The rate of human-caused warming has risen from about 0.18C per decade across the 1970s-2000s to roughly 0.27C per decade over 2015-2024, according to the peer-reviewed Indicators of Global Climate Ch

In 1840, Louis Agassiz established that the northern hemisphere had been covered by vast sheets of ice.

Satellite data reveals Earth’s cloud cover is shrinking. Far from a temporary aerosol effect, this warming-driven feedback loop threatens to accelerate future climate change.

A team of researchers has identified a novel atmospheric process that explains the formation of a massive cloud appearing daily above Mars' Arsia Mons volcano. The cloud, known as the Arsia Mons Elongated Cloud (AMEC), stretches up to 1,800 kilometers across the Martian landscape each morning during southern hemisphere spring and summer. Scientists had long puzzled over how such a large cloud could form in Mars' thin, dry atmosphere without the usual dust particles that typically serve as nuclei for cloud formation on Earth and other planets. The breakthrough comes from understanding that the cloud forms through homogeneous nucleation, a process where water vapor transforms directly into ice crystals without requiring dust particles to initiate the formation. This phenomenon has been theorized but never confirmed in a planetary atmosphere until now. The researchers discovered that the unique conditions above Arsia Mons - where rapid cooling of air rising over the volcano causes temperatures to plummet by 30°C in just 10 minutes, reaching below -143°C - create an environment where water vapor becomes extremely supersaturated. Supersaturation occurs when air contains more water vapor than it can normally hold at that temperature. The rapid cooling above the volcano allows water vapor to temporarily build up to extraordinary levels relative to saturation, enabling ice crystals to form spontaneously. When the researchers incorporated this process into their simulations, the cloud's characteristic elongated tail appeared, matching observations made by the Mars Express spacecraft since 2018. While the simulations successfully reproduced the cloud's formation and general characteristics, they were not a perfect match. The simulated cloud was 30-50% narrower than observed, formed about 90 minutes later than observed, and reached only about a quarter of the observed maximum length before detaching. The researchers acknowledge that direct observation of the ice crystal formation process remains elusive, with evidence coming solely from how well the simulations match the observations. This discovery has significant implications beyond Mars. It may provide the first compelling real-world evidence that water-ice clouds can form directly from vapor without dust or other particles, potentially prompting scientists to revisit cloud formation theories on Earth, Venus, and other planets. The study, published in Nature Geoscience, represents a significant advancement in understanding Martian atmospheric dynamics and the planet's water cycle, which has been found to include unusual phenomena such as widespread water vapor supersaturation during dusty seasons.