OCEANIA AND GLOBAL WARMING(I)

Unnatural Disasters

We should expect more potentially deadly avalanches to come, and also more frequent, and fiercer, volcanic eruption and earthquakes.

On the night of 13 December 1991, a group of climbers had gathered in a hut on New Zealand's highest peak, Mount Cook, in preparation for an attempt on the summit. The ascent would mean risking their lives, but that threat was nothing compared with what was about to come. Shortly after midnight, 12 million cubic metres of rock and ice crumbled from the peak and roared down the east face of the mountain, travelling at over 200 km per hour for more than seven kilometres before plunging to the valley floor. The cataclysmic rock avalanche narrowly missed the hut, leaving the stunned climbers safe, but awed. "Essentially, the top of Mount cook fell off - which is incredible," a mountaineer told TVNZ at the time. The group had a very lucky escape from what on the face of it was an act of God - a purely natural disaster.

But was it? A few analysis suggests that climate change may have helped to trigger this avalanche, as well as others in different parts of the world. given current projections of even warmer temperatures into the future, some scientists are now warning that we should expect more potentially deadly avalanches to come, and also more frequent, and fiercer, volcanic eruptions and earthquakes.

Until recently, the idea that current and future climate change could ramp up these sorts of geological hazards wasn't well appreciated. Climate scientists have until now been focussing on the atmosphere and the hydrosphere, most probably because those are the primary areas of interest for most of them. Now Earth scientists are starting to become involved in the study of future climate impacts - and they are bringing with them a knowledge of how past climate change has triggered a response from the Earth's crust. Scientists led the new work on the 1991 Mount Cook avalanche, and on four others that happened recently in Alaska and the European Alps. The scientists painstakingly analysed the meteorological conditions in the weeks leading up to the disasters and found that all had one thing in common: each of the avalanches was preceded by an unusually warm period.

For Mount Cook, between 1960 and 1990, the average year-round air temperature at the summit was -7.87 deg C. In 1991, the winter was particularly cold, then, in November and December, the summit temperature regularly rose above zero. Next came a cooling, which brought temperatures to below seasonal averages. But in the week immediately before the avalanche, the summit warmed again, with temperatures on December 11 soaring to 9.7 deg  - about 8.5 deg C above the long-term average for that date. The ice on the summit began to melt in earnest. Then 24 hours before the avalanche, the temperature plummeted below freezing. The unusually warm conditions melted more snow and ice than normal, causing relatively large amounts of water to leak through clefts and joints into the rock.

 

Then the plunge in temperature suddenly froze this water, making it swell and forcing some of the rock to break away. The team also analysed avalanches and landslides on Mount Steller in Alaska in 2005 and 2008, and on Mount Miller, also in Alaska, in 2008, and on Mount Miller, also in Alaska, in 2008, as well as on Monte Rosa in the Swiss Alps, in 2005 and 2007. They found that while the precise temperature patterns before each event varied, the weeks or days before were unusually warm.

 

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Several studies have found that during the 20th century, there have been more unusually warm periods, such as summer heat waves. In the past two to three decades, there has also been an increase in the number of large avalanches and landslides in some high-altitude regions, such as the peaks of the European Alps. They can never say that a particular event would not have happened even without global warming but the rising incidence of large rock and ice avalanches in Alaska and the Caucasus, together with an increase in rock-falls in the alps and elsewhere, is just what would be expected to be seen as the world warms. Since climate models suggest that warmer periods will become up to four times more common in the next several decades, this means we are likely to experience more avalanches. The main concern is very large events - like those in Alaska - will occur in more populated regions, like the Swiss Alps and it is rather likely that the probability for this will increase - but we cannot quantify it. Mountain regions are particularly sensitive to climate change because melting snow means less heat is reflected back towards space and more is absorbed. In fact, temperatures in the European Alps have been rising at double the rate of the global average since the late 19th century. Recent studies show that the permafrost in the European Alps has warmed by between o.5 and 0.8 deg C in the upper tens of metres during the 20th century.

