Greenhouse warming can get pretty extreme:
Scientists have found what might have been the ideal ancient vacation hot spot with a 74-degree Fahrenheit average temperature, alligator ancestors and palm trees. It’s smack in the middle of the Arctic.
First-of-its-kind core samples dug up from deep beneath the Arctic Ocean floor show that 55 million years ago an area near the North Pole was practically a subtropical paradise, three new studies show.[…]”Imagine a world where there are dense sequoia trees and cypress trees like in Florida that ring the Arctic Ocean,” said Pagani, a member of the multinational Arctic Coring Expedition that conducted the research.
Millions of years ago the Earth experienced an extended period of natural global warming. But around 55 million years ago there was a sudden supercharged spike of carbon dioxide that accelerated the greenhouse effect.
People who trumpet “natural cycles” will no doubt love this study. You have the Earth warming itself, relatively fast (if you call a few million years fast) and hitting peaks of CO2 that we today couldn’t imagine. There you have the upside anyway, although until we know why the CO2 spike happened comparing now with then will be a sucker’s game.
If we had to bet on a cause I would go with increased volcanoes, which kick amazing amounts of carbon into the air. Land plants don’t actually impact the atmospheric carbon levels that much, even if you burn them, since the world’s major sink of biological carbon lies in the ocean. Also marine carbon actually has a chance of being flushed out of the system forever (don’t tell a geologist that I said forever…) by mineralizing into calcite and getting buried in deep-sea sediment. The carbon fixed by land plants doesn’t actually weigh that much compared with marine algae and eventuall just washes into the sea anyway.
You could get a similar result if something acidified the oceans. Carbon minerals like calcite would dissolve before they reach the seafloor and circulate back into the atmosphere rather than get buried in sediment, but that sort of event would leave fingerprints all over the place. People have looked at enough seafloor sediment cores by now that I doubt that it happened.
The weirdest possibility takes a bit of mental gymnastics but it might stand an outside chance of being true. Like all stone silica-rich rocks break down into gravel, then sand and then their component ions in a process called weathering. Unlike other stone, silica weathering causesthe drawdown of CO2 from the atmosphere. Plant roots do a much faster job of weathering rocks than rain and wind alone, so if you burned off or extincted away the rooted plants from a significant part of the Earth’s surface you might slow down atmospheric carbon drawdown and over thousands to millions of years cause a major spike in CO2. The K-T boundary (dinosaur extinction) happened around 65 million years ago, 10 million years earlier than our CO2 spike, so it’s possible that a killer asteroid burned off a good fraction of one hemisphere’s land plants and the plants “left behind” weren’t nearly as good at breaking down silica. The difference would take time to manifest itself. Ten million years seems long, but not outside the realm of possibility.
One the downside, once CO2 gets into the atmosphere its effects can reach farther than we thought:
Many experts figured that while the rest of the world got really hot, the polar regions were still comfortably cooler, maybe about 52 degrees Fahrenheit.
But the new research found the polar average was closer to 74 degrees. So instead of Boston-like weather year-round, the Arctic was more like Miami North. Way north.[…]What’s troubling is that this hints that future projections for warming, several degrees over the next century, may be on the low end, said study lead author Appy Sluijs of the Institute of Environmental Biology at Utrecht University in the Netherlands.
Also it shows that what happened 55 million years ago was proof that too much carbon dioxide — more than four times current levels — can cause global warming, said another co-author Henk Brinkhuis at Utrecht University.
It had not occurred to me that informed people still doubt that CO2 causes warming. Not counting those paid to doubt it, of course.