Boreal lakes moderate seasonal and diurnal temperature variation and perturb atmospheric circulation: analyses in the Community Earth System Model 1 (CESM1)

ABSTRACT

We used a lake thermal physics model recently coupled into the Community Earth System Model 1 (CESM1) to study the effects of lake distribution in present and future climate. Under present climate, correcting the large underestimation of lake area in CESM1 (denoted CCSM4 in the configuration used here) caused 1 °C spring decreases and fall increases in surface air temperature throughout large areas of Canada and the US. Simulated summer surface diurnal air temperature range decreased by up to 4 °C, reducing CCSM4 biases. These changes were much larger than those resulting from prescribed lake disappearance in some present-day permafrost regions under doubled-CO₂ conditions. Correcting the underestimation of lake area in present climate caused widespread high-latitude summer cooling at 850 hPa. Significant remote changes included decreases in the strength of fall Southern Ocean westerlies. We found significantly different winter responses when separately analysing 45-yr subperiods, indicating that relatively long simulations are required to discern the impacts of surface changes on remote conditions. We also investigated the surface forcing of lakes using idealised aqua-planet experiments which showed that surface changes of 2 °C in the Northern Hemisphere extra-tropics could cause substantial changes in precipitation and winds in the tropics and Southern Hemisphere. Shifts in the Inter-Tropical Convergence Zone were opposite in sign to those predicted by some previous studies. Zonal mean circulation changes were consistent in character but much larger than those occurring in the lake distribution experiments, due to the larger magnitude and more uniform surface forcing in the idealised aqua-planet experiments.

• lake modelling
• climate model evaluation
• land–atmosphere interactions
• atmospheric dynamics
• boreal climate change

6. Acknowledgements

Michael Wehner (Lawrence Berkeley National Lab), John Chiang (University of California, Berkeley), Benjamin Santer (Lawrence Livermore National Lab), William Collins (Lawrence Berkeley National Lab) and Sarah Kang (Columbia University) provided helpful comments on interpreting large-scale atmospheric responses to regional changes in terrestrial surface forcing. David Lawrence (National Center for Atmospheric Research) facilitated interaction with the CESM Land Model Working Group and support in running and interpreting the model. One anonymous reviewer and one named reviewer (Sumant Nigam) provided helpful comments in clarifying and improving the manuscript. This work was supported by the Director, Office of Science, Office of Biological and Environmental Research, Climate and Environmental Science Division, of the US Department of Energy under Contract No. DE-AC02-05CH11231 to Berkeley Lab.