The number of hot days and nights very likely has increased globally in recent years,
according to a special report
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focused solely on extreme weather events from the Intergovernmental Panel on Climate
Change (IPCC),
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while the number of cold days has decreased. The future looks similar, the IPCC panel
says: If countries continue to increase emissions of carbon dioxide (CO2)—the greenhouse
gas produced by human activities in the greatest quantities—deadly heat waves and
heavy precipitation events will occur more often. Devastating tropical cyclones, on
the other hand, are likely to remain the same or even decrease.
A summary report for policy makers was released 18 November 2011 in advance of the
February 2012 publication of the full IPCC Special Report Managing the Risks of Extreme
Events and Disasters to Advance Climate Change Adaptation (SREX). Several aspects
of SREX are designed to inform governments and other decision makers struggling to
develop climate-change adaptation plans. The report offers adaptation measures that
planners can implement to protect human health during extreme weather events. These
include “low-regrets” activities that provide benefits now and under a variety of
future scenarios, such as installing systems that warn people of impending disasters
and improving systems for health surveillance, drinking water, and drainage.
This publication represents the first time that IPCC working groups I (which focuses
on the physical science basis of climate change) and II (which focuses on impacts,
adaptation, and vulnerability) have collaborated on a report, says SREX coordinating
lead author Sonia I. Seneviratne, an assistant professor at the Institute for Atmospheric
and Climate Science, ETH Zürich. It also includes several lead authors from the disaster
risk management community. “I think the report allows a better integration of information
all the way from the physical projections of climate extremes to disaster management
and climate adaptation options. This should make it particularly valuable for decision
makers,” Seneviratne says.
The analysis concludes that extreme weather events will particularly affect sectors
closely tied to climate: water, agriculture, food security, forestry, health, and
tourism. The severity of human health impacts from climate extremes will reflect how
prepared or how vulnerable a community is. For example, people living in areas with
rapid and unplanned urbanization, environmental degradation, and poverty are more
vulnerable to the hazards of extreme climate events than those living in better-planned,
better-protected, and higher-income communities. After a disaster, the summary notes,
planners should focus on reconstruction that improves a community’s resistance to
weather- and climate-related disasters rather than recreating or even worsening existing
vulnerabilities.
The report helps untangle some of the confusion nonscientists feel when reading news
reports about blockbuster blizzards at the same time the Earth is supposedly warming.
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Gerald A. Meehl, senior scientist at the National Center for Atmospheric Research
(NCAR) and a lead author on the near-term climate change chapter for the forthcoming
IPCC Fifth Assessment Report (due by 2014), explains that the very nature of global
warming exacerbates extreme weather events of all kinds—not just heat-related events.
“We know that CO2 traps heat in the atmosphere,” Meehl says. “That causes things to
warm up, and warmer air holds more moisture, which means there is more moisture available
as a source for precipitation in storms.” Precipitation intensity increases, he says,
even though the overall number of storms may not increase. Even in a much warmer climate,
Meehl adds, there will still be record cold temperatures and snow storms. However,
as the atmosphere continues to warm, “extreme cold will occur less frequently than
extreme heat,”
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he says.
At least one scientist thinks the SREX underestimates the extent to which human activity
affects climate. Kevin Trenberth, distinguished senior scientist in the Climate Analysis
Section at the NCAR, says the report “inherently assumes a null hypothesis of no human
influence. In reality, many studies have shown otherwise.”
Combined with short-term data sets that often contain variabilities and the fact that
many models don’t accurately simulate certain extremes such as tropical storms and
monsoons, the message would appear to be there is no human influence, according to
Trenberth. “The result of the null hypothesis is that the errors from imperfect models
and data fall on the side of saying there is no human influence when there really
is,” he says. “This is a fundamental issue with the science community as well as public
perceptions. . . . The result has been the appearance of overwhelming uncertainties
and paralysis of action.”
Changes in the mean, variance, or shape of weather probability distributions—or some
combination of those three—could mean a change in the number and severity of extreme
weather events.
(Source: IPCC
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)