Detection, Attribution And Projection Of Changes In Surface Temperature And Climate Classes Under Global Warming Background

Under global warming background, several topics were investigated in this paper using multiple observational data as well as CMIP multi-model outputs:1) attribution of warming during 1979-2005 on sub-continental and basin scale; 2) detection and attribution of significant changes in Koppen climate classification at global scale, together with projection of these changes in 21st century; 3) the spatial and temporal evolution of projected changes in Koppen climate classes over China in 21st century. We find that:1) Attributing observed SST trends and Sub-continental Land Warming to Anthropogenic Forcing during 1979-2005Observations show warming, significantly different from natural variations at the 95% confidence level, over one-third of all grid boxes, and averaged over 15 of 21 sub-continental regions and 6 of 10 ocean basins. Coupled simulations forced with all forcing factors, or greenhouse gases only, reproduce observed SST and SAT patterns. Uncoupled AMIP-like atmosphere-only (prescribed SST and atmospheric radiative forcing) simulations reproduce observed SAT patterns. All of these simulations produce consistent net downward long-wave radiation patterns. Simulations with natural-only forcing simulate weak warming. Anthropogenic forcing effects are clearly detectable at the 5% significance level at global, hemispheric, and tropical scales and in nine ocean basins and 15 of 21 sub-continental land regions. Attribution results indicate that ocean warming during 1979-2005 for the globe and individual basins is well represented in the CMIP5 multi-model ensemble mean historical simulations. While land warming may occur as an indirect response to oceanic warming, increasing greenhouse gas concentrations tend to be the ultimate source of land warming in most sub-continental regions during 1979-2005.2) Significant anthropogenic-induced changes of climate classes since 1950Percentage of total land area see changes in climate types, as well as three Koppen indices (area, absolute latitude and elevation) is used to depict changes in Koppen climate classes. Together with estimated internal variability from control simulations, detection and attribution analysis are performed to investigate changes in major Koppen climate types during 1950-2010. In the observation (University of Delaware data set), about 5.7% of the global total land area has shifted toward warmer and drier climate types during 1950-2010, and significant changes include expansion of arid and high-latitude continental climate zones, shrinkage in polar and midlatitude continental climates, pole-ward shifts in temperate, continental and polar climates, and increasing average elevation of tropical and polar climates. All these changes cannot be explained by internal natural variability at 95% confidential level. Except for the expansion of type B, other significant changes in Koppen indices are almost entirely induced by increasing temperature. Such observational detection results are very robust across data sets (both Hadley center data and GISS data). Using CMIP5 multi-model averaged historical simulations forced by observed anthropogenic and natural, or natural only, forcing components, we find that these changes of climate types since 1950 cannot be explained as natural variations but are alternatively driven by anthropogenic factors (e.g. green house gases). In the future, significant expansion and pole-ward shift of type A, as well as significant increase in area and elevation of type C are expected to emerge by around 2020. As Koppen climate classification is a potential distribution of vegetation and biome system, results here suggest that anthropogenic forcing might have already generated significant impacts on ecosystem in many areas worldwide.3) Projected Shifts in Koppen Climate Zones over China and their Temporal Evolution in CMIP5 Multi-Model SimulationsThe emergence time of climate shifts at a 1° scale over China from 1990-2100 are identified and the temporal evolution of Koppen-Geiger climate classifications computed from CMIP5 multi-model outputs are investigated. By 2010, climate shifts are detected in transition regions (7.5% of total land area), including rapid replacement of mixed forest (Dwb) by deciduous forest (Dwa) over Northeast China, strong shrinkage of alpine (ET) climate type on the Tibetan Plateau, weak northward expansion of subtropical winter-dry (Cwa) over eastern China and contraction of oceanic climate (Cwb) in Southwest China. Under all future RCP scenarios, reduction of Dwb in Northeast China and ET on the Tibetan Plateau accelerates substantially during 2010-2030, and half of the total area occupied by ET in 1990 is projected to be redistributed by 2040. Under the RCP 8.5 scenario, sub-polar continental winter dry climate over Northeast China disappears by 2040-2050, ET on the Tibetan Plateau disappears by 2070, and the climate types in 37.7% and 52.6% of China’s land area change by 2050 and 2100, respectively. Results here indicate imperative impacts of anthropogenic climate changes on China’s ecoregions in the future decades.