The temperature increase depends, in almost a straight-line fashion, on the accumulated burden of added carbon dioxide (CO2) and other greenhouse gases (GHGs) in the atmosphere: the more GHGs, the higher the global average temperature becomes. In other words, the world has made insufficient progress in recent years in reducing the use of coal, petroleum and natural gas (fossil fuels, which produce CO2 when burned), so that the atmospheric burden of GHGs continues to increase without meaningful restraint.
The Earth has already warmed by about 1.0°C (1.8°F) above preindustrial levels, causing many harms around the world. Even without further GHG emissions, the man-made GHG already added will remain in the atmosphere for thousands of years, causing continued long-term climate effects.
Comparing A Stringent Emission Goal to an Earlier, More Relaxed Goal. To avoid worse consequences, the countries of the world have to work toward limiting the total increase to 1.5°C (2.7°F) by 2050, which is lower and sooner than the 2.0°C (3.6°
F) originally set as the goal for 2100 in the Paris Agreement. Some comparisons of differences in projected changes between the two global average temperature increases, given in the report, are summarized here: