extreme weather

2012: 4th Warmest Winter for U.S.

NOAA reported today that this winter turned out to be the 4th warmest on record in the contiguous United States. That’s not surprising given how much the world has warmed over the past few decades. In fact, all of the seven warmest years in over 100 years of climate data have occurred since 1992, and over the past three decades, a warmer-than-average winter has been twice as likely as a cool one. These data are consistent with how scientists say global warming affects the weather. The risk of warm winters is increasing over time, but that doesn’t mean that cold winters disappear, similar to the way that loaded dice change the probability of a particular roll but don’t eliminate other possibilities.

Weather on the Juice?

A common analogy to explain the link between climate change and extreme weather is gambling with “loaded dice.” For people who aren’t the gambling type but love America’s pastime, perhaps Barry Bonds’ homerun statistics would be more enlightening, or at least more entertaining. A new video from the National Center for Atmospheric Research draws an analogy between a batter on steroids and the “doping” of the atmosphere with manmade CO2. 

Extreme Weather and Climate Change

Extreme Weather and Climate Change
Understanding the Link, Managing the Risk

Updated December 2011

by Daniel G. Huber and Jay Gulledge, Ph.D.

Download the paper (pdf)

Press release

Listen to the press briefing


Executive Summary:

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.


Box 1. Why can’t scientists say whether climate change “caused” a given weather event?

Climate is the average of many weather events over of a span of years. By definition, therefore, an isolated event lacks useful information about climate trends. Consider a hypothetical example: Prior to any change in the climate, there was one category 5 hurricane per year, but after the climate warmed for some decades, there were two category 5 hurricanes per year. In a given year, which of the two hurricanes was caused by climate change? Since the two events are indistinguishable, this question is nonsense. It is not the occurrence of either of the two events that matters. The two events together – or more accurately, the average of two events per year – define the change in the climate.

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.[1] This fact is illustrated by a large number of costly weather disasters in 2010, which tied 2005 as the warmest year globally since 1880.[2] 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.[3]

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.[4]  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.[5] 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.

What about climate change and tornadoes?

Scientists are unsure if tornadoes will become stronger or more frequent, but with increased temperatures changing the weather in unexpected ways, the risk is real that tornado outbreaks will become more damaging in the future.  The lack of certainty in the state of the science does not equate with a lack of risk, since risk is based on possibility.  The lack of scientific consensus is a risk factor itself, and we must prepare for a future that could possibly include increased tornado damage.

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.


[1] 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.

[2] National Climatic Data Center. (2010, December). State of the Climate Global Analysis: Annual 2010. Retrieved May 19, 2011, from http://1.usa.gov/fxdFai

[3] 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

[4] Munich Re. (2011, February). Topics Geo Natural catastrophes 2010: Analyses, assessments, positions. Retrieved May 19, 2011, from http://bit.ly/i5zbut

[5] Karl et al., Weather and Cliamte Extremes in a Changing Climate, Op. cit.



Daniel Huber
Jay Gulledge

Extreme Weather in 2011

For the second year in a row, unprecedented numbers of extreme weather events have occurred across the globe. However, more of 2011’s impacts occurred in the United States. From the drought in Texas to the floods in the Midwest and Northeast, this past year underscored the huge economic costs associated with extreme weather.  While specific weather events are not solely caused by climate change, the risks of droughts, floods, extreme precipitation events, and heat waves are already climbing as a result of climate change. This year reminded us of our vulnerability to those events.

That’s One Small Step for the IPCC; One Giant Leap for Understanding Our Climate Risk

The Intergovernmental Panel on Climate Change (IPCC) released a “special report” (that’s what they call topical reports they publish in between their better known comprehensive assessments) today that is worth a close look for anyone who wants to start getting ready for a future with weirder and often harsher weather.

About a year ago I published an opinion editorial taking the Intergovernmental Panel on Climate Change (IPCC) to task for neglecting risk-based information to help decision makers cope with inevitable uncertainties about the future impacts of climate change:

Since uncertainty is endemic to the future, when the second IPCC assessment concluded in 1995 that ‘The balance of evidence suggests a discernable human influence on the global climate’, the IPCC should have reconvened around the risk implications of this probable human influence. Instead, it redoubled its effort to reduce physical science uncertainties [which will not be resolved before action is required].

Global Warming Contributing to Texas Drought

This blog is co-written by Jay Gulledge

Recently, President Obama quipped about GOP presidential candidate and Texas governor Rick Perry: “You’ve got a governor whose state is on fire denying climate change.” While this type of election jousting risks further politicizing an issue that should be totally non-partisan, it raises a legitimate question: Is climate change increasing the risk of drought and wildfires in Texas?

