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Developing plans in the midst of multiple climate uncertainties

How exactly does sea level rise on the Dutch coast? Are we really getting the summer rain for sure? And what about drought?

Global temperatures are currently rising, that is for sure. The result is very intense weather. But it is uncertain how this will play out regionally. The KNMI report was released earlier this week Climate signal ’21 That is full of uncertainties. The company translates the latest findings of the IPCC, the United Nations climate agency, into the Dutch situation. To give an example: In 2300 the sea level on the Dutch coast may have risen by 30 centimeters. But this is possible17 Meters Turns out. Uncertainties are ideal for summer rains and droughts. How is that possible? How do you, as a policymaker, deal with this uncertainty?

Roughly speaking, uncertainty exists in two respects. It is not clear how greenhouse gas emissions are generated. In addition, how climate change affects local weather processes is not yet fully understood. In any case, chance is a big element in these processes – the weather is a chaotic system. This is naturally hard to predict.

There has been a lot of discussion about future emissions in recent years. Do all the scenarios used by the IPCC still apply?

In its 2013 report, the IPCC introduced Representative concentration pathways (RCBS). Under these conditions, each path corresponds to a different warming in 2100. In the worst case scenario, greenhouse gas emissions will continue to rise this century (warming to about 5 செல் C in rcp8.5 – 2100). Of the other three paths, emissions peak at 2080 (rcp6, warming 3 ° C), 2040 (rcp4.5, approximately 2.5 C) and 2020 (rcp2.6, approximately 1.5 C). The IPCC replaced the RCPs three years ago Shared socio-economic paths (ssp’s), through which emissions are translated into socio-economic descriptions – which are highly understandable to policymakers and the general public. But they represent the same amount of emissions and warming.

But what limitation – so, how much uncertainty – do you still need to take into account? Have we not had the Paris Agreement since 2015, which seeks to strictly control emissions? For example how true is rcp8.5?

There are still publications in the scientific literature that take into account the rcp8.5 scenario. But last year’s defendants Two researchers expressed themselves in a comment Inside Nature Because in their view it gives a false image. In that scenario, for example, coal use would increase fivefold in this century. Coal-fired power plants are being shut down in several places, and coal use is expected to peak in a few decades. So how realistic is that scene? This unnecessarily magnifies uncertainty. All the plans that countries are now drawing up in the context of the Paris Agreement are leading to global warming of 2.5-3 degrees Celsius.

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But the question is whether all those ambitious plans will be fulfilled in a timely manner. It is clear that the gradual cessation of the use of coal, oil and gas is not fast enough. Extraction of fossil fuels is expected to increase in countries including the United States, Saudi Arabia and Russia.

Expensive adjustment

Reply to comment Nature Wrote three scientists A letter. Not including rcp8.5 would actually give policymakers a false sense of security. When the world grows in unexpected ways it leads to costly changes. “It’s really good to add that level of uncertainty,” says Margoliz Hosnott, co-author of the letter and a water and climate researcher affiliated with the University of Deltaree and Utrecht.

However, just as the IPCC did, KNMI added a rcp8.5 display to its climate report. “Because if you look at the greenhouse gas emissions so far, it follows the 8.5 path very neatly,” explains Rob van Dorland, a KNMI climate scientist who co-authored the report.

That’s why the spread on the maps is huge. Of course the sea level rose until 2300. This is also the uncertainty surrounding some of the processes in the melting of glaciers in Greenland and Antarctica. Especially about the so-called The instability of the ice cliff, Von Dorland explains, there is “deep uncertainty”. Glaciers consist of glaciers, part of which ends in the ocean. Those hundreds of meters thick foothills, called glacier tongues, can become thin and brittle due to warming. “There are rocks at the edges of the pieces that will collapse under their own weight,” says Van Dorland. This process has already been observed in Greenland. The crushed ice melts faster. In addition, the broken glacier tongue does not reduce its speed when the glacier slides into the sea. This further speeds up the melting process.

If this process were to land on the horizon for Antarctica as well, it would have far-reaching consequences. The KNMI report states: “This could greatly accelerate the erosion of Antarctica, but the theory is still controversial.

A strong signal

There is also process uncertainty in the forecast of drought. “Because we’re at a turning point between the two regions,” Van Dorland explains. Northern Europe becomes wet even in summer. “As for southern Europe, there is a strong signal that the drought is continuing.” The Netherlands is somewhere in between and it is not clear in which direction our country is leaning.

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Central to this is the dynamic equilibrium between evaporation and precipitation. When it warms up, evaporation increases and the soil dries out. But at the same time, the air can hold more vapor, which basically leads to more precipitation, which keeps the soil moist.

There are analyzes that the wind blows frequently from the east in summer. “That air is drier than the westerly wind coming from the sea.” In such a situation there will be more drought. But the analysis is not so difficult. The KNMI report states: “Climate models do not provide a clear answer to the question of whether future circulation – and thus wind directions – will change.”

People are moving towards an end

Marjolijn Haasnoot Water and Climate Analyst

Then showers. You can expect more due to the simple fact that hot air holds more steam. That too is measured. Above the sea, absolute humidity increases by 7 percent with each degree of warming. But the sea is warming faster than the land. Due to the dominance of westerly winds in the Netherlands – which provides air from the oceans – the humidity in the ground rises to less than 7 percent per degree warming. Above ground, the humidity (how much moisture the air actually has compared to the maximum air) is actually reduced. Leads to a decrease in relative humidity Less Rain according to KNMI report.

In addition, climate models predict that air at a height of a few kilometers warms faster than air at the Earth’s surface. The mutual temperature difference decreases. It also prevents rain. This is because they arise when the surface is relatively hot and the air above is cool. “Both effects lead to a small increase in light rainfall, with the upper air warming slightly compared to the other,” says Van Torland. KNMI expects heavy rainfall (50 mm of rain per hour) to intensify. But there are uncertainties here as well. Domestically, rainfall formation is technically dependent on many factors – terrain, high and low pressure conditions, vertical temperature and humidity details. They may have a calming or strengthening effect. It is difficult to predict how rainfall will change in the county.

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Very different approach

What should policymakers do to address this uncertainty? What should they send? Hasnood, who specializes in climate adaptation policy, says, “People want to move towards a decision. But because of the great uncertainty, the climate problem requires a completely different approach. In fact, policymakers need to be prepared for a wide range of possible consequences. She calls it adaptive planning.” You explore what these weird results are. You can explore how you can modify it and how long those changes take. It requires a lot of flexibility. “You can definitely start already with things you don’t regret.” In the fight against sea level rise, think of sand feeding on beaches. “Long-term options. If the weather changes too much, you have to keep it on hand.” Good monitoring is essential, he says. “You will identify in a timely manner whether you need to adjust your plan.”

Van Dorland says the signal rests on three pillars. Like Hasnot, he is part of the Delta Program Signal Team. The Committee reports on significant improvements in the implementation of the current Delta project, which aims to keep the Netherlands safe and provide adequate freshwater. Those three pillars: Are there observations? Is it in the sample projects? And do we understand the process? Van Dorland: “If all three are ‘yes’, then we have to do something about it. If twice ‘yes’, we are extra careful.

According to Hasnut, the Netherlands, along with the United Kingdom and New Zealand, is at the forefront of adaptation planning. But in some areas it may be even better. He thinks specifically in building houses and infrastructure. “They’ve been there for hundreds of years.” That is why such investments should take into account long-term levels such as sea level rise, fall and rainfall. Where can you guarantee to build safely, and where not? Want to build more houses on stilts? Or houses that are easy to build and crumbling? “You see plans to build on charcoal lawns and floodplains. We need to think more about that.