Pearls and Irritations

For climate change, 2023 was an “unprecedented” year, “absolutely gobsmackingly bananas” and “scary” and “frightening”. And that was what climate scientists said! The UN Secretary General called it the year in which humanity crossed into a new climate era — an age of “global boiling”.

Climate disruption shocked climate scientists in 2023. “Surprising. Astounding. Staggering. Unnerving. Bewildering. Flabbergasting. Disquieting. Gobsmacking. Shocking. Mind boggling,” said Prof. Ed Hawkins when September 2023 exceeded the previous September record by a huge 0.5°C.

The decline in Antarctic sea-ice extent was much greater than model projections, leading the National Snow and Ice Data Centre’s Walt Meier to exclaim: “It’s so far outside anything we’ve seen, it’s almost mind- blowing.”

Many records were set for new climate extremes — record heat, rainfall and floods — with some of it driven by the destabilisation of the polar jet stream. “We are hitting record breaking extremes much sooner than I expected. That’s frightening, scary, and concerning, and it really suggests that we’re not as aware of what’s coming as we thought we were,” said Sarah Perkins-Kirkpatrick of the University of NSW.

Records broken everywhere

With devastating extreme heat and storms and floods, 2023 was the first year 1.5°C warmer than the 1850-1900 baseline, and both Antarctic sea-ice loss and record northern hemisphere sea-surface temperatures were way beyond the ranges projected by climate models.

Datasets of global temperatures vary a little depending on method, but two of the most significant are Berkeley Earth which put 2023 at 1.54°C above the pre-industrial (1850-1900) level, and Copernicus/ECMWF at 1.48°C.

Berkeley said that “a single year exceeding 1.5°C is a stark warning sign of how close the overall climate system has come to exceeding this Paris Agreement goal. With greenhouse gas emissions continuing to set record highs, it is likely that climate will regularly exceed 1.5°C in the next decade.”

2023 was notable for:

• Global average warming hitting the 1.5°C mark, and new monthly records for global temperature every month from June to December. The October to December period was 1.74°C.
• New national record high annual averages for an estimated 77 countries.
• The first year that global average ocean surface temperatures exceeded 1°C, with once-in-a-century levels of warmth in the North Atlantic.
• Two days in November when global average temperature, for the first time ever, reached 2°C above the pre-industrial levels.
• Catastrophic flooding from Greece to Beijing to Vermont, and earlier in the year major flooding in New Zealand associated with a rain bomb and then cyclone Gabrielle.
• Severe wildfires in Europe, Russia, Maui and North America; fires in Canada burned 18.5 million hectares of land.

The 2023 extremes were a shock. Prof. Katharine Hayhoe told the Guardian that: “We have strongly suspected for a while that our projections are underestimating extremes, a suspicion that recent extremes have proven likely to be true… We are truly in uncharted territory in terms of the history of human civilisation on this planet.”

Explanations for 2023 are incomplete, but warming is accelerating and 2024 is likely to be hotter

What happened in 2023 was not what scientists’ models anticipated at the beginning of the year and fell well outside the confidence intervals of any of the estimates. Carbon Brief says that “while there are a number of factors that researchers have proposed to explain 2023’s exceptional warmth, scientists still lack a clear explanation for why global temperatures were so unexpectedly high… researchers are just starting to disentangle the causes of the unexpected extreme global heat the world experienced in 2023”.

One person who has a clear view is the former NASA climate chief James Hansen who says that “the 1.5 degree limit is deader than a doornail” and warns that warming will accelerate to 1.7°C by 2030 and “2°C will be reached by the late 2030s”.

For a long time Hansen has been saying that the impact of sulfate aerosols — which are a byproduct of burning fossils fuels, cause acid rain, and have a strong but short-term cooling effect by reducing incoming radiation — is much greater than generally stated, so producing less of them under “clean air” policies will contribute to accelerated warming.

Whilst the orthodox estimates for aerosols are around 0.5°C of cooling, Hansen and his colleagues say it is likely above 1°C. More on Hansen’s analysis may be found in the 2023 paper Global warming in the pipeline, which former UK Chief Scientist Sir David King says is “one of the most important published on the state of the climate crisis in years”.

In Hansen’s view, the efforts to clean up maritime shipping emissions by mandating fuel with much lower sulfur content resulted in a “Faustian bargain”: as the sulfate cooling impact has reduced, greater warming has been revealed. This was allied with continuing high human greenhouse emissions, and the effects of the developing El Nino, to produce the 2023 heat records.

Whether warming is accelerating has caused sharp differences between scientists, but Hansen’s view is gaining more support. A paper published at the end of 2023 showed a “robust acceleration of Earth system heating observed over the past six decades”, where the “long-term acceleration of Earth warming aligns qualitatively with the rise in carbon dioxide (CO₂) concentrations and the decline in aerosol concentration during the same period, but further investigations are necessary to properly attribute these changes”.

Two key indicators — an acceleration in the rate at which the ocean is absorbing heat, and a spike in Earth’s Energy Imbalance — suggest Hansen is on the right track.

• Ocean heat content: 90% of the heat generated by the greenhouse effect warms the oceans (with only 2% to the atmosphere, and the balance melting the polar ice and warming the land). With this great store of heat, it is oceans that drive atmospheric warming. Research published in 2023 showed that the rate of increase in ocean heat content has accelerated over recent decades. Ocean temperatures started spiking in March-April 2023, and global temperatures in June. The heat stored in the world’s oceans increased by the greatest margin ever in 2023, absorbing more heat than in any other year since records began. Associated with the onset of a strong El Niño, the global sea surface temperature was an astounding 0.3°C above 2022 values for the second half of 2023.
• Earth’s Energy Imbalance: Earth’s energy imbalance (EEI) is the difference between incoming energy from the sun and the amount of heat radiating from Earth back into space. The CERES project uses satellites to estimate EEI. Their data suggests that EEI has more than doubled since 2000, resulting in an acceleration of global warming’s impact on the Earth system. If EEI is increasing over time, it should drive an increase in the world’s rate of warming.

In the second part of this series in tomorrow’s issue of P&I, after a record breaking 2023, we ask the question: Where is the climate heading?

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