 
Scientists and researchers have also studied avalanches, as well as rock-falls, landslides and floods in the European Alps during the 2003 heatwave - when temperatures in Central Europe were the hottest in 500 years - and 2005 summer floods, which caused the most catastrophic flood damage in the region in the last 100 years, battering central and eastern parts of the continent and closing many mountain passes in Switzerland and Austria. During the 2003 heatwave, the tem found permafrost and warmed even in high alpine areas, weakening the rock, and helping to trigger rock-falls and landslides, including a large rockfall on the iconic Matterhorn in Switzerland.
 
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It is tricky to use climate models to predict what will happen to mountain hazards, partly because the models don't work well for regions with big surface feature variations - such as mountain ranges - but warming permafrost seems very likely to mean more landslides, and what we do know is that landslides and related creatures, such as debris flows, usually start at the interface between 'warm' and 'cold' permafrost. As the area of 'warm' permafrost spreads, so will the places where the landslides are triggered. This response will play out over the coming decades. But if warmer temperatures increase the risk of avalanches, landslides and rockfalls, they may also boost the chances of another potential catastrophe: earthquakes.
There is compelling evidence that melting of ice during the last de-glaciation triggered a burst in volcanic activity.
 
STEP BACK IN TIME 9,000 years, and the geological record shows that Scandinavia was experiencing a flurry of earthquakes. Yet today, there are few. Researchers wondered why. When they looked into past conditions in the region, it was realised that the surge in quakes coincided with the melting of a massive ice sheet that had covered the area during the last ice age. Suspecting a link, a team of researchers used a computer model to investigate what being buried under several hundred metres of ice can do to geological faults. They found that a massive weight of ice can stop these faults from slipping, and so keep a lid of quakes. But the stresses in the ground continue to build up. When warming temperatures cause the ice to melt, the pent-up energy is released, unleasing stronger quakes, and more of them. Historicala records from some other regions of the world, such as the Yellowstone ice cap in the U.S., show a similar pattern to that in Scandinavia - large ice caps, glaciers and even lakes can suppress quakes, but if this weight vanishes, there's s surge in them. The idea that melting glaciers have altered the pattern of physical load on the planet - reducing it where the ice has melted, and increasing it where the sea level rises - and that this might influence earthquake activity is a reasonable one. The idea is that the same thing will happen with climate change resulting in removing loads from glaciers and adding load to the ocean. And that's a reasonable thing to propose.
 
 
The glacier-covered summit of Mount Cook, New Zealand, in 2006
 
Many glaciers around the world are now receding. By 2000, the alpine glaciers shrank to almost half their volume compared with 1850, In January 2010, a report was published saying that glaciers around the world are melting so fast that many will be gone by the middle of this century. The latest date for 2007-2008 on 96 glaciers found that, on average, they thinned by nearly half a metre. The most vulnerable are those in lower mountain ranges, including the Alps, Pyrenees, North American Rockies and parts of the Andes. It's difficult to predict, though, what the removal of a given weight of ice will do to earthquake activity in various parts of the world in the future. Although evidence of large earthquakes associated with the Late Pleistocene de-glaciation wee found in Scandinavia, evidence of only small and moderate earthquakes were found in northern Canada, where the ice changes were even larger. However, there is evidence that climate change may already be triggering earthquakes in Alaska.
 
Alaska is a great place to look for evidence linking melting glaciers to earthquakes, because the ice cap is directly above a shallow quake zone, caused by the movement of the pacific-Yakutat plate beneath continental Alaska. The frequency of small quakes in the Icy Bay region increased between 2002 and 2006, compared with the recent past - and they suggest that this is down to a significant increase in ice loss in that period. Warming temperatures might also mean more quakes for Greenland and Antarctica, the models suggest that the massive ice sheets in these regions are suppressing local seismic activity. But they are melting. According to a study by a tem at the University of California, for example, different glaciers in Greenland are losing between 0.7 and 3.9 metres of ice each day from underneath. This means we could see more small quakes in these two regions as soon as in the next 10 to 100 years. And melting glaciers seem likely to trigger yet another, perhaps even more surprising, danger: more, and more explosive, volcanic eruptions. About 130 km west of Bogota, in Colombia, lies the Nevado del Ruiz volcano. It's the northernmost volcano in a group known as the Andean volcanic Belt, which forms part of the notorious Pacific Ring of Fire.
 
