‘Attribution science puts numbers. It’s important to provide the evidence of what we’re experiencing in climate change’

3 OCTOBER 2026 | REPORTING ASEAN

Follow the numbers and follow the data, like a detective of sorts – that is what climate attribution science does. It’s a tool for investigating whether human-induced climate change impacted an extreme weather event – and if so, and where possible, by how much?

Attribution science has been around for just over two decades, looking into events ranging from extreme rainfall, drought, storms, wildfires to heatwaves. It allows the calculation of how much hotter a heatwave is compared to a time when there was no climate change, or how much more often it can now occur.

“When you have many different lines of evidence coming together and saying the same thing, then it is time to believe that that evidence holds,” explains Mariam Zachariah, a research associate who works alongside other scientists in the World Weather Attribution’s studies. She is a research associate with the Centre for Environmental Policy at Imperial College London.

In this conversation, Zachariah explains to Reporting ASEAN’s Johanna Son how attribution works – by combining information from climate models, satellite and station-based data and observational data, inputs from local experts (such as in Southeast Asia) as well as “lived experiences”. (It is common for an attribution study to have 10 or more co-authors.) At times, she adds, there is a lack of experts or data from some parts of the Global South. 

As of end-September 2026, WWA had released 19 rapid attribution studies on extreme events. It studied 22 events in 2025. “We often see that oh, these events, a similar event triggered last year, or we did a study last year on the same region,” Zachariah said. This shows how extremes have become “so close to normal” as the climate crisis “loads the dice” toward more and more of these events.

We also talked about the language around climate – why scientists use ‘climate change’ versus ‘climate crisis’ or ‘climate breakdown’ in the news, and why the adjective ‘human-induced’ for climate change works.

(This interview was done before the rock-ice avalanche disaster in Nepal-Tibet in August 2026, which was the subject of a WWA rapid study as well.)

Reporting ASEAN’s Johanna Son: How does weather attribution address or undercut disinformation or misunderstanding around the climate, when you’re able to say that this event is directly linked to climate crisis? And sometimes your reports are able to say ‘it made it [an extreme event] stronger by X times’.

Mariam Zachariah: So let’s just focus on heat waves because that’s the most easily felt phenomenon, even for all of us who are about 30 years of age, we can easily say that as compared to when we were children, we do feel that the summers are generally more hotter. So it is something that every person is experiencing or at least thinking at some point or the other.

And attribution science, what it actually does is, as you said, Johanna, it puts numbers. So it helps us to quantify how much more often are we likely to experience such conditions now and how rare it would have been, let’s say, a few years ago. We always use pre-industrial climate as a base mark because we know that the major driver of climate change or global warming is fossil fuel burning. 

If you even look as far back as just 10 years ago, when the global temperatures were one degree Celsius lower, you are still able to say [there is] some kind of quantifiable change. So attribution science sort of reinforces what we feel, and so it is important to provide the evidence of what we are experiencing in terms of climate change.

Do you think, though, that facts and numbers are enough? 

Numbers and figures does indeed strengthen the case because that is where how we can quantify, you know, what we are experiencing. But like I said, we have to interpret these numbers alongside the impacts that we see, to take the conversation forward.

I’ve read climate scientists also say that sometimes, if you’re willing to share data, people question the data or say your method was wrong or whatever else. So it makes you ask the question regardless of how many numbers I throw or show, is it ever enough?

I think the important thing is to understand that all data sets will have some kind of limitation, which is why it is important to rely on as many numbers of data sets as possible.

So, for example, when we do attribution studies, we do not just rely on data sets and climate models alone, but we also look into what has been the evidence so far, what have other groups said so far about their consensus. So when you have many different lines of evidence coming together and saying the same thing, then it is time to believe that, you know, that evidence holds.

Because you don’t have to just rely only on numbers put out. But then you have, for example, when we do these studies, we also talk to experts from the region who can vouch for what they have been seeing in terms of them monitoring the weather over the years. What changes can they see? And they might be able to explain it. Always, there is also this factor of some of these large-scale processes like El Niño, which is often talked about in the context of heatwaves, droughts and floods, especially in the countries closer to the tropics, it has a high level of influence. So while this sort of natural variability can maybe – ‘obscure’ is not the right word – but can alter the trends that you see.

