All countries experience extreme weather

The weather - more and more extreme?

For Nashville, Tennessee, the forecast is 50 to 100 liters of rain per square meter over the weekend. So people are prepared for uncomfortable weather. But when on Saturday, May 1st 2010, more than 150 liters had already fallen by noon, the situation became threatening. And it continues to pour like buckets.

In the city's emergency center, Mayor Karl Dean is looking through the first reports of floods when his eyes fall on a television screen. Live broadcast of the water from a tributary of the Cumberland River flooding the highway in the southeast of the city and rushing up on cars and trucks. Then a school drifts by on the hard shoulder: the Lighthouse Christian School, a twelve-meter-long mobile building. "A house rams cars," reports the news anchor. Dean has been in the emergency room for hours, but it's the sight of it that makes him realize what's really going on out there. Police, fire brigade and rescue workers set off in boats. They are bringing rooftop families and workers out of flooded warehouses.

By Saturday evening, the Cumberland had risen by four meters, the experts warn that the level could even reach seven meters. But the rain doesn't stop on Sunday either. The river does not reach its peak until Monday - another three meters above the predicted peak height, four meters above the high water mark. The floods cause $ 2 billion in damage to downtown Nashville. Eleven people are killed in the flooded city this weekend.

When the sun came out on Monday morning, in some parts of Nashville, more than 340 liters of rain fell on every square meter of ground. The record up until then was set by Hurricane "Frederic" in 1979 - with 167.5 liters.

Brad Paisley, a nationally known country singer and guitarist, lost all of his touring equipment in warehouses on the river: "All amplifiers, all guitars, the large video system - all over." The experience shocked him: “I always thought weather is weather, you can deal with that. But since that flood, I think anything is possible. Never before have I felt so powerless against the weather. " Paisley is in good company around the world.

The weather has changed. Extremes like the Nashville floods - classified by experts as a millennium event - are more common today than they used to be. The Elbe flood of 2002 is unforgettable in Germany: In Zinnwald in the Ore Mountains it rained 312 liters within 24 hours, more than had ever been measured before. In July 2008, parts of Dortmund's city center were devastated when more than 200 liters of water per square meter fell in just four hours. One month before the Nashville flood, torrential downpours dumped 280 liters of rain over Rio de Janeiro in 24 hours; the landslides caused by the water buried hundreds of people under them. Three months after Nashville, record rainfall caused flooding in Pakistan, affecting more than 20 million people. And it wasn't until the beginning of July this year that 170 people in southern Russia lost their lives in one day in extreme rainfall of more than 230 liters locally.

But it's not just heavy rain that makes the headlines. Unprecedented droughts have plagued Texas, Australia, Russia and East Africa for the past decade. According to the latest estimates, up to 70,000 people died in a heat wave across Europe in 2003. 2006 was followed by the hottest July in Germany since weather records began. The USA has kept new tornado records since 2000. With historic droughts, floods and heat waves, the past year was a time of never-before-seen nasty surprises. “2011 will be remembered as a year of extreme weather phenomena, in the USA and in the rest of the world,” says Kathryn Sullivan of the US Agency for Weather and Marine Research (NOAA). In July she presented a study in Washington, according to which 2011 was the most turbulent weather year in the past three decades. Worldwide, weather-related damage rose to an estimated 120 billion euros in 2011, 25 percent more than in the previous year.

What's going on there? Are these signs of a dangerous, man-made change in the world's climate? Or are we just going through a series of bad weather? The short answer: probably both.

The main causes of the recent disasters have been natural climatic phenomena, particularly El Niño and La Niña, two recurring current events in the Pacific. During an El Niño, a huge supply of hot water shifts from the central Pacific in an easterly direction to South America. Heat and steam rise from the warm water; the result is strong, high-reaching thunderstorms. They influence the weather far beyond the tropics to the temperate latitudes. An El Niño causes rainy storms over the southern United States and Peru, but leads to drought and bushfires in Australia.

El Niño is mostly replaced by its cool sister, La Niña. When it dominates, the air currents change in such a way that the rain floods parts of Australia while it does not occur in the American Southwest and Texas. The droughts will then intensify even in regions that are even further away, such as East Africa.

Such consequences are not inevitable because the atmosphere and ocean are chaotic water reservoirs and local factors also determine the weather at any point in time and in any place. The tropical Pacific, however, has a major impact, as it pumps huge amounts of heat and water vapor into the atmosphere. That is why strong El Niño or La Niña events create the conditions for extreme weather elsewhere as well. However, you alone cannot explain the series of record catastrophes in recent years. Something new has been added: the earth is heated up and the moisture content of the atmosphere rises.

Decades of measured data from thousands of weather stations, satellites, ships, buoys, deep-sea probes and balloons mean that there is no longer any serious doubt that the greenhouse gases generated by humans retain a greater proportion of the heat radiated by the sun in the atmosphere. Worldwide, the average temperature on the earth's surface has risen by half a degree since 1970, much more so around the poles, where the ice is thawing faster and faster.

