Treatment of uncertainty in the IMPACT2C web-atlas

Projections of future climate change and climate change impacts are subject to different layers of uncertainty. These layers include (and are not limited to) several factors such as the uncertain development of future greenhouse gas emissions, missing processes or other deficiencies of climate models and impact models as well as the chaotic nature of the modelled climate and natural systems, respectively. The webpage of the European Climate Adaptation Platform (Climate-ADAPT), among others, provides a good overview and further reading on the various issues regarding climate change uncertainty.

Within IMPACT2C, the uncertainties arising from the estimated future greenhouse gas emissions could be neglected due to the focus on the +2°C global warming period. Representing the uncertainty arising from the imperfect model systems is then emphasized by using an ensemble approach for all analyses. This approach is reflected in the maps as follows:

• All maps representing mean values for recent and future time periods always display ensemble mean values. The same holds true when seasonal maps are depicted. The ensemble size of the respective analyses is indicated in the accompanying text (usually under the 'Additional information' section).
• For the projected future changes additionally to the mean change also the 20^th, 50^th and 80^th percentile of projected changes can be displayed in order to show the ensemble bandwidth.