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Keeping an eye on climate change

Anna Rutgersson and her colleagues take measurements of what happens in the interface between sea and atmosphere.

As much as 90 per cent of the carbon dioxide we emit ends up in the seas, so it is important to keep track of the interaction between the seas and the atmosphere. Anna Rutgersson, Professor of Meteorology, conducts extensive research on the role of the seas in the climate system.

When global climate models began to be drafted, the main focus was on the atmosphere, but then came the realisation of the important role the ocean plays.
“The timescale for what is happening in the seas is much slower,” says Rutgersson. “The atmosphere has become warmer, but it will take much more time before the seas respond to this, so that’s why it’s important that the seas are included in the system.”
Anna Rutgersson and her colleagues take measurements of what happens in the interface between sea and atmosphere. What is the exchange of carbon dioxide like and how do the waves affect this exchange?
“You could say that the water surface affects how the air and sea interact. There is a friction that allows energy to be transported from the atmosphere to the sea and that friction is influenced by the water surface.”

The seas are an important sink for carbon dioxide, explains Rutgersson.
“We emit a lot of carbon dioxide and a large portion of that ends up in the seas. But even there, the timescale is rather slow. Even if we were to stop releasing carbon dioxide now, the seas would continue to absorb it for another 10,000 years. Ninety per cent of our carbon dioxide emissions will end up in the seas sooner or later.”
There are also marine areas that emit carbon dioxide. It is not quite clear whether the Baltic Sea acts as a source or a sink for carbon dioxide. It is in the Baltic Sea that the researchers are taking most of their measurements, at a monitoring station on the island of Gotland.
“We’re looking at what happens in the Baltic Sea, but much of what we are studying is processes that we don’t view as specific to the Baltic Sea. Our premise is that if you understand the process, you can apply it globally.”

It has been proven, for example, that the temperature difference between air and water is highly significant. The uptake is much more effective if the ocean is warmer than the air, which can be important to know in Arctic regions where there is a large temperature difference between sea and air.
The research findings are then used in large global models made by multi-research team consortia. These climate models can then be used to develop climate scenarios, such as: what happens if it gets two, or four, degrees warmer?
“These scenarios are quite good, but they can be improved with more detailed information on the consequences of the warming,” explains Rutgersson.
“The climate models provide a good average picture, but if we look at specific things, like storms in Sweden in 100 years, they don’t work quite as well. More detailed information is needed then.”

Anna Rutgersson’s research team cooperates with both SMHI and with the European consortium EC-Earth.
Can you say anything general about how the climate changes are affecting the weather?
“It’s a complex area,” says Rutgersson. “There are a lot of groups looking at different aspects and research that points in different directions, so it’s important to synthesise and consolidate different studies.”
A typical example is the IPCC report on the Baltic Sea.
“Based on this report, you can’t say if it will be more stormy or less stormy in Sweden, but it does show that the storm tracks are moving further north so the actual pattern is changing. This affects the average wind conditions in some areas.”
Many studies also show a slight increase in persistence, that is, low pressure that remains stationary for a long time over a certain area. Persistence also entails a risk of the weather becoming more extreme.
“We have not really been able to see that there will be more storms, but increased persistence is an interesting indication,” says Rutgersson.

Rutgersson believes that the media often presents an exaggerated picture of climate changes leading to storms and flooding.
“You can’t really take it that far, but this persistence phenomenon could indicate an increased risk of flooding, for example.”
Extreme weather interests researchers even disregarding climate change.
“It’s a combination of phenomena that very rarely occurs. With a flood that comes once every fifty years, it’s difficult to see changes over time. But in combination with changing land use, the consequences of extreme weather become greater.”
The climate models are used by both researchers and politicians to predict consequences of temperature increases on Earth. In industry, too, climate scenarios can be interesting.
“Not everything in society is affected, but most long-term investments are, such as investments in forests or infrastructure that have longer timescales.”

How quickly is the climate changing?
“What we are seeing is a combination of natural variability and climate change,” says Rutgersson. “If we say that there will be a two-degree warming over fifty years, this is not linear but rather varies up and down all the time. It is therefore difficult to say what the average temperature will be in 2030, but we are seeing an upward trend.”
Rutgersson has been working on climate models for the past ten years or so and thinks that a lot has changed in terms of acceptance in the research community, and just in general.“It’s less common for climate change to be questioned. There is a consensus that carbon dioxide has increased and that this has led to warming. There are different opinions as to what the consequences will be, but the underlying consensus is there.”

28 October 2016