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ECS over the Phanerozoic

12 Jul 2023 | Science Notes

You might have noticed that all the cool people are using CDN mugs like the one showing half a billion years of climate change. Now in a new study (h/t No Tricks Zone), three scientists have constructed a new temperature reconstruction of those same half billion years and matched it with three potential drivers of climate change: CO2 levels, solar luminosity and Galactic Cosmic Rays or GCRs. Which is how real science is done; competing hypotheses are measured against the data rather than political expediency. Now GCRs may sound like something out of Star Wars, but instead of being fired from a Death Star they are fired by dead stars, expired supernovas. They travel throughout the Milky Way including our solar system, and when they hit the Earth’s atmosphere they cause ionization and promote cloud formation, which affects the Earth’s temperature. Over millions of years variations in the intensity of GCRs hitting the atmosphere, due either to changes in the solar wind or changes in the angle of our solar system relative to the Milky Way, contribute to variations in climate. So much, in fact, that there isn’t much left for variations in CO2 to explain.

The three scientists, Nir Shaviv of the Hebrew University of Jerusalem, Henrik Svensmark of Denmark’s National Space Institute and Jan Veizer of the University of Ottawa, break down the influence of the three inputs as follows.

The vertical axis shows degrees C and the horizontal axis shows time (millions of years before now). The top solid black line is the new temperature reconstruction and the yellow dotted one behind it is an earlier version (which is the one on our mug and is very similar) shown for comparison. The green line is the prediction from their model, based on adding up the contributions from the three coloured lines below it. The red line is the contribution from CO2, which gradually declines over the whole interval because CO2 has been steadily declining. The purple line is the contribution from the sun, which gradually increases over time. The bottom gray line is the contribution from GCRs, which oscillate up and down and account for the largest changes.

Over the half-billion year record the authors work out that CO2 has an ECS of about 2.1 degrees C. In other words, doubling CO2 in the atmosphere leads to warming of about 2.1 C, which is not only a lot lower than the IPCC’s recent estimate of 3.1, but is almost exactly the same as the estimate published by Nic Lewis in 2022 after he corrected the IPCC’s math. Shaviv and his coauthors find that CO2 has about as much effect on the climate as changes in solar output, but because they move in opposite directions they roughly offset each other over the past 500 million years.

In order to believe the alarmist hype coming from climate model studies we have to believe that things that were true of the climate over the past 500 million years suddenly changed in 1750 and now it operates on completely different principles. But we think it makes more sense to assume that the same laws of physics that applied over the past half billion years are still in effect today and will be tomorrow. Just in case you’re wondering what the word denier means.

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