What’s the difference between extreme weather and climate change?


What’s the link between climate change and extreme weather?

Oxford climatologist Friederike Otto, named on this year’s Time 100 list of the world’s most influential people, tells David Aaronovitch what we all need to understand about the catastrophic weather sweeping the globe (it’s not all bad news)

September 25 2021, The Times [of London]

limatologist Friederike Otto, named on this year’s Time 100 list of the world’s most influential people, tells David Aaronovitch what we all need to understand about the catastrophic weather sweeping the globe (it’s not all bad news)

September 25 2021, The Times

People on a night-time Mediterranean ferry, evacuated from an island in flames, bright red dancing against the black sky and reflected on the water. School gyms in North America’s Pacific Northwest turned into emergency air-conditioned centres for local citizens who can’t take the 50C heat outside. German valley towns scoured by floodwater, buses tossed against housefronts and landslips suddenly abbreviating streets that used to go somewhere. It all seems to need explaining.


Friederike “Fredi” Otto has a strong, calm face and the patient smile of someone who is becoming used to providing explanations. Her fair hair is worn in a bun, displaying the three studs she wears in her upper left ear. My Mac screen shows her sitting at her kitchen table, a pink fridge and a large sunflower on one side and the open door to her north Oxford garden on the other. An extreme weather event for this summer is going on outside: the sun is shining. There could hardly be a more bucolic scene – like something from a 21st-century Vermeer.

Fredi Otto was born 39 years ago in Kiel on the Baltic coast of Germany, not far from Denmark. For now she’s in Oxford, part of the small Environmental Change Institute at Oxford University. Her speciality as a climatologist – the thing that has made her central to this autumn’s climate change discussions at the massive COP26 international climate conference in Glasgow – is something called “weather attribution”: the science of determining what causes extreme weather events.

Ten years ago this discipline barely existed, but now it’s the critical bridge between a vague appreciation of what man-made climate change might look like sometime in the future, and the increasingly uncomfortable here and now. When the most recent and most categorical report of the UN’s Intergovernmental Panel on Climate Change (IPCC) came out earlier this year, Otto was one of its lead authors. The weather woman is making the weather.

We’ll keep this simple for the time being. Weather attribution is, in essence, the science of calculating what contribution – if any – man-made climate change makes to extreme weather events. For years people have made all kinds of claims about this or that cataclysm having been caused by global warming, and others have just as assiduously denied that you could possibly tell. Otto’s life work so far has been to show that indeed you can.

I ask what started her on this particular quest. “What really got me into this was actually a heatwave in Russia in 2010,” she replies, in her perfect economical English. “It was huge and had a big impact on food prices.” The following year two climatological papers were published about the event: one from a group of American scientists and another by two Germans. “The American one was saying this event was natural in origin, and the German one was saying this event was made five times more likely due to climate change. I had just started my post-doc in Oxford working on climate models. I saw these papers and thought, ‘How can this be? It seems very contradictory. What happened?’ I was very interested in the question and tried to answer it myself.”

What she and her colleague Geert Jan van Oldenborgh realised was that the studies weren’t contradicting each other.

“We were finding out that actually they were both right but asking two different questions,” she says. But when you put the studies and their data together, what you saw was an event where natural variability played a large role and climate change played a smaller but measurable one.

Otto’s early work on this led to a meeting with an oceanographer called Heidi Cullen, who led a non-profit organisation called Climate Central (CC). One of CC’s jobs was to provide the army of American television meteorologists with climate change information to help them talk about and understand extreme weather events in their regions. Americans seem obsessed with the weather (far more than we Brits are), and for good reason. The US is a continental land mass straddling two great oceans and stretching from the Great Lakes to the Gulf of Mexico. It experiences a lot of extreme weather events. Weather attribution should be a very big deal.

The background to the Cullen meeting was the annual conference of the American Geophysical Union, the biggest regular conclave of climate scientists in the world. In 2014 this took place in San Francisco and Cullen and Otto met up in a local Starbucks – which, being a journalist, I think is quite droll, but which Otto the scientist obviously believes is unremarkable. In any case, Cullen’s imperative – to provide information about ongoing or recent extreme weather events – helped to turbocharge the work being done by Otto and her colleagues on attributing weather. Not only did they need to do studies on the causes of such events but they needed to publish them quickly while people were still thinking about them. Which added a new level of controversy to the process.


