Most Climate Change Damage Will Happen Before the Two-Degrees Warming Threshold

coral reefs and climate change
Coral reefs are highly sensitive to climate change, and may experience most damage at relatively low warming thresholds. “Once you've killed off the coral reefs you are no longer at risk of killing off the coral reefs,” explains Ken Caldeira, an environmental scientist at Stanford University. Dr. Line K Bay/Australian Institute of Marine Science

Most discourse regarding climate change is based around a simple premise: The more the Earth warms, the greater the damage done to the planet. But in new paper published in Nature Geoscience, a team of researchers found that presupposition is fundamentally flawed. The reality, they write, is more ominous.

Almost all the damage from climate change to vulnerable categories like coral reefs, freshwater availability and plantlife could happen before two degrees Celsius warming, the internationally recognized "do not cross" danger threshold. Beyond that point, further warming might have a relatively small impact. That's because, as Ken Caldeira, an environmental scientist at Stanford University and an author of the paper, put it, there won't be much left to ruin.

"Once you've killed off the coral reefs you are no longer at risk of killing off the coral reefs," he said.

Incentive to mitigate emissions greatest before most climate damage occurs. @KateRicke

— KenCaldeira (@KenCaldeira) December 8, 2015

In the chart below, Caldeira and his colleagues graphed the extent of damage from climate change on various sectors of the environment. They found that the sensitivity of some of these categories to small increases in temperature will be highest within the first several degrees of warming, and then tapers off, having hit a physical limit, or what the researchers call a "saturation of impacts," as in the case of coral reefs at two degrees Celsius. Once the planet gets into the higher degrees of warming, the rate of impact begins to plateau—because there won't be anything left to be affected.

Saturation of Impacts
Some climate change impacts rise fast with little warming, and then taper off, write a team of researchers in a paper published during the 2015 Paris climate talks. Ricke et al/NATURE GEOSCIENCE

Freshwater scarcity also appears to worsen rapidly prior to two degrees warming, and worsen more slowly after. The ruining of crop land appears to slow down around 3 degrees of warming, after significant damage, as indicated by the steep upward slope of the red line, has already been done. The same holds true for damage to UNESCO World Heritage sites.

The paper also does away with another common trope: that as the effects of climate change get worse, governments will feel more and more pressure to do something about it, like dramatically reduce emissions. But, Caldeira says, the opposite is probably true. "Once all the sensitive components of our planet are already damaged, incentive to decrease emissions may decrease.... The incentive to avoid climate change may be greatest before we have done substantial damage."

In short, explains Kate Ricke, a climate scientist at Stanford and another author of the paper, if the Paris climate agreement produces "insufficiently ambitious climate policy," it could "inadvertently push the world into a lower-mitigation and lower-welfare future."

Because once we've broken everything, what damage is left to prevent?