The year we crossed the danger threshold

In the story of man-made global warming, a saga now stretching back many decades, the year just gone will be remembered as a standout, one for the history books.

Scientists are innately cautious, and don’t like getting ahead of the big national assessments to be rolled out, here and in Europe, the US and Japan, over several weeks starting mid-January. 

Yet in late December the Copernicus Climate Change Service in Europe and California’s Berkeley Earth were saying it was over 99 per cent certain that 2023 would be recognised as Earth’s hottest year since the mid-1800s, when instrumental records became sufficiently widespread to provide a base for comparison.

It can be said with just as much certainty that 2023 will also be the first year with an annual average temperature above 1.5C, which was agreed to be a “safe” threshold by virtually every nation in the world in Paris in 2015. It will need more years like 2023 before it can be confirmed that threshold has been passed, but it’s an ominous sign.

There was no clear sign that anything especially unusual was afoot through the first five months of last year, with monthly average global surface temperatures close to the pattern of previous years. While they were amongst the top monthly readings for recent years, it seemed 2023 would be another of those nearly-but-not-quite years.

But behind those outward indicators were more fundamental ones. In late 2020, a little over three years ago, the World Meteorological Organisation predicted that the world’s chances of passing 1.5C by the end of 2025 were less than 20 per cent. In 2022 it increased that to 50 per cent. Last May it announced a greater than even chance, 66 per cent, that the threshold would be passed within five years.

Polar sea ice was a telling sign that something was afoot. Because its surface is white, sea ice reflects heat from the sun back into space, and when it melts it exposes more darker-hued ocean to solar heating.

In May 2023 it became clear that greatly diminished autumn freezing was exposing a vastly greater area of the Southern Ocean than usual to solar heating. In June, a study published in the leading scientific journal Nature Communications found a strong likelihood that within a decade, melting of multi-year ice would ensure that for the first time in thousands of years the North Pole was open water right through summer.

The next sign of something big happening came in with the release of June surface temperature data. After five months of near-record temperatures June leaped clear of the pack by an almost-unprecedented 0.2C.

But that was just the start. July was a record by a whopping 0.4C, a record repeated in the four months following – except for one. September was a standout for all the wrong reasons: it exceeded the previous September record by 0.5C – the biggest monthly temperature anomaly ever recorded. And by the way, it was more than 1.8C above the pre-industrial average for September.

So it continued in October and November, both months recording global average temperatures well clear of the pack. With September, those three months had the biggest temperature anomalies on record. 

The upshot is that after a warm but predictable start, 2023 exceeded all expectations, finishing up easily the hottest year on record, and well clear of that 1.5C threshold which expert pundits had thought might still be four or five years away. 

2023 has been a bad year for all sorts of reasons. The calamitous war in Ukraine, the even more dangerous Gaza conflict and economic disruption in Africa and Latin America drove millions of people to seek refuge and security in richer countries, in the process jeopardising governance everywhere.

At the same time oil, gas and coal interests continued trying to distract humanity from tackling what is ultimately the deadliest threat to everyone, climate change. The wars, the civil strife and the greenwashing all serve to take our attention away from the urgent need to end fossil fuel use.

There are two parts to the climate change story. There is the story that science is uniquely equipped to tell: the simple, physical facts of the matter – the story I’ve focused on here.

There is also the human story: how we respond to these often brutal facts, both collectively and personally. In the end that story is the most telling of all. I will return to it often in 2024, as we continue our struggle to resolve humanity’s greatest challenge.

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