Attribution of extreme weather to climate change

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Re: Attribution of extreme weather to climate change

Post by Bird on a Fire » Wed Jun 30, 2021 8:17 am

It's even becoming possible to attribute climate damage to individual polluters:
Rupert Stuart-Smith, researcher at the Oxford University sustainable law programme, and lead author of a new study, said more such cases were likely to be successful, as new science was making it possible to attribute the damages of climate breakdown more directly to companies’ activities.

“It’s no longer far-fetched to think that these companies can be taken to court successfully,” he said. “The strength of evidence is bolstering these claims, and giving a firm evidentiary basis for these court cases.”

That success could in turn unleash a further new wave of litigation, he said. “It’s possible that we will see precedents made that will make it easier to file future lawsuits on climate impacts.”
https://www.theguardian.com/environment ... sses-study

Which ties in nicely with the judicial instruments thread.

The full paper is free to read here, or there's a twitter thread from the lead author if (like most academics) you prefer.
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Re: Attribution of extreme weather to climate change

Post by IvanV » Wed Jun 30, 2021 9:48 am

Bird on a Fire wrote:
Thu Apr 01, 2021 1:59 pm
One thing I never understood from climate denialists was how they thought plants, birds and butterflies were in the big conspiracy ;)
I don't think this is a particularly difficult thing to rationalise, if you don't want to believe it.

Climate denialists generally don't say climate change doesn't happen, but they say it is natural, and nothing or very little to do with human CO2 emissions. For example the physicist William Happer, https://en.wikipedia.org/wiki/William_Happer who in the end was not appointed Trump's chief scientific denier, nevertheless had a briefing paper put out on official government paper, in which he calculates the forcing effect of CO2. He presents exactly the same estimate of CO2 forcing as any other competent physicist. Having calculated the forcing, the same number as anyone else, he just says, well that's a very small number, how can it make material any difference to anything. It's as if he thinks if you put a pan on a very low heat, it won't actually heat up at all. He forgets what thermal equilibrium is. So that kind of denier says, climate fluctuates, but it's nothing to do with us. The birds and butterflies are responding to natural changes.

Then there is the less extreme Lomborg kind of position, which says that plainly the laws of physics mean that CO2 does warm things up, but the feedback effects are overstated. They go on to say, in classic "inactivist" style, that adaptation is mostly cheaper than abatement. Clearly Lomborg has been caught very sneakily misusing statistics to try and bolster his "things are not so bad" schtick. But one of the things I have noticed is that this type are tending to say quite often at the moment is that what we are seeing currently is in part the bounce-back from the "little ice age". Thus climate sensitivity is overestimated by studies looking at the temperature trend starting from, say, early 19th century. They also say, look, at the moment we aren't warming up as much as you said we would, so that confirms it. So they will say, yes it's warming up, but that would have happened in part anyway. And clearly there are natural variations in climate which don't relate to human CO2 emissions. The fallacy is to think that there is some hidden forcing, a "bounce-back" forcing, that has been overlooked in trying to assess climate sensitivity to forcings. These climate variations all still result from forcings, albeit natural forcings, and climate scientists do take account of natural forcings.

So I don't think the butterflies and the birds worry the deniers, of varying colours, and the inactivists, because they have ways of rationalising it. And indeed we can see that many people rationalise much more obviously wrong things than this.

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Re: Attribution of extreme weather to climate change

Post by Bird on a Fire » Wed Jun 30, 2021 10:10 am

IvanV wrote:
Wed Jun 30, 2021 9:48 am
Bird on a Fire wrote:
Thu Apr 01, 2021 1:59 pm
One thing I never understood from climate denialists was how they thought plants, birds and butterflies were in the big conspiracy ;)
I don't think this is a particularly difficult thing to rationalise, if you don't want to believe it.

