The Guardian Weekly

Arctic warming’s chain reaction

Soaring temperatur­es linked to severe storms

- Damian Carrington

Ice melt also a factor in extreme global weather

The dramatic melting of Arctic ice is already driving extreme weather that affects population­s across North America, Europe and Asia, scientists on the cutting edge of climate research have said.

Severe “snowmagedd­on” northern hemisphere winters are now strongly linked to soaring polar temperatur­es, say researcher­s, with deadly summer heatwaves and torrential floods also probably linked. The scientists now fear the Arctic meltdown has kickstarte­d abrupt changes in the planet’s swirling atmosphere.

The northern ice cap has been shrinking since the 1970s, with global warming driving the loss of about three-quarters of its volume so far. But the recent heat in the Arctic has shocked scientists, with temperatur­es 33C above average in parts of the Russian Arctic and 20C higher in some other places. In November, ice levels hit a record low, and we are now in “uncharted territory”, said Prof Jennifer Francis, an Arctic climate expert at Rutgers University in the US.

“These rapid changes in the Arctic are affecting weather patterns where you live right now,” she said. “In the past you have had natural variations like El Niño, but they have never happened before in combinatio­n with this very warm Arctic.”

The chain of events that links the melting Arctic with weather to the south begins with rising global temperatur­es causing more sea ice to melt. Unlike on the Antarctic continent, melting ice here exposes dark ocean beneath, which absorbs more sunlight than white ice and warms further. This well-known feedback loop is why the Arctic is heating up several times faster than the rest of the planet.

This in turn narrows the temperatur­e difference between the Arctic and lower latitudes, which is crucial because it is the temperatur­e gradient between them that drives the jet stream wind, which streaks around the pole at up to 400km/h and about 8km above the surface.

The jet stream forms a boundary between the cold north and the warmer south, but the lower temperatur­e difference means the winds are now weaker. This makes the jet stream meander more, with big loops bringing warm air to the frozen north and cold air into warmer southern climes.

Furthermor­e, the researcher­s said, the changes mean the loops can remain stuck over regions for weeks, rather than being blown westwards as in the past. This “blocking” effect means extreme events can unfold.

“There have been recent studies showing very plausible physical mechanisms of how rapid warming in the Arctic can influence weather in the mid latitudes, both in summer and winter,” said Dim Coumou at the Potsdam Institute for Climate Impact Research in Germany, who has studied the link between extreme weather events and global warming since 2010. “A couple of years ago this was the main criticism on any such links, that the physics was not well understood,” he

said. “But the big question [now] is, how important are these mechanisms?”

The other main influence on the jet stream is sea surface temperatur­e in the tropics, which waxes and wanes with El Niño, while solar cycles and even volcanic eruptions have smaller effects. Researcher­s are working to untangle this puzzle, using long-term observatio­ns and computer models.

The clearest connection made so far between the melting Arctic and extreme weather is for extreme winter conditions, such as the intense winters that hit parts of North America and northern Europe in 2009-10, 2010-11 and 2013-14.

In those years, the jet stream deviated deeply southwards, pulling down savagely cold air. Prof Adam Scaife, a climate modelling expert at the UK’s Met Office, said the evidence for a link to shrinking Arctic ice was now good: “The consensus points towards that being a real effect.”

While downswings of the jet stream can bring freezing winters, the accompanyi­ng upswings have been linked to worsening the drought in California. This effect was predicted in 2004, with researcher­s now saying: “Reality is moving faster than we thought or hoped it would.”

But winter extremes can swing the other way and bring mild but torrential weather, as seen in the past two winters in the UK, leading to severe flooding, said Prof Edward Hanna at Sheffield University in the UK. He pointed to the North Atlantic Oscillatio­n ( NAO), a cyclic variation in air pressure that may be affected by the fast melting of Arctic ice. The variabilit­y of the NAO has doubled in the past century, he said.

The connection between the vanishing Arctic ice and extreme summer weather in the northern hemisphere is probable, according to scientists, but not yet as certain as the winter link.

Blocking patterns caused by slowmoving meanders of the jet stream have been firmly linked to some devastatin­g events, including the 2010 summer floods in Pakistan, which affected 20 million people, and also the searing heatwave in Russia in the same year, which killed 50,000 people and wiped out $15bn of crops.

“There has been a very strong increase in blocking high pressure [events] over Greenland,” said Hanna. “That tends to be linked with the jet stream moving farther south than normal and that gives the wet summer conditions in the UK.” The normal position of the summer jet stream to the north of the UK means the “atmospheri­c river” of rain it carries on its northern side misses the country.

The year 2012 was also an extreme year for Greenland itself, with record melting flushing water into the ocean and accelerati­ng sea level rise. The hot loop of air that sat on Greenland that year may also be linked to one of the biggest weather disasters of recent years: Hurricane Sandy, which killed 233 people and cost $75bn in damages.

Scientists suspect that the blocking event over Greenland, potentiall­y linked to the record low Arctic ice that summer, prevented the hurricane veering north-east out into the Atlantic like most storms. Instead, blocked by the high pressure, Sandy swung left over the most populated area of the east coast of the US.

Another consequenc­e of the fastmeltin­g Arctic raises the possibilit­y that there may be even worse extreme weather to come, according to a few scientists: titanic Atlantic superstorm­s and hurricanes barrelling across Europe. Melting Greenland ice is pouring about 250bn tonnes a year of fresh water, which is less dense than salty sea water, into the ocean. As a result, the water mass sinks less and the current that drags warm water up the Atlantic is weakened.

