25 June 2024

1.5 degrees Celsius is here and now

Surface air temperatures, 21 June 2024.
Credit: C3S/ECMWF (pulse.climate.copernicus.eu)
By David Spratt

Has the world already reached a global warming trend of 1.5°C (compared to ~1900 pre-industrial baseline)?

There have been some sharp disagreements between scientists over this question, with former NASA climate science chief James Hansen saying that for all practical purposes the climate system trend is now at the 1.5°C mark, whilst Penn State University’s Michael E Mann and others disagree and say we have up to a decade to go.

In May 2024, Hansen wrote that the 12-month mean global temperature “is still rising at 1.56°C relative to 1880-1920 in the GISS analysis through April. Robert Rohde reports that it is 1.65°C relative to 1850-1900 in the BerkeleyEarth analysis (for the same period).  El Nino/La Nina average global temperature likely is about 1.5°C, suggesting that, for all practical purposes, global temperature has already reached that milestone.”   [El Niño (the warm phase) and La Niña (the cool phase) lead to significant differences from the average ocean temperatures, winds, surface pressure, and rainfall across parts of the tropical Pacific. Neutral conditions are near their long-term average.]