A 1.5 target is needed to save the Baltic Sea

AirClim has published a report (1) about the possible effects of climate change in the Baltic Sea. The intention of the report is to try and predict what global warming of 2 or 4 degrees C may mean for the biodiversity of the Baltic Sea. 

At the UN Climate Conference in Paris in December 2015 on how to mitigate increased global warming it was decided among other things that:

  • global warming shall be limited to “well below 2 degrees” as compared with the pre-industrial era,
  • and the aim is to limit warming to just 1.5 degrees.

It is crucial that these decisions and goals are attained, but they will be virtually impossible to achieve unless we can curb current emissions of greenhouse gases like carbon dioxide. If these emissions continue at the present level the temperature is likely to rise by more than 4 degrees by 2100 according to the IPCC. The European Union still has a temperature target of below 2 degrees, but this report suggests that such a target is not strong enough to save the Baltic Sea ecosystems from dangerous climate change.

Below I have therefore tried to analyze the biological effects of increasing temperatures by 2 or 4 degrees and other drivers of environmental change on the biodiversity in the Baltic Sea. An additional effect of emissions of carbon dioxide is that they act as the primary source of ocean acidification, because one-third of the carbon dioxide emitted is absorbed by the world’s oceans. In the oceans it reacts with calcium and water to produce carbonic acid, which leads to a lowering of the pH. At lower trophic levels there will be decreased availability of carbonate ions, which are essential building blocks required by marine organisms to build their skeletons, shells and other calcareous structures. This phenomenon has already caused severe implications for the global distribution of economically important fish species and other sources of seafood, so global seafood security is at risk. In addition to the effects of temperature increase and increased acidification on marine biodiversity it should be mentioned that other drivers of biodiversity loss will also affect marine biodiversity, e.g. habitat modification, pollution, invasive exotic species and the extinction of species and unique local populations.

The longest continuous programme of monitoring atmospheric carbon dioxide was started back in 1958 by Charles Keeling at the Mauna Loa Observatory in Hawaii. His son Ralph continues his work. The Keelings have found a 3 per cent annual increase, and as early as 1963 Keeling and his colleagues predicted that carbon dioxide emissions at that time could raise global surface temperatures by as much as 4 degrees by 2063 (Figure). If this scenario takes place it is also logical to speculate what effect it will have on the biodiversity of the Baltic Sea. On a global time scale, species extinctions are already above the highest rates found in the fossil record, and past climate changes were much slower than those anticipated for the 21st century. Even so, slow rates of change in the past drove significant ecosystem shifts and mass extinctions of species.

What consequences could a temperature increase of 2 degrees have on Baltic Sea ecosystems?

Any sustained temperature increase in the Baltic will favour warm-water species and be harmful to cold-water species. A decrease in salinity, which is a likely side effect, will induce further stress in marine species, and changes in the oxygen concentration and pH are other climate-driven parameters that have profound effects on ecosystems. Those four factors will shape ecosystems in the Baltic Sea. Another factor mainly influencing human settlements and industries is the projected sea-level rise, the extent of which is still debated.

  • The sea-level rise will increase erosion of coastal ecosystems, mainly in the southern and eastern Baltic Proper. Even with an ambitious climate policy, sea levels are projected to increase by 20 to 60 centimetres by the end of this century.
  • Basically, marine species at all trophic levels, including fish, will be negatively affected. These effects will be most pronounced in the northernmost parts of the Bothnian Bay, in the Gulf of Finland and in shallow coastal waters of the Baltic states, Poland and Germany.
  • Logically, warmer and less saline water will benefit almost all freshwater species, but species that are dependent on low temperatures will become less abundant
  • There may be increased production of cyanobacteria (blue-green algae), which will influence both biomass and the composition of benthos (bottom-living organisms), phytoplankton, zooplankton and fish communities negatively.
  • Few exotic organisms will benefit from this moderate temperature increase, with the exception of the comb jelly, which on the other hand is capable of changing the entire marine ecosystem, as it has done in the Black Sea.
  • Freshwater fish such as pike, pike-perch and perch may extend their ranges and increasingly support local coastal fisheries.
  • On the other hand, stronger fishing quota restrictions must be applied to species such as cod, herring and sprat, and possibly also include a ban on off-shore fisheries targeting salmon and sea-trout. Otherwise, wild salmon populations in the Baltic Proper will face severe survival problems.
  • Reduced availability of mussels and other benthic micro- and macro-invertebrates as well as small shallow-water fishes may limit access to food for birds that rely on these resources. Such species include cormorants, long-tailed ducks, guillemots, eider ducks, terns, gulls, mergansers and common golden-eyes.
  • Decreased winter ice cover in the Baltic Sea will disfavour the reproduction of ringed seals.

What consequences could a temperature increase of 4 degrees have on Baltic Sea ecosystems?

It is hardly unexpected that this temperature increase will have much more severe impact on present day ecosystems in the Baltic Sea. Let us hope that this scenario will never take place. Below I have summarized what I believe might happen.

  • Coastal erosion and flooding of low-lying shore areas will impact human settlements, industries and present coastal nature reserves. The reserves will have to be extended further inland from the present shoreline. This impact will be particularly strong in the eastern, southern and south-western parts of the Baltic Proper.
  • The effects of this level of temperature increase depend on factors such as future discharge of nutrients, salinity and oxygen levels, but it is likely that the entire biomass of fish will diminish so much that open-sea fisheries will come to an end. Local coastal fisheries may still operate though.
  • Cyanobacteria (blue-green algae) may out-compete phytoplankton, leading to ecosystem changes at all trophic levels, in addition to a reduction in total fish production.
  • It is vital that ecosystem-based measures for fisheries are based on conservation measures that are triggered as soon as stock levels fall below biomass levels capable of producing maximum sustainable yield.
  • Most glacial relict species, like the fourhorn sculpin and the sea snail, are likely to become extinct, in addition to some exotic species, probably with the exception of the comb jelly, the zebra mussel and the round goby.
  • Fish- and mussel-eating birds will diminish in abundance, and the much lower level of fish production will negatively affect seals and the harbour porpoise.

Lennart Nyman, PhD

About the author: Lennart Nyman is a scientist and environmentalist from Sweden who has worked for some 50 years studying various aspects of the Baltic ecosystem and other marine, freshwater and terrestrial ecosystems world wide. He has served for many years as Conservation Director with WWF-Sweden, and prior to that e g as Director of the Institute of Freshwater Research at Drottningholm, Sweden. He has been a member of numerous national and international boards, committees and societies on environmental issues.

Climate change in the Baltic Sea region:
A 1.5 target is needed to save the Baltic Sea
Effects of global temperature increases on the biodiversity of the Baltic Sea. By Lennart Nyman PhD, Published in March 2016
Link to the report: http://airclim.org/publications/reports

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