There has been a lot of speculation since climate change doubter Donald Trump’s election about what the consequences could be for global climate action. Some analysts cite very dire implications, and others suggest that clean energy growth will continue apace.
But number-crunching analyses that actually calculate how much of a dent the election could have on the planet’s temperature have been rare. That’s in part because it’s no simple calculation.
Some have tried, though — and one such analysis from the think tank Climate Interactive, which we’ve unpacked here before, came up with a kind of middle-road result on this question. It found that if the United States delays addressing climate change domestically for four to eight years, this alone would not be enough to push the globe into the climate “danger” zone, which is generally described as allowing temperatures to rise more than 2 degrees Celsius above their pre-industrial level. However, if U.S. backsliding lasted longer, or if it led to corresponding actions by other countries, then the result could be severe for the planet.
A new commentary article published in Nature Climate Change on Monday presents some additional calculations that tend toward a similar conclusion.
Written by Benjamin Sanderson of the National Center for Atmospheric Research and Reto Knutti of ETH Zurich, the paper uses climate models to determine what the consequences would be if an eight-year delay in U.S. climate action, led by Trump, reverberates globally. The paper also considered a doubly bad scenario in which the United States also cuts back on clean energy research and then the world follows suit, and a triply bad scenario in which it also burns more fossil fuels and the world follows.
“Any delays to mitigation or cuts to renewable energy research by the U.S. will likely render the 2 °C target unachievable if a global precedent is set,” the authors write.
Let’s take this in pieces.
First and most important, the analysis finds that if the U.S. delays for eight years taking any climate action — meaning its current emissions remain steady — then that alone wouldn’t harm the planet much. This is basically the same result as the one reached by the Climate Interactive analysis. The United States is just one country and the second largest emitter. Even if it goes rogue, it cannot totally torpedo the planet.
But if the delay by the United States spreads globally — nobody cuts emissions, everybody waits for eight years — then it becomes a bigger deal. The study found that could lead to an additional 350 billion tons of carbon dioxide emissions, corresponding to a planetary temperature increase of .25 degrees Celsius and a lessened chance of keeping the warming of the planet within the safe range embraced in the Paris climate accord.
“The fear is that the U.S. coming out, or the U.S. having reduced ambitions in the near term, would destabilize the whole agreement,” Sanderson said in an interview.
The problem with such a delay is that there is a finite “carbon budget” before we reach 2 degrees of warming, and each successive year of emissions adds to the budget. So delays make staying within the budget a great deal harder and require much sharper cuts afterward.
In the case of an eight-year global delay (followed by global emissions cuts), that reduces the chances of staying within the 2-degree C goal from 66 percent to 50 percent, Sanderson said.
But it could be worse than that: The United States and globe could not only hold steady on emissions, but could actually emit more. And the United States might delay taking steps to create clean energy technologies better than the ones that we have now, causing a global turn away from clean energy research, including on key technologies such as carbon capture and storage.
The analysis finds that adding these problems for eight years worsens the overall problem still more, putting the 2-degree goal farther and farther out of reach.
“The bottom line is that a very short delay in global action would have very large consequences for the ability to meet these very aggressive targets, even if very globally coordinated and ambitious action happens post-2025,” said Sanderson.
Granted, the authors admit that this is a thought experiment only based on a particular set of assumptions — Trump’s policies don’t exist yet, so they cannot be evaluated directly. Nor can the world’s response to them. “We caution against overinterpreting the numbers of this analysis because of the large uncertainty in how the economic and ideological shift in U.S. governance will affect greenhouse gas emissions,” they write.
Indeed, some aspects of the analysis seem less realistic than others. The idea that the United States could withdraw from the Paris process, and that could then crack things up enough that other countries also slow their own ambitions to cut emissions, is not an unreasonable fear. And as the study shows, that’s a bad enough outcome.
What’s harder to believe, though, is that a global turn away from clean energy research and development could be precipitated by U.S. actions. The clean-energy trend seems too firmly entrenched at this point. In this sector, a U.S. withdrawal seems more likely to give advantages to its competitors (China, Germany, and others) than to lead them to cut back on investments as well.
As for whether an actual increase in emissions could happen globally over the next eight years — that’s also uncertain. In the past three years, global emissions have appeared to flatten but have not yet gone down. Less coal burning in China and the United States appears to be a key driver of this trend. Once again, it’s not clear that the United States’ intransigence alone could set off more emissions growth in a world in which clean energy growth is looking pretty dynamic.
Still, despite using a very different methodology, the new analysis fits with the previous one by Climate Interactive. A Trump administration hostile to international climate agreements cannot substantially change the planet’s temperature alone over eight years — but it can cause considerably more of an impact if it leads other nations to halt their own actions, or to step back from the clean energy revolution.
It is important to reiterate that keeping global warming below 2 degrees Celsius above preindustrial levels was already going to be extremely difficult no matter who the U.S. elected president — and that the climate impacts we have seen so far are already pretty grave.
So really, we are on a road to considerable damage no matter what, and likely some impacts that will be irreversible on any human time-scale. In this context, while we can’t know the future, we can definitely say that disengagement by the United States has the potential to make things worse — but that it will depend on how the entire world responds.
It is, after all, global warming.