When global warming finally gets going, it could last for 200,000 years

New evidence shows that, while we may not see severe climate change in our lifetimes, global warming could snowball into catastrophe in the distant future—and once the climate has shifted, it might not go back to normal for a very, very long time.

This is from two new studies on climate change this week. The first, published by researchers at the Scripps Institution of Oceanography in California, paints a disturbing picture of what our oceans will look like if we don’t ease up on the emission of greenhouse gases like carbon dioxide (CO2). Scientists looked at fossils from the so-called “greenhouse world” that existed about 50 million years ago (where the CO2 concentration in the atmosphere was more than double what it is now) and found that the conditions essentially killed ocean reefs.

It’s not hard to see why. At those levels of CO2, the new study shows, ocean temperatures in the tropics reached 95 °F (35 °C), with polar oceans hitting 50 °F, about the temperature of the waters around San Francisco today. Because of those balmy waters, researcher Richard Norris told redOrbit, “The ‘rainforests-of-the-sea’ reefs were replaced by the ‘gravel parking lots’ of the greenhouse world.” With reefs dominated by pebble-like, single-celled organisms instead of nutrient-packed plankton, the ocean couldn’t support larger animals, and mass extinction likely occurred. And while we could perhaps be comforted that the effects of the warming were limited mostly to the deep sea (though who’s to say what such an event would do to our food supply), what should disturb us is how long it lasted—200,000 years. On our current trajectory, we’ll reach that concentration of CO2 in only 80 years.

Meanwhile, a study by University of Hawai’i oceanographer Richard Zeebe also suggests that climate change effects could last much longer than we might have thought. Looking at feedback loops (for example, rising temperatures cause snow to melt, which in turn causes temperatures to rise even more because bare ground reflects less sunlight back into space than snow) throughout history, Zeebe found that some may occur very slowly, and on a larger scale. Over time, he found, the Earth can become more vulnerable to greenhouse gases, meaning that it takes smaller increases in CO2 to raise temperatures. That means that climate change could happen quite slowly during our lifetimes, but speed up suddenly at some point in the future, with every temperature increase making the atmosphere more vulnerable.

Taken together, these studies show that the climate shift we’ve already set in motion could last much, much longer than previously thought. Even if we don’t see the effects, countless generations of our descendants will. An abrupt drop in CO2 emissions now, Norris said, could see the climate drop back down to pre-industrial norms in less than 1,000 years. But if emissions continue to rise for another century, global warming could last for tens, if not hundreds, of thousands of years thereafter.

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