But some events were so anomalous that they sent a wave of consternation through the scientific community. Antarctic sea ice is at a historically low level for this time of year according to federal data. Sea surface temperatures across the North Atlantic have been “off the charts,” Europe’s Copernicus Climate Change Service reported, noting that the numbers set records for this time of year “by a very wide margin.” Water temperatures off the coast of South Florida rose to unfathomable levels in recent days, leading scientists to fear for the fate of the only living coral barrier reef in the continental United States.
“On the one hand, we knew these things would happen. These have been the predictions for a long time,” said Claudia Tebaldi, a scientist at the Pacific Northwest National Laboratory.
And yet, she said, “this year in particular has seemed so extreme. … The magnitude of the anomalies is surprising.”
For years, climate scientists have detailed again and again the many impacts likely as the world steadily warms, such as more intense storms, more intense rainfall, rapidly rising seas and melting ice caps.
But they have also been unequivocal that with more warming comes the possibility of unforeseen consequences – of rapid changes, irreversible collapses and other feedback loops.
More than ten years ago, a study from the National Academies of Sciences, Engineering and Medicine found that while many aspects of climate change and its effects “are expected to be roughly linear and gradual,” this will not always be the case.
“Clearly, the risk of surprises can be expected to increase with the duration and magnitude of warming,” the authors wrote.
That reality seems to be unfolding.
“We’ve always said that the chances of the unexpected grow with every increase in warming,” Tebaldi said. “The chance of triggering something (surprising) is directly proportional to how much we warm the planet.”
That’s not to say that the alarming month that just passed is entirely the result of a warmer atmosphere.
Scientists say part of the reason for some recent extremes is the weather pattern known as El Niño, which is characterized by warmer-than-normal tropical Pacific waters, following three years of its counterpart, La Niña, which brings cooler-than-normal waters to the surface.
El Niño began to develop this spring and is not likely to bring a crescendo of warmth to the Pacific Ocean until the end of the year. At the same time, there are other aspects of what scientists call natural variability, such as changes in wind patterns and ocean currents, which are also factors.
David Armstrong McKaya research impact fellow at the University of Exeter, said El Niño and other natural variability likely play a role in this summer’s extreme events.
“But it’s all happening on this baseline of human-driven warming,” he said. “What used to be a rare event is becoming more common, and what used to be impossible in an unchanged climate is now becoming a real possibility.”
Gavin Schmidt, director of the NASA Goddard Institute for Space Studies, largely agrees. Conditions in what was Earth’s warmest observed month on record were “shocking but not surprising,” he said.
But some data points — the massive increase in surface temperatures in the North Atlantic and minimal winter sea ice around Antarctica, for example — were unusual enough to surprise scientists.
From the British Isles to the coast of Newfoundland, temperatures in the North Atlantic have risen almost beyond scientists’ most extreme predictions, as much as 10 degrees Celsius (18 degrees Fahrenheit) warmer than normal last month.
Reduced cloud cover and the absence of Saharan dust plumes may allow more sunlight to reach the water’s surface, scientists say, although they don’t know for sure what has caused temperatures to rise so dramatically.
“It raises an eyebrow to me,” Schmidt said. “It seems to have happened very quickly.”
It was the most extreme example of a warming trend that extends over nearly half of the world’s ocean surface.
Global sea surface temperatures have increased by about 0.15 degrees Celsius per year. decade, when the oceans have absorbed most of the warming resulting from fossil fuel emissions and the greenhouse effect, said Gregory Johnson, an oceanographer at the National Oceanic and Atmospheric Administration’s Pacific Marine Environment Laboratory.
In June and July, surface water was closer to 0.25 degrees Celsius warmer than it was just last summer, he said.
“That’s about two decades of warming for the globe, year by year,” he said, a rapid increase that cannot be fully explained by El Niño.
“That,” he said, “makes it all the more alarming.”
‘Abrupt, irreversible and dangerous impacts’
Last September, McKay and other colleagues published a study in the journal Science, warning that allowing the world to warm more than 1.5 degrees Celsius (2.7 Fahrenheit) compared to pre-industrial levels could trigger multiple “tipping points” around the globe.
The planet has already experienced more than 1.1 degrees Celsius (2 Fahrenheit) of warming, with little sign of slowing. If this trend continues, it could eventually lead to the disappearance of coral reefs, massive sea level rise due to collapsing ice sheets, widespread thawing of permafrost, or the demise of critical biomes such as the Amazon rainforest.
McKay said in an interview that the various anomalies shown this summer, while disturbing, do not mean that large systems around the planet have crossed an immutable threshold. Such critical shifts are likely to become apparent only over a longer period of time.
“I don’t expect these warm years to directly trigger climate tipping points,” he said.
At the same time, he said, that doesn’t mean that certain regions or specific locations aren’t already experiencing catastrophic consequences that large-scale models struggle to predict.
“On a smaller scale, individual coral reefs or individual rainforests can topple much faster,” he said. “I think it’s quite likely that these warm years will cause a lot of damage and stress to a lot of ecosystems.”
Tebaldi describes it this way: “Tipping points can happen for different people, for different communities, at different times.”
In its latest assessment of the latest science, the Intergovernmental Panel on Climate Change detailed how different ecosystems, from boreal forests to permafrost, could change in “irreversible” ways at different levels of warming.
One system scientists are watching closely is Antarctica’s sea ice, which has been so slow to build up this year that it has led to questions about whether it is headed for collapse.
Antarctica’s ice is always prone to fluctuations – it hit a record low in 2017, but came so close to its average extent. Over the past two years, however, it has hit repeated record lows during the Southern Hemisphere summer. Now it’s headed for a September maximum that will be by far the smallest on record — so small that scientists say it could be expected to occur once in millions of years if it were just a matter of natural variation.
“I can’t come out and say a tipping point has been passed,” said Marilyn Raphael, director of the UCLA Institute of the Environment and Sustainability. “I can say that everything points in that direction.”
“Will these impacts turn up the pressure?”
As the sweltering summer of 2023 heads into August, with another round of triple-digit heat advisories, scientists and environmentalists hope that recent extremes will somehow spur the kind of global, collective action that has been largely absent.
“This could be an example of what normal will be in a 1.5C world,” Tebaldi said. “Even if we stop (greenhouse gas) emissions tomorrow, we have to deal with this kind of climate. … This should be a stark reminder that we live in a reality that has already changed, and if we want to be resilient, we need to invest on all possible fronts.”
McKay said the lack of adequate climate action in recent years has not been a lack of information about the problem or examples of the damage caused by a warming planet. Rather, it corresponds to a lack of political will.
“Will these impacts turn up the pressure?” he said. “You would hope that some of these extremes would remind politicians and businesses that this is what we’re starting to see at only about 1.2 Celsius of warming.”
António Guterres, the UN Secretary-General, hopes for a similar realization among presidents, prime ministers and those in charge of the world’s largest industries.
“Leaders must lead. No more hesitation. No more excuses. No more waiting for others to move first,” he said at a recent news conference about July’s extremes.
He cited positive signs such as the continued growth of renewable energy and a recent international agreement to ensure the shipping industry reaches net-zero emissions by mid-century.
But much more needs to be done, Guterres said, and if July is a harbinger of what lies ahead, there is not a moment to waste.
“The evidence is everywhere: Humanity has unleashed destruction. This must not inspire despair, but action,” he said. “We can still stop the worst. But to do that, we must turn a year of scorching heat into a year of burning ambitions.”