Over the past century, many animals—including tortoises, common toads and iguanas—have started to reduce in size. ©John T. Andrews

Animals and plants are shrinking, and most scientists believe that global warming is the cause. Recently, researchers examined 85 species and found that 45 percent of them have been steadily decreasing in size from generation to generation. What’s more, this downward trend seems to coincide with an uptick in temperatures: each degree of warming worldwide has been found to decrease the size of marine life by as much as 22 percent; and over the past century, tortoises, common toads, iguanas, red deer and sheep in Scotland have all started to reduce in size.

But if a large number of species gets smaller at the same time, will our new, tinier world of plants and animals make much of a difference?

Getting smaller, but working harder

It’s been shown that rising CO2 levels in the atmosphere make ocean water more acidic, which causes plankton, corals and mollusks to decrease in number. This lessens the amount of food available to species, which filters all the way up to the top of the food chain. Those reduced food supplies are likely to mean that animals at the apex—including humans—will grow to smaller sizes, have fewer offspring, and be more vulnerable to disease.

As more CO2 enters the atmosphere, plants should grow larger. But they, too, are shrinking. ©John T. Andrews

In theory, plants—which use CO2 for fuel—should be growing bigger as more carbon dioxide enters the atmosphere. But they, too are shrinking, likely because of droughts caused by climate change. One study examined 1,700 plant, insect, bird and amphibian species and found that in order to deal with these changes, 80 percent of them were moving three miles closer to the poles every 10 years, and 87 percent were breeding or flowering more than two days earlier each decade. Cold-blooded animals, particularly amphibians, were shown to be at the highest risk because having a smaller size meant a greater chance of their drying up in warmer temperatures.

It’s clear that as certain types of flora and fauna diminish or grow smaller in size, we’ll all have to work harder to procure food.

Bears barely there

The consequences of shrinking—linked to the problems of a warming planet—are seen most notably in polar bears.

Polar bears are getting smaller, probably as a result of a warming planet. ©Brad Josephs

A few years ago, BBC News reported on a study published in the Journal of Zoology that found that after studying 300 polar bear skulls—which are an indicator of body size—those from the latter half of the 20th century were 2 to 9 percent smaller than those from the early part of the century. The researchers believe the changes could be linked to an increase in pollution and the reduction in sea ice. Because the ice is melting, the bears have to use more energy to hunt. This increased effort needed to find food, they postulate, likely limits the animals’ growth.

Not only that, but changes in skull shape were noted, too. While it’s not possible to unequivocally determine the cause (it could be related to a reduction in genetic diversity; hunting over the last century may have depleted the gene pool, leaving polar bears to suffer the effects of inbreeding), it might be that the shape changes are related to pollutants that have built up in the Arctic and in the polar bears’ bodies. In the past hundred years, concentrations of many man-made pollutants in the Arctic have significantly increased, including carbon and halogen compounds: fluorine, chlorine, bromine or iodine. While some of these substances have been phased out, many are still being used in solvents, pesticides, refrigerants, adhesives and coatings. In one researcher’s words, “Polar bears are one of the most polluted mammals on the globe.”

Female polar bears now weigh an average of 506 pounds, a full 143 pounds less than in 1980; and they measure almost nine inches smaller than before. As their weight has fallen, their health has suffered, impairing their ability to reproduce and have cubs that survive. And some scientists report that, in their desperation, polar bears are turning on each other. They deliberately hunt other bears, for example, by attacking females in their dens.

Woodrats decreased in size during previous periods of global warming. Is the trend toward species diminution, then, just part of a normal cycle rather than a result of anthropogenic climate change? ©California Department of Fish and Wildlife, flickr

Recently, a U.S. government study predicted that global warming would cause the world’s polar bears to be gone by 2050. But this is now thought to be optimistic: the melting is accelerating so fast that many scientists believe the Arctic Ocean will be completely ice-free in summer by 2030. This lack of ice will mean smaller bears—if they are able to survive at all.

It should be pointed out, however, that fossil evidence from the Paleocene-Eocene Thermal Maximum 55 million years ago, when temperatures rose by 9 degrees Fahrenheit over a period of approximately 20,000 years (carbon is now being released into the atmosphere at a rate 10 times faster) and precipitation levels dropped 40 percent, shows that invertebrates like beetles, bees and ants became 50 to 75 percent smaller. Other species ranging from single-celled diatoms to woodrats have also been shown to decrease in size during previous periods of global warming. Some would say that our current shrinking of animal species is just another natural period in Earth’s history.

Do you think this trend toward smaller species should sound an alarm? Or are we experiencing just another cyclical diminution of the world’s biota?

Here’s to finding your true places and natural habitats,