At this point we need to understand a bit better what Otto does and why it’s come to matter so much. And the first thing she explains to me is that it isn’t a crude matter of event X being caused by factor Y. “People ask, is this the result of climate change or not? But that is not really the right way of framing the question. All weather events always have multiple causes. Climate change can be one of these causes, and it can be a big one. But it’s never the only one.”

For some events there is more global warming at work than others. Indeed there are plenty of extreme weather events where climate change plays no role at all. Not so heatwaves. “Today when we look at heatwaves we always find climate change is one of the main causes,” she says. “The last two heatwaves we looked at – the one in Canada this summer and one in 2020 in Siberia – we found that both events were impossible at such intensities without climate change. In previous events we hadn’t seen anything like such a big role for climate change.”

The methodology? As her website puts it, Otto and her colleagues “use very large ensembles of simulations of regional climate models to run two different analyses: to represent the current climate as it was observed, and to represent the same events in the world that might have been without human-induced climate change.” In other words they use the sophisticated climate models developed by the big meteorological agencies and then look to answer the question – what would this event have looked like if there had not been warming due to man-made carbon emissions?

This approach can even be applied retrospectively. Otto tells me that when she looked back at the American dust-bowl phenomenon of the Thirties she discerned a distinct effect from the carbon emissions of earlier industrialisation. It’s not huge, but it’s there. And something John Steinbeck and his climate-battered characters in The Grapes of Wrath had no inkling of at the time.

The contribution of any factor – including climate change – to something like the rainfall that caused the German floods or the “bell” of extreme heat that settled over British Columbia and the US states of the Pacific Northwest, is stated in terms of how they alter the likelihood of such an event. “The basic idea is pretty straightforward,” says Otto, “We look at, say, the North American heatwave in July, which led to temperatures of almost 50C in Canada, and we ask, ‘Is it a 1 in 100 years event, or 1 in 1,000 years?’ To answer that, first we use observations of the weather event, past weather events and climate models. And we know that today we already have 1.2C of global warming from greenhouse gases in the atmosphere.

“So we found that the July heatwave was one that used to be a thousand-year event. Which sounds very rare and it is very rare in that one area. But the world is a big place. It will happen somewhere in the world relatively frequently. And that’s not terribly new.

“But because we know very well how much greenhouse gas has been emitted since the beginning of the industrial revolution, we can simulate the world basically the same as it is today but without the greenhouse gas emissions. What would have happened then? We can then compare. Then we ask is this event still a thousand-year one – as before this level of warming – or more frequent? In the case of the American heatwave, though it’s still rare today we found it would be almost impossible for it to have occurred without climate change.

“Today, with most heatwaves we find that what was, say, a 1 in 100 years event has now become a 1 in 10 years event. And with the most recent heavy rainfall floods in western Europe, we found that climate change made this event up to nine times more likely.”

Essentially, then, for some really challenging extreme, often catastrophic weather events, the global warming that has already happened is pushing them from being vanishingly rare to just unusual. And – this bit is really important too and Otto is keen to stress it – we have not yet adapted to a world in which these phenomena are more common.

I put it to her that the very act of weather attribution is itself controversial. It plays on what the behavioural psychologists call the availability heuristic, but which most of us know as the far-off elephant. While the animal is a long distance away, its size doesn’t bother us. Only when it is imminent do we worry about how on earth we’ll accommodate such a large beast. Weather attribution tells you that the elephant is right there, and that alters people’s level of concern. Which is why those who have dubbed themselves “climate change sceptics” – highly influential in some quarters – distrust attribution so much. I ask Otto if she had been aware of that when she started out on this path?

“Hmm, probably not very much, to be honest,” she says, laughing. “The paper about the Russian heatwave was the first scientific paper I’d ever written. It wasn’t as if I had huge experience.” And besides, she says, if anything the battle over whether man-made climate change is real has become less difficult. “When I started it was all much more controversial and political and debated than it is now.”

And now? “I’m aware that my work is seen as political. That’s fine. But it’s only fine if the scientific community is not having huge problems with what we’re doing. Which at the beginning it did a bit,” she admits, adding, “I think it’s not any more. Because if it did that would divide the community – and that would not help the public debate.”

Which would be a big pity. And now she becomes coolly passionate. “Attribution is a powerful tool to bring the message home that climate change is not something happening somewhere else to someone else, or about some abstract metric like global mean temperature, but is actually happening in every region in the world and affecting daily weather sometimes in a very dramatic way.”

