But global warming does not happen gradually. Like house prices, the general trend is upward, but there are also ups and downs along the way.
Behind much of the ups and downs is the El Niño phenomenon, which is a rearrangement of water in the vast expanses of the Pacific Ocean. El Niño is very important to the functioning of the global climate, as it increases air temperatures on average across the Earth’s surface, not just in the Pacific. Between El Niño episodes, conditions can be neutral or in an opposite state called La Niña, which tends to cool global temperatures. The swing between these extremes is irregular, and El Niño conditions tend to return after three to seven years.
The warm El Niño phase of this cycle began to manifest a year ago, peaked around the end of 2023, and is now trending neutral, which is why the record streak is over.
The 2023-24 El Niño was strong, but not super-strong. It doesn’t fully explain the remarkable degree to which temperature records were broken last year. The exact influence of other factors remains to be unraveled.
We know that there is a small positive contribution from the Sun, which is in a phase of its 11-year sunspot cycle when it radiates a fraction more energy to Earth.
Methane (also a byproduct of the fossil fuel industry, along with livestock and wetlands) is another major greenhouse gas, and its concentration in the air has been increasing. More quickly in the last decade than in the previous decade.
Scientists are also assessing the extent to which measures to clean up air pollution could contribute to warming, since certain air pollution particles can reflect sunlight and influence cloud formation.
A temperature ratchet
Across the global ocean, 2023 was a devastating summer for coral reefs and surrounding ecosystems in The Caribbean and beyond. This was followed by severe bleaching on the Great Barrier Reef off the coast of Australia during the southern hemisphere summer. While El Niño years tend to trigger mass mortality events on reefs around the world, it is the underlying trend of climate change that is the long-term threat, as corals struggle to adapt to rising temperature extremes.
