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(Nearly) coldest in 485 million years

02 Oct 2024 | Science Notes

There has been a lot of discussion lately about a new study which reconstructs global average temperatures over the past 485 million years. It has taken many people by surprise to see that we are in an unusually cold era, but if you had purchased your CDN mug showing climate change over the past half billion years you’d already have seen the deep blue patch at the end, indicating the relative coolness of the interval we inhabit. That reconstruction does have at least one colder era in the distant past, as does the new one. And both show that for about the past 250 million years the world was warmer but has been gradually getting cooler. The new study nevertheless bravely, or brazenly, tries to maintain that despite all the cooling CO2 is driving the climate, except for 200 million years during the Mesozoic when, um, it didn’t. If it does once again, we might just get back to something like a normal level of warmth on Earth.

The reconstruction looks like this:

The red arrow, which we added, shows the “You Are Here” spot such as you find on those maps in the shopping mall where you still wonder where you are. And according to the colour codes along the top the late Paleozoic (the pre-dinosaur era) was cooler, about 300 to 350 million years ago, then it warmed steadily until the Cenozoic 50 million years ago and it’s been downhill ever since.

Another version of the graph from the same study plots it against a CO2 reconstruction, with temperature the top line:

What stands out here is that while the two lines do move together during the Paleozoic, they diverge during the Mesozoic, then move together again in the Cenozoic. Which means CO2 isn’t the main climate driver because if it was there wouldn’t be a 200-million year stretch when they don’t track each other. And it’s also worth noting that even where they do track each other, the authors don’t show whether temperature moves first, or something else causes both to change. Correlation famously is not causation, and the long Mesozoic even shows a lack of correlation.

Compared to the study we used in our stripes mug this new one doesn’t have the warming spike 250m years ago. Also our stripes version has it being much colder 440m years ago than theirs. But they both show steady cooling over the past 100 million years, so they agree that on the geological scale, many of the plants and animals around us, including primates, evolved under much warmer conditions than today, and judging by the incredible profusion of life today in the tropics compared to the poles, they thrived in warm conditions. As is still the case today.

3 comments on “(Nearly) coldest in 485 million years”

  1. Tried to buy the 15oz half-billion yr mug; got back the following. What's that about??
    Your account cannot currently make live charges. If you are the site owner, please activate your account at https://dashboard.stripe.com/account/onboarding to remove this limitation. If you are a customer trying to make a purchase, please contact the owner of this site. Your transaction has not been processed.

  2. Oddly, the conclusion one is led to from the charts is that Temperature controls CO2 level, not the other way around.
    CO2 only causes .7 degrees warming per doubling, whereas this chart in places shows up to 20 degrees warming for a 500 to 1000 ppm changes (both ways). Volcanoes, ocean cocolithophore growth, soil and vegetation sequestration rate change varying with temperature, we don’t really know but CO2 is always the lipstick on our pig.

  3. My Order #30592] (September 18, 2024) also has not been prcessed and there does not appear to be any way to follow up with the store's page.

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