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Climate change: "Venice will definitely go under"

2019-11-19T04:52:38.710Z

Can Venice be saved from the sea? No, says climate researcher Anders Levermann after the record flood. Her downfall is only a matter of time.




Café chairs as a breakwater on St. Mark's Square: For the third time in a few days, the level increased over 1.50 meters.
Elsewhere in town, the water is not much higher than a double espresso in the cup. Since you can between two attractions ever break while sitting down.
Silent water, knee-deep: After the third tidal wave, St. Mark's Square was closed again on Sunday for safety's sake.
A mobile bridge will allow locals and tourists to cross the square despite "acqua alta".
With plastic covers over the shoes, it goes over the Behelfssteg carefully.
A weather where you carry your dog out the door. Behind the heavy rains and the strong wind, which together are responsible for the flood, not only Venice's mayor suspected the effects of climate change.
Panini, Pizza, Spritz: The light is on, the little restaurant has opened despite the flood.
Through a hose, water from a flooded building is pumped onto the street.
The people in the streets of Venice wear rubber boots, Botticelli's Venus a pair of diving goggles.
In museums and other buildings, valuable items such as these musical instruments are brought to higher floors to protect them from the water. Bound books stand upright and fanned out to dry better.
Guests of this hotel can leave the building with a dry foot over a bridge - but what then?
Those who live in this hotel in Venice's Old Town must wade through the corridor to their room. Mayor Luigi Brugnaro asked for donations from abroad so that Venice could "shine again".
The question remains: is a bridge still a bridge when it ends in the water?

Slowly, the water retreats. The water level of the northern Italian city of Venice had previously increased three times to more than 1.50 meters within a week. Since records began in 1872, water has never risen so rapidly during a flood season. Venice's Mayor Luigi Brugnaro said he was convinced that climate change was partly responsible for these floods. In what way this happens, the climate researcher Anders Levermann from the Potsdam Institute for Climate Impact Research (PIK) explains in an interview.

ZEIT ONLINE: Mr. Levermann, every autumn there is a flood in Venice, the Acqua alta . That is normal. Now something seems to change. To what extent does climate change really matter?

Anders Levermann: Of course, if climate change has certainly intensified the extreme flooding in Venice this year, we as scientists can only say that we have compared this event with many, many similar events - that is, only through statistically significant calculations in a few decades. Acqua alta , however, is a combination of precipitation and wind phenomena, along with the tidal range: between fall and winter, when rainfall is high, the tidal range pushes more water into the Venetian lagoon. Based on the power of physical laws, we can say that in the future we will experience extreme weather events like this with climate change more frequently and more intensively.

Professor Anders Levermann is Head of the Department of Complexity Research at the Potsdam Institute for Climate Impact Research and was one of the main authors of the Chapter on Sea Level Rise in the Fourth Assessment Report of the IPCC. © PIK / Karkov

ZEIT ONLINE : How exactly could climate change make acqua alta worse?

Levermann: The warmer we make the planet, the more powerful the heavy rainfall and the higher the sea level. All of this may have intensified the flooding in Venice. In this case, another factor could have been added: the jetstream.

ZEIT ONLINE: These are powerful air currents that pull in the northern hemisphere in kilometers of wind turbines from west to east and the weather worldwide. Do they behave differently than before due to climate change?

Levermann: Yes, with global warming, the jetstream is coming off its original course and is probably starting to wobble more and more - it meanders. A look at the current course of the stream shows that the winds do not blow from west to east, as they usually do north of Italy, but that they have made a slight break under Europe and are moving from south to northwest in Italy. Thus, the local winds that trigger Acqua Alta may have been amplified by the jet stream - normally they tend to counteract it.

Stefan Rahmstorf, one of my colleagues at the Potsdam Institute for Climate Impact Research, has published a current, automatically generated graphic for the Jetstream in a tweet:

The automatic jetstream analysis of the Potsdam Institute shows how the current makes a loop south over the Mediterranean before flowing north against the Alps. pic.twitter.com/JBouQN4MQ0

- Stefan Rahmstorf (@rahmstorf) November 18, 2019

This also implies a possible connection between climate change and the currently very heavy snowfalls in Austria. Exactly so could there be a connection with the high water in Venice. Whether that is true, but must be examined in more detail.

TIME ONLINE: Venice is not built on stilts for nothing. Since its construction, the city defies the tides. What about Venice when sea levels continue to rise?

Levermann: For every degree that the Earth is warming, according to our calculations, which IPCC has taken on board, we will see a sea level rise of about two and a half meters. Although this happens very slowly - possibly within hundreds of years - it also means: In the long run, Venice will be under the mirror of the oceans. If we kept the 2-degree target of the Paris Climate Agreement, we would have to expect about 5 meters sea level rise in the long term. Venice will definitely go down. Large coastal cities such as Hamburg, Shanghai, Hong Kong and New York would also have to adjust to the fact that then large parts are meter-wide below the sea level.

ZEIT ONLINE: That Venice and many other cities have to cope with a rising water level, has long been certain. What did the city do to arm yourself?

Levermann: First of all: In the past, Venice has additionally lowered itself by pumping out drinking water from the ground. The problem was already recognized a few decades ago, meanwhile that does not happen anymore. There are also efforts to protect the entire lagoon from flooding. For example, with specially built retractable walls to stop the water in the future ( see video below ). But we will not stop the ocean from taking up more space when it heats up. A city like Venice has an expiration date as the sea level rises. Unless we find a fundamentally different way of adapting - like raising a whole city a few meters. As far as I know, there is still no solution in the event that a megacity such as Shanghai gets below the global sea level.

ZEIT ONLINE: Until then, how well can such flood events as now in Venice predict? How much sooner can people adapt to it?

Levermann: Flood warnings come with the weather forecast, not much earlier than a few days. And even here it is always possible that the weather turns out much worse or milder than predicted. Weather models must increasingly incorporate global phenomena. The colleagues have accepted the challenges that arise with the change in the global climate - a good example is the already mentioned changed behavior of the jet stream. This makes the life of weather experts much harder and is one reason why we are so bothered by the increasing extreme weather events.

ZEIT ONLINE: Venice is a UNESCO World Heritage Site. Numerous historical buildings, museums, bridges and monuments adorn the city: How much are these and other cultural treasures already in danger?

Levermann: The fact that climate change is threatening Venice and comparably valuable sites has been a long-standing phenomenon. In 2014, I summarized with a colleague at the University of Innsbruck in which countries a loss of land area is to be expected as the sea level rises and which UNESCO sites would be affected ( Environmental Research Letters : Marzeion & Levermann, 2014). We have created a list that - if we look at Italy alone - would not only affect Venice, but also the historic center of Naples or the Piazza del Duomo in Pisa. An increase in global temperatures by three degrees would endanger every fifth Unesco site in the long term. The only way to really limit the rise of the oceans is to stop burning coal, oil and gas.

Climate change - What if we do nothing? Forest fires, ice melt, storms: Man feels the global warming. What's the future like? Climatologist Stefan Rahmstorf explains our world 4 degrees more.

Source: zeit

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