Re: Global warming: It's happening
by Kevin E. Trenberth
(naturalSCIENCE Article of December 4, 1997)
Return-path <firstname.lastname@example.org> Date: Mon, 28 Sep 1998 18:20:56 +200
Published: Mon, 7 Dec 1998
From: Patrice Francourfrancour@unice.fr (Patrice Francour)
Subject: Kevin Trenberth's paper
Global Warming and Ocean Biodiversity?
In his article Global Warming: It's Happening, Kevin Trenberth states that it takes hundreds of years for ocean temperatures to adjust fully to changes in climate. At present, therefore, the effects of global warming on ocean temperature are presumably quite small.
This suggests that climate change is having little immediate impact on ocean life. However, working in marine protected areas (MPA's) in the northwestern Mediterranean, we have observed obvious changes over time in the composition of plant and animal assemblages. For example, "thermophilic" species are increasingly abundant or newly observed (Francour et al., 1994). Both adults and juveniles are present indicating that reproduction is occurring.
Working in MPA's, one can assume that human modifications through exploitation or destruction (hunting, fishing, local pollution) are minimal. Consequently, the observed changes in species composition in superficial layers (0-50 m depth) have to be explained by another hypothesis. Is warming a possible explanation?
The lack of clear information on ocean temperature trends makes the question hard to answer. However, the success or failure of particular species may reflect natural climatic variations over the organism's life-span. In that case, such species may provide a biological "thermometer" that is a more sensitive than the existing ocean temperature monitoring network.
But, some scientists think that small changes in sea surface temperature are insufficient to explain the appearance or disapearance of marine species. As an alternative, therefore, I would like to raise the possibility that marine species are generally more sensitive to short-term fluctuations in temperature that to slow long-term changes. Statistically, this means that if we remove the trend (upward) in temperature, the residual variance will explain the appearance or disappearance of species. The question, then, is whether there is evidence in the recorded data of change in the variance of detrended ocean temperature. It would be of great interest to hear from anyone who can offer evidence to test this hypothesis.
Dr. Patrice Francour