Diagnosing atmosphere‐ocean general circulation model errors relevant to the terrestrial biosphere using the Köppen climate classification

Abstract

Coupled atmosphere‐ocean‐land‐sea ice climate models (AOGCMs) are often tuned using physical variables like temperature and precipitation with the goal of minimizing properties such as the root‐mean‐square error. As the community moves towards modeling the earth system, it is important to note that not all biases have equivalent impacts on biology. Bioclimatic classification systems provide means of filtering model errors so as to bring out those impacts that may be particularly important for the terrestrial biosphere. We examine one such diagnostic, the classic system of Köppen, and show that it can provide an “early warning” of which model biases are likely to produce serious biases in the land biosphere. Moreover, it provides a rough evaluation criterion for the performance of dynamic vegetation models. State‐of‐the art AOGCMs fail to capture the correct Köppen zone in about 20–30% of the land area excluding Antarctica, and misassign a similar fraction to the wrong subzone.

Changes in Arid Climate over North China Detected by the Koppen Climate Classification

“…The criteria used in the Köppen classification are mutually exclusive across the primary and secondary types and so is the demarcation of climate regimes. Therefore, the two subtypes in the arid climate are clearly distinguishable from each other and from the rest of the major climate types and their subtypes (Gnanadesikan and Stouffer 2006;Peel et al 2007). …”

“…The Köppen climate classification has been widely used to evaluate climate change impacts on climate types (Fraedrich et al 2001;Peel et al 2002;Dang et al 2007;Diaz and Eischeid 2007;Roderfeld et al 2008) and to diagnose numerical models (Lohmann et al 1993;Kleidon et al 2000;Shin et al 2004;Gnanadesikan and Stouffer 2006). The data used in the previous studies cover not only limited areas but also the entire global land-mass with the various spatial resolutions ranging from 4-km pixel to 2°−3° grid box, indicating the applicability of the Köppen scheme to the study of the regional climate changes.…”

Pace of shifts in climate regions increases with global temperature

“…The Köppen scheme is very sensitive to thresholds as it distinguishes between different climates based for example upon whether conditions are warmer than some temperature or wetter than a particular precipitation amount. Therefore, model biases are critical to this analysis and models do exhibit quite large discrepancies in their Köppen climates compared to those derived from observations 7 . To help reduce errors in climate classification changes in this work, only anomalies from the model output are used, and these are added to a 20 y observational base period (see Methods).…”

“…Its purpose is to predict biome distribution based not only on monthly temperature and precipitation values but also on the annual cycles of both. This classification also takes into account plant sensitivity to thresholds 7,8 . Such bioclimatic classification schemes have the advantage that they are easily applied to climate model output, and therefore possible future changes in ecosystem types can be evaluated on a grid cell level as for every grid cell bioclimatic information becomes available.…”

Climate projections in the Hornsund area, Southern Spitsbergen

“…Our estimates of air temperature and precipitation result in a different classification of Köppen climate type in Southern Spitsbergen than in the reference period. According to the criteria described in Gnanadesikan and Stouffer (2006), present climatic conditions in Southern Spitsbergen are classified as Polar tundra Et (area covered by tundra with 0°C <T max <10°C and T min <-3°C). According to projections, the climatic conditions in the far future would be classified as a maritime subarctic climate or subpolar oceanic climate (Cfc).…”