A new study published in the Science journal, has suggested that a drop in the number of low-altitude clouds was behind unexplained warming that contributed to the world’s hottest year on record in 2023.
Key findings
- Global mean temperatures in 2023 reached nearly 1.5 degrees Celsius above pre-industrial levels, and 0.2°C of this rise may be attributed to declining low-altitude cloud cover.
- Low-altitude clouds play a crucial role in cooling the planet by reflecting sunlight back into space. Their global cover fell by 1.5 per cent in 2023 compared to average levels, continuing a decade-long decline of 1.27 per cent.
- In 2023, there were far fewer low clouds over the northern mid-latitude and tropical oceans, particularly in the Atlantic, and this could account for the 0.2C of warming.
- This reduction has caused a measurable drop in planetary albedo. Albedo is the proportion of solar radiation reflected into space after interacting with Earth’s atmosphere and surface.
Clouds warming and cooling effects
- All clouds have some level of cooling effect on the planet as they reflect the Sun’s rays away from the planet.
- High-level clouds, which form in cold atmospheric layers, also act like a blanket, trapping warmth from below.
- Low-level clouds, which form within 2 kilometres of the Earth’s surface, reflect radiation, but don’t trap as much heat.
- The El Niño phenomenon and the expected long-term anthropogenic greenhouse gas emissions remain primary drivers of the 2023 temperature.
- El Niño phenomenon is the warm phase of a natural climate pattern across the tropical Pacific known as the El Niño-Southern Oscillation.
