Unprecedented bouts of extreme weather and related events around the world raise the question of whether climate scientists have underestimated how fast the world is warming and how severe the consequences will be. Here are the key facts you need to know.
Is the world warming faster than we expected?
No, it isn’t. The rise in the average global surface temperature measured so far is well within the range that climate models have projected for levels of greenhouse gases that resemble those actually observed so far.
Even the projections of the first simple models created in the 1970s are pretty close to what has happened since then, and the increasingly sophisticated models that followed have proved to be even better at forecasting the warming to date.
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“If anything, temperatures have been a bit on the low end,” says at US non‑profit Berkeley Earth.
This July, global average surface temperatures suddenly soared to their highest levels to date, but this is probably natural variability, driven by events such as El Niño, a warming of waters in the Pacific. It will take a decade or so for it to become clear whether there is any change in the long-term trend.
However, while or so above pre-industrial levels by 2100, we could yet exceed this.
The performance of computer models so far suggests that they are good at forecasting how much global warming a given level of greenhouse gases will produce. However, there is still a lot of uncertainty about climate feedbacks, which could result in more greenhouse gases in the atmosphere than currently expected – for instance, if forests die off at lower levels of heat and drought than expected.
In 2020, Hausfather estimated that there could be up to 25 per cent more warming than currently projected as a result of these uncertainties. “This means that we cannot fully rule out a small chance of close to 5°C warming [by 2100] in a current-policy world where our best estimate is 3°C,” he told żěè¶ĚĘÓƵ in 2021.
Today, Hausfather thinks there is no longer even a small chance of this. “I think the progress made on clean energy does help rule out 5°C warming, though we still cannot exclude the possibility of 4°C warming by 2100.”
Are we seeing more extreme weather than predicted?
In March 2022, temperatures up to 38.5°C higher than normal were seen in the interior of East Antarctica – the most extreme such anomaly ever recorded on Earth. That was followed by the worst heatwave in human history, with China enduring months of record-breaking warmth during its summer.
Are weather events of this kind more extreme than those the Intergovernmental Panel on Climate Change (IPCC) has projected for the current level of warming? Here the picture is less clear.
“I have yet to see hard evidence that our physical assessment of climate change is an underestimate,” says at the University of Leeds in the UK, though he adds that his and he does now think this is at least possible. “We don’t have enough statistical information to tell us if there is anything that is really outside our predictions,” he says.
“For the record-breaking extremes, in both temperature and rainfall, I think there is some evidence that the main IPCC models tend to underestimate these,” says at the Met Office, the UK national weather service. “But the jury is still out.”
The fundamental issue here is that most of the simulations used are designed to model climate, or average weather, over decades or centuries. They don’t have enough resolution to model individual weather events in detail over shorter periods of days or weeks, for example, though researchers are now starting to use higher-resolution models for some studies that address this.
Regardless of whether or not recent extreme weather events can be described as worse than forecast, they are horrifying many climate scientists. “I do still find it shocking that this is actually happening around the world and in such a rapidly escalating way,” says Stott.
Beyond extreme weather events, have the impacts of our current level of warming been underestimated?
Here the answer is clear: yes, they have. Compared with earlier assessments, the risks of serious impacts “increase to high and very high levels at lower global warming levels” states the .
This change is simply because the observed impacts so far are already more severe than expected. For instance, coral bleaching and die-off events have been more extensive, as have mass tree deaths.
In fact, not only are the impacts worse, the report says, societies are also turning out to be more vulnerable to these effects than thought and adapting to a warmer world is proving harder than thought. “What we can do is limited,” says Forster. “There’s lots of evidence that when people have tried to adapt, this has been insufficient or has not been done in an appropriate way.”
When it comes to future consequences, for sea level rise in particular, IPCC projections have got higher and higher over the years. The 2021 IPCC report says that a global rise of nearly 2 metres by 2100 can’t be ruled out if emissions are very high, whereas its 2007 report had 0.6 metres as the highest possible by 2100.
at the Potsdam Institute for Climate Impact Research in Germany has criticised earlier IPCC reports for underestimating the risks of future sea level rise. He thinks the latest reports are . “I don’t think the IPCC really still underestimates sea level rise,” he says.
Are we closer to tipping points than anticipated?
Yes, we are, though a great deal of uncertainty remains. The term tipping points refersĚýto large-scale events thatĚýcan’t be reversed anytime soon if at all if they happen, suchĚýas the die-off of the AmazonĚýrainforest or the collapseĚýof the West Antarctic iceĚýsheet. The 2022 IPCC report onĚýimpacts says the risks of such events are “higher at both recent and projected warming than” assessed to be the case in its previous assessments.
What’s more, since that IPCC report was written, a number of studies have suggested that the Atlantic meridional overturning current (AMOC) may be slowing faster than thought. Among other things, the AMOC keeps northern Europe relatively mild by carrying warmer waters there. If it stops altogether, it would have catastrophic consequences.
“I used to think (as did the IPCC) that the risk of an AMOC collapse this century is less than 10 per cent. Unlike some colleagues, I did not find that reassuring, since I think the consequences would be so disastrous that we really want to rule out such a risk,” says Rahmstorf. “In the light of the [recent] evidence, I now consider that risk to be larger than 10 per cent.”
This story is part of a series in which we explore the most pressing questions about climate change. Read the other articles below:Ěý
What made July the hottest month ever? |ĚýThe dangers of climate doom|ĚýThe pace of the renewable energy revolution | Can humans adapt to heat? | Fight doomism and denial | Climate change and extreme weatherĚý
