"Trends in Extreme Weather and Climate Events: Issues Related to Modeling Extremes in Projections of Future Climate Change"

   In this paper, Zwiers et al provide an overview of significant simulations that have been published thus far on possible future changes in extreme weather events under circumstances of increased greenhouse gas concentrations and higher global mean temperatures. At the time of this paper’s publishing, some computer and simulation technology advancements had allowed for more accurate simulation experiments to be undertaken, however they are still far from definite in their conclusions.

   The first weather aspect to be discussed is temperature. The authors find that a higher mean global temperature will increase the number of extreme warm days as compared to the number of extreme cold days. These results have generally held weight so far, although changes in extreme temperatures vary by region: for example, much smaller increases in minimum temperatures were found at the boundaries of the polar oceans, while a simulation in Australia found that the number of extreme minimum temperature days were cut in half when this minimum temperature increased by 2⁰C.

   Next, the authors move on to the topic that has been a source of more certainty in its future changes: precipitation. There is some evidence that an increase in precipitation as a result of anthropogenic forces is already taking place in some regions of the world. It is projected that higher greenhouse gas concentrations in the atmosphere lead to more intense precipitation, though this varies strongly by geographical region. As precipitation levels increase in variability as a result of higher global temperatures, there is also more likely to be an increase in drought and floods during the monsoon seasons in regions such as Asia-Pacific.

   The possible future changes in extratropical storm frequency and intensity have been more difficult to predict. One simulation showed that when CO₂ and sulfate aerosol levels in the atmosphere were increased, the number of storms in the Northern Hemisphere actually decreased, although their intensity increased. ENSO events also come into play here. As temperatures rise, the pacific climate will be more likely to move into more El Niño-like state whose events can create more precipitation variability. However, since ENSO events are already extremely variable, it is very difficult to predict at all if changes in these events are anthropogenic in nature.

   Tropical cyclone future simulations are also very difficult to assess with any certainty. Some simulations have found that fewer cyclones will occur in a more greenhouse gas rich environment, while the intensity of these events might increase. Tropical cyclone occurrences, however, often rely on ENSO events and therefore are difficult to predict.

Meehl G, Zwiers F, Evans J, Knutson T, Mearns L, and Whetton P (2000) “Trends in Extreme Weather and Climate Events: Issues Related to Modeling Extremes in Projections of Future Climate Change.” Bulletin of the American Meteorological Society 81(3): 427-436.

Extreme Weather Map (USA)

The Natural Resources Defense Council recently created an interactive map of the USA that shows all of the extreme weather events that have taken place in 2011 alone. "In 2011, there were at least 2,941 monthly weather records broken by extreme events that struck communities in the US."

http://www.nrdc.org/health/extremeweather/

Click the play button to see the map- pretty cool!

USA Expenditures on Extreme Weather Events

The USA's National Climatic Data Center (NCDC) has published a list of all of the extreme weather events that have occurred within the past three decades or so that the US government has spent more than $1 billion USD in damages on (adjusted to the 2011 dollar). While conclusions should not be reached based on such crude data, the simple numbers can be interesting to observe. For example, from 2006-present there have been over 40 extreme weather events that have necessitated over $1 billion in damages. Between 1995 and 1990, there were 19 such events, and between 1985 and 1980, there were 8. The complete data can be found at: http://www.ncdc.noaa.gov/oa/reports/billionz.html. 

