We know that during major climate change events,warming ocean waters cause cracks in the ocean floor to open up and release large quantities of methane gas into the air. Methane is an extremely powerful greenhouse gas, which results in even more devastating heat retention and dramatic climate change. But now it turns out that methane causes even more problems than thought.
During a great climate change event 55 million years ago, the excess of methane in the atmosphere had an unexpected side-effect. Large species--animals our size and larger--either died out or evolved into much smaller forms.
Methane is quickly converted in the atmosphere into carbon dioxide, another greenhouse gas, and more CO2 means less oxygen in the air. Researcher Philip D. Gingerich says, "?If you grow plants in a carbon dioxide-rich atmosphere, the plants love it. They grow fast. It's easy for them." But it has the opposite effect on animals. He says, "Horses from this period that had been the size of a small dog were reduced to the size of a Siamese cat."
One reason animals shrank could be that they were eating plants that had absorbed more CO2 and were thus less nutritious. Gingerich says, "If an animal has a one- or two-year period in which to grow to maturity and reproduce, and it's trying to do that on a diet that's difficult to digest and not very nutritious, it's not surprising that it would evolve to be smaller. And it's also not surprising that when times are good again and carbon dioxide levels are lower and plants grow like they normally should, that the animals would go back to what we think of as their normal size."
This cycle is already starting again. One of the wonderful things that birds do is eat insects that would otherwise devour our plants and trees, but birds don't like the taste of insects that have been feeding on leaves with high amounts of carbon dioxide in them. Due to large amounts of CO2 in greenhouse gas emissions, there is much more of it in the leaves of plants than usual. This means the birds may starve, or become much smaller, and the bugs may take over, killing off plants and trees.
Researchers Martina M
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