According to the Paris Agreement, global temperature rise over pre-industrial times needs to stay well below 2 degrees Celsius (3.6 degrees Fahrenheit), preferably 1.5 degrees Celsius (2.7 degrees Fahrenheit). (In 2017, warming reached 1.8 degrees Fahrenheit over pre-industrial times.) If nations fail to act, the United Nations’ Intergovernmental Panel on Climate Change (IPCC) warns, runaway climate change will expose hundreds of millions of people to extreme climate events, including heatwaves, droughts, severe flooding and tropical cyclones.
The Paris Agreement, signed by nearly 200 countries, seeks to limit warming as much as possible by aiming for the more ambitious goal of 2.7 degrees Fahrenheit. This would require global greenhouse gas emissions to be cut in half by 2030 and then to zero by mid-century. But the longer nations wait, the more drastic cuts to emissions are needed.
Right now the globe is on a trajectory to reach between 4.5 and 4.9 degrees Fahrenheit (2.5 to 2.7 degrees Celsius) of warming by 2100. Scientists predict that when we reach somewhere between 2.7 and 3.6 degrees Fahrenheit (1.5 degrees and 2 degrees Celsius) of warming sometime around mid-century, the Arctic shelf will enter a feedback loop of melting. In this scenario, sea levels would continue to rise for thousands of years.
But there is some hope. Climate scientists had previously thought that many decades, or even centuries, of warming were guaranteed even after greenhouse gas emissions stopped. But they now believe that warming would stop within a couple of decades.
—Agya K. Aning