Alexandria Herr, Shannon Osaka, and Maddie Stone report:

In 2019 an international team of scientists published a commentary in the celebrated science journal Nature, sounding the alarm of a planet in crisis — and calling for transformative change.

“We are in a state of planetary emergency,” they wrote, departing from the usual sterility of scientific writing. “The stability and resilience of our planet is in peril.”

Yes, they were writing about climate change, but of a particular kind: climate tipping points, elements of the Earth system in which small changes in global temperature can kick off reinforcing loops that ‘tip’ a system into a profoundly different state, accelerating heat waves, permafrost thaw, and coastal flooding — and, in some cases, fueling more warming. The planet has already warmed by roughly 1.2 degrees Celsius (2.2 degrees Fahrenheit) since the Industrial Revolution, and if humans keep flooding the atmosphere with greenhouse gases at the same rate, we’re on track to increase that to 2.7 to 3.1 degrees C (4.9 to 5.6 degrees F) by the end of the century.

So those small changes are getting bigger — increasing the likelihood of triggering those reinforcing loops, known as positive feedbacks. (For example, warming increases the frequency of wildfires, which in turn increases the amount of carbon dioxide released into the atmosphere from burning trees, which leads to an increase in global temperature, which means, you guessed it, even more wildfires.)

The scientists identified various elements of the Earth system at risk of reaching points of no return. These elements broadly fall into three categories — ice, sea, and land — and range from the melting of the Greenland ice sheet to the death of coral reefs to the raging of more and more wildfires.

The concept of tipping points challenges the dominant understanding of how climate change fundamentally works, says Will Steffen, one of the Nature article’s co-authors and an emeritus professor of climate science at Australian National University. Rather than a dial slowly turning up, tipping elements could compound, he says, combining to build a greater, planetary-wide tipping point. Alternatively, they could push one element out of whack, triggering another to fall out of phase, and then another in a domino-like effect, resulting in a “rapid acceleration of warming until the Earth stabilizes in another state.” These possibilities are far from certain, he admits, but the consequences of a planetary tipping point are severe enough that even a slim risk needs to be taken seriously.

The particular danger, according to the Nature paper’s authors, is that even though change in a tipping element may happen slowly on a human timescale, once a certain threshold in the system is crossed, it can become unstoppable. This means that even if the planet’s temperature is stabilized, the transition of certain Earth systems from one state to another could pick up speed, like a rollercoaster car that’s already gone over the apex of a track. [Continue reading…]