Reconciling divergent trends and millennial variations in Holocene temperatures
- Univ. of Wyoming, Laramie, WY (United States). Department of Geology and Geophysics
- Univ. of Oregon, Eugene, OR (United States). Department of Geography
- USGS, Corvallis, OR (United States)
- Univ. of Utah, Salt Lake City, UT (United States). Department of Geography
Cooling during most of the past two millennia has been widely recognized1,2 and has been inferred to be the dominant global temperature trend of the past 11,700 years (the Holocene epoch)3. However, long-term cooling has been difficult to reconcile with global forcing4, and climate models consistently simulate long-term warming4. The divergence between simulations and reconstructions emerges primarily for northern mid-latitudes, for which pronounced cooling has been inferred from marine and coastal records using multiple approaches3. Here we show that temperatures reconstructed from sub-fossil pollen from 642 sites across North America and Europe closely match simulations, and that long-term warming, not cooling, defined the Holocene until around 2,000 years ago. The reconstructions indicate that evidence of long-term cooling was limited to North Atlantic records. Early Holocene temperatures on the continents were more than two degrees Celsius below those of the past two millennia, consistent with the simulated effects of remnant ice sheets in the climate model Community Climate System Model 3 (CCSM3)5. CCSM3 simulates increases in ‘growing degree days’—a measure of the accumulated warmth above five degrees Celsius per year—of more than 300 kelvin days over the Holocene, consistent with inferences from the pollen data. It also simulates a decrease in mean summer temperatures of more than two degrees Celsius, which correlates with reconstructed marine trends and highlights the potential importance of the different subseasonal sensitivities of the records. Despite the differing trends, pollen- and marine-based reconstructions are correlated at millennial-to-centennial scales, probably in response to ice-sheet and meltwater dynamics, and to stochastic dynamics similar to the temperature variations produced by CCSM3. Although our results depend on a single source of palaeoclimatic data (pollen) and a single climate-model simulation, they reinforce the notion that climate models can adequately simulate climates for periods other than the present-day. They also demonstrate that amplified warming in recent decades increased temperatures above the mean of any century during the past 11,000 years.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF)
- Sponsoring Organization:
- USDOE Office of Science
- OSTI ID:
- 1565673
- Journal Information:
- Nature (London), Journal Name: Nature (London) Journal Issue: 7690 Vol. 554; ISSN 0028-0836
- Publisher:
- Nature Publishing Group
- Country of Publication:
- United States
- Language:
- English
Similar Records
The Quaternary fossil-pollen record and global change
A Holocene East Asian winter monsoon record at the southern edge of the Gobi Desert and its comparison with a transient simulation