On 13 November 1985, Nevado del Ruiz erupted. It was relatively small, as eruptions go, scoring only three out of eight on the volcanic Explosivity Index. But it unleashed four deadly lahars - mixtures of mud and debris - that careened down the sides of the mountain. They buried the town of Armero and struck the town of Chinchina, killing more than 23,000 people in total, and going down as one of the deadliest in history.
"We have to face the fact that unmitigated climate change is going to be catastrophic."    
 
The summit of Nevado de Ruiz, like those of the other mountains in the Los Nevados Natural National Park, is topped by large glaciers. A hundred years ago, the ice covered an area of about 100 km. By the end of the 1950s, warmer air temperatures had reduced it to about 34 km. Could the melting ice have had anything to do with the eruption? Some scientists think it is possible - and that melting glaciers could boost volcanic activity in other regions too. As with earthquakes, there is a good historical basis for the suspicion. Jump back once more to the end of the last ice age, and to Iceland. The island lies along the Mid-Atlantic Ridge, where the North American tectonic plate and the Eurasian plate are diverging from each other. This causes hot rock to well up from deep within the planet, triggering melting in the mantle region and eruptions at the surface. Work published in 2005 shows that as the country's vast glaciers melted, there were 10 times as many volcanic eruptions as there are today.
 
Since 1890, Iceland's glaciers, which cover parts of this ridge, have been thinning. Some researchers argue that, based on the historical data, the country is heading towards another period of devastating eruptions. And Freysteinn Sigmundsson of the Nordic Volcanological Centre at the University of Iceland thinks he can explain why. Sigmundsson and his colleagues have created a model of what would happen to the production of magma if the ice on top of an Icelandic volcano melted. This would reduce the downwards pressure and so, they think, increase the upwelling of molten rock towards the surface, making eruptions more frequent and more explosive. The team has looked closely at the Vatnajokull glacier, the largest in Iceland, covering 8% of the country. The ice cap is receding at a rate of about 50 cm per year, which, according to their model, will relieve enough pressure to generate significantly more magma. And this, they say, should lead to more frequent, or bigger, eruptions.
 
The 2010 eruptions of Eyjafjallajokull are very unlikely to be linked to climate change, however, the team adds, as their model suggests that extra magma produced as a result of warmer temperatures is likely to take anywhere between decades and centuries to reach the surface. In the Andes, too, it's thought likely that the melting of ice caps will increase volcanic activity. At least, the geological date suggests that this is what happened in the past, and it may be happening again. The U.S. Geological Survey Team pointed out in a paper published back in 1990, the deadly 1985 eruption of Nevado del Ruiz followed a loss of covering ice, and the same is true for other recent eruptions, like that of Villarrica in Chile in 1971, which released large mudflows caused by lava melting ice.
 
 
A heavily damaged school in Yingxiu, China,
where 80% of the town was destroyed by the 12 May 2008 earthquake.
 
But melting ice doesn't have to increase the chance of an eruption to make a volcano more deadly. Researchers have also recently studied Italy's Mount Etna, the largest active volcano in Europe, and one of the most active in the world. since historical records began, a massive five by eight kilometre portion of the volcano's eastern flank has been missing. Based on their analysis of samples from the site, the team concludes that this portion collapsed 7,500 years ago, when the climate became wetter, as well as warmer. They think that heavy rainfall destabilised the structure of the volcano, triggering its partial disintegration. And some regions of the world, including the eastern parts of South America, are predicted to get even wetter as a result of climate change.
 