Climate denialists generally don't say climate change doesn't happen,
There certainly used to be plenty of them about - they used to post on Bad Science and everything. All sorts of weird excuses, like temperature gauges being sited incorrectly, or spurious claims of analytical shenanigans (remember when the BEST project was set up to re-analyse the climate data independently from IPCC? Climate deniers loved the idea, right up until it also showed that the world was indeed warming).

I've had relatives send me clippings from the Daily Fail "proving" that climate change wasn't happening. Plenty of mainstream politicians (mostly from the right, of course) have called it a hoax. Every time it snows some c.nt chirps up with "what about global warming hur hur".

So yeah, various flavours of denialist, with only slight variation in levels of wrongness, and even less in levels of tedium engaging with them. But I've never seen a full-on denialist (ie, claims that the climate isn't warming) address other indicators of warming, such as the ecological ones (bud burst, flowering times, insect emergence, bird migration, etc etc etc.). I'd possibly be interested to skim-read one in a point-and-laugh kind of way.
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Re: Attribution of extreme weather to climate change

Post by IvanV » Wed Jun 30, 2021 10:57 am

Bird on a Fire wrote:
Wed Jun 30, 2021 10:10 am
IvanV wrote:
Wed Jun 30, 2021 9:48 am
Bird on a Fire wrote:
Thu Apr 01, 2021 1:59 pm
One thing I never understood from climate denialists was how they thought plants, birds and butterflies were in the big conspiracy ;)
I don't think this is a particularly difficult thing to rationalise, if you don't want to believe it.

Climate denialists generally don't say climate change doesn't happen,
There certainly used to be plenty of them about - they used to post on Bad Science and everything. All sorts of weird excuses, like temperature gauges being sited incorrectly, or spurious claims of analytical shenanigans (remember when the BEST project was set up to re-analyse the climate data independently from IPCC? Climate deniers loved the idea, right up until it also showed that the world was indeed warming).

I've had relatives send me clippings from the Daily Fail "proving" that climate change wasn't happening. Plenty of mainstream politicians (mostly from the right, of course) have called it a hoax. Every time it snows some c.nt chirps up with "what about global warming hur hur".

So yeah, various flavours of denialist, with only slight variation in levels of wrongness, and even less in levels of tedium engaging with them. But I've never seen a full-on denialist (ie, claims that the climate isn't warming) address other indicators of warming, such as the ecological ones (bud burst, flowering times, insect emergence, bird migration, etc etc etc.). I'd possibly be interested to skim-read one in a point-and-laugh kind of way.
Yes, there are too the complete denialists. But I don't generally worry about them. When your position starts by denying the basic laws of physics, you don't even get into the room to discuss things, as there is literally no talking to such people. Likewise I don't worry about creationists when the topic is evolution. But those who at least start by acknowledging the laws of physics, and acknowledge the forcing effect of CO2, like Lomborg, these are people are sufficiently mainstream to get into the room, and their rationalisation is much more subtle. This is really what one has to worry about. Plenty of people out there who religiously put their plastic in the recycling bin, and think they are doing their bit.

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Re: Attribution of extreme weather to climate change

Post by Woodchopper » Wed Jun 30, 2021 2:13 pm

IvanV wrote:
Wed Jun 30, 2021 10:57 am
Bird on a Fire wrote:
Wed Jun 30, 2021 10:10 am
IvanV wrote:
Wed Jun 30, 2021 9:48 am

I don't think this is a particularly difficult thing to rationalise, if you don't want to believe it.

Climate denialists generally don't say climate change doesn't happen,
There certainly used to be plenty of them about - they used to post on Bad Science and everything. All sorts of weird excuses, like temperature gauges being sited incorrectly, or spurious claims of analytical shenanigans (remember when the BEST project was set up to re-analyse the climate data independently from IPCC? Climate deniers loved the idea, right up until it also showed that the world was indeed warming).

I've had relatives send me clippings from the Daily Fail "proving" that climate change wasn't happening. Plenty of mainstream politicians (mostly from the right, of course) have called it a hoax. Every time it snows some c.nt chirps up with "what about global warming hur hur".

