How does rising atmospheric CO2 affect marine organisms?

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Butterfly Biodiversity in Britain
Menendez, R., Gonzalez-Megias, A., Hill, J.K., Braschler, B., Willis, S.G., Collingham, Y., Fox, R., Roy, D.B. and Thomas, C.D. 2006. Species richness changes lag behind climate change. Proceedings of the Royal Society B 273: 1465-1470.

There have been many sensationalist claims that CO2-induced global warming will drive innumerable species of plants and animals to extinction. However, as we demonstrate in The Specter of Species Extinction: Will Global Warming Decimate Earth's Biosphere?, such statements are based on an incomplete understanding of many pertinent phenomena; and when these other pieces of knowledge are considered, we find that the opportunity that is provided by warming for species to expand their historical ranges poleward in latitude and upward in altitude, together with the demonstrated propensity for many species to not be forced to abandon equivalent areas of the warmer parts of their ranges (particularly when the air's CO2 content rises concurrently), leads to a greater overlapping of species' ranges and concomitant increases in local biodiversity throughout the world.

What was done
In an important study of this subject, Menendez et al. "provide the first assessment, at a geographical scale, of how species richness has changed in response to climate change," concentrating on British butterflies. This they do by testing "whether average species richness of resident British butterfly species has increased in recent decades, whether these changes are as great as would be expected given the amount of warming that has taken place, and whether the composition of butterfly communities is changing towards a dominance by generalist species."

What was learned
The nine UK scientists determined that "average species richness of the British butterfly fauna at 20 x 20 km grid resolution has increased since 1970-82, during a period when climate warming would lead us to expect increases." They also found, as expected, that "southerly habitat generalists increased more than specialists," which require a specific type of habitat that is sometimes difficult for them to find, especially in the modern world where habitat destruction is commonplace. In addition, they were able to determine that observed species richness increases lagged behind those expected on the basis of climate change.

What it means
The results obtained by Menendez et al. "confirm," in their words, "that the average species richness of British butterflies has increased since 1970-82," as our thinking has suggested it should. However, some of the range shifts responsible for the increase in species richness take more time to occur than those of other species; and they say their results imply that "it may be decades or centuries before the species richness and composition of biological communities adjusts to the current climate."

Reviewed 11 October 2006