Animals, Plants Shrinking as Climate Warms

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Contradicting a century-old hypothesis, increased global carbon dioxide levels seem to be shrinking plants instead of fostering their growth. Animals from polar bears to marine iguanas are being stunted too.

In 1896, Svante Arrhenius published calculations predicting that doubling CO2 levels would trigger a global temperatures increase of about 5-6 degrees C.

"We would then have some right to indulge in the pleasant belief that our descendants, albeit after many generations, might live under a milder sky and in less barren surroundings than is our lot at present," Arrhenius said during a lecture that same year.

But it seems reality hasn't lived up to Arrhenius' verdant dreams of vigorous vegetation.

"Plants were expected to get larger with increased atmospheric carbon dioxide," but changes in temperature, humidity and nutrient availability seem to have trumped the benefits of increased CO2, said researchers from the National University of Singapore in the journal Nature Climate Change.

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Forty-five percent of the species studied now reach smaller adult sizes than they did in the recent past. The researchers, led by Jennifer Sheridan and David Bickford, point to climate change induced warmer temperatures and changing habitats are possible culprits in the case of the shrinking creatures.

"We do not yet know the exact mechanisms involved, or why some organisms are getting smaller while others are unaffected," the researchers said in an interview with PhysOrg. "Until we understand more, we could be risking negative consequences that we can't yet quantify."

The change was dramatic in cold-blooded animals. Only two decades of warmer temperatures were enough to make reptile runts.

An increase of only one degree Celsius caused nearly a 10 percent increase in metabolism. Greater use of energy resulted in tiny tortoises and little lizards.

Fish are smaller now too. Though overfishing has played a part in reducing piscine proportions, the researchers also point to experimental results showing that warmer temperatures also stunt fish growth.

Discovery News recently reported on warmer temperature's size-stifling effect on plankton, the base of the marine ecosystem.

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Warm-blooded animals weren't immune from the climate change caused size change.

Many birds are now less bulky, including passerines (the order that includes cardinals, blue jays, and crows) as well as goshawks and gulls.

Mammals have been miniaturized too. Soay sheep are scrawny. Red dear are runts. And polar bears are puny, compared to historical records.

This isn't the first time this has happened in Earth's history.

Fifty-five million years ago, a warming event similar to the current climate change correlated to beetles, bees, spiders, wasps and ants shrinking by 50 to 75 percent over several thousand years.

Woodrats and squirrels also shrunk by about 40 percent.

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That event, the Palaeocene-Eocene Thermal Maximum, happened over a longer time than the current global warming.

The speed of modern climate change could mean, "organisms may not respond or adapt quickly enough", especially those with long generation times, said the authors in PhysOrg.