- Par Nidale Abou Mrad
- BBC World Service
13 minutes ago
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A dried up lake in Iraq – but is it due to man-made climate change?
Parts of India and Pakistan have seen record temperatures reaching 50C in a series of heat waves in recent weeks.
Ethiopia and Somalia are experiencing their worst droughts in decades, and in Iraq a series of severe dust storms have sent hundreds of people to hospital since April. “Look what climate change is doing to the planet,” people frequently comment on social media.
But is it possible to know if extreme weather events like the ones we are witnessing are linked to global warming?
Attribution of weather phenomena
The short answer is yes. Scientists largely agree that they can in principle answer the question of how much an event was caused or exacerbated by climate change, thanks to a field of science known as extreme event attribution. .
It is a relatively new branch of science, but one that is progressing “by leaps and bounds”, according to Dr Thomas Smith, associate professor of environmental geography at the London School of Economics. “Since the first detailed attribution of extreme weather event in 2018 (Hurricane Florence), hundreds of studies have attempted to attribute certain aspects of extreme weather to human-caused climate change,” he told the BBC. “This has now been demonstrated for wildfires, hurricanes, heat waves, droughts and extreme rainfall events.”
A group of scientists in this field – World Weather Attribution (WWA) – recently published a guide on how to interpret this link between extreme weather events and climate change.
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Attribution science seeks to establish how human-caused climate change influences extreme weather events such as heat waves.
One of the lead authors, German climatologist Friederike Otto of Imperial College London, told the BBC that although more and more people are aware of how global warming is affecting weather patterns, “we still do not understand how it acts differently depending on the region”.
She and her colleagues draw a parallel with a heavy smoker who develops lung cancer. They explain that in such a case, the doctors cannot say definitively that the cigarettes caused the cancer, but they can certainly say that the damage caused by the cigarettes increased the likelihood.
“In the same way, climate change cannot cause an event because all weather events have multiple causes, but global warming can affect the probability and intensity of an event. And so it can affect the impact of a specific event on people, property and nature.
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Scientists are using computer models to study the link between extreme weather events and climate change.
The method uses computer models to run two scenarios. The first simulates the climate as it is today, including human-induced global warming.
This means running climate model simulations over and over once more with the same conditions, producing many years of weather in the current climate.
The second type of experiment removes the influence of greenhouse gas emissions, simulating a climate closer to that which existed before the industrial revolution.
Scientists then count the number of times such an extreme event has occurred in both cases – with and without global warming.
By comparing these numbers, they can say that if an event occurs three times more often in the first scenario, human-caused global warming has made it three times more likely.
“All heat waves are influenced by climate change”
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India and Pakistan experienced unprecedented high temperature waves.
But in practice, the degree of influence of climate change on extreme weather events varies widely.
“Due to global warming, all heat waves are influenced by climate change,” says Dr. Otto.
Accordingly, the relevant question to ask when a country is experiencing extreme temperatures is: “How has global warming made the situation worse or perhaps lessened?”.
“When we looked at the 2021 Siberian heat wave, we found that climate change made the event possible and you would never have seen it without climate change,” says Dr Otto, “whereas when we After analyzing some European heat waves in 2019, in parts of the UK high temperatures were made five times or more likely.”
Precipitation is also relatively simple, according to WWA experts, as there is usually more moisture in the warmer air.
However, for other events such as cyclones, droughts, floods and wildfires, the question is whether climate change played a role in their occurrence.
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Fueled by a heat wave in June, millions of hectares of Siberian forest will burn in 2021.
They explain that, for example, droughts are often due to a combination of causes, including low rainfall, high temperatures and interactions between the atmosphere and the land surface.
Floods, too, are caused by a variety of factors, including heavy rains, of course, but also many human influences, such as land use and defences.
According to them, the global number of tropical cyclones per year has not changed, but climate change has increased the occurrence of the most intense and destructive storms.
In the case of wildfires, data records can be limited, making attribution studies difficult, but they note that fire weather is increasing in parts of every continent.
Two approaches in one
Photo credit, World Attribution Initiative
Friederike Otto leads an international project on the attribution of extreme events.
Dr. Otto’s history with the award dates back to when a heat wave hit Moscow in 2010.
“At the time, the question of whether global warming had an impact on it was not answered.
Around 2012, she came across two articles dedicated to this event. “One presented climate change as a factor that made it five times more likely and the other reported it as a natural event. I read them and wondered: how might the same event be natural and also [rendu] five times more likely by [changement] climatic?”
“In fact, they were just asking very different questions.”
At the time, she was working on climate models at Oxford University following studying physics and earning a doctorate in philosophy.
“I decided to write an article reconciling the two approaches. And from there, I chose to invest myself more in this field.”
Together with his colleagues at the WWA, Dr. Otto then developed a method that was adopted by the IPCC, the United Nations expert group on climate. Currently, she co-leads an international effort to analyze and communicate the possible influence of climate change on extreme events.
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Heavy rain causes flooding in Bangladesh
Since then, the attribution has gone from being a potentially promising area to being part of the IPCC assessment for the first time in 2021.
“When we talk regarding climate change, we usually talk regarding global thermal temperatures and that’s an abstract measurement,” says Dr Otto.
“We don’t experience climate change in the same way. If you’re wealthy and have a well-insulated house, you’re immune to heat stress or flooding. In reality, it’s the most vulnerable people who pay the price. price of climate change.”
Dr. Otto views climate change as one of the greatest threats to fairness and justice, and “changes in the weather are how they manifest in the physical system,” she says.
“Adapt better”
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It is hoped that attribution science can help vulnerable areas better prepare for extreme weather events.
Ms. Otto hopes that her group’s research will serve several important purposes.
Sometimes, for example, official reports are quick to attribute disasters to climate change. However, according to the experts, it is important to avoid making the rise in temperatures responsible for all the extreme events.
“Our team’s studies have shown that, contrary to what some officials have reported, the drought that hit Madagascar in 2021 is a rare event, but it was not influenced by climate change,” recalls- she.
Climate researchers suggest that attribution results can also be used by plaintiffs suing emitters as evidence to pressure them to limit their emissions or seek compensation.
Furthermore, the more attribution science can tell us regarding what the future is likely to bring in terms of extreme weather and its impacts – especially in regions that have not seen such events. frequent or intense in the past – the better we can adapt to climate change, it is hoped.
“The main benefit,” says Dr Otto, “is still helping us understand the loss and damage caused by climate change, versus that caused by just climate. If we know how much we’ve emitted, we don’t We don’t have an inventory of the impacts. Attribution allows us to uncover it and better adapt.”
