Some scientists are at a loss to explain the 2024 heat bump, 0.2C above what models predicted.
Fewer low-altitude clouds may explain 'missing' 0.2C of warming from Earth's hottest year: study
By environment reporter Peter de Kruijff
Fri 6 Dec
In short:
Fewer-than-expected low-lying clouds has been identified as a potential reason behind mystery global warming in 2023.
Last year was the hottest on record, reaching 1.45 degrees of warming since pre-industrial times, well over climate predictions of 1.25C of warming for 2023.
What's next?
More research is needed to understand why there were fewer clouds and whether drops in cloud cover are tied to global warming.
A drop in the number of low-altitude clouds was behind unexplained warming that contributed to the world's hottest year on record, a new study suggests.
The record-breaking heat of 2023, which saw the planet warm an average 1.45 degrees Celsius over pre-industrial surface temperatures, took many climate scientists by surprise.
Their closest predictions, which simulated the effects of human-created warming and other known drivers, were around 0.2C lower than observed temperatures.
...
NASA's Goddard Institute for Space Studies director and climatologist Gavin Schmidt, who was not involved in the study, said the research "goes some way into explaining the process of recent warming.
"But we still aren't able to say why the albedo has been changing so much, and so there is still more to do before we can say what this means going forward."
...
The study referenced by the article above;
Recent global temperature surge intensified by record-low planetary albedo
HELGE F. GOESSLING, THOMAS RACKOW AND THOMAS JUNG
5 Dec 2024
DOI: 10.1126/science.adq7280
Abstract
In 2023, the global mean temperature soared to almost 1.5K above the pre-industrial level, surpassing the previous record by about 0.17K. Previous best-guess estimates of known drivers including anthropogenic warming and the El Niño onset fall short by about 0.2K in explaining the temperature rise. Utilizing satellite and reanalysis data, we identify a record-low planetary albedo as the primary factor bridging this gap. The decline is apparently caused largely by a reduced low-cloud cover in the northern mid-latitudes and tropics, in continuation of a multi-annual trend. Further exploring the low-cloud trend and understanding how much of it is due to internal variability, reduced aerosol concentrations, or a possibly emerging low-cloud feedback will be crucial for assessing the current and expected future warming.
There is a fairly obvious possible explanation for unusual weather anomalies this year. Note I first heard this prediction from climate scientist Jennifer Marohasy, but I can't recall if she published a paper.
Tonga eruption increases chance of temporary surface temperature anomaly above 1.5 °C
Published: 12 January 2023
Stuart Jenkins, Chris Smith, Myles Allen & Roy Grainger
On 15 January 2022, the Hunga Tonga-Hunga Ha'apai (HTHH) eruption injected 146 MtHO and 0.42 MtSO into the stratosphere. This large water vapour perturbation means that HTHH will probably increase the net radiative forcing, unusual for a large volcanic eruption, increasing the chance of the global surface temperature anomaly temporarily exceeding 1.5 °C over the coming decade. Here we estimate the radiative response to the HTHH eruption and derive the increased risk that the global mean surface temperature anomaly shortly exceeds 1.5 °C following the eruption. We show that HTHH has a tangible impact of the chance of imminent 1.5 °C exceedance (increasing the chance of at least one of the next 5 years exceeding 1.5 °C by 7%), but the level of climate policy ambition, particularly the mitigation of short-lived climate pollutants, dominates the 1.5 °C exceedance outlook over decadal timescales.
The drop in global cloud cover might not be related to Hunga Tonga - it could be Hunga Tonga had no impact, and the drop in cloud cover driven by unknown forcings is the culprit. But a prediction of a global temperature bump and unusual weather, followed by a global temperature bump and unusual weather, seems to be one hell of a coincidence.
If Hunga Tonga is the mystery factor behind the global drop in cloud cover, if one single volcanic eruption can take scientists like Gavin Schmidt by surprise by causing a 0.2C bump in global temperature, natural forcings surely deserve far more attention as potential contributors to global warming. At the very least this is a potent reminder there are still large gaps in our understanding of the global climate system.
The other takeaway from the current bump is wild predictions 1.5C of global warming will cause climate disasters has now been demonstrated to be nonsense. If it wasn't for climate scientists pronouncing the 0.2C rise in temperature, who of us would have noticed?