Veille 2.1

Global warming is accelerating because the drive for warming, Earth’s energy imbalance, has doubled in the past decade. Measurement of the acceleration is hampered by unforced tropical (El Nino/La Nina) variability, but a good measuring stick is provided by warming between successive large El Ninos. Strengthening of the current (2023-24) El Nino has raised it to a level similar to the 1997-98 and 2015-16 El Ninos. The first six months of the current El Nino are 0.39°C warmer than the same six months of the 2015-16 El Nino, a global warming rate of 0.49°C/decade, consistent with expectation of a large acceleration of global warming. We expect the 12-month mean temperature by May 2024 to eliminate any doubt about global warming acceleration. Subsequent decline of the 12-month temperature below 1.5°C will likely be limited, confirming that the 1.5°C limit has already been passed.

It’s hot and getting hotter. The first six months of the year are about 0.2°C cooler than the first six months of 2016 and 2020 (Fig. 1), but that’s only because the current La Nina continues to cool the tropics. Global temperature is rising despite the La Nina. Earth is out of energy balance (more solar energy absorbed than heat radiated to space) by an astounding amount – more than any time with reliable data – so, within a few years, we will be setting new global temperature records.

What else is new? Hotspots are getting hotter. The major hotspot in April stretched from Iraq to India and Pakistan, and toward the northeast through Russia (Fig. 1). Temperature exceeded 45°C (113°F) in late April in at least nine Indian cities,[1] on its way to 50°C (122°F) in Pakistan in May,[2] where a laborer says “It’s like fire burning all around” and a meteorologist describing growing heatwaves since 2015 says “The intensity is increasing, and the duration is increasing, and the frequency is increasing.” Halfway around the world, Canada and north-central United States were cooler than their long-term average, but people in British Columbia and northwest United States remember being under their own record-breaking hotspot last summer.

The past season – meteorological NH winter, SH summer – was the 5th warmest Dec-Jan-Feb in the instrumental record, despite the continuing La Niña (the cold tongue in the equatorial Pacific). Most of Eurasia was remarkably warm, 2-5°C above normal. The winter seemed cold to many people in North America, but a very warm December (Fig. 1) made the season well above normal in the U.S.

There’s a new horse race in 2022. It’s one that we would rather lose than win. If our analysis is right, the world will probably blow through the 1.5°C global warming ceiling this decade; if we’re wrong, it could be delayed a decade. We argue[1],[2] that the apparent acceleration of global warming in the past decade is driven by an acceleration in the growth rate of human-made climate forcings, especially reduced human-made aerosol cooling – an effect that is not going away and may grow.