Exactly how high will sea level rise off the Dutch coast? Are we really getting more summer rain for sure? And what about dehydration?
Global temperature will continue to rise for now, that’s for sure. The result is harsher weather. But it is uncertain how this will be implemented at the regional level. The KNMI report was published earlier this week Climate signal 21 full of those doubts. The institute translates the latest findings of the IPCC, the United Nations climate agency, into the Dutch situation. To give an example: In the year 2300, the sea level off the Dutch coast may have risen by 30 cm. But it is also possible 17 meter converted to. Uncertainties are also great for heavy summer rain and drought. how is that possible? How do you, as a policy maker, deal with these uncertainties?
Roughly speaking, the uncertainty lies in two things. It is not certain how greenhouse gas emissions will develop. In addition, it is still not fully understood how climate change affects local weather processes. In any case, there is a large element of chance in these processes – the weather is a chaotic system. This makes it inherently difficult to predict.
There has been much discussion about future emissions in recent years. Are the scenarios that the IPCC uses for this still valid?
In its 2013 report, the Intergovernmental Panel on Climate Change presented Representative focus pathways (RCPS). In these scenarios, each path corresponds to a different warming in 2100. In the worst case scenario, greenhouse gas emissions will continue to rise this century (rcp8.5 – about 5°C warming in 2100). In the other three pathways, emissions peak in 2080 (rcp6, warming ~3 °C), 2040 (rcp4.5, ~2.5 °C) and 2020 (rcp2.6, ~1.5 °C). Three years ago, the Intergovernmental Panel on Climate Change replaced RCPs with Shared social and economic pathways (ssp’s), where emissions are translated into social and economic narratives – more understandable to policy makers and the general public. But they represent the same range of emissions and warming.
But what scope – and thus, how much uncertainty – do you still have to consider? Haven’t we had the Paris Agreement since 2015, which tries to severely reduce emissions? So how real is rcp8.5 for example?
In the scientific literature there are still publications that take the rcp8.5 scenario into account. But last year, two researchers complained about it in a comment temper nature Because it gives a wrong picture in their eyes. In this scenario, for example, coal use should triple this century. While coal-fired power plants are shutting down in many places, coal use is expected to peak within a few decades. How realistic is this scenario then? It makes the uncertainty unnecessarily great. All the plans that countries have now made in the context of the Paris Agreement lead to a global warming of 2.5-3°C.
But the question is whether and on time these ambitious plans will be met. It is clear that phasing out the use of coal, oil and gas is not happening fast enough. Fossil fuel extraction is expected to increase in the United States, Saudi Arabia, and Russia, among other countries.
Reply to comment in temper nature Three scholars wrote a letter. Not including rcp8.5 may give policy makers a false sense of security. It leads to costly alterations as the world develops in unexpected ways. “It’s actually good to include this wide range of uncertainty,” says Margolin Hassnot, co-author of the letter and a water and climate researcher affiliated with Deltares University and Utrecht.
In any case, KNMI simply included the rcp8.5 scenario in its climate report, as did the IPCC as well. “Because if you look at greenhouse gas emissions so far, they follow the 8.5 path very well,” explains Rob van Dorland, a climate scientist at KNMI, who coordinated the report.
This is why the spread in the charts is large. Certainly in relation to sea level rise up to the year 2300. But this is not only about the uncertainty in greenhouse gas emissions. It is also the uncertainty surrounding some of the processes in the melting of the Greenland and Antarctic ice sheets. Especially about the so-called Ice cliff instabilityThere is “deep uncertainty,” explains Van Dorland. Ice caps consist of glaciers, part of which ends in the sea. These ridges hundreds of meters thick, called glacier tongues, can pile up and disintegrate due to rising temperature. “At the edges of the fragments there are slopes that can collapse under their own weight,” says van Dorland. This process has already been observed in Greenland. The collapsed ice melts faster. In addition, a fractured ice tongue does not slow the glacier as it slides into the sea. This speeds up the dissolving process even more.