Warmer oceans release more water vapor into the atmosphere. "If you turn on the stove, the water in the pot evaporates faster," explains Jay Gulledge, scientist at the Center for Climate and Energy Solutions (C2ES), a private think tank in Virginia. The amount of water vapor in the atmosphere has increased by four percent in the past 25 years alone. And the more water vapor the air contains, the greater the risk of heavy precipitation.

By the end of this century, the average temperature in the world of our children and grandchildren could rise by 1.5 to 4.5 degrees, depending on how much oil, gas and coal we still burn by then. Then, so say experts, the weather will change significantly. In the direction of the poles it will be warmer, many plants and animals will follow their preferred climates. The tropical rain belt is already getting wider today. The subtropical arid regions on both sides of the equator move north and south and reach areas such as the southwest of North America, South Australia and southern Europe. High temperatures and long, intense periods of drought are more likely here. As early as this summer, people in Greece and Bulgaria were moaning about temperatures above 40 degrees. The patterns of extreme rainfall and hot days will also intensify in the temperate latitudes where Germany is located.

The Arctic Ocean is one of the greatest unknowns in forecasting future weather. In the past few years it has lost 40 percent of its summer ice cover. The autumn temperatures over the now open sea have risen by two to five degrees because the dark water absorbs sunlight - the ice that used to be there had reflected it into space. New findings suggest that the warming also shifts wind currents around the poles. That could explain why it was so warm in North America and so cold in Europe in winter 2010/11. Here air masses from Siberia penetrated unusually far into Western Europe.

Today, researchers are least able to say how global warming affects the development of individual storms. In theory, more water vapor in the atmosphere should also pump more heat - and therefore energy - into hurricanes, typhoons and similar weather phenomena. According to some calculation models, the average strength of hurricanes and typhoons could increase by up to 11 percent by 2100. But the same models that predict stronger hurricanes in the future say at the same time that their number could decrease.

The picture is still completely unclear for the tornadoes. A hotter, more humid atmosphere should actually favor heavier thunderstorms, but it could also mean that the conditions for the formation of such vortex tubes are less good. It is true that tornadoes are being reported more and more frequently - not only in the USA, but also in Europe. On the other hand, there have never been so many people with cell phone cameras who never miss a hurricane. It has not been proven that the number of severe tornadoes actually increased. And even if the spring of 2011 was one of the worst tornado phases in US history, with monster eddies in Alabama and Missouri, among others, scientists so far have neither the data nor the theories with which they could establish a connection to global warming.

At other extremes, however, this is clear. The warmer the atmosphere, the greater the potential for heat waves. In 2010, new national temperature records were set in 19 countries around the world. And of course the amount of rain increases with the moisture content of the atmosphere. "A storm brings more rainfall today than it did 30 or 40 years ago," says Gerald Meehl, a scientist at the state center for atmospheric research in Boulder, Colorado. For him there is little doubt that the likelihood of extreme weather events has increased due to global warming. "You can compare it to a baseball player who is doped with hormones," explains Meehl.

“If he hits the ball well with his bat, it's impossible to tell whether he succeeded in this particular case because of the hormones. However, the doping agent increases the likelihood that he will hit the ball well more often. " Likewise, says Meehl, be it with the weather: “Greenhouse gases are the hormones of the climate system. If you inject more carbon dioxide, everything gets a little warmer and the likelihood of extreme events increases. What was rare in the past is less rare at some point. "

In recent times no one has seen doped weather more often than Texans. For example the residents of Robert Lee, a small town in western Texas. In 2011 they had to watch their water supply dry up. Like many other reservoirs in the region, their local reservoir also lost more than 99 percent of its content.

In January, the community therefore began building a 19-kilometer pipeline to Bronte, a place that also gets its water from wells. "We hope that we will be ready in time, before our taps run out," said Mayor John Jacobs in May, "but it will be running out."

From October 2010 to September 2011, Texas had less rain than any other 12 month period since weather records began in 1895. In many places, the water level fell below the reach of the pumps. The drought is causing pastures to wither and forcing some livestock farms to move their herds north to greener areas. However, today it is not cowboys who drive the cattle across the country on horses. Workers at the Four Sixes Ranch, for example, loaded more than 4,000 Angus cattle onto two-story trucks and drove them to leased pastures in Nebraska and northern Montana.

“It was more than 100 years ago that the“ Four Sixes Ranch ”last had to do something like this,” explains operations manager Joe Leathers. At that time, the ranch moved its herds to Oklahoma. But this time the drought was worse. In July of last year, the ranch even ran out of water in its tanks - precious drinking water that had been used to fill dry ponds in the pastures so that the cattle could drink. "Nobody has ever seen anything like this before," says Leathers.

"It was the most pronounced annual drought of all time," confirms the official climate expert John Nielsen-Gammon. In addition, the Texans suffered from the hottest summer in their history in 2011. In Dallas, the mercury climbed to more than 37 degrees Celsius on 71 days.

The main cause, says Nielsen-Gammon, was La Niña. The cooling of the Pacific caused the rain-bringing thunderstorms to shift far north over the USA. In the south there was no precipitation - in a band from Arizona in the west over Texas to North Carolina on the east coast. But without global warming, La Niña would not have had such dramatic consequences.

