President Donald Trump is withdrawing the U.S. from the Paris Agreement on climate change, announcing today that he hopes to negotiate a new and "fair" climate deal. What will the withdrawal mean for the climate?
Following the Paris agreement, the Obama administration pledged to cut the country's greenhouse gas emissions to 26-28 percent below their 2005 levels. According to Climate Interactive, that would account for 21 percent of the world's greenhouse gas reductions by 2030. In the unlikely scenario that the U.S. adopts no climate policies at all, Climate Interactive estimates that American emissions would amount to 6.7 gigatons of CO2 equivalents per year by 2025, compared to emissions of 5.3 gigatons per year if the U.S. follows through on its Paris commitments. Global annual emissions would be 57.3 gigatons per year instead of 55.8 gigatons per year, a difference of nearly 3 percent:
Climate Interactive
In March, the Rhodium Group consultancy calculated what would happen to U.S. greenhouse gas emissions if President Trump's executive order rolling back most Obama-era energy and climate regulations were fully implemented:
Rhodium
Basically, emissions would stabilize at around 14 percent below their 2005 levels—nowhere near Obama's 28 percent Paris pledge.
So what would happen to global temperatures' trajectory if Trump repudiates the Paris Agreement and stops trying to cut U.S. greenhouse gas emissions?
Humanity would have to stop emitting greenhouse gasses entirely by around 2065, if the goal is to keep the future temperature increase below 1.5 degree Celsius. The folks at the Climate Action Tracker basically concur that the Paris pledges would limit warming to about 2.8 degrees Celsius above pre-industrial levels—or in probabilistic terms, that they would likely limit warming below 3.1 degrees Celsius.
In the November 2016 issue of Global Environmental Change, a group of European climate researchers modeled the impact of the policies implied by the Paris Agreement on future global average temperatures:
GEC
The researchers considered (1) all climate policies announced before the Paris Agreement; (2) each country's pledged emission reductions after Paris; and (3) the reductions it would actually take to keep the average global temperature increase below 2 degrees Celsius by 2100. As you can see, merely implementing the Paris pledges would implies a global average temperature increase of 3 degrees Celsius.
In a November 2015 article published in Global Policy, Copenhagen Consensus Center head Bjorn Lomborg calculated that implementing just the Paris pledges over the course of the entire century would reduce future warming by 0.17 degree Celsius by 2100:
Lomborg
Clearly all climate modelers calculate that much deeper cuts in greenhouse gas emissions would have to be made in order to meet the Paris targets.
My own solution for any problems that might arise from man-made climate change (and for most other challenges faced by humanity) is to adopt policies that boost technological innovation and wealth creation. For details on what that would entail, go here.
