A cliché that describes getting the big picture is to go out to “the 30,000 foot view”. In this study we go out in time, and much, much farther, getting the 540 million year view of climate history (which, by the way, you can enjoy with your morning coffee by purchasing one of the mugs or shirts from the CDN store). People may quibble that some of the studies we talked about in this series only covered a short time span. But that criticism doesn’t apply to one that covers the entire Phanerozoic Eon. Over half a billion years during which some major changes occurred, including formation of mountain ranges that changed regional climates, the drifting about, separating and colliding of entire continental plates that made those mountains, and orbital variations that cycle over hundreds of thousands of years without adding any long-term trend. Indeed at the 540 million year time scale many things cause temporary changes, as geologists use the word “temporary”, but very few cause persistent trends. So the authors of this week’s study focused just on the ones that do, including the long, undulating decline in CO2 levels. And yes, yet again, the ECS revealed in this analysis is 1.7 ° C, close to the many others we have reported on based on modern data.
We actually reported on this study previously but made a mistake in that posting. We said the ECS value was 2.1° C, when in fact it was 1.7° C. The 2.1 figure referred to the change in forcing (in Watts per square meter) from doubling CO2, not the change in temperature in degrees C and we apologize for the error.
The data these authors assembled is shown here:
The dotted yellow line is the so-called Scotese temperature reconstruction, the same one shown on our mugs and other merch. The solid black line is the new temperature reconstruction Shaviv and his coauthors presented. The green dash-dot line is the predicted temperature path from the statistical model they fit to the other data series. The red line is the estimated CO2 concentration, the upward-sloping purple line is the solar luminosity record and the bottom blue line is the Galactic Cosmic Ray (GCR) record.
GCRs are high energy particles originating in deep space that bombard the atmosphere and, among other things, influence cloud formation. And because variations in solar wind driven by variations in solar activity change the amount of GCRs entering our atmosphere, the sun has a powerful indirect influence on the climate.
Shaviv and coauthors combined the above climate drivers and found the combination of parameters that yields a temperature curve (green line) that fits the temperature record as well as possible. It was from that calculation that they concluded temperature variations over the Phanerozoic are best explained by assigning only a small role to CO2. Just as so many authors in this series have also found modern temperature changes are best explained by assigning to CO2 a relatively small role, less than 2° C for CO2 doubling, which is too small to justify the policy agenda of the alarmists.