So yeah, various flavours of denialist, with only slight variation in levels of wrongness, and even less in levels of tedium engaging with them. But I've never seen a full-on denialist (ie, claims that the climate isn't warming) address other indicators of warming, such as the ecological ones (bud burst, flowering times, insect emergence, bird migration, etc etc etc.). I'd possibly be interested to skim-read one in a point-and-laugh kind of way.
Yes, there are too the complete denialists. But I don't generally worry about them. When your position starts by denying the basic laws of physics, you don't even get into the room to discuss things, as there is literally no talking to such people. Likewise I don't worry about creationists when the topic is evolution. But those who at least start by acknowledging the laws of physics, and acknowledge the forcing effect of CO2, like Lomborg, these are people are sufficiently mainstream to get into the room, and their rationalisation is much more subtle. This is really what one has to worry about. Plenty of people out there who religiously put their plastic in the recycling bin, and think they are doing their bit.
For the US about 12% believe that climate change isn't happening, and about 32% believe that it is, but is caused by natural causes, and 38% believe that the seriousness of the effects are generally exaggerated. Those are minorities, but large ones.

In the UK about 4% believe that it isn't happening, and 13% that it is but for natural reasons. These numbers haven't changed over the past few years. So fewer than the US, but still large in aggregate.

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Re: Attribution of extreme weather to climate change

Post by plodder » Wed Jun 30, 2021 2:45 pm

What’s happening in Canada right now is sufficiently f.cked up to get people’s attention, and of course there will be plenty more where that came from. People who put their plastic in the right bin are doing their bit btw. It’s down to policy makers to give them simple solutions exactly like this.

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Re: Attribution of extreme weather to climate change

Post by Fishnut » Fri Aug 20, 2021 3:06 pm

It's raining on the Greenland icecaps.
Rain has fallen on the summit of Greenland’s huge ice cap for the first time on record...

Scientists at the US National Science Foundation’s summit station saw rain falling throughout 14 August but had no gauges to measure the fall because the precipitation was so unexpected...

The rain fell during an exceptionally hot three days in Greenland when temperatures were 18C higher than average in places. As a result, melting was seen in most of Greenland, across an area about four times the size of the UK.
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Re: Attribution of extreme weather to climate change

Post by dyqik » Fri Aug 20, 2021 4:49 pm

Woodchopper wrote:
Wed Jun 30, 2021 2:13 pm
For the US about 12% believe that climate change isn't happening, and about 32% believe that it is, but is caused by natural causes, and 38% believe that the seriousness of the effects are generally exaggerated. Those are minorities, but large ones.

In the UK about 4% believe that it isn't happening, and 13% that it is but for natural reasons. These numbers haven't changed over the past few years. So fewer than the US, but still large in aggregate.
Obviously cynical right wing culture wars are a big chunk of the US's problem here, but I do wonder how much is also due to the fact that the US is large with a national news market, and there's extreme weather of some kind going on a lot of the time. Hurricanes, tornados, heavy snow storms, flooding, and extreme heat and drought were happening in at least some parts of the US before climate change kicked in, so it's harder to see increased incidence of them as drastically new. The Weather Channel, for example, has news about extreme weather in the US every single day, even if it's stretching a bit for some of it.

A post hurricane tropical storm remnant hitting the UK and causing high winds, flooding and possible tornados is massive news, but even up here in New England, it happens more than once a decade, and big snow storms are even more common. Tornados in Texas and Oklahoma, and hurricanes in Florida and the gulf are basically just spring and summer.

Wildfires in the west are maybe more obvious in New England, particularly since we've had several days up here with "Stay Indoors" air quality warnings in the past month.

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Re: Attribution of extreme weather to climate change

Post by Bird on a Fire » Sat Aug 21, 2021 12:41 am

Fishnut wrote:
Fri Aug 20, 2021 3:06 pm
It's raining on the Greenland icecaps.
Rain has fallen on the summit of Greenland’s huge ice cap for the first time on record...

