When I first started paying attention to the climate wars in the 1990s, the political component of the science debate seemed fixed on the question – “Is it warming.” That debate – the deniers at CO2Science notwithstanding – seems over. Among working scientists in the climate field, the interesting action now on the detection side involves how much it is warming – or, to be more precise, how much climate is changing – and what effect it is having.

In today’s issue of the journal Science, a fascinating new analysis of a longstanding data set on plankton offers new evidence that the change is real, ongoing, and measurable. Anthony Richardson of the Sir Alister Hardy Foundation for Ocean Science the U.K. and David Schoeman of the University of Port Elizabeth in South Africa used a powerful data set that has been collected by instruments hitched on the backs of North Atlantic freighters since the 1930s, collecting plankton. (Their abstract is free, subscription required for the full paper.) What they found was that as cool regionsof the ocean warm, the plankton population increases. But as warmer regions warm further, the population tends to decline.

“This impact propagates up the food web (bottom-up control) through copepod herbivores to zooplankton carnivores because of tight trophic coupling. Future warming is therefore likely to alter the spatial distribution of primary and secondary pelagic production, affecting ecosystem services and placing additional stress on already-depleted fish and mammal populations.”