Yes, there was global warming in prehistoric times. But nothing in millions of years compares with what we see today

By | September 24, 2023

Michael E. Mann writes:

“The climate is always changing!” So goes a popular refrain from climate deniers who continue to claim that there’s nothing special about this particular moment. There is no climate crisis, they say, because the Earth has survived dramatic warming before.

Republican presidential hopeful Vivek Ramaswamy recently exemplified misconceptions about our planet’s climate past. When he asserted that “carbon dioxide as a percentage of the atmosphere is still at a relative low through human history,” he didn’t just make a false statement (carbon dioxide concentrations are the highest they’ve been in at least 4 million years). He also showed fundamentally wrong thinking around the climate crisis.

What threatens us today isn’t the particular concentration of carbon dioxide in the atmosphere or the precise temperature of the planet, alarming as those two metrics are. Instead, it’s the unprecedented rate at which we are increasing carbon pollution through fossil fuel burning, and the resulting rate at which we are heating the planet.

Consider the warming event that paleoclimatologists point to as the best natural comparison for the rapid greenhouse-driven trend we’re seeing now. The Paleocene-Eocene Thermal Maximum happened 56 million years ago, roughly 10 million years after the demise of the dinosaurs, which itself was caused by climate change (a massive asteroid impact event led to a global dust storm and, in turn, rapid cooling). The PETM warming resulted from an unusually large and rapid injection of carbon dioxide into the atmosphere from volcanic eruptions in Iceland. Global temperatures increased by approximately 10 degrees Fahrenheit in as little as 10,000 years, rising from an already steamy baseline of 80 degrees Fahrenheit possibly up to a sauna-like 90 degrees Fahrenheit.

That warming rate of about 0.1 degree Fahrenheit per century is extremely rapid by geological standards. But it’s still roughly 10 times slower than the warming today. [Continue reading…]

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