Setting the Stage for Risk Management: Severe Weather Under a Changing Climate

The most recent evaluations of the state of changes occurring in the Earth’s climate through the 2013 Assessment Report 5 (AR5) of the Intergovernmental Panel on Climate Change and through the 2014 U.S. National Climate Assessment clearly indicates that climate change is happening now, it is changing rapidly, and that the primary cause is human activities. These assessments draw upon the latest scientific understanding of climate and climate change, synthesizing recent advances in the understanding of the science of climate change, and providing a succinct overview of the past and projected effects of climate change on the United States and the world. Findings include new analyses of the observed trends and projected future climate changes. Along with increasing temperatures over most of our planet, the pattern of precipitation change in general is one of increases at higher northern latitudes and drying in the tropics and subtropics over land. One of the major findings is that there has been an increase in some key types of extreme weather events, especially in heat waves and large precipitation events, in the U.S. (and throughout the world) over the last 50 years. There has been an increase in the number of historically top 1 % of heavy precipitation events across all regions of the U.S.—this is not surprising, as the atmosphere warms it holds more moisture. The analyses also indicate the trend towards large precipitation events is likely to continue to increase throughout this century. The drying of the subtropics and wetter conditions at more northern latitudes means that both droughts and floods are likely to be increasing issues in various parts of the world. Scientific analyses indicate a strong link between changing trends in severe weather events and the changing climate. In addition, there are many concerns about potential impacts of the changing climate, e.g., the effects of sea level rise on coastal areas. The aim here is to summarize the findings from the new assessments, plus provide a discussion of the current understanding of severe weather in relation to the science of climate change, with a special emphasis on the issues and remaining uncertainties affecting our future.