Abstract
A global warming of 2 °C relative to pre-industrial climate has been considered as a threshold which society should endeavor to remain below, in order to limit the dangerous effects of anthropogenic climate change. The possible changes in regional climate under this target level of global warming have so far not been investigated in detail. Using an ensemble of 15 regional climate simulations downscaling six transient global climate simulations, we identify the respective time periods corresponding to 2 °C global warming, describe the range of projected changes for the European climate for this level of global warming, and investigate the uncertainty across the multi-model ensemble. Robust changes in mean and extreme temperature, precipitation, winds and surface energy budgets are found based on the ensemble of simulations. The results indicate that most of Europe will experience higher warming than the global average. They also reveal strong distributional patterns across Europe, which will be important in subsequent impact assessments and adaptation responses in different countries and regions. For instance, a North–South (West–East) warming gradient is found for summer (winter) along with a general increase in heavy precipitation and summer extreme temperatures. Tying the ensemble analysis to time periods with a prescribed global temperature change rather than fixed time periods allows for the identification of more robust regional patterns of temperature changes due to removal of some of the uncertainty related to the global models’ climate sensitivity.
Highlights
There is an ambition to limit global average surface temperature to 2 ◦C relative to pre-industrial levels.1748-9326/14/034006+11$33.00 c 2014 IOP Publishing LtdThis is in broad alignment with Article 2 of the objectives of the United Nations Framework Convention on Climate Change (UNFCCC 1992), i.e. ‘stabilization of greenhouse gas (GHG) concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system’
The Third Assessment Report (TAR: IPCC 2001) outlined greater negative impacts and more widespread and greater risks with rising temperature, while the Fourth Assessment Report (AR4: IPCC 2007) stated it was ‘very likely that all regions will experience either declines in net benefits or increases in net costs for increases in temperature greater than about 2–3 ◦C’
The European Union agreed to the proposed goal (CEU 1996, 2004, CEC 2005, 2007), and at the UNFCCC Conference of the Parties in Cancun (UNFCCC 2010), there was international agreement to ‘establish clear goals and a timely schedule for reducing human-generated GHG emissions over time to keep the global average temperature rise below two degrees’
Summary
There is an ambition to limit global average surface temperature to 2 ◦C relative to pre-industrial levels. In order to have a comprehensive picture of the consequences of a 2 ◦C warmer climate for Europe, climate projections with a higher spatial resolution than global climate projections (such as provided by the World Climate Research Program ‘Climate Model Intercomparison Project’ CMIP3 (Meehl et al 2007) and CMIP5 (Taylor et al 2012)) are needed, with a rigorous assessment of uncertainties These goals can be achieved by ensembles of climate projections using regional, limited-area models to downscale global climate projections. Our method is to collect changes in climate parameters associated with these different times and a reference period for each simulation and gather them in a ‘2 ◦C ensemble’ This ensemble includes uncertainties in the simulation of regional processes simulations and their responses to the global warming and reduces some of the uncertainty due to driving GCM sensitivity. We provide a unique assessment of what the 2 ◦C goal might mean for Europe’s climate, overall and across regions, and how this compares to the global average
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