Record flooding in UK: Latest symptom of El Nino and climate change?

By Chelsea Harvey | Special to The Washington Post | Published: January 1, 2016

December witnessed a spate of extreme global weather events, from deadly tornadoes in the southern U.S. to bushfires in Australia – and the latest development is a series of record-breaking floods in the United Kingdom, brought on by torrential rain starting in the first week of the month. Thousands of homes in the north of England are believed to have been affected already, and the region is reeling again from a new wave of flooding just brought in this week with the onset of Storm Frank.

There's been much discussion about the causes behind the surprising rash of winter storms in the region (Frank is the third major storm to hit within a month), and equal suspicion has fallen on the effects of climate change and the influences of this year's particularly potent El Nino event. It can be difficult to parse exactly what's going on, though.

Nicola Maxey, a press officer from the Met Office (the UK's national weather service) noted in an email that it was too early to say for sure whether climate change was a major contributor to this winter's extreme rainfall – but added that evidence from both physics and the study of weather systems suggests that it may have played a part.

The Met Office, in fact, recently published a report in the Bulletin of the American Meteorological Society examining the causes behind dozens of extreme weather events in 2014, including similarly severe rainfall in the UK in the winter of 2013/2014. Using models, the report concluded that anthropogenic climate change likely had a hand in the extreme conditions that winter - the highest rainfall since 1931 - and that climate change increases the chances of extreme rainfall during a time period of 10 consecutive winter days by a factor of seven.

So while scientists frequently warn that individual weather events can't always be considered an indicator of long-term climatic patterns, the research in this case suggests that climate change is increasing the odds of extreme winter weather events in the UK. This is in keeping with research from all over the world that suggests that extreme weather, in general, is likely to increase in frequency and intensity all around the world as a result of climate change.

"I think it is fair to conclude that human-caused climate change here too increased the flooding potential of the recent storms," said Michael Mann, distinguished professor of meteorology at Penn State University, in an email to The Post. "While climate change didn't 'cause' the storms themselves, it has increased the potential for heavy rainfall and flooding with these storms." 

On the other hand, Maxey pointed out that El Nino, which increases the likelihood of warmer and wetter winters in the UK, could also be at play in the recent events - but she added that it's "just one of many drivers that affect the UK weather and there are many other factors which could override this signal."

So parsing between the two - human-caused climate change, on the one hand, and naturally occurring El Nino, on the other - can seem confusing. But experts are increasingly arguing that the UK downpours - along with many of the other unusual weather events being witnessed around the globe as 2015 came to a close - are likely the product of both forces interacting and ultimately making each other worse.

El Nino itself is not a product of climate change at all. Rather, it's a naturally occurring cycle, coming around every four to seven years or so, that brings unusually warm temperatures to the Pacific Ocean, generally with significant consequences for global weather patterns. This year's is believed to be among the strongest El Nino events ever recorded.

Because its effects are often similar to those predicted to be caused by climate change, including unseasonably warm temperatures in some regions and an increase in storms and other extreme weather events, it can be hard to definitively say which events are caused by which phenomenon. In fact, the claim that certain extreme weather events are the product of El Nino, and not human-caused climate change, is sometimes seized upon by climate doubters arguing that increases in extreme weather patterns are simply the product of naturally occurring processes.

However, this doesn't change the fact that climate change is a continuous process that's still happening even in El Nino years. What's more likely, given the severity of this season's event and the strange weather that's accompanied it, is that the ongoing influence of climate change is simply making this year's El Nino event even worse.

"Some scientists have found that human-caused climate change may increase the intensity of El Nino events, because a warmer atmosphere means more moisture in the air, a key ingredient in the energetics that drives El Nino," Mann said in his email.

So the fact that this year's El Nino is among the strongest on record is probably not a coincidence either, but rather another product of the changing climate. In this way, "climate change may be favoring the extreme weather we've seen this year both directly and, indirectly, through its impact on El Nino itself," Mann said.

And this effect has manifested itself in other places besides the UK. A spree of deadly tornadoes in the southern and midwestern U.S. last week, for instance, has been potentially linked to the severity of this year's El Nino event. And the same goes for record flooding in South America, as well as the less dramatic but nevertheless unusual warm winter temperatures in the northeastern U.S. this season.

The combination of both human-caused climate change on the one hand, and El Nino on the other, can lead to dramatic upticks in these types of extreme weather events, Mann said in his email.

Scientists believe that the unusual weather patterns will persist into 2016, which some have predicted will be the warmest year on record. While uncharacteristically warm years frequently follow strong El Nino events, it should be noted that 2014 and 2015 both broke records as the warmest years recorded. Should 2016 join the series, it will also be an unmistakable symptom of a long-term pattern of human-caused global warming.

And while this season's El Nino event will subside soon enough, the effects of climate change are expected to continue making themselves apparent in the coming years - meaning crazy weather is something we may need to start getting used to.


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