It was the reason that a strong heat wave was intensified again. Nielsen-Gammon explains the mechanism as follows: “Normally, a large part of the incident solar energy is released up again when the water evaporates from the soil or the plants. But when there is no more water to evaporate, the heat remains in the soil and then heats the air. Given the low rainfall, we would probably have had record temperatures in Texas last year even without climate change. But global warming has probably added another degree. "

This additional degree increased evaporation and made the land even more dry. "During a drought," says Nielsen-Gammon, "even a small increase has a big impact." For the forests it was like a shot of gasoline in an open fire: Texas experienced the worst forest fire season in living memory in 2011. Together, the fires reduced an area larger than Schleswig-Holstein to rubble - more than twice as much as in the worst year to date.

One of the most expensive fires broke out southeast of Austin in September 2011. The frankincense pines there were dry as tinder. Strong winds swept the flames over residential areas on the outskirts; 1685 houses burned down. The firebreak was so sharply delimited that owners of spared buildings only shook their heads in disbelief.

That's what happened to Paige and Ray Shelton. When they drove out to check on their estate on the state forest border, the sawmill Ray was running was just a pile of ashes, and Paige's ceramics workshop had burned to the ground as well. But her bungalow was still there. Then Ray Shelton walked over to the chicken coop. All around the trees were black. Shelton feared the worst, but “as I got closer, the rooster stuck its head out and crowed. I just couldn't believe it ». The flames were within inches of the barn, but for some reason the Virginia juniper wood walls hadn't caught fire, and the birds - five hens and 18 pigeons - had survived the heat and smoke, a small miracle in the midst of it great destruction.

In the same summer, forest fires raged in a similarly devastating manner on the other side of the world, in Russia. In June, the civil protection ministry announced that more than 6,000 square kilometers of forest and moor were on fire - almost three times as much as at the same time last year. According to a report by the news agency, "11060 sources of fire have emerged" since the end of winter Novosti a consequence of the extreme drought in summer and early autumn 2010. The forest and peat fires hit 199 villages, 62 people were killed, 3200 houses were destroyed by fires. The total damage by the end of summer was more than 12 billion rubles (300 million euros). In October there was a second wave of forest fires, which killed another 30 square kilometers of forest.

However, the increasing damage from natural disasters can only be partially attributed to the weather. Another cause is that more and more people are living in disaster-prone regions. In Texas, Arizona, and California, housing developments are being built in wooded areas, and more and more beach villas and hotels are being exposed to hurricanes along the coasts of Florida, North Carolina, and Maryland.On the outskirts of large cities in booming countries such as Brazil and India, new residential areas are threatened by landslides after heavy rain, and millions of people are also settling in the fast-growing giant cities of developing countries in Asia and Africa, constantly at risk from heat waves and floods.

But instead of preparing for the foreseeable consequences of climate change, those responsible maneuver their way from catastrophe to catastrophe without much foresight. "To put it brutally: When it comes to preparing for the coming disasters, we are doing damn badly," says climate researcher Michael Oppenheimer, co-author of a recent report by the Intergovernmental Panel on Climate Change (IPCC) on extreme weather.

In any case, the insurance industry is alarmed. Extreme weather events made 2011 the year with the highest losses from natural disasters to date. Worldwide, the losses - excluding earthquakes and tsunamis - totaled more than 100 billion euros, reported Munich Reinsurance in January. “Whether this is the“ new normal ”or not, the insurance industry recognizes an extraordinary regularity in the damage,” says Frank Nutter of the American Reinsurance Association.

In Florida, where hurricanes, forest fires and drought pose enormous risks for insurers, some established insurance companies no longer issue new policies at all. Small new companies are filling in, and in 2002 the government founded the Citizens Property Insurance Corporation, which has now become the largest provider of home insurance in Florida.

It remains to be seen whether the new system actually has sufficient funds to financially cover a major storm. The test case could occur if a storm like Hurricane “Andrew” raged again. In 1992, it caused damage of the equivalent of 20 billion dollars.

Elsewhere, governments have taken initial steps to better prepare for extreme weather. After the heat of the summer of 2003 in Europe, French cities built air-conditioned lounges and the elderly were registered to be taken there in an emergency. When a heat wave hit France again in 2006, the number of deaths there was two-thirds lower. In Germany, the German Weather Service set up a heat warning system that automatically informs municipalities and hospitals when a phase of threateningly hot days is looming.

In Bangladesh, too, the government developed an early warning system and built concrete shelters for evacuated families. As a result, hurricanes mean that significantly fewer people are killed there.

The risks could be reduced further: with crops that can withstand drought better, with buildings that can withstand floods and storms, with policies that discourage people from building in endangered locations - and, of course, by generating fewer greenhouse gases .

“We know that the warming of the earth's surface causes more water vapor to get into the atmosphere,” says climatologist Jay Gulledge. Therefore the probability of extreme weather only develops in one direction: upwards. "We have to accept this reality," adds Michael Oppenheimer. And then do everything possible to save lives and prevent damage. "It would be wrong to just wait and see what happens."

(NG, issue 09/2012, page (s) 38 to 57)