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Land and sea temperatures have warmed much more than models forecast in the last year, and as of these articles various new factors being considered appear not enough to account for that spike. Relatively speaking it's quite large.
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Nature
9 March 2024
For the past nine months, mean land and sea surface temperatures have overshot previous records each month by up to 0.2 °C — a huge margin at the planetary scale. A general warming trend is expected because of rising greenhouse-gas emissions, but this sudden heat spike greatly exceeds predictions made by statistical climate models that rely on past observations. Many reasons for this discrepancy have been proposed but, as yet, no combination of them has been able to reconcile our theories with what has happened.
...
So, what might have caused this heat spike? Atmospheric greenhouse-gas levels have continued to rise, but the extra load since 2022 can account for further warming of only about 0.02 °C. Other theories put forward by climate scientists include fallout from the January 2022 Hunga Tonga–Hunga Ha‘apai volcanic eruption in Tonga, which had both cooling effects from aerosols and warming ones from stratospheric water vapour, and the ramping up of solar activity in the run-up to a predicted solar maximum. But these factors explain, at most, a few hundredths of a degree in warming (Schoeberl, M. R. et al. Geophys. Res. Lett. 50, e2023GL104634; 2023). Even after taking all plausible explanations into account, the divergence between expected and observed annual mean temperatures in 2023 remains about 0.2 °C — roughly the gap between the previous and current annual record.
There is one more factor that could be playing a part. In 2020, new regulations required the shipping industry to use cleaner fuels that reduce sulfur emissions. Sulfur compounds in the atmosphere are reflective and influence several properties of clouds, thereby having an overall cooling effect. Preliminary estimates of the impact of these rules show a negligible effect on global mean temperatures — a change of only a few hundredths of a degree. ...
www.nature.com
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Also, related is more information about another factor that could turn the wrong way, increasing warming. Normally the Earth absorbs about 1/2 of emitted CO2 each year, but that might change in a bad way:
"That one-half figure is an approximation. It varies from year to year depending on weather conditions and other environmental factors, resulting in the jagged lines you see in the chart above. For example, in a warm and dry year with many wildfires, the land may absorb less carbon dioxide than usual.
As the Earth warms further, climate scientists expect the land and the ocean to absorb a smaller share of carbon dioxide emissions, causing a larger share to end up in the air, said Doug McNeall, who studies these effects at Britain’s Met Office.
Xin Lan, the lead scientist responsible for NOAA’s global carbon dioxide measurements, referred to the natural absorption as a “carbon discount.”
“We pay attention to it because we don't know at which point that this discount is gone,” she said.
In addition to carbon dioxide, the levels of other potent greenhouse gases like methane and nitrous oxide are also on the rise, which further contribute to warming."
www.nytimes.com
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Nature
9 March 2024
Climate models can’t explain 2023’s huge heat anomaly — we could be in uncharted territory
Taking into account all known factors, the planet warmed 0.2 °C more last year than climate scientists expected. More and better data are urgently needed.For the past nine months, mean land and sea surface temperatures have overshot previous records each month by up to 0.2 °C — a huge margin at the planetary scale. A general warming trend is expected because of rising greenhouse-gas emissions, but this sudden heat spike greatly exceeds predictions made by statistical climate models that rely on past observations. Many reasons for this discrepancy have been proposed but, as yet, no combination of them has been able to reconcile our theories with what has happened.
...
So, what might have caused this heat spike? Atmospheric greenhouse-gas levels have continued to rise, but the extra load since 2022 can account for further warming of only about 0.02 °C. Other theories put forward by climate scientists include fallout from the January 2022 Hunga Tonga–Hunga Ha‘apai volcanic eruption in Tonga, which had both cooling effects from aerosols and warming ones from stratospheric water vapour, and the ramping up of solar activity in the run-up to a predicted solar maximum. But these factors explain, at most, a few hundredths of a degree in warming (Schoeberl, M. R. et al. Geophys. Res. Lett. 50, e2023GL104634; 2023). Even after taking all plausible explanations into account, the divergence between expected and observed annual mean temperatures in 2023 remains about 0.2 °C — roughly the gap between the previous and current annual record.
There is one more factor that could be playing a part. In 2020, new regulations required the shipping industry to use cleaner fuels that reduce sulfur emissions. Sulfur compounds in the atmosphere are reflective and influence several properties of clouds, thereby having an overall cooling effect. Preliminary estimates of the impact of these rules show a negligible effect on global mean temperatures — a change of only a few hundredths of a degree. ...
Climate models can’t explain 2023’s huge heat anomaly — we could be in uncharted territory
Taking into account all known factors, the planet warmed 0.2 °C more last year than climate scientists expected. More and better data are urgently needed.
www.nature.com
-----------
Also, related is more information about another factor that could turn the wrong way, increasing warming. Normally the Earth absorbs about 1/2 of emitted CO2 each year, but that might change in a bad way:
"That one-half figure is an approximation. It varies from year to year depending on weather conditions and other environmental factors, resulting in the jagged lines you see in the chart above. For example, in a warm and dry year with many wildfires, the land may absorb less carbon dioxide than usual.
As the Earth warms further, climate scientists expect the land and the ocean to absorb a smaller share of carbon dioxide emissions, causing a larger share to end up in the air, said Doug McNeall, who studies these effects at Britain’s Met Office.
Xin Lan, the lead scientist responsible for NOAA’s global carbon dioxide measurements, referred to the natural absorption as a “carbon discount.”
“We pay attention to it because we don't know at which point that this discount is gone,” she said.
In addition to carbon dioxide, the levels of other potent greenhouse gases like methane and nitrous oxide are also on the rise, which further contribute to warming."
Carbon Dioxide Levels Have Passed a New Milestone
There’s 50 percent more carbon dioxide in the air than before the Industrial Revolution.
