Warmest April on record – but a possible return to predictability?

While temperatures in 2023 were "gobsmacking", 2024 is shaping up to be a more normal El Nino year

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But on to the more important climate stuff!

April was the warmest on record…

…and was the 11th month in a row to set a new record. This is second only to the 16-month stretch of records set in 2015/2016 during the super-El Nino event.

The figure below shows monthly global surface temperature anomalies relative to preindustrial (1850-1900) from ERA5. Note that while it will not meaningfully change the final monthly value, the dot for April 2024 is only through the 30th of the month as of publication.

Global temperatures have been modestly declining in recent months from their peak in February as El Nino conditions have started to fade. This is even more noticeable in the daily ERA5 data shown below:

Are we getting back to a more normal post-El Nino regime?

Global temperatures were being set by historic margins in the second half of 2023. While September’s “absolutely gobsmackingly bananas” record margin of 0.5C stands out, every month between July and December beat the prior record by at least 0.3C.

By contrast, 2024 so far has been a bit more “normal” – at least to the extent that anything is normal on a rapidly warming planet. Global temperature records are being set by around 0.1C compared to the prior record during the super El Nino of 2016, which is roughly in line with what we’d expect to see as a result of the 8 years of warming between 2016 and 2024 due to emissions of CO2 and other greenhouse gases.

If 2024 continues to follow its expected trajectory, global temperatures will fall out of record territory in the next month or two and continue to fall as El Nino fades and La Nina conditions develop. Annual temperatures year as a whole will end up at around 1.5C, similar to 2023, rather than the ~1.7C that we have experienced to-date.

But what about the oceans?

If you are part of a certain crowd on X (nee Twitter), your response here is likely to say “ok, global temperatures might not be as crazy, but what about the oceans?”. The oceans have indeed been exceptionally warm in the latter part of 2023 and into 2024, nearly 0.2C warmer than global sea surface temperatures were in 2016. Daily SSTs in the last three big El Nino years (1998, 2016, and 2024) from NOAA’s OISSTv2.1 are shown in the figure below:

This is a bit higher than we would expect given the global warming experienced between the last big El Nino in 2016 and today – particularly as the oceans have been warming more slowly over time than the global average. This might be a fruitful area for further exploration of drivers of recent warmth.

At the same time, the evolution of SSTs in 2024 has not itself been that unusual, at least so far. There is not evidence that SSTs in 2024 are staying unusually elevated compared to what we saw in past El Nino years (e.g. 1998) compared to where they were at the beginning of the year, as shown in the plot below.

Watching and worrying

The next few months will be important to see if we return to a “normal” progression of cooler global temperatures as El Nino fades and La Nina conditions develop, or if global temperatures remain highly elevated as they were in the latter half of 2023.

If the latter half of 2024 ends up similar to 2023, we may end up closer to 1.6C for the year as a whole, and might be entering what Gavin Schmidt described in his recent Nature commentary as “uncharted territory” for the climate:

“If the anomaly does not stabilise by August – a reasonable expectation based on previous El Niño events – then the world will be in uncharted territory. It could imply that a warming planet is already fundamentally altering how the climate system operates, much sooner than scientists had anticipated. It could also mean that statistical inferences based on past events are less reliable than we thought, adding more uncertainty to seasonal predictions of droughts and rainfall patterns.”

We will have to wait and see. And in the mean time, double down on calling for our politicians to take more meaningful action to reduce the GHG emissions ultimately driving this warming.