My recent posts on climate change and reinsurance ( "http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/000311
climate_change_and_r.html">Part 1 and "http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/000312
climate_change_and_r.html">Part 2) led to a wide-ranging and fruitful
discussion with a number of colleagues in the U.S. and Europe. (Thanks
all!)

To bring you up to date, Part 1 made the case for a clear conflict of
interest when reinsurers attribute or project increasing disasters because
of climate change. Part 2 sough to evaluate the merits of such claims,
which to be fair are made by many people well beyond just some in the
reinsurance industry. The central question is, when looking to the past, to
what degree is climate change responsible for the growth in disasters and
disaster costs up to the present? I asserted in Part 2 that the answer is
“not at all.”

In this post, Part 2.5, I’d like to expand on the information presented in
Part 2 drawing on additional information and analyses drawing from my recent
discussions with colleagues. Specifically, there seems to be a strong
consensus within the climate impacts community that the trends of increasing
damage related to storms (whether tropical, extra-tropical, thunder, hail or
other extreme weather) is completely the result of trends in societal
impacts. Questions were raised about trends in impacts related to floods,
heat waves and drought. Let’s consider each in turn.

Floods

I noted in Part II that while the IPCC identified some regional trends in
the incidence of what it calls “extreme” precipitation, it did not find
similar trends in extreme streamflow (i.e., floods). After talking with
colleagues and reading up on some of the more recent literature, it seems
clear that there is no evidence for global trends in floods, although there
may be some regional trends. There is considerable mixed evidence depending
upon definitions of “flood” and the time period selected. It will be
interesting to see how the next IPCC comes out on this. It is abundantly
clear that flood damage is increasing around the world.

While it is conceivable that trends in precipitation and streamflow are
responsible for some part of the growing impacts of floods, I await data and
analyses making such a case quantitatively and globally. It is both logical
and shown in our own research that flood damage tends to increase with
aggregate precipitation (i.e., imagine a graph of such a relationship; it
necessarily starts at the graph’s origin – no precip, no flood damage), but
exactly how much and how significant are open questions. My hypotheses,
resulting from my work with Mary Downton on this "http://sciencepolicy.colorado.edu/admin/publication_files/resource-60-2000.
11.pdf">paper .

Pielke, Jr., R.A., and M.W. Downton, 2000: Precipitation and Damaging
Floods: Trends in the United States, 1932-97. Journal of Climate, 13(20),
3625-3637,

. are that (a) trends in damage will be most closely connected to trends in
precipitation and streamflow at the regional and local level, and (b)
attempts to aggregate regional data to national or global levels will
necessarily result in a much smaller connection because of the contextual
nature of flood impacts. Even if a signal could be found in the noise, it
would be tiny when compared with the effects of societal vulnerability on
flood damage.

Heat Waves

I am not an expert on heat waves or their impacts, so I called up someone
who is, Larry
Kalkstein from the University of Delaware. Here is what I asked him:

1. Is there evidence for an increase (globally) in heat waves?
2. Is there evidence for a trend of increasing societal impacts related to
heat waves?
3. Is there evidence for growing societal vulnerability to heat waves?

His answers:

1. No. There is no evidence of an increase in the number of heat waves, in
the U.S. or globally, but there are regional variations (e.g., Great Britain
may have seen an increase). (Note that what he reported to me is completely
consistent with the IPCC TAR.)

2. Yes and no. In the United States heat mortality has decreased since the
1960s by about 20-25%, which is less than what others have reported in the
literature. Europe, by contrast has seen an increase in heat related
mortality over the past decade. But there are large data gaps around the
world.

3. Yes. Vulnerability has increased largely because of two factors –
demographics and the costs of energy. There are growing numbers of elderly
people, particularly in Europe, and the elderly are more vulnerable to heat.
Air conditioning is ever present in the United States, so its availability
is less of a problem than is the cost of running the units. Many poor
people choose not to run their air conditioners because of the cost, leading
to an increase in their vulnerability. The urban structure of Europe makes
its populations much more vulnerable to heat related impacts.

My conclusions: There is a lot that we don’t know about global trends in
the impacts of heat waves. Any trends that exist in the incidence of heat
waves would seem to be regional in nature. If so, then we can narrow our
focus on the role of climate changes as a factor in trends in impacts to
those places that have seen (a) an increase in heat waves, and (b) an
increase in impacts. This area would seem to be far smaller than global.
Even so, better data will be useful from around the world. But clearly
there is no evidence that would allow for a connection to be made between
trends in heat waves and their societal impacts. I’ll stick with my
hypothesis that any trends in impacts are the result of increasing societal
vulnerability and ask for falsification.

Drought

What we know about the societal impacts of heat waves seems to similar to
what we know about the societal impacts drought. Drought has tremendous
societal impacts, yet there seems to be no systematic collection of data on
those impacts and how they have changed over time and space. For example,
Donald Wilhite’s two volumes on drought provide no trend data (Drought: A
Global Assessment, 2000. Natural Hazards and Disasters Series, Routledge
Publishers, London).

A recent NCAR "http://www.ucar.edu/news/releases/2005/drought_research.shtml">study
argues that one measure of drought shows a significant increase in areal
extent over the past 20 years. But a connection to societal impacts remains
to be made.

My conclusions on drought echo those on heat waves: There is a lot that we
don’t know about global trends in the impacts of droughts. There may be
robust trends in the incidence of drought that are global in nature. Better
data on impacts will be useful from around the world. But clearly there is
no evidence that would allow for a connection to be made between trends in
drought and their societal impacts. I’ll stick with my hypothesis that any
trends in impacts are the result of increasing societal vulnerability and
ask for falsification.

So the bottom lines:

1. Anyone making assertions that changes in climate (whether human
caused or not) are responsible for any part of the global trend of
increasing disaster losses had better provide some new scientific evidence
to back up such claims. Future research may tell a different story, but my
reading of the current state of science is that, today, such claims are
groundless.

2. This series should be viewed as an intellectual challenge to the
IPCC WG2 and the climate impacts community. I propose that we in this
community first begin with a hypothesis, namely, “All trends observed in
recent decades indicating growing damage related to weather and climate can
be explained through the growth of societal vulnerability to those trends.”
Then, the second step is to conduct research that seeks to falsify this
hypothesis.

It is important to reiterate that the discussion thus far has been
retrospective, focused only on the attribution of factors responsible for
the global trend in disasters. I will next turn to Part 3 which will
explore the question, in the future to what extent should we expect climate
changes to be responsible for increasing disasters and disaster costs?