Cosmic Rays Are Doing What CO2 Gets Blamed For | Henrik Svensmark

Link to full episode: https://www.youtube.com/watch?v=k2UCiBNwteU

In the ice age record, temperature moves first and CO2 follows it. That reversal is where Henrik Svensmark starts, and he is careful about what it does and does not mean. Burning fossil fuels does put extra carbon dioxide into the air, carbon dioxide is a greenhouse gas, and that does raise the temperature a little. What he rejects is the idea that it is the main control knob. Over the long stretches that built the ice ages and the warm periods between them, he argues the bigger driver is cosmic radiation arriving from deep space and the clouds it helps create.

The mechanism runs opposite to how most people picture the sun. When the sun is quiet, with very few sunspots, its shield weakens, more cosmic rays reach the atmosphere, more clouds form, and Earth cools. When the sun is active, it sweeps those rays away, cloud cover thins, and Earth warms. Svensmark counts six or seven deep minima in solar activity over the past 10,000 years, each one matched by a cold climate, and the Little Ice Age sits on top of a stretch with almost no sunspots at all.

His evidence here is physical rather than modeled. Icebergs drifting across the North Atlantic carry small stones inside the ice, and when they melt those stones drop to the seafloor. Drill the cores, count the stones by depth, and you have 12,000 years of climate history. Laid against reconstructed cosmic ray levels, Svensmark says the two curves follow each other. He also walks the deep past: Earth roughly 10 degrees warmer 50 million years ago, palm trees and baobabs growing in Antarctica, then a steady cooling across the last few million years. During the ice ages CO2 fell so low that plants were in trouble, which is part of why C4 plants developed. Go low enough, he says, and all life dies.

The last time the climate turned on people, they went hunting for someone to blame. Through the Little Ice Age, storms and ruined harvests were treated as witchcraft, and thousands of women and men were burned at the stake for it, including after a bad storm struck a Danish princess sailing to marry an English king. Solar activity has been climbing for the past century, and Svensmark’s own admission is that nobody can reliably predict what the sun does next.

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Written by Danny Jones Clips