Scientists at the US National Science Foundation’s summit station saw rain falling throughout 14 August but had no gauges to measure the fall because the precipitation was so unexpected...

The rain fell during an exceptionally hot three days in Greenland when temperatures were 18C higher than average in places. As a result, melting was seen in most of Greenland, across an area about four times the size of the UK.
Yes, this is quite bad. Things are melting faster than expected, which isn't great news. Uncertainty around the rate of melting of Greenland's ice was a major source of uncertainty in sea level rise last time I looked, so we should probably start expecting the worse end of predictions.
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Re: Attribution of extreme weather to climate change

Post by dyqik » Sat Aug 21, 2021 1:38 am

It's also a bugger because we're trying to put a 120 ton telescope on top of a compressed snow foundation there.

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Re: Attribution of extreme weather to climate change

Post by Bird on a Fire » Sat Aug 21, 2021 1:53 am

I suspect a lot of long-term polar installations will be in trouble. I know they've already had to relocate some bases in Antarctica.

It's probably a bit more difficult to put a 120 ton telescope on skis though, I guess.
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Re: Attribution of extreme weather to climate change

Post by dyqik » Sat Aug 21, 2021 1:55 am

Bird on a Fire wrote:
Sat Aug 21, 2021 1:53 am
I suspect a lot of long-term polar installations will be in trouble. I know they've already had to relocate some bases in Antarctica.

It's probably a bit more difficult to put a 120 ton telescope on skis though, I guess.
The Antarctic thing I'm working on is for much smaller telescopes at the south pole, which should be good for a while yet.

If we start getting rain there, everything is f.cking f.cked.

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Re: Attribution of extreme weather to climate change

Post by Bird on a Fire » Sat Aug 21, 2021 2:02 am

W. A. P. (Wet Adélie Penguins)
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Re: Attribution of extreme weather to climate change

Post by Bird on a Fire » Tue Mar 01, 2022 7:58 pm

Carbon Brief have a cool page mapping all the extreme weather studies that have taken place around the world:
https://www.carbonbrief.org/mapped-how- ... -the-world
– 70% of the 405 extreme weather events and trends included in the map were found to be made more likely or more severe by human-caused climate change.

– 9% of events or trends were made less likely or less severe by climate change, meaning 79% of all events experienced some human impact. The remaining 21% of events and trends showed no discernible human influence or were inconclusive.

– Of the 122 attribution studies that have looked at extreme heat around the world, 92% found that climate change made the event or trend more likely or more severe.

– For the 81 studies looking at rainfall or flooding, 58% found human activity had made the event more likely or more severe. For the 69 drought events studied, it’s 65%.
Even back when I did my masters (2014-16), scientists were generally quite reluctant to say that an individual event was climate change-related: the best we could do was note trends in ~similar events over time. The field has really developed fast.

The results aren't remotely surprising - if you increase the amount of energy in a system, as humans are doing to the planet we live on, you'll generally find its behaviour becomes more energetic. We've known that the long-term average was getting hotter for decades, so it shouldn't be surprising that the right-tail has shifted too.

But it's always good to have decent quantitative evidence.
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Re: Attribution of extreme weather to climate change

Post by Bird on a Fire » Tue Mar 01, 2022 8:31 pm

As Ivan asked on another thread,
IvanV wrote:
Tue Mar 01, 2022 5:01 pm
So is there anything interesting in the IPCC report you could point me to which assesses weather statistics, rather than forecasts?
might as well link to a piece summarising what the latest report said on climate attribution:
Since the publication of AR5, “attribution science” has “emerged as a growing field of climate research with an increasing body of literature”, the AR6 report says. These studies assess whether – and to what extent – human-caused climate change and other drivers have affected the frequency and/or intensity of extreme weather events.

Attribution research has shown that, for example, climate change made Europe’s record-breaking heatwave in 2019 as much as 100-times more likely and also tripled the chances of the record rainfall that Hurricane Harvey dumped on Texas in 2017.