So all of that put together is what we present as evidence. And so to strengthen the evidence, we just go beyond the facts and numbers, but we also contextualize it in terms of all the other kinds of lived experiences.

So,when you do the studies, you use data, meteorological data, and then over time, I guess. And then, if I give the example, let’s say, of the 2023 and 2024 heat waves in Southeast Asia, so in that case, you use global data and then you also talk to the experts in the countries. Is that correct?

That’s right. So on the one hand, to put out the numbers, we use these observed data sets. There are satellite-based observations, then there are station-based observations. Station-based observations is what we would ideally want more of in many regions, especially when you cannot resolve some of these differences that you see in the more widely available, publicly available, globally gridded products.

And then there is the climate models. So, in observations, you will see a trend or you will not see a trend. But to know whether it is due to climate change, we rely on climate models to sort of look into factual and counterfactual simulations as to how the world has been without climate change and whether what you see in the observations is sort of stacking up against the climate change-driven climate models.

So that is when you say, okay, the trends that we detect in the observations is attributable to climate change because we see that in the climate models too, and then the experts can offer us feedback as to, you know, okay, what are the other sort of processes that we should take into account? And depending on, especially when it is when rainfall, when you look at rainfall from small islands, sometimes these data sets won’t be enough because there are a lot of, you know, oceanic processes sort of converging, and then there would be even, you know, topographical changes over the islands, like mountains, anything can sort of obscure the trend or it can induce a lot of variability in the trend.

So yes, so looking at different observed data sets, different climate models, then also sort of combining it with an understanding of how the local climatology works, helps us to strengthen the evidence.

In the WWA report for 2025, actually there was discussion of what it called ‘climate inequity’ in science. And I bring this up in relation to the discussion around using data from the region or locally. So I think that resonates for Southeast Asia and the Global South that the report said that “WWA found gaps in observational data and the reliance on climate models developed primarily for the Global North prevented us from drawing confident conclusions”.

It also said, “This unequal foundation in climate science mirrors the broader injustices of the climate crisis.” For me as a consumer of WWA, there probably seems to be more [reports] from outside Southeast Asia. I was wondering if this climate inequity or the lack of information or I don’t know, lack of experts, means that you are able to study some events in Southeast Asia less?

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When we decide on what studies or what events to look at, the primary goal is to sort of help increase the evidence of attribution literature, especially in regions where we do not have enough literature to sort of take the climate change conversation forward.

So as much as possible, what we try to do is if we can find the capacity within the team and we can find at least one person to sort of come on board from the region to help us frame the definitions properly, we still, we always try and do the study. But as we do the study, we have often encountered that, you know, in some cases, especially when you’re focusing on small islands, data might be available, but sometimes there might be. . . the stations are not so well maintained.

So then we want station data and sometimes we might not always be able to access the station data within the timeframe of the study, or it might be that it might not often be available for sharing to groups outside of the country, if it is especially like a nationally maintained record or something. So in those cases, when you cannot access the data and there is inconsistencies in what we see and we see some results that we cannot contextualize with what we know of how climate change is expected to influence these events, then we have to acknowledge that we are not able to confidently communicate.

So if past literature has also said the same thing and observations say the same thing as climate models, and then all the local literature and the expertise also confirms the same thing, then we have more confidence.

So it can be a mix of things? It can be data and then thatcan be shaped by infrastructure, it can be lack of expertise or, like lack of meteorologists, for example? 

Yes. it’s not always easy for meteorologists to come participate in a collaborative study at these rapid timescales. So over [the] years, when we keep doing these studies in these regions, we keep building contacts also, and you know the good thing about doing these studies more and more is that, you know, sometimes even people in the region reach out, saying ‘do you think you can do a study on this event?’ and that encourages us to keep, keep doing this more.

I wanted to switch a bit to the news part – and since we journalists use a lot of this information that you’ve been discussing, in the WWA webpage, there’s a space for tools for journalists, and it lists actually weaknesses in the news reports. One of the most common is, it says, “the attribution of climate change as a sole cause of an extreme weather event”. So that’s not correct…. Climate change makes it worse often, [more intense], right? It’s not a cause and effect relationship.

No. So you know, even without climate change, it could have happened, but maybe not as more likely or more frequent. So in that sense, yes. There is this natural variability in the climate that can still cause these events to happen regardless due to something else sort of converging. But because, we are now fueling the climate by adding fossil fuels and increasing the overall temperatures, it’s like loading the dice. So you’re loading the dice to sort of cause it to occur more.

