Extract from ABC News
One of the world's leading climate scientists says the world could be in "uncharted territory", with the researchers unable to fully explain why the world has been breaking heat records to such extremes for 10 months straight.
Last month was the hottest March on record, marking the 10th month in a row to reach that title, according to the European Union's key climate service Copernicus.
In Europe, the temperature for March was 2.12 degrees Celsius above the historical average, marking the second-warmest March on record for the continent.
Around the rest of the globe, temperatures were furthest above average over parts of Antarctica, Greenland, eastern North America, eastern Russia, Central America, parts of South America, and southern Australia.
The continuation of record-breaking heat comes after 2023 was officially declared the hottest year on record, by a long way.
NASA's senior climate advisor Gavin Schmidt says while climate change and the onset of El Niño explain a significant portion of last year's heat, together with other contributing factors, there is still a margin of heat at the top that can't be explained.
He said that was concerning.
"If we can't explain what's going on, then that has real consequences for what we can say is going to happen in the future," Dr Schmidt said.
Predictions 'failed ugly'
For about a decade, he and other climate science institutes have been making predictions of global temperatures for the year ahead.
Each has a slightly different method for doing this.
Generally, it's done by looking at the baseline of global warming that the world is starting the year on, and then factoring in known climate drivers.
But all of those predictions for 2023 fell short of what occurred – the closest prediction was still almost 0.2 degrees Celsius off the mark.
It may not sound like much, but Dr Schmidt said in the context of the world's climate, it's huge.
"Those predictions, based on what was happening right at the beginning of the year failed ugly."
Dr Schmidt said there was always room for error, but usually scientists could explain what occurred upon looking back at the data.
He said this time it was not adding up. And the climate models were giving them no answers either.
"It means there's something missing in what we're thinking about here," he said.
"Either something has changed in the system and things are responding differently to how they responded in the past, or there are other elements that are happening that we didn't take into account."
What are the possible explanations?
Scientists have been investigating several different possible explanations for the higher-than-expected global heat.
Air pollution
Among them, is the theory that the amount of air pollution around the world is less than what the climate models had been accounting for, thanks to new international shipping regulations.
Many aerosols act like a "shade" to incoming sunlight, reflecting it into space. So, fewer of them would have a warming effect.
But Dr Schmidt said, while it made some difference, it didn't seem to be enough to explain just how hot it had been.
"When you put that into a model and you say, 'Is that warming effect large enough to give you this the big difference between 2022 and 2023,' the answer is no, not really as far as we can tell," he said.
The underwater volcano
Another factor that has been looked at is the underwater volcano Hunga Tonga-Hunga Ha'apai eruption in January 2022, which shot ash and other particles more than halfway into space.
Similar to pollution, volcanoes generally have a cooling effect.
But the Tonga volcano was different.
Because it was an underwater volcano, it also ejected a significant amount of water vapour – a strong greenhouse gas — into the stratosphere, and therefore is thought to have had a net warming impact.
Dr Schimdt said from what they could tell so far, this still only represented a very small change, overall.
"The magnitude of the change is in the hundredths of a degree level, so not commensurate with the size of the thing we're trying to explain," he said.
The solar cycle and other explanations
Some have looked to the solar cycle for a mean of explanation, which is reaching solar maximum – something that can also have an impact on surface temperature.
Solar maximum refers to the period of greatest solar activity during the sun's 11-year solar cycle.
But again, Dr Schmidt said it was not large enough to explain what they had seen in 2023, and it was "baked into the calculations" anyway.
"And maybe it was just random things happening in the Antarctic, and in the North Atlantic, all at once, that were unconnected and are adding up, and the reason we haven't seen it before is because we haven't had 200 years of good data," he said
"We're looking into those kinds of things as well."
A previous climate mystery
A similar climate model mystery has played out before, according to Dr Schmidt.
In the early 2000s, the trend of rising surface temperatures appeared to plateau for over a decade, despite greenhouse gas emissions in the atmosphere reaching record levels.
It was something that climate scientists couldn't fully explain at the time, becoming known as the "global warming hiatus".
It was also used heavily by climate change sceptics as evidence that the earth wasn’t getting much hotter.
However, later studies revealed there was no hiatus in global warming, rather it was being buried in the deep layers of the oceans.
Minor revisions to data inputs, uptake of heat by the oceans, natural variability and observations helped make that clear.
Dr Schmidt said it was possible something of a similar nature was happening this time too, and that the climate models were missing something, or the data wasn't quite right.
"Perhaps we haven't fully characterised the Hunga Tonga volcano, or perhaps we haven't been tracking appropriately the emissions from China, because they're not necessarily the most trustworthy of global reporters," he said.
He said it's important they work it out so they could tell whether this was simply a "blip" or the start of something different.
On this, he said the global temperatures during the northern hemisphere could give them some clues.
All eyes on northern summer
So far, the heat of 2024 has been largely in line with expectations, according to Dr Schmidt, because scientists expect a boost to global temperatures a few months after the peak of El Niño.
But he said if everything was behaving as normal, it would cool down by June.
"The key will be what happens in the next few months. If things stay super anomalous then we are looking at a systematic change, not just a blip," he said.
In the meantime, he said they will be re-examining data sets, including looking at newly available aerosol data from a recently launched NASA satellite, to try to explain the gap.
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