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Tip your planet! —
Multiple tipping points may do far more than eliminate glacial cycles.
We tend to use “ice age” to mean a period where large ice sheets push south to what are now temperate regions. But from a geologist’s perspective, even current conditions are part of an ice age, since large ice sheets exist at the poles. The term provides a contrast to what are called hothouse conditions, which the Earth has experienced for periods that were long enough to entirely melt the poles. The planet hasn’t seen hothouse conditions for more than 2.5 million years.
But this week, headlines were full of discussion of a possible return of a hothouse Earth courtesy of climate change. The sudden worries weren’t the product of any new research; instead, they were simply the product of a perspective some researchers had written on our current understanding of the climate, plus some potential risks associated with it. The perspective argued that there are multiple tipping points in the climate, and we can’t rule out shooting past them even if we get emissions under control within a few decades.
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So how seriously should we view this risk, and why are scientists suddenly talking about it now?
The perspective that set all of this off was written by a large group of Earth scientists, many of them European, and their work was published in the journal PNAS. Perspectives, rather than focusing on new or specific research findings, typically provide a broad overview of what we know about some aspect of a field of research. In this case, the focus was on possible trajectories for our future climate as human carbon emissions become an ever-growing driver of the climate’s trajectory.
The authors point out that, for the last few million years, the Earth has cycled between a heavily glaciated state and one in which the ice has been largely limited to the poles. The details of these warmer periods vary—carbon levels and orbital influences differed, leading to differences in temperatures, the loss of ice, and resulting sea levels. But the differences were never large enough to drive the climate into a new state. When the orbital influences cycled back, the planet returned to a glacial state.
That’s no longer the case. Even at current levels of carbon dioxide in the atmosphere, it would take something exceptional to allow glacial conditions to return, and emissions are set to push those levels up ever higher over the next few decades. And, if we’re no longer in a situation where the Earth can cyc