Science
Thomson Reuters
President Trump has announced that the US will withdraw from the Paris Climate Agreement, the 2015 international accord by which 195 nations agreed to limit greenhouse gas emissions in order to prevent global temperatures from rising more than 2 degrees Celsius above pre-industrial levels.
However, the US has contributed more the problem of excess carbon dioxide than any other country on the planet. It wouldn't be wrong to say that climate change was "made in America."
"In cumulative terms, we certainly own this problem more than anybody else does," David G. Victor, director of the Laboratory on International Law and Regulation and climate politics scholar, told The New York Times. And that's why a commitment from the US to reduce emissions and to help fund global emissions reductions is considered so important.
In the US, Americans started burning fossil fuels at higher rates than the rest of the world early, which means that the US is responsible for almost a third of the excess CO2 that's already in the atmosphere, despite having just more than 4% of the global population.
World Resources Institute
It's true that now, China emits more CO2 overall, as this chart from the World Resources Institute shows.
However, that's a recent change, and the US is still responsible for far more in terms of CO2 emissions per capita (more than twice as much as citizens of China, Japan, or Europe).
Climate Interactive
It's for these reasons that reductions in US emissions (and US contributions) were considered so important for the Paris Climate Agreement. According to calculations by Climate Interactive based on the Paris and Marrakesh climate agreements, the US agreed to be responsible for more than a fifth of global emissions avoided as a result of the agreements.
Without the involvement of the US, Climate Interactive calculates that the world can expect to see an additional .3 degrees Celsius of warming by 2100. If other countries decide to drop out of the accord due to the Trump decision, that number could be even higher.
In order to avoid catastrophic effects of climate change, most experts think we need to limit warming to less than 2 degrees C above pre-industrial levels. Doing so would require more intense cutbacks than the Paris Agreement established. That was just considered a starting point.