James Hansen, NASA, on Global Temperature Jump

NASA:

Continuing the temperature trend from this summer, September 2023 was the hottest September on record, according to scientists at NASA’s Goddard Institute for Space Studies (GISS). The month also set the record for the highest temperature anomaly – the largest difference from the long-term average.

“What’s remarkable is that these record values are happening before the peak of the current El Nino event, whereas in 2016 the previous record values happened in the spring, after the peak,” said Gavin Schmidt, director of GISS. El Nino is the warm phase of a naturally recurring pattern of trade winds and ocean temperatures in the Eastern Tropical Pacific that influences global temperatures and precipitation patterns.

Meanwhile, NASA’s former Chief Climate scientist James Hansen has been making noise about his projections of increased warming related to diminished particulates in the atmosphere, allowing more solar heating. Hansen says the current El Nino is not particularly strong, that the increased insolation is showing up in the data, and, once the El Nino settles down, the mythical 1.5° C Temperature barrier will have been breached.

James Hansen:

September 2023 smashed the prior global temperature record. Hand-wringing about the magnitude of the temperature jump in September is not inappropriate, but it is more important to investigate the role of aerosol climate forcing – which we chose to leave unmeasured – in global climate change. Global temperature during the current El Nino provides a potential indirect assessment of change of the aerosol forcing. Global temperature in the current El Nino, to date, implies a strong acceleration of global warming for which the most likely explanation is a decrease of human-made aerosols as a result of reductions in China and from ship emissions. The current El Nino will probably be weaker than the 1997-98 and 2015-16 El Ninos, making current warming even more significant. The current near-maximum solar irradiance adds a small amount to the major “forcing” mechanisms (GHGs, aerosols, and El Nino), but with no long-term effect. More important, the long dormant Southern Hemisphere polar amplification is probably coming into play.

The September global temperature anomaly leaped to more than +1.7°C relative to the 1880-1920 mean (Fig. 1). Public discussion has focused on the remarkable magnitude of this monthly anomaly, which exceeds the prior warmest September in the period of instrumental data by about +0.5°C; we will comment on this extreme September anomaly below. However, the average anomaly of the past 4 months (+0.44°C relative to the same months in 2015, the origin year of the 2015-16 El Nino) is probably more important. If this relative anomaly is maintained through this El Nino (through Northern Hemisphere 2024 spring) the peak 12-month mean global warming will reach +1.6-1.7°C relative to 1880-1920. Decline of global temperature following an El Nino peak is 0.2-0.3°C. Thus, if this El Nino peak is as high as we project it will be, global temperature will oscillate about the yellow region in Fig. 2. The 1.5°C global warming level will have been reached, for all practical purposes. There will be no need to ruminate for 20 years about whether the 1.5°C level has been reached, as IPCC proposes. On the contrary, Earth’s enormous energy imbalance (references 8, 13, 14 below) assures that global temperature will be rising still higher for the foreseeable future.