Climate change is reducing the body size of many animal and plant species, including some which supply vital nutrition for more than a billion people already living near hunger's threshold, according to a study released on October 17.
From micro-organisms to top predators, nearly 45 percent of species for which data was reviewed grew smaller over multiple generations due to climate change, researchers found.
The impact of rapidly climbing temperatures and shifts in rainfall patterns on body size could have unpredictable and possible severe consequences, they warned.
Jennifer Sheridan and David Bickford at the National University of Singapore looked at scientific literature on climate-change episodes in the distant past and at experiments and observations in recent history.
Fossil records, they found, were unambiguous: past periods of rising temperatures had led both marine and land organisms to became progressively smaller.
During a warming event 55 million years ago - often seen as an analogue for current climate change - beetles, bees, spiders, wasps and ants shrank by 50 to 75 percent over a period of several thousand years.
Mammals such as squirrels and woodrats also diminished in size, by about 40 percent.
The pace of current warming, though, is far greater than during this so-called Palaeocene-Eocene Thermal Maximum (PETM). It, too, has begun to shrink dozens of species, the study found. Among 85 examples cited, 45 percent were unaffected. But of those remaining, four out of five had gotten smaller, while a fifth got bigger.
Some of the shrinkage came as a surprise. "Plants were expected to get larger with increased atmospheric carbon dioxide," but many wound up stunted due to changes in temperature, humidity and nutrients available, the researchers said.
For cold-blooded animals - including insects, reptiles and amphibians - the impact is direct: experiments suggest that an upward tick of one degree Celsius translates into roughly a 10 percent increase in metabolism, the rate at which an organism uses energy. That, in turn, results in downsizing.
The common toad, for example, has measurably shrivelled in girth in only two decades, along with some tortoises, marine iguanas and lizards.
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