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Everyone agrees: 2024 the hottest year since the thermometer was invented

Over the last 24 hours or so, the major organizations that keep track of global temperatures have released figures for 2024, and all of them agree: 2024 was the warmest year yet recorded, joining 2023 as an unusual outlier in terms of how rapidly things heated up. At least two of the organizations, the European Union's Copernicus and Berkeley Earth, place the year at about 1.6Β° C above pre-industrial temperatures, marking the first time that the Paris Agreement goal of limiting warming to 1.5Β° has been exceeded.

NASA and the National Oceanic and Atmospheric Administration both place the mark at slightly below 1.5Β° C over pre-industrial temperatures (as defined by the 1850–1900 average). However, that difference largely reflects the uncertainties in measuring temperatures during that period rather than disagreement over 2024.

It’s hot everywhere

2023 had set a temperature record largely due to a switch to El NiΓ±o conditions midway through the year, which made the second half of the year exceptionally hot. It takes some time for that heat to make its way from the ocean into the atmosphere, so the streak of warm months continued into 2024, even as the Pacific switched into its cooler La NiΓ±a mode.

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Β© Copernicus

Study: Warming has accelerated due to the Earth absorbing more sunlight

2023 was always going to be a hot year, given that warmer El NiΓ±o conditions were superimposed on the long-term trend of climate change driven by our greenhouse gas emissions. But it's not clear anybody was expecting the striking string of hot months that allowed the year to easily eclipse any previous year on record. As the warmth has continued at record levels even after the El NiΓ±o faded, it's an event that seems to demand an explanation.

On Thursday, a group of German scientistsβ€”Helge Goessling, Thomas Rackow, and Thomas Jungβ€”released a paper that attempts to provide one. They present data that suggests the Earth is absorbing more incoming sunlight than it has in the past, largely due to reduced cloud cover.

Balancing the numbers on radiation

Years with strong El NiΓ±o conditions tend to break records. But the 2023 El NiΓ±o was relatively mild. The effects of the phenomenon are also directly felt in the tropical Pacific, yet ocean temperatures set records in the Atlantic and contributed to a massive retreat in ice near Antarctica. So, there are clearly limits to what can be attributed to El NiΓ±o. Other influences that have been considered include the injection of water vapor into the stratosphere by the Hunga Tonga eruption, and a reduction in sulfur emissions due to new rules governing international shipping. 2023 also corresponds to a peak in the most recent solar cycle.

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Β© NASA

Google’s DeepMind tackles weather forecasting, with great performance

By some measures, AI systems are now competitive with traditional computing methods for generating weather forecasts. Because their training penalizes errors, however, the forecasts tend to get "blurry"β€”as you move further ahead in time, the models make fewer specific predictions since those are more likely to be wrong. As a result, you start to see things like storm tracks broadening and the storms themselves losing clearly defined edges.

But using AI is still extremely tempting because the alternative is a computational atmospheric circulation model, which is extremely compute-intensive. Still, it's highly successful, with the ensemble model from the European Centre for Medium-Range Weather Forecasts considered the best in class.

In a paper being released today, Google's DeepMind claims its new AI system manages to outperform the European model on forecasts out to at least a week and often beyond. DeepMind's system, called GenCast, merges some computational approaches used by atmospheric scientists with a diffusion model, commonly used in generative AI. The result is a system that maintains high resolution while cutting the computational cost significantly.

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