THANKFULLY, SUCH AN EXTREME scenario isn't likely. While the historical data can help us understand what might happen in the future, the end of the last ice age involved a much more serious change in climate than is predicted now. The de-glaciation after the last ice age involved a very substantial change in load. Back then, the glaciers were kilometres thick, and the global sea rise associated with their melting was a little over 100m. Whereas with climate change, we're talking about glaciers that aren't as big and a change in global sea level of about one metre. So while a statistical increase in quake activity is very possible, it would be a surprise if we saw a very large increase in large quakes.
 
 
While there may be an increase in small quakes, large quakes which pose most risk to people, will still be caused by natural movement of tectonic plates. Glaciers and ice sheets on many active volcanoes are rapidly receding. And there is compelling evidence that melting of ice during the last de-glaciation triggered a burst in volcanic activity. Ice melting was massive, and it is very hard to know exactly how current climate change, and predicted ice melting, will affect the planet's volcanoes - and when. Researchers' model cannot yet reveal how quickly volcanoes will react to melting ice, or whether they're sensitive to small changes in ice thickness, or not. There is a strong potential for melting ice to increase volcanism - but much more research to better understand this is now needed.
 
More volcanic eruptions could also act against climate change. Major eruptions cause a local cooling in air temperatures, as the ash clouds block incoming heat from the sun. Indeed, mimicking a volcanic eruption by injecting sulphate particles into the atmosphere is one idea for 'geoengineering' our way out of deleterious climate change. So quite how these two processes will interact is not clear. Ultimately, an increase in volcanic activity could actually act to cool the planet - at least for a time. some climate scientists have been accused of disaster-mongering, and that critics may put the work on geohazards into that category.
 
But the risks are real that a balance has to be struck between informing people and scaremongering. We have to face the fact that unmitigated climate change is going to be catastrophic - and that the Earth's crust will certainly become a source of increased hazardous activity. The bottom line remains that global greenhouse gas emissions must now be reduced. If they are not stablised within five years or so - and the prospects for this do not look that bright - it will be almost impossible to avoid all-pervasive, devastating climate change. This will mean that we need to tackle the resulting geohazards as they occur, using a combination of education, risk communication, land-use planning - and engineering solutions.     
TSUNAMIS

Deep beneath the oceans lie monumental deposits of methane, a potent greenhouse gas. The methane is trapped in ice, and no one is sure exactly how much is down there - but about 2,000 gigatonnes of carbon (almost three times the amount of carbon in the atmosphere) could be stored in this form. warming oceans could release some of this carbon, speeding climate change and also destabilising the ocean floor, potentially unleashing tsunamis.

A global warming of 3 deg C could release about 900 gigatonnes of carbon from these 'gas hydrate' deposits, adding 0.5 deg C to air temperatures. But about 400 gigatonnes of carbon is also stored in methane trapped in permafrost - and temperature increases of more than 12 deg C are predicted for permafrost regions of North America and north Asia. Already, 100 times more methane than normal is being released from some regions of the Siberian Arctic, according to work published in 2008. Rising temperatures will also release methane from peatlands, though just how much is not yet clear. This is one of the greatest uncertainties in carbon cycle science. Thawing permafrost generally releases methane from surface soils. But if that thawing of permafrost also exposes deeper gas hydrates to release, we have a much more serious problem in terms of greenhouse gas emissions. The tsunami risk comes if gas hydrates below the ocean floor break down. These deposits can act like cement for the sediment, and if they fail, there could be massive underwater landslides.

But plumes of methane gas bubbles rising from the sea floor to the surface could pose other threats. If enough methane is released in relatively shallow water, it could cause ships to lose their buoyancy, and to flounder.

The picture of the 2004 Boxing Day Asian Tsunami captured from the balcony of the Sheraton Grande Laguna Resort on Phuket Island, Thailand. The tsunami resulted in the deaths of 225,000 people (see below).
 
 

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