2024 was the warmest year on record. The most reliable indicator of the warming planet is the global ocean heat content (OHC), which acts as an integrator of all heating. It continues to break records year after year. The sea surface temperatures (SST) vary quite a lot from year to year especially with El Niño events. The global mean surface temperature (GMST) is most commonly used, but also varies with El Niño and is affected by weather variability. The latest El Niño began in 2023 in April and continued for a year. From April 2023 until June 2024, the global SSTs were the highest on record, but as the El Niño has waned, global SSTs have declined.
Graphic 1: Monthly global Surface Sea Temperatures (60°N to 60°S) for the years colour-coded as at right. The red stars indicate 2024 values.
At the same time, the atmospheric concentrations of carbon dioxide have also been at record high values and are now more than 50 percent above the preindustrial values. These increases are mostly from human activities burning fossil fuels, although wildfires have also contributed. It shows that the efforts to transition away from fossil fuels faltered in 2024.
Higher atmospheric temperatures mean that the atmosphere sucks more moisture out of the land, leading to drying where it is not raining, leading to wilting plants, heatwaves, and increased risk of wildfire. The consequences of increased ocean temperatures are much more water vapour in the atmosphere, which adds to heating and gets caught up in all storms, fuelling their developments and leading directly to heavier rains. This includes hurricanes, typhoons, cyclones and atmospheric rivers. The result is increased risk of severe weather, heavy rains, and flooding extremes.
Drought, crop failure, heat waves and wildfires became common in many areas of the world in 2024. Now wildfire is devastating Los Angeles area. Mass bleaching occurred in the Great Barrier Reef in March, and multiple hurricanes in the Caribbean in July and southeast United States (especially Helene) caused havoc in September. Yagi was a deadly and destructive super typhoon in early September in Southeast Asia. Major floods in Chad and Nigeria also occurred in September, followed by a devastating deluge in Valencia, Spain in October. As well as loss of life and livelihood, the costs and disruption locally were shattering. Increased awareness of the risks, and how to build resilience to weather extremes is always a good investment.
From New Zealand, Dr. Kevin E. Trenberth is a Distinguished Scholar at the National Center for Atmospheric Research in Boulder, Colorado, USA, and he is an honorary affiliate faculty at the University of Auckland in New Zealand, who studies climate variability and change. He is part of an international team of 54 scientists that has completed an analysis of measurements of the Earth’s ocean temperatures in 2024.