New Scientist - USA (2020-07-25)

44 | New Scientist | 25 July 2020

can also define a heatwave as a very local

thing, as the heat stress that affects the

human body, which depends not just on

temperature, but humidity too. In that

case, you will find that climate change

maybe doubles the likelihood.

If you are interested in mortality because

of a heatwave, you will frame it differently to

someone interested in agriculturally relevant

summer temperatures. What we do have

convergence on is methodology: there is

agreement that we need to use at least two

different models for every calculation to

understand the errors they can produce.

In a warmer world, we can expect more

extreme events like the drought that

preceded the Australian bush fires. Is that

going to make attribution easier or harder?

The main difficulty is in whether we have

models that really represent the processes

behind extreme weather events. For example,

do we have models that are able to simulate

strong enough hurricanes in the first place?

That doesn’t really change with increasing

temperatures. On the other hand, the signal

of human-caused climate change gets bigger

with increasing temperatures, so it is getting

easier to disentangle it from the noise.

What has attribution achieved so far,

and what is next for this science?

I think the impact so far is really in raising

awareness of the fact that climate change is

happening right now, and that wherever you

live in the world, there are damages from

extreme events that you would not have

had without climate change.

On what comes next, one of the things

I’ve learned relatively recently is that it

would be better not just to say the weather

today has changed because of climate

change, but also to say something about

what that means in the future. So now we

have a world that is 1°C warmer than in

pre-industrial times. How would weather

patterns change in a 2°C-warmer world?

We do not only want to understand what

climate change means right now, but what we

will need to adapt to. Which are the types of

events and areas of the world where climate

change is a real game changer, so that we

have to completely alter how we deal with

the impacts of such events? With limited

resources, it is important to understand

where to best focus them.

I understand you are also looking at whether

attribution could be used as evidence in legal

cases in which people claim for damages

against companies or governments.

The legal community is realising that this is

now a possibility. In many older climate

litigation cases, the reason for not admitting

evidence that humanity’s greenhouse gas

emissions are to blame for extreme weather

events and the damage they cause, was that

you can’t say the chain of causality is

complete. But I’ve been working with lawyers

to see whether you can use attribution

studies in courts in a meaningful way. We are

not far off seeing successful cases using that

kind of argument – in one, two or three years.

The way society sees climate change has

changed too, and judges are a part of society.

It would be very strange if that shift in public

perception would not also filter through to

the courts; that understanding that climate

change and the damages it causes are real.

You have said before that the results of

attribution studies are quite conservative.

Is that still true? And does it really matter,

given that they still reveal the link between

extreme weather and climate change?

At the moment, especially with heatwaves,

we can only give a lower bound: we can say

OK, climate change made it at least 30 per

cent more likely. It would be better to be

able to also at least quantify the upper

bound. So that is a problem. If you want to

quantify damages, and if you want to

understand the extent of the adaptation

measures you are going to need to put in

place, such as higher flood defences, then

you need more detail.

We seem to be good at doing attribution studies

for events in the developed world, but not so

much in poorer countries. Is that a problem?

We absolutely need to redress the balance. On

the one hand, it would help us to understand

what climate change means globally. But

more than that, if we really want to adapt to

climate change, understanding the extreme

cold snaps in the US, for example, might not

be the most important thing. It might be

more important to understand the droughts

we see in East Africa. At the moment, there is

US

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MY

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“ Wherever you

live, there is

damage from

extreme weather

that you wouldn’t

have had without

climate change”