2020 matched all global heating records. In 2021 carbon releases will reach a milestone. Soon we face a 2°C hotter future.
We Earthlings are now unmistakably on our way to the global climate we promised barely six years ago we’d never reach − a 2°C hotter future.
Some time this year, thanks to fossil fuel combustion and the destruction of natural ecosystems, the levels of carbon dioxide in the planetary atmosphere will be half as high again as the average for most of human history. That is, they will be more than half-way to doubling.
And the warming already driven by this extra charge of greenhouse gas has reached new heights: 2020, according to one calculation, shares with 2016 the grim accolade of the hottest year in history, at the end of the hottest decade since systematic records began.
A third study warns that yet more warming is now inevitable: the greenhouse gases already released must take average planetary temperatures from the present rise of more than 1°C to beyond 2°C − the limit that 195 nations vowed not to exceed when they met in Paris in 2015.
All three studies are simply progress reports on climate change itself. It is more than a century since scientists began to link carbon dioxide levels in the atmosphere with planetary temperatures, and more than 50 years since researchers began systematically monitoring atmospheric CO2 at an observatory in Hawaii, and since the first warnings that rising greenhouse gas levels could precipitate potentially catastrophic climate change.
“Our results suggest we have most likely already emitted enough carbon to exceed 2°C”
And this year, says the British Met Office, the ratio will creep up by more than 2 parts per million on last year. That will take the average to beyond 417 ppm for a number of weeks this northern hemisphere spring. And that will be 50% higher than the 278 ppm that was the norm at the close of the 18th century, when humans began to exploit coal, oil and gas as global sources of energy.
“The human-caused build-up of CO2 in the atmosphere is accelerating,” said Richard Betts, of the Met Office. “It took over 200 years for levels to increase by 25%, but now, just 30 years later, we are approaching a 50% increase.”
The last six years have all been in the hottest six years ever recorded, European scientists say in their calculations of the planetary pecking order of annual temperatures. It was 0.6°C warmer than the average for the years 1981-2010. And it is fully 1.25°C above the average for 1850 to 1900.
Europe in particular felt the heat: an average of 1.6° higher than the average for 1981 to 2010. And in the Arctic and in Siberia, temperatures were up to 6°C above the average for the same period.
“It is no surprise that the last decade was the warmest on record, and is yet another reminder of the urgency of ambitious emissions reductions to prevent adverse climate impacts in the future,” said Carlo Buontempo, who directs Europe’s Copernicus Climate Change Service.
Carbon dioxide is durable: it stays in the air, and each year’s emissions are added to those of the previous year. To keep the planet’s average temperature to a rise of no more than 1.5°C − the ideal of the Paris Accord in 2015 − then nations must bring global emissions to zero within the next 30 years. In fact the limit of 2°C explicit in the Accord must now, and inevitably, be exceeded at some point: there is already enough greenhouse gas in the mix to guarantee that. The big question is: when.
Chinese and US researchers report in Nature Climate Change that they looked more closely at the pattern of changes in the planet’s surface temperatures, and the impact of low-level clouds that normally reflect heat back into space. And they see regions that have yet to warm, but must do so sooner or later to raise average global temperatures to levels so far not accounted for.
“The important thing to realise is that this has not happened − it is not in the historical record,” said Chen Zhou of Nanjing University, the lead author. “After accounting for this effect, the estimated future warming based on the historical record would be much higher than previous estimates.”
And his co-author Andrew Dessler, of Texas A&M University, said: “The bad news is that our results suggest we have most likely already emitted enough carbon to exceed 2C.”
But this could be delayed by urgent action. “If we can get emissions to net zero soon, it may take centuries to exceed 2°C.”
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