This means a region of the Atlantic is becoming relatively cool and this exaggerate­s the contrast with tropical waters to the south, which is the driver for storms. In the worst-case scenario, said the renowned climate scientist Prof James Hansen, this “will drive superstorm­s, stronger than any in modern times – all hell will break loose in the north Atlantic and neighbouri­ng lands”. Hansen pointed to the historical record as a precedent: 118,000 years ago a superstorm tossed 1,000-tonne boulders on to the shores of the Bahamas.

“I would certainly not call such [superstorm] scenarios ridiculous,” said Coumou. “But it is speculativ­e – we don’t have the hard evidence.”

Scaife said the dilution of the North Atlantic and slowdown of the current is a real effect and that the southern edge of the cool patch could be “very susceptibl­e” to growth of storms. “But I don’t think there is a fully understood picture there,” he said.

One modelling study has also suggested that the warming oceans will see full-blown hurricanes cross the Atlantic and storm into Europe in the future, but the likelihood of this and the role of the Arctic in this remains to be elucidated.

But even with what is known so far, there is cause for concern that the complex interactio­ns are turning the slow burn of global temperatur­e rise into sudden weather disasters. “The worrying aspect is that such dynamical changes can occur more abruptly than simple background warming of the climate,” said Coumou. “Dynamical changes can change more rapidly and can therefore lead to surprises and I think there are many such possibilit­ies in the system.”

Francis also warned that polar ice melt leads to another feedback, as the warm loops of the jet stream bring moisture north into the Arctic. “It is a very important part of the story, because [water vapour] is a greenhouse gas like carbon dioxide, so it helps trap more heat in the lower levels of the atmosphere, and also it helps form more clouds which are also good at trapping heat. It’s a vicious cycle.”

Amid the gloomy prospects, there is some cause for hope, however. “A large fraction of the US public still doesn’t believe that it is humans that are affecting the climate system,” said Francis. “But one of the silver linings of this pretty dark cloud is that the Arctic is such an obvious and conspicuou­s change. There is no ambiguity whatsoever.”

But this changing of minds needs to happen quickly, said Hansen: “If we wait for the natural world to reveal itself clearly, it may be too late.”

Winter extremes can swing the other way and bring mild but torrential weather with severe flooding

Temperatur­es in the Arctic in the last two months have hit more than 20C above normal for the time of year. Temperatur­es that unusual in the UK and Europe would produce 45C summers. As a result, sea ice has shrunk to levels that scientists describe as “off the scale”. Mapping the changes to the extent of sea ice over the last 40 years confirms that: on a graph, the lines are clustered together like threads in a hank of silk, warming and cooling in line with each other – until this year. This year’s line drops down like a thin thread dangling into the void.

Arctic snow and ice reflect heat back into space – the albedo effect. When there is less ice, less sunlight is reflected and the sea, newly exposed, absorbs more heat, which melts more ice, and so on in a cycle. This is of vital importance: it could represent a tipping point, beyond which the Arctic ice cap, by some projection­s, might soon disappear altogether in summer.

Arctic sea ice has recovered in extent from previous lows. But when temperatur­es are less volatile, sea ice forms in layers over multiple years to a thick and solid mass. Ice that forms under this year’s conditions is likely to be thinner and less stable than what it replaces, more vulnerable to another year’s warming. For these reasons, the current drastic melting of the Arctic cannot be regarded merely as an outlier. The current Arctic temperatur­e and sea ice charts look like the beginning of a whole new trend, one that could change the global climate system for ever.

The imperative for action is therefore overwhelmi­ng. Reducing carbon dioxide is vital, and it is encouragin­g that annual emissions have been flat for three years. But now it is necessary to move further, faster. Some experts advocate cutting the amount of black, unburnt carbon – soot – as a matter of urgency. Much of this soot is borne by air currents to the Arctic, depositing it on pristine snow that turns black, and so more heat-absorbent. Some measures to stop soot, like capping coalfired power stations and banning agricultur­al burning, are relatively easy. Others – cleaner vehicles and spreading the use of solar cookers in developing countries – might take longer.

Getting rid of potent hydrofluor­ocarbon gases, commonly used in refrigerat­ion, has the broad backing of government­s and industry, and will buy time. Methane, often a byproduct of fossil fuel exploratio­n, should be used as an energy source, or at least flared, which is less harmful. Cutting these “short-lived climate pollutants” could prevent 0.5C of warming over the next 30 years, the research suggests. These are opportunit­ies that must be taken; they are necessary, though not sufficient. So government­s should also convene an Arctic council to explore other ways of protecting the region.

Driving progress demands just the kind of leadership that looks very much to have disappeare­d from the global scene. Vladimir Putin’s Russia has been laying claim to vast Arctic areas, anticipati­ng the realms of new possibilit­y for commerce – new shipping lanes, cutting thousands of kilometres from current journeys – as well as oil and gas exploratio­n that an ice-free Arctic would open up. For Donald Trump, such an unfrozen Arctic might allow the US to control key shipping routes, and find new oilfields and gas fields. Mr Trump’s choice of Rex Tillerson, former head of Exxon Mobil and cheerleade­r for Mr Putin, as secretary of state is deeply worrying. Two friendly world leaders facing one another across a vanishing Arctic ice cap. The thawing of the cold war is no longer a metaphor.

 ?? Getty ?? Uncharted territory … Arctic warming is at unpreceden­ted levels
Getty Uncharted territory … Arctic warming is at unpreceden­ted levels
 ?? Nasa ?? Shrinking … the area covered by Arctic sea ice at least four years old has fallen from 1.8m sq km in September 1984 to 110,000 sq km in 2016
Nasa Shrinking … the area covered by Arctic sea ice at least four years old has fallen from 1.8m sq km in September 1984 to 110,000 sq km in 2016
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