And to get on track for 1.5°C of warming, the world would have to halve greenhouse gas emissions from current levels by 2030.
That’s a staggering task, and there are huge technological and political hurdles standing in the way.
It projects that temperatures could rise at least 2°C (3.6°F) by the end of the century under many plausible scenarios — and possibly 4°C or more.
A more recent study by scientists in the United Kingdom found a narrower range of expected temperatures if atmospheric carbon dioxide doubled, rising between 2.2°C and 3.4°C.
Yes, the planet’s temperature has changed before, but it’s the rise in average temperature of the Earth's climate system since the late 19th century, the dawn of the Industrial Revolution, that’s important here.
Temperatures over land and ocean have gone up 0.8° to 1° Celsius (1.4° to 1.8° Fahrenheit), on average, in that span: Many people use the term “climate change” to describe this rise in temperatures and the associated effects on the Earth's climate.
However, these facts have failed to register with the Trump administration, which is actively pushing policies that will increase the emissions of heat-trapping gases.
Ever since he took office, President Donald Trump has rejected or undermined President Barack Obama’s signature climate achievements: the Paris climate agreement; the Clean Power Plan, the main domestic policy for limiting greenhouse gas emissions; and fuel economy standards, which target transportation, the largest US source of greenhouse gases.
The US government’s National Climate Assessment, with input from NASA, the Environmental Protection Agency, and the Pentagon, also reported that the consequences of climate change are already here, ranging from nuisance flooding to the spread of mosquito-borne viruses into what were once colder climates.
Left unchecked, warming will cost the US economy hundreds of billions of dollars.