I mean, I’m making the case that it’s something that we can explain clearly in a story as to the relationship between an event and the current state of the climate. In WWA, the term that it uses in the reports is usually ‘climate change’. News outlets use different terms. A lot of them use some ‘climate change’, some ‘climate crisis’. I saw ‘climate breakdown’ yesterday, ‘climate collapse’ in others. But I noticed that for scientific minds, the use seems to be more ‘ climate change’ itself. Newspapers, they might choose something else, but I think it’s good for us to understand why the scientists use ‘climate change’.

‘Climate change’ is a scientifically established language. It helps us to build our evidence or it helps us to sort of describe the scale or the causes or the impacts rather than, you know, building on the urgency itself. So I think the difference in the lingo or the difference in the phrase is sort of related to what the mission is, right?

Right.

So, when you say ‘climate urgency’ or ‘climate breakdown’ or ‘climate collapse’, it essentially we’re saying the same thing. But you know, when you’re writing it out to the general audience, you’re also focusing on the urgency of stepping away from fossil fuels. Whereas in scientific literature, you’re just providing the evidence as to why we should step away from fossil fuels. It’s about using the right words or a universally accepted phrase to communicate essentially the same thing.

You mentioned the other phrase that I was going to ask you about, which is ‘human induced’. So some people say ‘human-driven’ or ‘human-induced’ climate change, and there are more news outlets now that consciously or mindfully use that term as an adjective to just ‘climate change’ or ‘climate crisis’, which drives home the point that it has something to do with our behaviour.

When you talk about human induced climate change, it can also be contributed from other factors like land use changes or land use changes or urban heat islands. Burning fossil fuels is the main thing, so that is felt everywhere. But some of these other changes are sort of more local and regionally constrained. But regardless, this human-induced climate change covers both these fossil fuel effects as well as these regional effects as well.

When I was listening to the briefing about the 2025 report, it said: “Every December,” WWA is saying this, “Every December, we are asked the same question, Was it a bad year for extreme weather? And each year, the answer becomes more unequivocal. Yes. Fossil fuel emissions continue to rise, driving global temperatures upward and fueling increasingly destructive climate extremes across every continent.”

We’re reading all of this heat stuff around us, right? And we read a lot about Europe, North America. And then we also read about China and then Hong Kong. So, how does the year look so far in terms of that question?

I think you already answered part of the question when you sort of placed all of these events. So, definitely with every year, you keep seeing more and more of these heat and droughts in the summer and extreme rainfall events when the monsoons hit, or in the winter, depending on where in the world you are.

So far, we often see that, oh these events, a similar event triggered last year, or we did a study last year on the same region. So that itself shows how often we are often seeing these extreme events unfurling in different parts of the world. So far, it’s been a busy year for us. We have already looked at wildfires in Europe, we’ve looked at wildfires in Canada, we’ve looked at droughts in Europe, we’ve done a few extreme rainfall studies in Africa, and the last one we did was on the Assam floods.

But it looks like this is sort of the reality that we are now living with, where it’s becoming so close to normal, such events, also highlighting how important it is to start stepping away from fossil fuels as our primary initiative, but also scaling up our adaptation measures to help people come out of harm’s way.

Now we also talk about how El Niño is expected to peak in the. . . .  Now, El Niño will come and go. With El Niño, it’s just adding one more additional weight in favour of increasing the likelihood of these extreme weather events, which is already being increased by climate change – and all of these which would have been less likely to happen had there been no climate change. 

It’s an interesting year, and it’s not exactly interesting in a good way, but sort of like a peek or a preview as to what we can expect in a warmer world. In one of the earlier El Niño events, you know, what we all said was that adding El Niño on top of climate change is giving you a preview into what it would be like in a world under future warming conditions.

So El Niño adds that additional fuel. But next year, if it drops, you might not see as many. But that doesn’t mean that the problem has gone away completely. But it’s part of a longer issue.

It’s a bit scary the way you describe it, if it’s a preview of the future.

It’s just a way to sort of see what can happen in the future and if nothing, that should encourage us to start going in the right direction with regards to the climate change mitigation.

Okay. Thank you, Mariam. I think we learned a lot from that. 

Thank you very much.

(END/Reporting ASEAN)