Is Global Warming Linked to Severe Weather?

Posted on Saturday, October 15th, 2011 by Renata Brillinger

Reposted from permission from the Union of Concerned Scientists

As Earth warms, powerful storms are becoming the new normal. Overhead, tall, dense clouds are poised to burst, their presence a sign of an imminent deluge.

These cumulonimbus masses are a reminder of the destructive floods that are occurring around the globe, which, taken together, are potent signals of one of the greatest environmental challenges of our time: global warming.

Powerful rain and snow storms—and, ironically, intense drought periods—are a well-known consequence of a warmer planet.

1.              What is the relationship between global warming, climate, and weather?

Weather is what’s happening outside the door right now; today a thunderstorm is approaching. Climate, on the other hand, is the pattern of weather measured over a number of decades.

Over the past 30 years there has been a pattern of increasingly higher average temperatures for the whole world. In fact, the first decade of this century (2001–2010) was the hottest decade recorded since reliable records began in the late 1800s.

These rising temperatures—caused primarily by an increase of heat-trapping emissions in the atmosphere created when we burn coal, oil, and gas to generate electricity, drive our cars, and fuel our businesses—are what we refer to as global warming.

One consequence of global warming is an increase in both ocean evaporation into the atmosphere, and the amount of water vapor the atmosphere can hold. High levels of water vapor in the atmosphere in turn create conditions more favorable for heavier precipitation in the form of intense rain and snow storms.

2.             The United States is already experiencing more intense rain and snow storms.

As the Earth warms, the amount of rain or snow falling in the heaviest one percent of storms has risen nearly 20 percent on average in the United States—almost three times the rate of increase in total precipitation between 1958 and 2007.

In other words, the heaviest storms have very recently become even heavier.

The Northeast has seen a 67 percent increase in the amount of rain or snow falling in the heaviest storms.

3.             As storms increase in intensity, flooding becomes a larger concern.

Flash floods, which pose the most immediate risks for people, bridges and roads, and buildings on floodplains, result in part from this shift toward more extreme precipitation in a warming world.

Regions previously thought to be safe from floods are increasingly threatened by them; agencies such as the National Oceanic and Atmospheric Administration (NOAA), National Aeronautics and Space Administration (NASA), and the US Geological Survey (USGS), among others, are working to gather information that can be used to redraw flood maps to help anticipate vulnerable areas.

In 2008 two scientists, Sharon Ashley and Walker Ashley, of Northern Illinois University, analyzed flood fatalities between 1959 and 2005 in the mainland United States, excluding those from Hurricane Katrina.

Their research found that Texas had the largest number of fatalities from flash floods and river floods over the study period. When standardized for population, South Dakota, Mississippi, West Virginia, and Montana had the highest numbers of fatalities from flooding per 100,000 people. Those between the ages of 10 and 29 and those over 60 years old were disproportionately at risk.

4.             Does global warming create more frequent and more intense tornadoes?

Tornadoes are relatively small, short-lived phenomena and scientists don’t have robust enough data to determine whether and how climate change may be affecting tornado frequency, intensity, or the geographic range where tornadoes are most likely to form.

Tornadoes often form when warm, moist air near the Earth’s surface rises and interacts with cooler and drier air higher in the atmosphere. This creates unstable conditions that are favorable for thunderstorms and sometimes tornadoes.

Unlike thunderstorms, tornadoes need a rotational source such as when warm, moist air from the Gulf of Mexico wafts over the southeast and strong Jetstream air aloft arrives from a westerly direction, as during the tragic string of tornadoes in April 2011.

While one study found that the number of tornadoes reported in the United States has increased by around 14 per year over the past 50 years, the trend may have more to do with how tornadoes are tracked and reported rather than how many are actually forming.

Similarly, the study found that severity ratings for tornadoes are usually based on the damage they cause to structures and may not have been consistently applied over the past fifty years.

5.             What can be done to deal with severe weather?

This pattern of intense rain and snow storms and periods of drought is becoming the new normal in our everyday weather as levels of heat-trapping gases in the atmosphere continue to rise.

If the emissions that cause global warming continue unabated, scientists expect the amount of rainfall during the heaviest precipitation events across country to increase more than 40 percent by the end of the century. Even if we dramatically curbed emissions, these downpours are still likely to increase, but by only a little more than 20 percent.

Regardless of what actions we take to cut emissions, we must adapt to the likelihood that severe storms are becoming ever more commonplace.

Efforts such as modifying local infrastructure to withstand floods, adjusting agricultural patterns to account for droughts, as well as establishing emergency planning in our homes, would be far less costly to implement when compared to the costs of responding to washed out bridges, deluged homes, or loss of life.

Clearly, the time has come to develop smart planning and engineering solutions to cope with storms of the future.

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