Extreme Weather and Climate Change
Understanding the Link, Managing the Risk
Updated December 2011
Thousands of record-breaking weather events worldwide bolster long-term trends of increasing heat waves, heavy precipitation, droughts and wildfires. A combination of observed trends, theoretical understanding of the climate system, and numerical modeling demonstrates that global warming is increasing the risk of these types of events today. Debates about whether single events are “caused” by climate change are illogical, but individual events offer important lessons about society’s vulnerabilities to climate change. Reducing the future risk of extreme weather requires reducing greenhouse gas emissions and adapting to changes that are already unavoidable.
Typically, climate change is described in terms of average changes in temperature or precipitation, but most of the social and economic costs associated with climate change will result from shifts in the frequency and severity of extreme events. This fact is illustrated by a large number of costly weather disasters in 2010, which tied 2005 as the warmest year globally since 1880. Incidentally, both years were noted for exceptionally damaging weather events, such as Hurricane Katrina in 2005 and the deadly Russian heat wave in 2010. Other remarkable events of 2010 include Pakistan’s biggest flood, Canada’s warmest year, and Southwest Australia’s driest year. 2011 continued in similar form, with “biblical” flooding in Australia, the second hottest summer in U.S. history, devastating drought and wildfires in Texas, New Mexico and Arizona as well as historic flooding in North Dakota, the Lower Mississippi and in the Northeast.
Munich Re, the world’s largest reinsurance company, has compiled global disaster for 1980-2010. In its analysis, 2010 had the second-largest (after 2007) number of recorded natural disasters and the fifth-greatest economic losses. Although there were far more deaths from geological disasters—almost entirely from the Haiti earthquake—more than 90 percent of all disasters and 65 percent of associated economic damages were weather and climate related (i.e. high winds, flooding, heavy snowfall, heat waves, droughts, wildfires). In all, 874 weather and climate-related disasters resulted in 68,000 deaths and $99 billion in damages worldwide in 2010.
The fact that 2010 was one of the warmest years on record as well as one of the most disastrous, begs the question: Is global warming causing more extreme weather? The short and simple answer is yes, at least for heat waves and heavy precipitation. But much of the public discussion of this relationship obscures the link behind a misplaced focus on causation of individual weather events. The questions we ask of science are critical: When we ask whether climate change “caused” a particular event, we pose a fundamentally unanswerable question (see Box 1). This fallacy assures that we will often fail to draw connections between individual weather events and climate change, leading us to disregard the real risks of more extreme weather due to global warming.
Climate change is defined by changes in mean climate conditions—that is, the average of hundreds or thousands events over the span of decades. Over the past 30 years, for example, any single weather event could be omitted or added to the record without altering the long-term trend in weather extremes and the statistical relationship between that trend and the rise in global temperatures. Hence, it is illogical to debate the direct climatological link between a single event and the long-term rise in the global average surface temperature.
Nonetheless, individual weather events offer important lessons about social and economic vulnerabilities to climate change. Dismissing an individual event as happenstance because scientists did not link it individually to climate change fosters a dangerously passive attitude toward rising climate risk. The uncertainty about future weather conditions and the illogic of attributing single events to global warming need not stand in the way of action to manage the rising risks associated with extreme weather. Indeed, such uncertainty is why risk managers exist – insurance companies, for example – and risk management is the correct framework for examining the link between global climate change and extreme weather.
An effective risk management framework accommodates uncertainty, takes advantage of learning opportunities to update understanding of risk, and probes today’s rare extreme events for useful information about how we should respond to rising risk. Risk management eschews futile attempts to forecast individual chaotic events and focuses on establishing long-term risk certainty; that is, an understanding of what types of risks are increasing and what can be done to minimize future damages. An understanding of the meaning of risk and how it relates to changes in the climate system is crucial to assessing vulnerability and planning for a future characterized by rising risk.
For more on the relationship between extreme weather and climate change, visit our Extreme Weather web page, where you'll find our extreme weather events map, along with other reports and C2ES resources.
 Karl, T. R., Meehl, G. A., Miller, C. D., Hassol, S. J., Waple, A. M., & Murray, W. L. (2008). Weather and Cliamte Extremes in a Changing Climate; Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Washington, D.C., USA: Department of Commerce, NOAA's National Climatic Data Center.
 BBC News. (2011, January 1). Australia's Queensland faces 'biblical' flood. Retrieved May 19, 2011, from http://bbc.in/fNzGgK; Associated Press. (2011, May 1). Federal fire crews bring expertist to huge TX fire. Retrieved May 19, 2011, from http://bit.ly/iz6JRs; Associated Press. (2011, June 16). Concern over human-caused blazes grows as wind-driven wildfires promp more evacuations. Retrieved June 22, 2011, from Washington Post: http://wapo.st/iWxirz; Sulzberger, A.G. (2011, June 26). In Minot, N.D., Flood Waters Stop Rising. Retrieved November 22, 2011, from New York Times: http://nyti.ms/ufT9jY; Doyle, R. (2011, September 8) U.S. sweltered through hottest summer in 75 years. Retrieved November 22, 2011, from USA Today: http://usat.ly/o73h4o; Robertson, C. (2011, May 15). Record Water for a Mississippi River City. Retrieved November 22, 2011, from New York Times: http://nyti.ms/lp0cTA; Freedman, A. (2011, September 12). Historic Flooding Recedes in Pennsylvania, New York; at least 15 dead. Retrieved November 22, 2011, From Washington Post: http://wapo.st/qvywOo
 Karl et al., Weather and Cliamte Extremes in a Changing Climate, Op. cit.
Authors: Nick Mabey, Jay Gulledge, Bernard Finel and Katherine Silverthorne
Download this report (pdf)
There is a growing consensus in the security community that climate change presents significant risks to the delivery of national, regional and global security goals. Through sea level rise, shortages of food and water and severe weather events, climate change will have significant impacts on all countries, which in turn could affect their social stability and economic security. In the coming decades such impacts will increase the likelihood of conflict in fragile countries and regions. Peaceful management of even moderate climatic changes will require investment in increased resilience in national and international security and governance systems.
Security analysis has mainly examined the implications of climate change over the coming two decades. These are largely unavoidable under all plausible greenhouse gas emissions reduction scenarios, given the inertia in energy infrastructure and the global climate system. However, if immediate action is not taken to reduce the steady rise in global emissions, there will be a rapid increase in the risk of far more severe impacts, resulting in security challenges that are much more significant than current estimates indicate.
But climate change is not currently well-managed. Agreements at the most recent UN climate negotiations in Cancun in 2010 included a goal of limiting climate change to, at most, a 2°C average global temperature rise. However, the emissions reductions pledged by countries at the same conference would actually result in a 50 percent chance of global temperatures rising by 3-4°C. Fragile areas such as Southern Africa could experience 50 percent more warming than the global rate. If countries failed to deliver on their emissions pledges, or if we have underestimated climate sensitivity, increases of up to 7°C are also possible. But the risks are not symmetrical. There is a ‘long tail’ on the probability distribution which makes more severe outcomes much more likely than more benign ones. In addition, above 3°C of warming the probability of breaching thresholds for “tipping elements” in the climate system rises sharply. For example, events such as a major die-back of the Amazon rain forest or release of methane from the Arctic tundra would further increase global warming levels.
E3G is an independent not-for-profit organization that works to accelerate the global transition to sustainable development. Visit E3G's website at www.e3g.org