, from which they reconstructed climatic conditions that prevailed during the prior or Eemian Interglacial.
What was learned
In the words of the five researchers, "macrofossils of warmth-demanding shrubs and aquatic plants, occurring farther south today, indicate that local mean temperatures of the warmest month were at least 12.5°C, thus c. 10°C higher than today at that time," when maximum atmospheric CO2 levels were on the order of 290 ppm, or about 100 ppm less than they are today.
What it means
This finding is just one of many that indicate that various places on the planet have been much warmer than they are today at various times over the past million years, and when the air's CO2 content was also much lower than it is today. For more such examples, see our Major Report Carbon Dioxide and Global Change: Separating Scientific Fact from Personal Opinion, which also presents evidence refuting many of Hansen's other outlandish claims.
Hansen, J., Sato, M., Ruedy, R., Lo, K., Lea, D.W. and Medina-Elizade, M. 2006. Global temperature change. Proceedings of the National Academy of Sciences USA 103: 14,288-14,293.