Why the Latest Thinking on Global Warming Is Setting Off Alarms

Wildfires, heat waves, droughts, flooding, and more are no longer “natural” disasters exclusively, because humanity has a substantial role in making many of them more extreme. That’s a key takeaway from the latest comprehensive assessment from the world climate-science profession. The assessment -- “Climate Change 2021: The Physical Science Basis,” released in August -- is the first part of a larger report from the United Nations Intergovernmental Panel on Climate Change, or IPCC. It’s likely to shape negotiations during a crucial period in the fight against global warming.

Humanity has raised global average temperatures by 1.1° Celsius since the end of the 19th century and has dumped enough greenhouse gas into the atmosphere to heat the planet by 1.5°C -- the globally agreed-upon threshold after which global warming becomes more destructive. (The reason for the discrepancy is that fine-particle pollution from fossil fuels provides a cooling effect that masks some of the impact.) Global average temperatures are higher than at any point in 125,000 years. Carbon dioxide (CO2) levels are higher than at any point in 2 million years, and methane and nitrous oxide concentrations higher than in 800,000 years.