Does climate change also mean more bad weather in our future?
In its annual review of major US weather disasters, the National Oceanic and Atmospheric Administration (NOAA) figures now show a possible climate link to the weather problems we’ve been experiencing.
U.S. Weather Disasters in 2013
NOAA reviews annually the cost to U.S. society of weather disasters, concentrating on those events which individually exceed a billion dollars.
During 2013, there were seven such events (see the map below) primarily damage resulting from tornadoes in March, April and May and also in November.
For an extended period from Spring to Fall, drought occurred in several Midwestern and plains states while in Colorado saw September floods were experienced in Colorado. In summary, damage to property and crops occurred through wind, hail, rain – and lack of rain.
The details were obviously different, but the main causes of loss to society were much like any other year, but perhaps more so.
Weather Disasters Since 1980
The figure shows the number and cost of all weather disasters since 1980.
While it is difficult to see any overall trend in the total cost, except possibly in the last few years, there is a suggestion that the number of incidents has increased significantly during the period 1980 – 2013.
2011 was a record year with 14 such high-dollar events (after subsequent data revision, up from 12 as initially reported).
Combined with 7 events last year and 11 events in 2012, the three-year average for 2011-2013 is almost 11, which itself would have been higher than all the other years in the record.
In the 1980s, 5 events per year was exceptional (1985), while in the 1990s, 4 or 5 events became the norm.
2000 – 2002 were relatively quiet, but from 2003 onwards, there have been at least 4 major weather disasters each year. Apart from these recent years it would be difficult to detect a trend.
NOAA has recorded 151 events since 1980, an average of 4.4 per year, with a total inflation-adjusted cost to the economy of over $1 trillion. NOAA also shows a map of the distribution of the weather disasters, and it’s clear that Texas receives the worst of Nature’s ire with 57 of the 151 recorded events.
In the northern states this time, 2014 has already started with severe winter weather, although whether this will attain the billion dollar threshold is too early to say.
The world’s leading reinsurance intermediary, Aon Benfield, is directly concerned with the impact of weather damage. In its annual review of worldwide weather disasters, the company indicates that 2013 had 41 billion-dollar events, and using slightly different criteria than NOAA, records 9 of them for the USA.
Although in the long term only 16% of the financial losses have occurred in the USA, because of higher insurance levels the US Insurance industry accounted for 45% of the worldwide losses. The most deadly event recorded in the year was the Typhoon Haiyan in the Philippines, leaving nearly 8000 missing or dead. The largest financial impact were the floods in May and June in Central Europe, with an estimated $5.3 billion insured loss and $22 billion in economic losses.
The Climate Change Connection
The considered opinion of most climate scientists is that our confidence to detect trends in severe events is low. The difficulty of course is that extreme events by the nature are rare and very variable. To detect any change above a level of noise is often difficult, if not impossible.
As it happens the confidence of seeing a change in extreme events itself varies from location to location. In other words, for some parts of the world, it is easier to detect changes in severe weather events than in other parts. As it happens, North America is one such region where we can be more confident of the data to be able to detect a climate change.
There is a possibility, then, that severe weather events are becoming more frequent. The problem is quite complex, because we can only be sure of the change over the observational record, and as far as billion-dollar events are concerned, the above record is only available since 1980. So, even though there is evidence that climate change has occurred over the last 30 odd years, climate change acts on all time scales from multi-decades to beyond. So, in short, there is no reason at the moment why in principle the above changes might not reverse again.
NOAA also determines a climate extreme index as shown in the above figure. This is a measure of the climate extreme itself, and is not skewed by considerations of financial impact.
This figure shows the same general picture of an overall increase in the occurrence of extremes since about 1970, similar to the number of billion-dollar events.
However, the index also shows an apparent drop from 1910 to 1970, so we cannot be certain that the most recent events are not simply climatic fluctuations.
The way forward to try to understand scientifically the causes of extreme weather, and to try to simulate the processes by computer. This is made doubly difficult by the fact that extreme weather may have multiple causes. So, even though it may be possible to identify a possible cause for one such event, not all extreme events are caused by the same phenomenon.
For example, the recent severe winter weather in the USA was likely caused by the meandering of the jet stream, so that it was in a different position than its normal location.
A Plausible Climate Change Explanation?
The IPCC report provides a plausible reason as to how climate change might affect extreme weather: namely, a shift of the mean climate will also tend to shift the extreme values in the same direction, making a particular temperature or wind strength more likely. The challenge of climate research will be to put this argument on a more careful footing and to determine whether any changes seen are human induced.
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