Our initial analytical focus was on the differences in ecosystem carbon budgets when comparing symmetric versus asymmetric climate change. For this, we used four different scenarios 20 : ambient scenario corresponding to the historical recorded temperature **data** during the period of 1961-1990 (T amb ), symmetric warming (T sym ), double asymmetric warming (T asy2 ) and triple asymmetric warming (T asy3 ). The three scenarios for temperature increases were based on a combination of recorded recent temperature increases (SI: Figure S2) and the predicted future magnitude of temperature increases simulated by a regional climate model (RegCM3) under the A2 IPCC CO 2 emission scenarios (SRES A2) 40 (SI: Figure S3). In the second step, the interactive effects of changes in temperature, precipitation, and atmospheric CO 2 concentrations were investigated. The precipitation treatment had two levels: an ambient level corresponding to the historical mean precipitation amounts recorded during the period of 1961-1990 (P amb ), and precipitation change based on the 2071-2100 predictions from the RegCM3 (P cha ) 40 . The model MT-CLIM (Version 4.3) was used to compute meteorological variables not included in the standard weather station records and required by the Biome-BGC model 41 . The CO 2 treatment also had two levels: an ambient level corresponding to the historical concentrations recorded during the period of 1961-1990 (C amb ) based on the Mauna Loa measurements (http://co2now.org/), and a scenario taking into account the gradual predicted increase in atmospheric CO 2 concentrations from 626 ppm v in 2071 to 836 ppm v in 2100 (C inc ) as predicted by the SRES A2 emission scenario **data** 42 .