Q&A: What role does climate change play in recent extreme weather events?

We are experiencing a summer of weather extremes encapsulating heatwaves, wild fires and intense rainfall followed by flash floods.

This has come in the form of blistering heatwaves throughout the Northern Hemisphere – the most destructive being the "heat dome" which sat over a vast area of North America – and unprecedented flooding events in Germany and China causing widespread devastation.

Nearer home, we have experienced a heatwave with temperatures breaching 30 degrees on successive days in the UK and Ireland; prompting unprecedented extreme heat warnings from Met Éireann and the UK Met Office.

Such events are becoming not only more frequent but also more ferocious. There is every indication this is a scenario predicted to occur due to ever increasing global heating. But blaming the accelerating climate crisis in all instances is a step too far.

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We do know, for instance, that warmer air holds more moisture, which means more water will be released eventually, though natural variations in rainfall and heat mean they could be an example of a weather extreme that could have been feasible in the pre-industrial climate.

Floods always happen, and they are like random events, ie rolling the dice. But we’ve changed the odds on rolling the dice, scientists point out. But without a specific attribution study it is impossible to know whether weather events are linked to climate change.

How are climate scientists interpreting recent weather events?

Using the science of event attribution, it's possible to say if climate change made an event more likely or not, says Dr Clare Noone of ICARUS climate research unit in Maynooth University.

“Many scientific reports have consistently found heatwaves and extreme rainfall events have been made more likely due to climate change. It’s clear that human-induced climate change is already affecting our weather patterns. This will have major impacts on our health, lives, and economy and if we continue to burn fossil fuels we will unfortunately continue to see more extreme weather events around the globe,” she adds.

The techniques using a complex suite of models are getting more reliable and quicker. Recent record-shattering temperatures in the US and Canada were found by scientists with World Weather Attribution to be "virtually impossible without climate change"; global warming caused by human activity made it at least 150 times more likely to happen. A verdict on the German floods has yet to emerge.

Why is this summer different?

In short, because everything seems to be happening a lot faster and are very obvious.

"Global warming was well projected, but now you see it with your own eyes," says Corinne Le Quere of the University of East Anglia. Scientists had long predicted such extremes were likely but many are surprised by so many happening so fast, she notes.

"It's not so much that climate change itself is proceeding faster than expected – the warming is right in line with model predictions from decades ago," says US climate scientist Michael Mann. "Rather, it's the fact that some of the impacts are greater than scientists predicted."

That suggests climate modelling may have been underestimating the potential for a dramatic rise in persistent weather extremes.

Are scientists worried by current climate trends?

A study published in Nature Climate Change on Monday concludes very rapid warming means we must expect extreme event records to be broken – not just by small margins but quite often by very large ones. This highlights the huge challenge to improve preparedness, build resilience and adapt society to conditions that have never been experienced.

The impact of climate change on heatwaves is often quantified by how much a current or future event compares to itself in a world with less (or no) climate change. A given heat extreme is usually slightly hotter and more frequent today than it would have been in the past; however, these changes can seem marginal when measured in this manner. "Another way to view such extremes is by how much they surpass or 'shatter' the previous heatwave record," according to lead author Erich Fischer a specialist on climate and weather extremes.

This suggests if human-induced global warming was stabilised by aggressive mitigation, the frequency and intensity of heatwaves would still be higher; however, the probability of record-shattering extremes would be notably reduced.

Dr Karsten Haustein of Climate Service Centre in Germany says "it is one of those papers which couldn't be any more timely in light of the recent record-shattering extreme heat event in the US and Canada".

She adds: “Almost as if the authors foresaw what’s coming. Combining different observation and model based climate data, they found that heatwaves which not just exceed, but shatter old records become multiple times more likely (up to 20 times between 2051-2080) if we fail to drastically reduce our carbon emissions.”

When will leading climate scientists provide their latest verdict?

Climate experts are meeting online this week under the UN Intergovernmental Panel on Climate Change. They will finalise a report which will update the established science around greenhouse gas emissions and projections for future warming and its impacts.

Their evaluation will be released on August 9th – Prof Peter Thorne of Maynooth University is a lead author.

It will show there is now a better understanding of the attribution of extreme weather to climate change and provide the latest indications the world is approaching “tipping points” that once crossed could trigger and amplify cascading crises across the planet, with one ecosystem collapsing after another.

With 1.2 degrees of warming already above pre-industrial levels, they are expected to confirm there is a risk the dreaded 1.5 degree threshold will be reached in less than a dozen years.