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Alarm bells raised about ocean warming

Havforsker Geir Ottersen

Geir Ottersen is one of the main authors behind the chapter on the Polare Regions in the new IPCC special report on the oceans and cryosphere. Download picture here.

Photo: Erlend A. Lorentzen / Institute of Marine Research

Today the UN’s Intergovernmental Panel on Climate Change (IPCC) is launching its special report on the oceans and cryosphere. Geir Ottersen, a scientist at the Institute of Marine Research (IMR) and one of the main authors of the report, is concerned about the changes taking place in the Arctic.

The special report provides an update on the latest research on topics such as sea level rise, ice melt, ecosystem changes and ocean acidification. The unequivocal conclusion is that changes are already underway, and that they are occurring more quickly than was previously thought.

That is also true of the Polar Regions – the subject of the chapter that Geir Ottersen is one of the main authors of. He believes that what is happening in the Arctic will affect the whole planet.

“The atmosphere in the Arctic is warming at around double the average global rate, partly because when ice melts, light surfaces become darker, which means that less of the Sun’s heat is reflected back into the atmosphere. This is resulting in warmer air over the Arctic Ocean and the northern Barents Sea. That in turn affects the warming of the whole planet, on account of atmospheric circulation”, explains Ottersen.

Growing ice-free areas

The complex interactions in the climate system are one reason why the UN commissioned a special report on the impacts of climate change on the ocean and cryosphere (areas covered by ice or snow). The report is part of the work towards the IPCC’s next main assessment report, which is due in 2022.

The IPCC began its work as long ago as 1988, around the same time that Geir Ottersen started doing research into fisheries oceanography at the IMR. In those days his fellow researchers showed little interest in climate change, but some time after the turn of the millennium they noticed that something unusual was happening with fish stocks in the north.

“In recent years, we have observed cod and haddock further north and east than in the past during our big fish stock assessments. The reason is simply that the ice-free areas have grown. This is causing conflicts with ‘native’ species, which are being forced to compete for food with the bigger, stronger cod”, says Ottersen.

He also explains that species which have adapted to the environment at the ice edge over thousands of years are now struggling because the ice edge is suddenly in a completely different place from in the past.

Good for the cod fishery

However, what has been negative for biodiversity in the north has so far been good for Norway’s commercial fisheries. This is particularly true of our most productive sea, the Barents Sea. “There has hardly ever been as much cod as in the past five years”, says Ottersen, before adding:

“That doesn’t mean that if the temperature rises another two degrees, there will be masses of cod. There’s a limit. In the North Sea, that limit appears to have been reached already: it’s beginning to get too warm for the cod.

The coastal cod in Southern Norway and Oslofjorden are also struggling because it has become too warm for the species that the juvenile cod feed on. In their case, climate change comes on top of other factors that are affecting fish stocks, such as tourist fishing and the number of cormorants and seals.

Mackerel problems

Another important species that is being affected by the changing ocean climate is the mackerel. Traditionally it has not ventured very far north, but in the recent years it has expanded its range northwards – first to Iceland, then to Eastern Greenland and now all the way to Svalbard.

“It’s happened quickly, and it’s also had an impact on fisheries management”, says Ottersen.

“Before the mackerel came to Iceland, nobody had thought of setting quotas for it there, so when it arrived, local fishers could catch as much as they liked. Naturally they took advantage of this, which led to conflicts with the people who had historically had the fishing rights to the mackerel. This conflict has yet to be resolved.

Ottersen believes that this kind of situation, where climate change affects fisheries management and international diplomacy, may occur again in the future. For instance in the Barents Sea, where the cod swim freely across the border between Norway and Russia.

“If the cod start to spend relatively more time on the Russian side and less on the Norwegian one, Russian fishers may start arguing that the cod are Russian. That may require renewed discussions over our current fisheries agreement with Russia”, he thinks.

Ice is melting and the sea level is rising

Perhaps the topic in this special report that affects most people, and that causes most concern, is sea level rise. The latest projections, which are both more confident and more dramatic than previous ones, show that we may be heading for an average sea level rise of 80 centimetres by the year 2100. On top of this, natural variations are becoming bigger due to more extreme weather.

In the long term this may cause serious problems, not just for small island nations, but also for highly populated countries like Bangladesh and large coastal cities such as Tokyo and New York – not to mention Bergen and Stavanger.

There are two main reasons why the sea level is rising: first, water expands when it warms; and second, ice and snow on land is melting. In Greenland and Antarctica, the ice is now melting faster than was expected just a few years ago”, explains Ottersen.

He stresses that the 80 cm estimate, with a margin of error of 20 cm, is the worst case scenario the researchers examined – but unfortunately also the one that now looks most realistic.

If we manage to limit global warming to two degrees above pre-industrial levels, we will still see the sea level rise by around 50 cm, according to the calculations in the report.

Big difference between best and worst case scenarios

The researchers examined two scenarios: business as usual, in other words what would happen if emissions continue on their current path; and the best case, which is what would happen if we actually manage to reduce emissions in line with climate action goals.

“Warming will continue for some time whatever happens, as a result of past emissions. But there are significant differences between the best and worst case scenarios. If we continue emitting large quantities of greenhouse gases, change will be faster and greater.

The most important advice in the report is therefore to reduce greenhouse gas emissions. However, it’s also true that we must prepare ourselves for, and adapt to, the changes that are inevitable.

Ottersen notes that a number of municipalities, in Norway and other countries, have started incorporating sea level rise forecasts into their planning, which he thinks is a good idea.