ON JANUARY 10th a number of the bodies which monitor the world’s climate put out their assessments of 2024. They confirmed that it was the hottest year since modern record-keeping began and thus, it is believed, in human history. It also contained the hottest day in that record. Among the five main data sets that try to capture global temperatures, one showed the average in 2023 to be more than 1.5°C above pre-industrial levels. In 2024 three did.
Temperatures passed 50 degrees Celsius (122 Fahrenheit) in northern India as an unrelenting heatwave triggered warnings of water shortages and heatstroke. 2024 is confirmed by the Copernicus Climate Change Service (C3S) to be the warmest year on record globally, and the first calendar year that the average global temperature exceeded 1.5°C above its pre-industrial level. (AFP)(HT_PRINT)
That figure has taken on an iconic value. A single year of data is widely seen as insufficient to judge the success or failure of “efforts to limit the temperature increase to 1.5°C above pre-industrial levels”—which is what nearly 200 countries committed themselves to in the Paris agreement of 2015. People tend to look instead at trends, or the average over a decade. But if 2024 did not break the Paris “limit” in that sense, it hardly matters. It was a new record, and it made clearer than ever that there is no plausible scenario in which the trend will not breach the limit before too long.
The first chart shows how each day’s temperature compares with what would have been typical in the late 19th century. The unmissable trend is towards warmth; it is driven by emissions of carbon dioxide and other greenhouse gases which are continuing to increase.
Last year built off a remarkable 2023, in which temperatures took off to an unprecedented extent in the middle of the year. By the end of 2023 the El Niño Southern Oscillation, a linked system of winds and currents centred on the tropical Pacific, was firmly in its warm, El-Niño mode. With this El Niño in full swing, 2024 rose to early heights. As El Niño faded, so did global temperatures; but they staged a comeback towards the end of the year. Data from Copernicus, an EU agency, show that 11 months were over the 1.5°C limit.
That a year which starts with a full-blown El Niño should be the hottest in history is not surprising. The second chart, which compares individual years with the broader warming trend, shows that El Niño often sets new temperature records. But even so, 2024 stands out. Along with 2023 it makes up the biggest two-year excursion from the smoothed record since the late 1870s, when particular circumstances around a strong El Niño led to famines in which tens of millions of people died.
This two-year excursion suggests the trend today is steeper than it used to be. Between 1978 to 2008 the world warmed at a rate of 0.19°C per decade. The Copernicus report says today’s rate is 0.24°C per decade. If the current rate continues, the trend is quite likely to pass through 1.5°C limit before the decade is out.
The third chart focuses on sea-surface temperature. The x-axis shows how much that temperature in a particular part of the tropical Pacific is above or below normal (this is what is used to diagnose El Niño events). The y-axis shows global average sea-surface temperature. In past decades, all years with big El Niño events had record hot months. Because temperatures have also been rising overall, the hot El Niño months have become even hotter over time. One thing to note is that the previous record-setting El Niño years saw more extreme El Niño conditions; by comparison 2024’s was milder.
On average El Niño also makes the atmosphere wetter (although it can also deliver droughts to some regions). Chart 4 shows year-to-year variation in the amount of water vapour in the atmosphere. Again, there is a general heating trend and a specific El Niño effect; again, both contributed to making 2024 a record year.
Because water vapour is a greenhouse gas, this amplifies the warming driven by carbon dioxide and other long-lived greenhouse gases. More water vapour also means more precipitation. Of the 16 flooding events in 2024 studied by the World Weather Attribution, the NGO’s scientists classed 15 as showing “clear or probable” signs of having been made more likely or exacerbated by global warming.
The effect of heat on human health is worse when the atmosphere is moist. In terms of this composite “heat stress”, 2024 was a bad year. Official measures class “strong heat stress” as a temperature that “feels like” 32ºC or more. Chart 5 shows how many days like these were experienced around the world. On July 10th around 44% of the globe was affected by “strong” or “extreme” heat stress: a new world record.
Because the 2023-24 El Niño is now over, scientists think it is highly unlikely that 2025 will set a new global temperature record. Those at Berkeley Earth, an American research group, put the chances at a mere 6%. Much likelier, they say, is that it will be the third-hottest year: cooler than 2023 or 2024, but warmer than anything which came before. Analysis by Britain’s Met Office concurs. That would make it the hottest non-El-Niño year on record.