IPCC's SREX

Recently, the Intergovernmental Panel on Climate Control (IPCC) published its Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX). In it, the body outlined the results of simulations to predict how extreme weather events might be affected in the future due to anthropogenic climate change, as well as other natural weather variations. It also outlines how global institutions should respond to these projected events, and how we as a human population can prepare ourselves for dealing with them. The IPCC concedes that it is incredibly difficult to make any definite conclusions, and sites the lack of extreme weather event data as a source of possible misinterpretations of their projected frequency and intensity. However, they did manage to point out a few areas in which anthropogenic climate change is “very likely” (90-100% probability) or “likely” (66-90% probability) to affect extreme weather events. It is likely that we will see a global trend of increased precipitation, as well as extreme coastal high water due to rising sea levels. There will also likely be longer, more frequent, and more intense heat waves, going along with the conclusion that some areas might see more intense droughts. The IPCC is very certain that there will be a marked increase in minimum and maximum daily temperature extremes by the end of this century. They found it very likely that, therefore, there will be an overall decrease in the number of cold days and nights and increase in warm days and nights. What I found most striking about this report, however, was its claim that extreme weather events that might now be a 1 in 20 year event might become a 1 in 10 or 1 in 5 year event. 

Source:

Intergovernmental Panel on Climate Change, "Special Report on Managing the Risks of Extreme Weather Events and Disasters to Advance Climate Change Adaptation." Can be found at: http://ipcc-wg2.gov/SREX/images/uploads/SREX-SPM_Approved-HiRes_opt.pdf

El Niños and Global Warming

It is well established that the El Niño phenomenon is not a result of global warming. The El Niño/La Niña periodical warming and cooling phenomenon is part of a natural climate pattern that causes extreme weather events such as floods and droughts. The question now is, has climate change affected the intensity and/or frequency of these events? Some studies suggest that the recent increase in El Niño (warming) events as compared to La Niña (cooling) events cannot solely be described by natural cycles (Trenberth, 1997). However, it is important to note that many of these studies are conducted using evidence from only about 100 years prior, which is in all likelihood not an adequate amount of elapsed time after which to attempt to suggest anomalies in the data. It has been suggested that El Niño events are changing due to the already rising SSTs that can perhaps be attributed to anthropogenic climate change. However, this begins a which came first scenario: El Niño and wind speed changes help create SST patterns, and higher SSTs themselves can enhance the El Niño effect. Scientists are well on their way towards proving that rising SSTs can be linked at least partially to climate change. Its possible effect on El Niño events are an interesting subject that has yet to be adequately researched. 

Snow in New York

Just a quick article I stumbled upon while checking up on weather conditions back home across the pond...

http://www.nytimes.com/2010/02/11/science/earth/11climate.html

Hurricanes and SST

Current studies investigating the possible link between more frequent or more intense hurricanes and global climate change have been quite contradictory. Not enough time has passed for researchers to accurately and definitively assess hurricane trends for anomalies and their possible connections to global warming. We can observe these trends, but it is extremely difficult at this point to separate anthropogenic effects from natural oscillations. Evidence on both ends of the debate can be convincing in different ways. A few things must be understood about hurricanes before their relevance to climate change can be discussed. To put it simply, hurricanes are caused by a combination of wind shear and ocean temperatures. Warm water fuels hurricanes, and they are more destructive the higher the temperatures rise (Realclimate.org). It is this characteristic that can put hurricanes in danger of being affected by climate change. Some studies have found that the sea surface temperature (SST) of our earth’s oceans has increased by .6⁰C (Realclimate.org). Even a rise as small as this can have major effects on weather events (Xie et al). The question then becomes, is climate change responsible for this rise in SST? Hopefully I will be able to investigate this further in the coming weeks. For now, I leave you with a study published in Science a decade ago, simulating the possible increase of hurricane intensity as CO₂ levels rise in our atmosphere. Researchers compared 51 Western Pacific storms under present climate conditions with 51 storms under high CO₂ conditions. They found that when SST was raised by 2.2⁰C, they simulated hurricanes whose wind speed increased by 5-12%. Surface pressure was also found to increase (Knutson et al).

Sources: 

RealClimate.org: "Hurricanes and Global Warming- Is there a connection?"

Xie et al, "Global Warming Pattern Formation: Sea Surface Temperature and Rainfall," Journal of Climate, September 2009. 

Knutson et al, "Simulated Increase of Hurricane Intensities in a CO2-Warmed Climate," Science, February 1998.