If this process were on the horizon for Antarctica, it would have disastrous consequences. The KNMI report says: “This could greatly accelerate the erosion of Antarctica, but this theory is still controversial. If the theory is correct, we could be the first to observe this phenomenon in 20 to 30 years in the currently rapidly retreating Thwaites glacier, which flows into the Amundsen Sea.
There is also uncertainty in the drought forecasting process. “Because we’re at a tipping point between two regions,” Van Dorland explains. Northern Europe will get wetter, even in summer. “For southern Europe, there is a strong sign of continued drought.” The Netherlands lies somewhere in between, and it is not clear in which direction our country is tilted.
The basis for this is the changing balance between evaporation and precipitation. As the weather becomes warmer, evaporation increases and the soil dries out. But at the same time, the air can hold more water vapor, which basically leads to more precipitation, which keeps the soil moist.
There are analyzes that indicate that we will get winds from the east more often in the summer. “And this wind is drier than the westerly winds that come from the sea.” In such a situation, there will be more dehydration. But the analyzes are not so difficult. The KNMI report states: “Climate models do not provide an unambiguous answer to the question of whether circulation – and thus wind directions – will change in the future.”
People tend to go for one outcome
Marjoline Hasnott Water and Climate Researcher
Then it rains. You might expect more, due to the simple fact that warmer air can hold more water vapor. This is also measured. Above sea level, absolute humidity increases by 7 percent with each degree of warming. But the sea is warming less quickly than the Earth’s temperature. Because the Netherlands is dominated by westerly winds – which supply winds from the sea – the moisture content above land rises by less than 7 percent for each degree of warming. Above ground, relative humidity (how humid the air actually is compared to what it would be maximum) has actually decreased. A decrease in relative humidity leads to less Take a shower, according to a KNMI report.
In addition, climate models predict that air at an altitude of a few kilometers warms faster than air at the Earth’s surface. The mutual temperature difference decreases. This also prevents showering from occurring. Because they arise when the surface is relatively warm and the air above it is cold. “Both effects lead to a lower increase in light showers, compared to a case where, among other things, the upper air is slightly warm,” says van Dorland. KNMI expects the heaviest rains (more than 50 mm of rain in an hour) to become more intense. But here, too, there are doubts. Locally, the composition of the shower subtly depends on many factors – topography, location of high and low pressure areas, vertical temperature and humidity profiles. It can have a damping or strengthening effect. The complexity makes it difficult to predict how showers will change locally.
very different approach
What should policy makers do out of all this uncertainty? What should they send? “People tend to be one outcome,” says Hasnott, who specializes in adaptation policy. “But because of the great uncertainty, the climate problem requires a completely different approach.” Indeed, policymakers need to prepare for a wide range of possible outcomes. Label adaptive planning. “You’re exploring what all of these different results mean. You’re exploring how you can adapt to that, and how much time you need for these adjustments.” It requires a lot of flexibility. “You can actually start with the things you definitely won’t regret.” Think of feeding sand on beaches, in the fight against sea level rise. “The long-term options, if the climate changes further, you have to keep them close at hand.” She says good oversight is essential. “Until you realize in time that you need to adjust your plan.”
Van Dorland says this reference rests on three pillars. Like Haasnoot, it is part of the Delta Program Signal Group. This group reports on important developments for the implementation of the current Delta programme, which aims to keep the Netherlands safe and continue to provide enough fresh water. These three pillars are: Are they in the notes? Is it in the projection model? Do we understand the process? Van Dorland: “If all three are ‘yes’, we have to do something about it. If ‘yes’ twice, we’re on extra alert.”
According to Haasnoot, the Netherlands, along with the United Kingdom and New Zealand, is an international leader in adaptive planning. But in some areas it could still be better. You especially think about building homes and infrastructure. “They’ve been there for hundreds of years.” That is why such investments must take into account more long-term, rising sea levels, subsidence, and heavy rains. Where can you guarantee safe construction and where not? Should more homes be built on stilts? Or homes that are easily buildable and degradable? “You see plans to build in the areas of peat meadows and floodplains. We need to think more about that.”
A version of this article also appeared in NRC Handelsblad on October 30, 2021
A version of this article also appeared on NRC on the morning of October 30, 2021
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