The geographical spread of these studies is “uneven”, the AR6 report says, with fewer carried out in the developing world. There are various reasons for this, including “a lack of observational data, lack of reliable climate models and other problems”.

Nonetheless, the authors say, the large number of event-attribution studies “provide evidence that changes in the properties of these local and individual events are in line with expected consequences of human influence on the climate and can be attributed to external drivers”.

The maps below, taken from the report’s Summary for Policymakers, shows how climate change is “already affecting every inhabited region” across the world. The maps show a “synthesis of assessment” for hot extremes (top), heavy precipitation (middle) and drought (bottom), with each hexagon showing a single region.

The colour of shading in each hexagon shows whether there has been an observed increase or decrease in that region since the 1950s, while grey shading or cross-hatching indicates limited data or low agreement, respectively. The number of dots within the hexagons show the level of confidence in the influence that humans are having.
Maps-show-the-synthesis-of-assessment-of-weather-and-climate-extremes-IPCC.jpg
Maps-show-the-synthesis-of-assessment-of-weather-and-climate-extremes-IPCC.jpg (486.83 KiB) Viewed 1609 times
Maps show the synthesis of assessment of weather and climate extremes IPCC
Note too that the IPCC now refer to climate impacts on extreme weather as an "established fact" - something they really don't do too often.

Heat, rain, flooding, drought, cyclones and "compound events" all get their own special section. Full report is here: https://www.ipcc.ch/report/sixth-assess ... g-group-i/
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Re: Attribution of extreme weather to climate change

Post by IvanV » Tue Mar 01, 2022 9:24 pm

Thank you very much for posting that, BOAF.

So what we see there is that we have high confidence of climate change driving heat events, as I thought. It is unsurprising, when our primary metric of climate change is an increase in average temperature. So it is not surprising for that to drive an increase in high temperature events. Though denialists try to squirm around it. An increase in average temperature can in principle happen without an increase high heat events, if you narrow temperature range sufficiently. But Mr Occam doesn't like it very much. And so it is unsurprising to see that the actual stats give us high confidence in increasing high heat events.

There are smaller numbers of green and yellow tiles, and they generally have only one dot in them - low confidence. This bears out what I was saying in the other thread. It has long been hard to demonstrate a statistically clear climate change signal for unpleasant weather events other than heat. A lot of places don't even show that. Where we see it, the quantity of data is such that we have low statistical confidence in the conclusion.

Though maybe the collective data is giving us overall statistical confidence in a direction of change, even if each individual locality shows, roughly equally divided, either no change, or low confidence of a unpleasant change.

It is important to be able to show things with high statistical confidence. Because otherwise the denialists just play merry hell.

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Re: Attribution of extreme weather to climate change

Post by Bird on a Fire » Wed Mar 02, 2022 4:07 pm

I'm not 100% sure if we're talking at cross-purposes here, so I've tried to be very explicit in the following about dividing the question into its two parts:
1. Is there a trend?
2. Can it be attributed to anthropogenic climate change?

The second question is concerned with trying to link observed changes in whatever climatic trend of interest in directly to anthropogenic radiative forcings. So whether or not something is attributed to climate change is a different question - perhaps counter-intuitively - from whether or not that aspect of the climate is observed to be changing.
IvanV wrote:
Tue Mar 01, 2022 9:24 pm
There are smaller numbers of green and yellow tiles, and they generally have only one dot in them - low confidence. This bears out what I was saying in the other thread. It has long been hard to demonstrate a statistically clear climate change signal for unpleasant weather events other than heat. A lot of places don't even show that. Where we see it, the quantity of data is such that we have low statistical confidence in the conclusion.
Note that the dots represent confidence specifically in human contribution to the observed trends - it's the colours that tell you if there's agreement on the direction of the trend. As you can see there are quite a lot of regions with well-characterised trends, and
IvanV wrote:
Tue Mar 01, 2022 9:24 pm
Though maybe the collective data is giving us overall statistical confidence in a direction of change, even if each individual locality shows, roughly equally divided, either no change, or low confidence of a unpleasant change.
Yes, the piece I linked to goes into that in more detail. It's often the case that there are observable global trends, but pinning them down locally is trickier. Similarly, there are fewer studies assessing anthropogenic causation of trends at regional scales than globally - as I say, attribution is a very young field. (When I looked at that map I thought "Wow! They've done that many regional studies already?" because even in AR5 there was still a lot of uncertainty attributing extreme weather to climate globally). There are also still serious issues with a lack of good data in the most vulnerable regions.

