Monday, August 5, 2013

New paper finds Greenland temperatures were ~8C warmer than the present during the last interglacial

A new paper published in Climate of the Past finds that "the previous interglacial (Eemian, 130,000–114,000 years ago) had a mean sea level ...4 to 7 meters above the current level, and, according to climate proxies, a 2 to 6 C warmer Arctic summer climate." The paper also finds temperatures above the Greenland ice sheet were a remarkable 8C higher than the present, far exceeding the most catastrophic of IPCC predictions.
"Various Greenland ice cores show lower rates of depletion for the Eemian, suggesting that the Greenland Ice Sheet had a significantly warmer climate during the Eemian than today (Johnsen et al., 1997). For example, Eemian δ18O values at NorthGRIP and NEEM are about 3–4‰ higher than present. Using the temperature-δ18O relation observed for the present interglacial, this represents an Eemian warming of 8 ± 4 K (NEEM community members, 2013)"
All of which suggests the warming periods of the current interglacial, including the current warm period, are entirely within natural variability, not unprecedented, and not unusual. Furthermore, there is no evidence of a runaway greenhouse effect or runaway positive-feedbacks despite an Arctic climate that was much warmer in the past.

Clim. Past, 9, 1589-1600, 2013

Importance of precipitation seasonality for the interpretation of Eemian ice core isotope records from Greenland

W. J. van de Berg1, M. R. van den Broeke1, E. van Meijgaard2, and F. Kaspar3
1IMAU, Utrecht University, Utrecht, the Netherlands
2KNMI, De Bilt, the Netherlands
3Deutscher Wetterdienst – DWD, Offenbach, Germany

Abstract. The previous interglacial (Eemian, 130–114 kyr BP) had a mean sea level highstand 4 to 7 meters above the current level, and, according to climate proxies, a 2 to 6 K warmer Arctic summer climate. Greenland ice cores extending back into the Eemian show a reduced depletion in δ18O of about 3‰ for this period, which suggests a significant warming of several degrees over the Greenland ice sheet. Since the depletion in δ18O depends, among other factors, on the condensation temperature of the precipitation, we analyze climatological processes other than mean temperature changes that influence condensation temperature, using output of the regional climate model RACMO2. This model is driven by ERA-40 reanalysis and ECHO-G GCM boundaries for present-day, preindustrial and Eemian climate. The processes that affect the condensation temperature of the precipitation are analyzed using 6-hourly model output. Our results show that changes in precipitation seasonality can cause significant changes of up to 2 K in the condensation temperature that are unrelated to changes in mean temperature.

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