Can climate change cause animals to shrink in body size over time? Ecologists say yes, but that it is not likely to occur for years to come. Ecologists have long understood that animals living in warmer climates are generally smaller than those inhabiting colder climates. Since smaller animals have more surface area relative to the volume of their bodies, they can radiate heat more efficiently than larger animals so they can cope better in warm climates.
Scientists have studied the fossil record to observe how past climate events resulted in animal size evolution. For example, when the Earth’s temperature cooled during the Cenozoic Era, deep sea ostracods, which are tiny bivalve-like crustaceans, actually got larger. The fossil records also show that prehistoric ostracods living during warmer periods were much smaller than those living in more recent cooler periods.
As temperatures today are warming due to climate change, it is possible that some species may get smaller over time. Species in the Arctic may be the first to exhibit size evolution as the region is warming at twice the rate of the rest of the planet.
For more on climate change see http://oceana.org/climate.