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Wall Street History
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06/27/2008
Extreme Weather
The National Oceanic and Atmospheric Administration recently came out with a report on extreme weather and how we can expect it to become more common. Should this pan out over the coming decades, it of course has major economic implications. Ergo, it’s far from a stretch to write of this topic for this column.
From NOAA’s report:
Weather and climate extremes affect all sectors of the economy and the environment, including human health and well-being. During the period 1980-2006, the U.S. experienced 70 weather- related disasters in which overall damages exceeded $1 billion at the time of the event. Clearly, the direct impact of extreme weather and climate events on the U.S. economy is substantial.
There is scientific evidence that a warming world will be accompanied by changes in the intensity, duration, frequency, and geographic extent of weather and climate extremes. Changes in extremes are already observed to be having impacts on social, economic and natural systems, and future changes associated with continued warming will present additional challenges.
The impacts of changes in extremes depend on both changes in climate and ecosystem and societal vulnerability. Vulnerability is shaped by factors such as population dynamics and economic status, as well as developing and utilizing adaptation measures such as appropriate building codes, disaster preparedness, and water use efficiency. Some short-term actions taken to lessen the risk from extreme events can lead to increases in vulnerability to even larger extremes. For example, moderate flood control measures on a river can stimulate development in a now “safe” floodplain, only to see those new structures damaged when a very large flood occurs.
Within a changing climate system, some of what are now considered to be extreme events will occur more frequently (e.g., heat waves) and some less frequently (e.g., cold snaps). More frequent extreme events occurring over a shorter period reduce the time available for recovery and adaptation. In addition, extreme events often occur in clusters. The cumulative effect of compound or back-to-back extremes has far larger impacts than the same events spread out over a longer period of time. For example, heat waves, droughts, air stagnation, and resulting wildfires often occur concurrently and have more severe impacts than any of these alone.
What Changes Have Already Occurred?
Many extremes and their associated impacts are now changing. For example:
--Most of North America is experiencing more unusually hot days and nights and fewer unusually cold days. The last 10 years have seen fewer severe cold waves than any other 10-year period in the historical record, which dates back to 1895. The number of heat waves has also been increasing since 1950.
--There has been a decrease in frost days and a lengthening of the frost-free season over the past century.
--Extreme precipitation episodes (heavy downpours) have become more frequent and intense and now account for a larger percentage of total precipitation.
--Droughts are becoming more severe in some regions.
--Atlantic tropical storm and hurricane destructive potential has increased substantially since about 1970.
--Storm tracks have shifted northward in both the North Atlantic and North Pacific over the past fifty years. The strongest cold season storms are becoming even stronger in the North Pacific.
Why Have These Changes Occurred?
As the climate has warmed, primarily due to human activities, we have also seen a variety of changes in extremes. Some examples of extremes that have an identifiable cause.
--Human-induced warming has likely caused much of the average temperature increase in North America over the past fifty years and, consequently, changes in temperature extremes. For example, the effect of human-induced emissions of greenhouse gases has been associated with the very hot year of 2006 in the U.S.
--Heavy precipitation events averaged over North America have increased over the past 50 years, consistent with the observed increases in atmospheric water vapor, which have been linked to human-induced increases in greenhouse gases.
--It is likely that the human-induced increase in air temperatures, and the associated increase in evaporation potential over land, are already contributing to droughts that are longer and more intense.
--It is very likely that the human-induced increase in greenhouse gases has contributed to the increase in sea surface temperatures in the hurricane formation regions. Because there is a strong statistical connection between Atlantic tropical sea surfaces temperatures and Atlantic hurricane activity, this suggests a human contribution to recent hurricane activity (a confident assessment will require further study).
--Human influences on changes in sea-level pressure patterns have been detected over the Northern Hemisphere and this affects the location and intensity of cold season storms.
How Will Extremes Change
Projected continued warming of North America has direct implications for the occurrence of extreme weather and climate events. For example, climate models indicate that many currently rare extreme events will become more commonplace. For a mid-range scenario of future greenhouse gas emissions, a day so hot that it is currently experienced only once every 20 years would occur every three years by the middle of the century over much of the continental U.S. and every five years over most of Canada. By the end of the century, it would occur every other year or more.
--Future changes in extreme temperatures will generally follow changes in average temperature. Abnormally hot days and nights and heat waves are very likely to become more frequent. Cold days and cold nights are very likely to become much less frequent. The number of days with frost is very likely to decrease.
--Sea ice extent is expected to continue to decrease and may even disappear entirely in the Arctic Ocean in summer in the coming decades. This increases extreme coastal erosion in Arctic Alaska and Canada due to the increased exposure of the coastline to strong wave action.
--On average, precipitation is likely to be less frequent but more intense, and precipitation extremes are very likely to increase.
--In the future, droughts are likely to become more frequent and severe in some regions, leading to an increased need to respond to reduced water supplies, increased wildfires, and various ecological impacts. These regions include the U.S. Southwest and parts of Mexico.
--For North Atlantic and North Pacific hurricanes, it is likely that rainfall and wind speeds will increase in response to human- caused warming. Analyses of model simulations suggest that, for each 1.8-degree F increase (1 C.) in tropical sea surface temperatures, core rainfall rates will increase by 6 to 18% and the surface wind speeds of the strongest hurricanes will increase by about 1 to 8%.
--In the future, there are likely to be more frequent strong cold- season storms in both the Atlantic and Pacific basins, with stronger winds and more extreme wave heights.
Source: National Oceanic Atmospheric Administration, noaa.gov
Note: NOAA was only able to utilize data through 2006 for their report but clearly the catastrophic Midwest rains and tornadoes from this current season play into the above theories.
Wall Street History returns July 11.
Brian Trumbore
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