American Meteorological Society Seminar, Washington, DC, October 25, 2005 - Climate Change and Hurricanes]

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De l'information qui est tombée sur mon bureau et qui est très pertinente.

De l'info très intéressente aux points 4, 7, 8, 12 et 13.


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The American Meteorological Society (AMS) held a seminar on Capitol Hill in
Washington, DC on October 25, 2005 that concluded that anthropogenic climate
change is causing increased hurricane intensity. Scientists presenting also
noted that increased air pollution over the past several decades may have led
to erroneous interpretations of natural North Atlantic hurricane cycles. The
scientists were not willing to make long term projections about the impact of
global warming on future hurricanes, noting that hurricane modeling is not yet
sophisticated enough and computers are not yet powerful enough to process the
countless climate change variables involved in hurricane formation. However,
they did say that climate change will make reliance on past storm data for
forecasting more problematic and that there is a serious risk of storms of
increasing intensity and unpredictability in the near term.


2. As requested by the Climate Change and Non-Nuclear Energy Policy
Section/Foreign Affairs Canada, Environment and Fisheries Section/WSHDC
attended a seminar hosted by the AMS on Capitol Hill on October 25, 2005. There
were three speakers: Dr. Kevin Trenberth, head of the federally funded Climate
Analysis Section at the National Center for Atmospheric Research in Colorado;
Dr. Kerry Emanuel, a professor of atmospheric science at the Massachusetts
Institute of Technology (MIT); and Dr. Judith Curry, a professor and chair of
the School of Atmospheric Sciences at the Georgia Institute of Technology.

3. Trenberth, a lead author on the 1995 and 2001 UN Intergovernmental Panel on
Climate Change (IPCC) Scientific Assessment of Climate Change and is a
Coordinating Lead Author of the 2007 assessment, was first to speak. He is
listed among the top 20 authors in highest citations in all of geophysics. The
purpose of his discussion was to isolate and analyse the various forces that
contribute to hurricane development. Trenberth noted that while natural factors
like El Niño and multidecadal variability do lead to natural phases of
increased hurricane activity, anthropogenic climate change is at least partly
responsible for creating the conditions required for more intense hurricanes.

4. Trenberth began by describing some of the main forces that lead to the
creation of hurricanes. The first criteria is that sea surface temperatures
must be above 26.5°C. Hurricanes act as a global thermoregulation device by
drawing heat from tropical oceans and eventually radiating it into space.
Scientists estimate that a hurricane releases heat energy at the rate of
50200 trillion watts, about the same amount of energy released by exploding a
10-megaton nuclear bomb every 20 minutes. Trenberth pointed out that an
intuitive conclusion is that sea surface temperature increases caused by global
warming will require larger storms to have the same dissipating effect. Sea
surface temperatures have increased by 0.5°C on average since 1970. Another
ingredient crucial to hurricane formation is high atmospheric water vapour
content. This moisture is fuel for hurricanes that increases intensity and the
likelihood of heavy rains. Observations indicate that atmospheric vapour has
increased by about 3.8% since 1970. Trenberth estimated that about 1 of
additional rainfall over New Orleans during Katrina might be attributed to
climate change.

5. El Niño episodes are sustained sea surface temperature anomalies that are
greater than +0.5°C across the central tropical Pacific Ocean. It occurs at
irregular intervals of 2-7 years and usually lasts one or two years. El Niño
suppresses North Atlantic hurricane activity. The 2005 North Atlantic hurricane
season has not been an El Niño period. Trenberth estimates that the absence of
an El Niño could account for about 25% of the increased hurricane activity seen
this year.

6. Atlantic Multidecadal Oscillation (AMO) is a natural pattern of temperature
variability in North Atlantic hurricane activity caused by changing ocean
currents that alter sea surface temperatures. There have been periods of high
North Atlantic hurricane activity from 1870-1899, 1926-1960, and 1995 to the
present. Meanwhile periods of relatively low activity were observed from
1840-1870, 1900-1925, and 1970-1994. Trenberth estimates that AMO, like El
Niño, could account for about 25% of the increased hurricane activity seen this
year. He points out that the recent spike in hurricane activity is global, not
just in the North Atlantic, and that AMO cannot sufficiently account for that

7. The sea surface temperature through this years hurricane season averaged
about 2°C warmer than in 1970. Trenberths research indicates that global
warming is responsible for 50%, or 1°C, of this warming. Trenberth was asked
whether increased warming could eventually lead to hurricanes beyond the worst
Category 5 storms seen to date. Though he was unwilling to make predictions
about the specific nature of future storms, Trenberth did say a warmer climate
increases the speed-limit for storms. In fact, computer modeling of climate
impacts of the Cretaceous period asteroid that led to the dinosaur extinction
indicate that under the right conditions hurricanes with speeds of Mach 1 could
theoretically have formed. Of course, this kind of effect would never be seen
as a result of global warming, but a 2-3°C increase in sea surface temperature
through the next century would lead to a 20-30% increase in hurricane intensity
according to Trenberth.

