Preface

Extreme weather has affected human society since the beginning of recorded history and certainly long before then. Humans, along with every other living thing on the Earth, have adapted to a certain range of variability in the weather. Although extreme weather can cause loss of life and significant damage to property, people and virtually every other creature have, at least to some degree, adapted to the infrequent extremes they experience within their normal climatic zone.

Humans’ use of fossil fuel since the start of the Industrial Revolution has begun to modify the Earth’s climate in ways that few could have imagined a century ago. The consequences of this change to the climate are seemingly everywhere: average temperatures are rising, precipitation patterns are changing, ice sheets are melting, and sea levels are rising. These changes are affecting the availability and quality of water supplies, how and where food is grown, and even the very fabric of ecosystems on land and in the sea.

Despite these profound changes, climate change and its associated risks still may appear to many people as distant and remote in both time and space. The natural daily and seasonal variability of the weather can mask the changes in the overall climate. Yet, when people experience extreme events that they believe may be occurring with different—usually greater—frequency or with increased intensity, many ask about the connection between climate change and extreme events.

Effective, rigorous, and scientifically defensible analysis of the attribution of extreme weather events to changes in the climate system not only helps satisfy the public’s desire to know but also can provide valuable information about the future risks of such events to emergency managers, regional planners, and policy makers at all levels of government. A solid understanding of extreme weather event attribution in the context of a changing climate can help provide insight into and confidence in the many risk calculations that underpin much of society’s building codes; land, water, health, and food management; insurance; transportation networks; and many additional aspects of daily life.

There are compelling scientific reasons to study extreme weather event attribution as well. The basic physics of how the climate system works and the broad-scale impacts of rapid addition of greenhouse gases on the climate system are well understood. However, much is still to be learned about how the changing climate affects specific