Certain species are especially vulnerable to climate change

Changes in temperatures and weather patterns are affecting the food supplies of certain species, causing them to grow to smaller sizes. Species like polar bears are especially vulnerable as warmer weather is destroying the ice floats they fish from, meaning both lost territory and lost fishing opportunities, the Telegraph reports. 

Fossil records indicate that a similar warming period 55 million years ago resulted in a similar reduction in animal body size. One difference, however, is the current global trend is warming much faster than its ancient predecessor, said AFP.

One problem is that some species shrink faster than others. If all species were reduced by the same size, food supplies would remain the same. Smaller flora and fauna will no longer be able to adequately feed species whose size has been unaffected, Live Science reports. 

Other environmental factors have contributed to species shrinking, including ocean acidification due to carbon dioxide pollution in the atmosphere.