8. The second speaker was Dr. Kerry Emanuel. Emanuel published a study in the
July issue of /Nature/ that found that the destructive power of hurricanes has
increased by 50% over the last 50 years. He showed that, while the global
number of hurricanes has remained constant at about 90 (plus or minus 10) per
year, there has been a profound upward trend in the proportion of Category 4
and 5 storms since the 1950s, which is when reliable aircraft monitoring began.
Emanuel pointed out that the damage caused by hurricanes increases dramatically
with increased storm intensity. He presented graphs which illustrated a very
close correlation between progressively increasing global hurricane intensity
and global sea surface temperature increases caused by global warming. Emanuel
predicts "a substantial increase in hurricane-related losses in the
twenty-first century".

9. Emanuel also pointed out that air pollution could be confounding
interpretations of AMO significance. Sulphate aerosol air pollution released
over the past several decades causes negative radiative forcing. The pollutants
in the atmosphere reflect incoming sunlight which makes ocean surface
temperatures cooler. This means that more recent AMO data may have exaggerated
the degree of cyclical cooling is deemed to be natural and amplified the
perceived scale of AMO variation.

10. The final speaker was Dr. Judith Curry, who serves on the National
Academies Climate Research Committee and the NOAA Climate Working Group. She
published a study in last months issue of /Science/ which further supports the
findings of the other two speakers. The study found that the number of Category
4 and 5 hurricanes worldwide has nearly doubled in the last 35 years. As with
the other panellists Curry attributed this increase primarily to warming
surface temperatures produced by global warming.

11. Currys presentation focussed on explaining the importance of the
distinction between hurricane forecasters and climatologists. Forecasters,
according to Curry, do a good job projecting hurricane tracks, but are not as
good at projecting intensity. She cited the recent case of Hurricane Wilma as
an example. Wilma surprised forecasters by intensifying from a Category 1 storm
to the strongest Category 5 ever recorded in a remarkably short span of time
and to the surprise of most forecasters. Curry suggested that the weakness
forecasters have is that they base their predictions on the data extrapolated
from previous storms. She contrasted this approach with that of the
climatologist, who seeks to understand the underlying forces driving hurricanes
over long periods.

12. Curry argues that many forecasters in the United States have developed
tunnel vision by only concentrating on hurricanes that make landfall in the
United States. Only 11 percent of hurricanes worldwide occur in the North
Atlantic, and only 2 percent of all hurricanes make landfall in the US. Curry
argues that this sample size is not large enough to enable scientists to spot
the effects of climate change on storm activity. Furthermore, she argues that
an analysis of worldwide hurricane activities makes it clear that anthropogenic
climate change is creating more devastating storms.

13. Curry singled out National Hurricane Center director Max Mayfield for
specific criticism. Mayfield testified before a Congressional subcommittee last
month in the wake of the recent spate of devastating storms. He stated that
there is no evidence that recent storms have been enhanced substantially by
global warming. Curry opined that the only way that you could come to that
conclusion would be if you willed yourself not to see the patterns in global
storm activity.

14. Curry argues that as the effects of climate change become more pronounced,
the reliance on the behaviour of past storms will become more and more
problematic. For example, melting ice caps will change ocean currents and alter
the basic conditions for hurricane creation that have remained relatively
constant in the past. There is anecdotal evidence that hurricanes may begin to
form and strike in novel ways. Hurricane Catarina, a Category 1 storm that
struck Brazil in March of 2004 was the first South Atlantic Hurricane to make
landfall ever recorded. Earlier this month, hurricane Vince became the first
hurricane on record to make landfall on the Iberian Peninsula. Vince, which
developed farther east and north than any other Atlantic tropical storm, struck
Huelva, Spain on October 11. In addition to greater storm intensity, changing
ocean dynamics brought about by climate change may bring the threat of damaging
hurricanes to new populations.

Re: American Meteorological Society Seminar, Washington, DC, October 25, 2005 - Climate Change and Hurricanes]

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Miguel Tremblay wrote:

> De l'information qui est tombée sur mon bureau et qui est très
> pertinente.

Ceci me rappelle un article que j'ai lu il y a peut-être 1-2 mois qui
parlait des effets de plus en plus dévastateurs des ouragans. L'article
argumentait que la cause était non-pas une augmentation de la férocité
des ouragans, mais plutôt l'augmentation des populations cotières. De
plus en plus de gens vivent le long des côtes, ce qui les rends beaucoup
plus vulnérables aux ouragans et tsunami.


Stefan Michalowski
Email: mitch(à)
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