Flood Damages Stacking Up in Northeast

With the Northeast still reeling from the impacts of Hurricane Irene, the possibility of even more flooding was almost too much to comprehend. But last week the remnants of Tropical Storm Lee stalled and sent plumes of precipitation toward the Northeast, creating a replay of the floods a few weeks earlier. This time the area along the Susquehanna River in Pennsylvania and New York was in the bulls-eye. Since the ground was still saturated from Irene, this new round of flooding was worse, surpassing the previous record event set in 1972 when Hurricane Agnes dropped a torrential downpour on the area.

Adding More Weather Risk to the Climate System

This op-ed appeared in CQ Researcher.

September 2011

By Jay Gulledge

The risk of extreme weather is rising because of climate change. In the United States, long-term trends show an increasing number of heat waves and heavy downpours and longer, more destructive droughts and wildfires. Climate models simulate these same trends when scientists examine the effects of increases in global warming’s main ingredient – greenhouse gases.

Risk is the best way to understand the link between climate change and extreme weather. Just as smoking and high cholesterol are risk factors for heart disease, natural cycles and global warming are risk factors for extreme weather. This year’s weather impacts have been particularly severe because multiple risk factors are aligned: A long, intense La Nina – a temporary cool period in the equatorial Pacific Ocean that is associated with extreme temperatures, droughts, and flooding in other parts of the world – is occurring at the same time we are experiencing the warmest decade in at least 130 years. The big difference between these risk factors is that natural cycles come and go, whereas global warming increases over time as atmospheric greenhouse gases grow, constantly adding more weather risk to the climate system.

Escalating weather impacts are cutting deeply into the economy. The world’s largest re-insurance company says the number of weather- and climate-related disasters worldwide more than doubled over the past 30 years. Economic losses attributable to weather variability run $485 billion annually. Several multi-billion-dollar events have occurred this year, including Texas’ worst single-year drought, the Mississippi floods, and Hurricane Irene, which is expected to rank among the ten costliest hurricanes in U.S. history.  As the weather becomes more volatile, economic risk will continue to grow.

As recent weather events teach us more and more about our vulnerabilities, the taxpayer-funded National Flood Insurance Program is already $18 billion in debt. Because most of the damage from Hurricane Irene is not privately insured, this financially-strapped program is under pressure once again. And the Federal Emergency Management Agency (FEMA) is running out of money to respond to disasters, even as Congress bickers over how to refill the coffers.

Flood insurance is the federal government’s second-largest fiscal liability after social security. Ignoring rising climate risk will only allow these hidden costs to suck up more taxpayer money. Reducing greenhouse gas emissions and adapting to changes already under way bends down the risk curve, just as exercise and medical insurance lower health risks. If we don’t take these steps, our children and grandchildren will inherit a more dangerous and costlier climate.

Jay Gulledge is the Senior Scientist and Director of the Science and Impacts Program at the Pew Center on Global Climate Change.

by Jay Gulledge--Published in CQ Researcher

Irene’s Impacts Hit Home

During the last weekend of August, the Eastern U.S. braced for a walloping. Hurricane Irene spiraled up the Atlantic coast, ripping trees out of the ground in North Carolina and drenching much of the rest of the coast. When I heard that Irene was making her way up toward my hometown of Ridgewood, NJ, I had flashbacks to Hurricane Floyd, a devastating storm in 1999 that brought us much destruction and devastation.

Learning about Our Risks from Hurricane Irene

So how bad was Hurricane Irene? Some commentators seem to think Irene didn’t match up to the media, yet  preliminary assessments suggest Irene will be one of the top 10 costliest hurricanes ever in the United States. New Yorkers are indeed fortunate that the worst case scenario did not play out in their fair city, but that doesn’t mean there were no worst case scenarios elsewhere.

The worst fears about wind intensity did not play out, but a different devastating outcome did occur: Historic inland flooding across a huge swath of the interior Northeast. From New Jersey to Vermont, as much as 12 inches of rain fell in a matter of hours, swelling creeks and streams to well beyond flood stage. Paterson, New Jersey, is still under several feet of water five days after the storm passed and many residents have not be able to return home. Thirteen towns in Vermont were cut off from the outside world, and relief workers were unable to reach one town for days. More than 250 Vermont roadways are damaged and 30 bridges were destroyed.

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