Delay and Pay: Tipping Point Costs Quadruple After Waiting

“You either shoulder the cost now, just before the threshold is crossed,” said Kooloth, “or you wait. And if you wait, the degree of intervention needed to bring the climate system back to where it was rises steeply. A key insight from this work is the confirmation that corrective action after the fact is much more costly and intrusive than preventive action.”

Each tipping point is unique. The physical qualities that determine its behavior—the extent of cloud cover or, say, the transport of heat in the nearest ocean waters—determine how post-tipping changes take shape in the climate system. In turn, those qualities dictate the nuts and bolts of an actual intervention strategy.

At the heart of each tipping point, however, is a shared, core equation that describes its basic nature. This universality allows researchers like Kooloth to probe the fundamental, shared behavior of tipping points using simplified mathematical models. 

From their findings, scientists can then glean broad stroke details that could inform future intervention plans and perhaps, as Kooloth hopes, even a way to identify early warning signals that a tipping point is drawing near.

“It’s actually really hard to pin a tipping point down,” said Kooloth. “We know a great deal about the climate system today. But even now we’re never really sure how far or close we are to a tipping point. Could we one day use observable precursors to provide early warning? My hope is that we can.” 

The team behind the new study uncovered one other interesting phenomenon: that some tipping points have an “overshoot window.” In this window of time just after a tipping point is crossed, the cost of intervention doesn’t start its steep climb right away. Instead, cost only grows linearly with time. This can happen because nearby ocean waters take longer to heat up, for example, delaying the onset of rapid change. 

It’s a fortunate thing, Kooloth points out, a gift of additional time before dire changes start piling on. But this is “no free lunch,” she adds. The extra leeway comes with an even steeper increase in intervention costs once the overshoot window is fully crossed. The bigger the overshoot window, the mightier the cost. 

The authors point out that not all effects of climate change are reversible, like flora and fauna lost to rapid and prolonged environmental change. And some effects could demand a great deal of effort to reverse—even more than the effort it took to push the climate system past a tipping point. 

There is an asymmetry at play, said Kooloth. We could approach and pass a tipping point rather quickly, but the journey to revert the climate system to where it was could take much, much longer. 

“The path forward and the path backward are often not the same,” said Kooloth. “Imagine that we go down a high-emissions pathway, where the planet warms enough to melt all our sea ice by the end of the century. If we arrive in the year 2100 with no sea ice, it may not be sufficient to bring the ice back if we dialed our emissions down to the levels we’re emitting now in 2024, when we still have some ice left. We may need to dial emissions down much further, to levels predating 2024—that asymmetry is important for us to consider as we choose our path forward.”

Brendan Bane is a Pacific Northwest National Laboratory (PNNL) Media Relations Specialist. The article was originally posted to the website of PNNL.