Friday, October 12, 2007

Al Gore and coral reefs

A UK high court judge has criticised Al Gore's An Inconvenient Truth for innacuracies, including the statement that "coral reef bleaching events are due to global warming".

In New Scientist's enviroment blog Catherine Brahic reminds us that:
[According to] the IPCC [2007 Fourth Asssessment] report, if the temperature were to rise by 1 °C to 3 °C, there would be increased coral bleaching and widespread coral mortality, unless corals could adopt or acclimatise, but that separating the impacts of climate change-related stresses from other stresses, such as over-fishing and polluting, is difficult.

The IPCC states that most corals will bleach if temperatures rise by more than 1 °C over what they were in the 1980s and 1990s (Table SPM-1 in IPCC's WGI ). Temperatures over the past 50 years have warmed by 0.13°C per decade (p 5 of WGI summary for policy makers).

Many scientists agree that limiting warming to 2°C above 1900 temperatures will need CO2 emissions to be cut by more than half from their 2006 levels by 2050. So unless drastic, world-wide policy measures are agreed, increased coral bleaching looks pretty likely.

Bleaching is caused by other factors as well, namely disease. There is some evidence warming will also increase the incidence of disease.
Other factors that can cause bleaching include a sudden influx of large amounts of fresh water. This happened, for example, to coastal reefs in Jamaica after exceptionally heavy rainfall associated with a hurricane some years back. The link has, I think, been quite well understood for years.

Understanding of the role of diseases in coral mortality, and the interaction of disease with other factors, including warming, has been developing over a number of years (see, for example this article from back in 1997) and has a long way to go. Among those publishing in the field are James Cervino and colleagues, and Drew Harvell and colleagues. But I doubt any knowledgeable scientist would deny that Al Gore's statement captures an essential truth and a central concern, if not the whole truth plus footnotes.

I'll hazard that most scientists in the field would say that, pace the IPCC, the chances of coral reefs acclimatising and thriving under a temperature rise of more than 2 °C during the 21st century are about as great as my acclimatising to having a tonne of concrete dropped on my head (which may be a good idea for other reasons).

[As Spencer Weart tells Andy Revkin, “The I.P.C.C. was set up to be the lowest common denominator, to weed out anything anyone could disagree with. It was deliberately created, largely under the influence of Reagan administration, because governments didn’t want a bunch of self-appointed scientists from academies and so on out there. It’s no accident that it’s the Intergovernmentalpanel. Even the Saudi government has to agree. That means that when the I.P.C.C. says you’re in trouble, you’re really in trouble.”]

Perhaps Nobel laureate Gore could nuance a future statement along these lines: "Manmade global warming plays a significant and growing role in the bleaching and death of coral reefs, with devastating effects for some of the richest and most wonderful life on Earth and the human communities that depend on them. On present trends this is likely to get much worse. There are a lot of other ways in which humans damage coral reefs and these need to be managed too."

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