The woman may be cool, but Otto’s science is not cold. It comes from a place that feels the need for urgent action. Two years ago she wrote a book about her work. The English translation of the title is Angry Weather, though the German title, Wütendes Wetter, is somehow more expressive. It begins with the statement that, “We are the first generation to experience a different type of weather. Weather that palpably deviates from what was encountered by our grandparents, their grandparents, their grandparents, and so on.” And that could kill our grandchildren.


In order to help maintain a sense of urgency about what’s happening to the planet, Otto and her team made one very tricky and not universally popular decision. They decided to publish their findings about extreme events before meeting the scientific gold-standard of a peer review. Such a strategy might easily be taken as a sign of a lack of confidence in the integrity of your own work.

In Otto’s case the motivation was salience. Peer review, she explains, is a process that takes a lot of time. You write up the study for publication – that’s around six months. The scientific journal puts it out for review. The reviewers scrutinise its methods, which takes a few more months. Then there may be amendments. More time. “Then a year and a half after the weather event you have your result, telling you to what extent climate change is responsible. The huge disadvantage is that no one is talking about that event any more. Public discourse has moved on. Decisions have already been made on relocation, or rebuilding. If the public asks the question in the wake of an event, they need an answer based on scientific evidence. We have decided to do it as fast as possible.”

But, she reassures me, they don’t cut corners. Her team only applies the speeded-up approach to types of events where their previous methodology has been peer reviewed. And they also publish all their data so other scientists can look and see if their findings are “replicable”. And so far they have won round the scientific community. “Transparent” is a favourite Otto word, and I’m pretty sure she means it.


There is some sugar in the pill for us beleaguered Brits. It turns out that openness to novel ideas and methods was one of the reasons Otto and her small family came to Oxford. “To do something new it’s important to have an environment where that is encouraged and [you are] helped to take risks. Also where you have a culture that is interdisciplinary. Here,” she looks round her kitchen, “you’re surrounded by people who are using very different methodologies on very different questions all the time. It’s the kind of environment that creates new ideas.”

Germany is not, on the whole, such a place. Its universities are famously sclerotic. “In the UK you have an academic culture that is much less hierarchical. In Germany you are a professor and you are God or you are nothing.”

However, this compliment to Oxford is also Otto’s leaving gift to the city of Morse. She’ll shortly be taking up an appointment at Imperial College London’s climate hub, the Grantham Institute.

And how did she get to be a lead author on the latest IPCC report? In most countries scientists nominate themselves and their governments put them forward, apparently. “Plus gender balance and regional representation,” she tells me, “so it’s not just a bunch of blokes from Reading.” Which I think is a climatologist’s in-joke referring to a period when Reading University was one of the few institutions doing a lot of work on climate change. Once involved, however, she was then promoted by the IPCC bureau to be one of the lead authors who write the all-important summary for policymakers.

As well as helping her to be named as one of the Time 100 – the most influential people of 2021 (a distinctly unscientific honour that she delightedly and rather delightfully tweeted about as soon as she knew) – her prominence is an optimistic sign. It means that the fact of man-made global warming affecting the weather now is no longer a conjecture. It makes a huge difference to the debate.

But in its own way it’s also rather depressing. Because, I say to her, that means that these events being more frequent and intense is now baked in. It’s based on what we’ve already done. “No matter what we do we will reach 1.5C of warming within the next two decades. And that will mean another three tenths of a degree more warming and even more severe extreme events. And we have to prepare for that. We saw in Germany this summer, in one of the richest countries in the world, how people are not prepared for the weather that we have today. We have to pay attention to adaptation.” Which means spending money on resilience.

All very worrisome. But then Otto decides to lighten my psychic burden. Because she adds, “The good news is that we are much more certain now that when we actually reach net zero CO2 emissions [as many governments have agreed to do], temperatures will stop rising pretty much at that point.” Which is a repudiation of the deep pessimists’ view that it’s already too late. And, she continues, “The other good news is that at this point in time the likelihood that we have passed some climate tipping point is quite low. And it will stay low if we stay within the 1.5C.

“But it will increase a lot if we don’t. So stopping burning fossil fuels as fast as we can is really crucial.”

I thank her, not least for her patience. And then, while I was reflecting on interviewing this impressive woman, I heard that the Wombles are being enlisted to promote Boris Johnson’s pre COP26 Together for Our Planet campaign. I felt vaguely insulted, but then reflected that the pragmatic Dr Otto would tell me that if that’s what it takes, then I should embrace even this family of unattractive toys. Anything to get to net zero. To stay within the 1.5C. To avoid bigger fires, worse floods and deadlier heatwaves.

[This is followed by photos of the year so far in photographs.]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.