So for instance, for trends in heavy precipitation we have:
The frequency and intensity of heavy rainfall events “have likely increased at the global scale over a majority of land regions with good observational coverage”, the IPCC says. Regional increases in the frequency and/or intensity of heavy rainfall “have been observed with medium confidence for nearly half” of regions, the report adds.

Since 1950, the annual maximum amount of rainfall falling in a day or over five consecutive days “has likely increased” for land areas with sufficient observations, the report notes.

In general, the evidence for increasing rainfall extremes for Europe, North America and Asia is the most robust, the report says, and heavy precipitation has likely increased on the continental scale over these three continents.

For example, “there is a significant increase in heavy rainfall” in central India during the South Asian monsoon season, the report says, which has occurred alongside “a significant decrease in moderate rainfall”.

Whereas across Africa, for example, there is a “general lack of continent-wide systematic analysis” and a “sporadic nature” of available data, the report says. So, while “increases in the frequency and intensity of extreme precipitation have been observed over the well-gauged areas during 1950-2013”, this only covers “15% of the total area”.

Similarly, in Central and South America, “evidence shows an increase in extreme precipitation, but in general there is low confidence”, the report says. And in small island states, “there is a lack of evidence showing changes in heavy precipitation overall”.
But then for the attribution of those trends to human activity, we get:
For the increases that are observed, human influence – particularly through greenhouse gas emissions – “is likely the main driver of the observed scale intensification”, the report says, adding:

“In particular, detection and attribution analyses have provided consistent and robust evidence of human influence on extreme precipitation of one- and five-day durations at global to continental scales.”

Evidence for human influence on extreme precipitation at regional scales is limited, the report notes, but “new evidence is emerging”. For example, studies have shown that “the increase in widespread extremes over the South Asian Monsoon during 1950-2015 is due to the combined impacts of the warming of the Western Indian Ocean (Arabian Sea) and the intensification of irrigation water management over India”.

The picture is broadly similar for other types of extremes. (I won't bother quoting everything, but if you are interested in the science here I suggest you take a look at the article.) In terms of trend vs. attribution:
  • Generally speaking, flooding has more data issues (as people rarely measure the extent of a flood, and we're lucky if there's good data on river flow). Obviously floods themselves are also an interaction between weather and infrastucture making generalisation trickier. They are confident attributing increased flooding to climate change in well-studied regions like the UK, fwiw.
  • Droughts can be defined in multiple ways, which is part of the reason for the disagreement about trends. When using an index that combines plant physiology along with rainfall they find increases “on all continents and several regions” - for some reason they can tie drought to evapotranspiration, and evapotranspiration to heating, but have lower confidence tying drought to heating directly. Science is hard, I guess.
  • Tropical storms are deffo getting heavier, moving polewards and spending more time in the same places over land. Reasonably likelihood of anthropogenic attribution in this case too - perhaps unsurprisingly as they're basically the result of SST(?), but they seem happy that ENSO et al. isn't sufficient explanation now.
  • The area affected by "compound threats" is going up. This is stuff like where drought plus a heatwave causes fires. There are some attribution studies of individual fires upthread, but nothing big-picture mentioned yet.
So (TLDR) I'd say that there are very often clear signals of trends even at regional levels, as long as the variable is defined consistently in the literature, the data exists, and there are enough climate scientists working on the area (sorry, African agronomists). Attributing those observed trends to human activity has come on leaps and bounds since AR5 in 2013, but seems to be much easier when the chain of causation is short, as it is with heatwaves, storms and evaporative stress, compared with precipitation and flooding.
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Re: Attribution of extreme weather to climate change

Post by Bird on a Fire » Wed Mar 02, 2022 4:25 pm

BTW I thought this was interesting on the relationship between means and extremes, from the AR6 WG1 report FAQs:
FAQ 11.1: How do changes in climate extremes compare with changes in climate averages?

