The Great Reset Is "What They're Doing" - Question Is, What're You Going To Do?

bloomberg |  A major new study of the relationship between carbon dioxide and global warming lowers the odds on worst-case climate change scenarios while also ruling out the most optimistic estimates nations have been counting on as they attempt to implement the Paris Agreement.

A group of 25 leading scientists now conclude that catastrophic warming is almost inevitable if emissions continue at their current rate, even if there’s less reason to anticipate a totally uninhabitable Earth in coming centuries. The research, published Wednesday in the journal Reviews of Geophysics, narrows the answer to a question that’s as old as climate science itself: How much would the planet warm if humanity doubled the amount of CO₂ in the atmosphere?

That number, known as “equilibrium climate sensitivity,” is typically expressed as a range. The scientists behind this new study have narrowed the climate-sensitivity window to between 2.6° Celsius and 3.9°C.

That’s smaller than the current range accepted by  the United Nations-backed Intergovernmental Panel on Climate Change, which has for almost a decade used a spread between 1.5°C to 4.5°C—a reading of climate sensitivity that has changed little since the first major U.S. climate science assessment in 1979. Improving these estimates is “sort of the holy grail of climate science,” says Zeke Hausfather, director of climate and energy at the Breakthrough Institute and one of the study’s authors.

Climate sensitivity is one of the most iconic numbers in climate science, but it’s not necessarily intuitive. The range isn’t a projection; it’s more like a speed limit that influences projections. “It informs all the other things—like 2100 warming projections, for example—that depend on the sensitivity of our models, and our scenarios,” Hausfather says.

What gave the authors confidence is that three independent lines of evidence—the modern temperature record, geological evidence, and the latest Earth systems models—all agreed on the same answer. Kate Marvel, a research scientist at NASA’s Goddard Institute for Space Studies and Columbia University’s applied math and physics department, also contributed to the new paper. She answered questions for Bloomberg Green about the scope and meaning of the new work.

What is “equilibrium climate sensitivity,” and why is it so important?

It's basically answering this question: How hot is it going to get? People are sometimes really surprised. They’re like, “You guys have one job like, why do you not know this?”

The number one determinant in how hot it's going to get is what people are going to do. If we gleefully burn all the fossil fuels in the ground, it's going to get very hot. If we get extremely serious about mitigating climate change—cutting our emissions, moving off fossil fuels, changing a lot about our way of life—that will have a different impact on the climate. As a physical scientist, “What are we going to do?” is totally above my pay grade.