Because the past three years have shattered temperature records (see 'Temperature boost'), researchers have been exploring whether global warming is accelerating, and if so, why. Many scientists agree that the rate at which it is increasing has picked up. This is mainly because of a reduction in air pollution following the introduction of fuel regulations for international shipping (which has resulted in fewer pollutant particles that reflect sunlight into space and seed insulating clouds). In the data, 'you can practically see by eye that it has accelerated', says Stefan Rahmstorf, a climate scientist at the Potsdam Institute for Climate Impact Research in Germany. Rahmstorf and Grant Foster, a statistician in Orono, Maine, say they have the strongest evidence yet that global warming has sped up, to a rate of around 0.35 'C per decade. That's faster than some other estimates2. But, the pair say their analysis captures a more accurate picture because of the way it accounts for and removes the effects of natural factors, such as weather events and volcanic eruptions, that cause climate fluctuations. The study was published today in Geophysical Research Letters1....

My first post here was a sketch of my view of the consequences of climate change, that there are both good and bad effects and we do not know enough to say whether the net effects is positive or negative. It now occurs to me that I can say a little more. There are two approaches to answering that question. The first is to ask whether there are general reasons to expect climate change along the predicted lines, a gradual increase in average temperatures due mainly to increased CO2 in the atmosphere, to have net negative effects. The second is to look at specific externalities, make some rough estimate of their size, and add them up. That is a short run effect, relevant over decades but not centuries. Over centuries people can adjust what crops they grow and how they grow them, where they live, how they heat and insulate their houses. More warmth is generally a good thing when you are cold, a bad thing when you are hot. Due to the physics of the greenhouse effect, it warms cold times and places more than hot, raises the temperature of winter more than summer, of the polar regions more than the equator....

Dozens of researchers from around the world are now part of a scientific group that will analyse the impacts of artificial intelligence. Observers have compared the group, called the Independent International Scientific Panel on Artificial Intelligence and convened by the United Nations, to the influential Intergovernmental Panel on Climate Change (IPCC), which informs governments about the latest climate-change science. For more than 35 years, it has amassed evidence showing that current global warming is caused mostly by human activity. The AI panel's 40 members, approved in a vote by the UN's General Assembly on 12 February, are from 37 nations. The UN says the panel will act 'as an early-warning system and evidence engine, helping distinguish between hype and reality' and produce 'policy-relevant' reports. The panel is not the first prominent group to study AI impacts; the Global Partnership on AI and the International AI Safety Report are some of the most significant so far. But the UN group is 'much bigger in scope and is truly global', says Wendy Hall, a computer scientist at the University of Southampton, UK. Hall was a member of the panel's governance-specific precursor, the UN High-level Advisory Body on AI, which ran between 2023 and 2024....

Volcanoes and wildfires can inject millions of tons of gases and aerosol particles into the air, affecting temperatures on a global scale. But picking out the specific impact of individual events against a background of many contributing factors is like listening for one person's voice from across a crowded concourse. In a study appearing this week in the Proceedings of the National Academy of Sciences, the researchers report that they detected statistically significant changes in global atmospheric temperatures in response to three major natural events: the eruption of Mount Pinatubo in 1991, the Australian wildfires in 2019-2020, and the eruption of the underwater volcano Hunga Tonga in the South Pacific in 2022. While the specifics of each event differed, all three events appeared to significantly affect temperatures in the stratosphere. The stratosphere lies above the troposphere, which is the lowest layer of the atmosphere, closest to the surface, where global warming has accelerated in recent years. In the new study, Pinatubo showed the classic pattern of stratospheric warming paired with tropospheric cooling. The Australian wildfires and the Hunga Tonga eruption also showed significant warming or cooling in the stratosphere, respectively, but they did not produce a robust, globally detectable tropospheric signal over the first two years following each event. This new understanding will help scientists further pin down the effect of human-related emissions on global temperature change....