Linking global warming levels to local climate scenarios: applicability, prospects and uncertainties

Recently, interest in analysing regional climate change impacts in light of global warming levels (GWLs) has risen, not least because the IPCC used them in their current report cycle. GWLs shift the focus point in the uncertainty chain compared to classical scenario approaches like SRES or RCPs, and allow a more comprehensive analysis of the differences and implications of a 1.5°C vs. a 2°C warmer world. Although a lot of research has been done to link GWLs to regional climate change signals within global circulation model (GCM) outputs, or between GCMs and regional climate model (RCM) outputs, there is a lack in studies to link GWLs to localised climate scenarios. In contrast to analysing regional signals within GCMs and between GCMs and RCMs, often no direct link can be established between the global and the downscaled models, especially when they are driven by an older version of GCMs (e.g. CMIP3, CMIP5), because many local climate scenarios have not been updated since the release of CMIP6.

Here, a version-agnostic methodology of linking local climate scenarios to GWLs derived from CMIP6 GCMs is presented for the example of the Austrian climate scenarios (ÖKS15). It is an extension of the time sampling method where time slices around the crossing point of global mean temperature over the respective GWL threshold are derived from GCMs. When using those time slices directly, uncertainties emerging from the local scale would intersperse the anthropogenic warming signal with natural climate variability. To avoid this, instead of explicit time periods, the respective climate change signals are used to select the period of interest from the local scenarios. This approach promises a more robust analysis compared to the time sampling method, because it considers error propagation biases due to the downscaling method and ambiguous reference periods to derive the anomalies.

The study is expected to contribute to locally adapted assessment reports on climate change impacts that intend to use the IPCC methodology, like the second Austrian Assessment Report on Climate Change (AAR2).