Human-caused climate change alters the frequency and intensity of climate variables (e.g., surface
temperature) and phenomena (e.g., tropical cyclones) in a variety of ways. We now know that the ways in
which average and extreme conditions have changed (and will continue to change) depend on the variable
and the phenomenon being considered. Changes in local surface temperature extremes follow closely the
corresponding changes in local average surface temperatures. On the contrary, changes in precipitation
extremes (heavy precipitation) generally do not follow those in average precipitation and can even move in
the opposite direction (e.g., with average precipitation decreasing but extreme precipitation increasing).
So for some variables you do need data on extremes themselves, rather than averages. As extremes are by definition uncommon, this massively increases data requirements and presents a hard limit to what can be done spatially and temporally using observations alone, which is where forecasts can also be a useful tool for understanding the present: we might not be able to say anything about two recent extreme events observed in a region, but we can note that an increase in those extremes is what we'd expect given anthropogenic heating.
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Re: Attribution of extreme weather to climate change

Post by IvanV » Wed Mar 02, 2022 4:47 pm

Many thanks again, that has improved my understanding of what I am looking at. I ought to go and read the papers myself. But I'm hoping your distillations have help others also.

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Re: Attribution of extreme weather to climate change

Post by Bird on a Fire » Mon Jul 11, 2022 3:01 pm

Spain and Portugal suffering driest climate for 1,200 years, research shows
The researchers found that winters featuring “extremely large” Azores highs have increased dramatically from one winter in 10 before 1850 to one in four since 1980. These extremes also push the wet weather northwards, making downpours in the northern UK and Scandinavia more likely.

The scientists said the more frequent large Azores highs could only have been caused by the climate crisis, caused by humanity’s carbon emissions.

“The number of extremely large Azores highs in the last 100 years is really unprecedented when you look at the previous 1,000 years,” said Dr Caroline Ummenhofer, at Woods Hole Oceanographic Institution in the US, and part of the research team.

“That has big implications because an extremely large Azores high means relatively dry conditions for the Iberian peninsula and the Mediterranean,” she said. “We could also conclusively link this increase to anthropogenic emissions.”

The Iberian peninsula has been hit by increasing heatwaves and droughts in recent years and this year May was the hottest on record in Spain. Forest fires that killed dozens of people in the region in 2017 followed a heatwave made 10 times more likely by the climate crisis, while the Tagus River, the longest in the region, is at risk of drying up completely, according to environmentalists.
Full study is here: Twentieth-century Azores High expansion unprecedented in the past 1,200 years (should be OA). Here's the bit on attribution:
Attribution of the unprecedented twentieth-century Azores High expansion
The coherence of Azores High expansion seen between the fully forced simulations within the LME (Fig. 3) suggests that Azores High expansion is not due to internal climate variability, but instead is driven by external forcings that are common to all simulations. For each of these external forcings, the LME includes a sub-ensemble (3–5 simulations) in which only one of the external forcings was varied. We performed an analysis of extreme AHA events within each of these sub-ensembles to explore the drivers of the change in Azores High behaviour. The only sub-ensemble members that show the expansion identified in the full-forcing simulations are the simulations in which GHG concentration is the only varied forcing (Fig. 3e). This indicates that the dramatic industrial-era expansion of the Azores High in a warming climate is a result of the anthropogenic increase in atmospheric GHG concentrations.
Admittedly this is really a long-term climatic trend, rather than weather, but it's still rather specific and localised, and they're able to attribute it to anthropogenic emissions in much the same way global climate models do: use the force.
We have the right to a clean, healthy, sustainable environment.

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