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Acidification

PML

WHAT IS ALREADY HAPPENING WHAT COULD HAPPEN
  • The ocean is becoming more acidic as increasing atmospheric carbon dioxide (CO2) is absorbed at the sea surface. Models and measurements suggest that surface pH has decreased by 0.1 pH unit since 1750.
  • The surface ocean has absorbed nearly half of the increased CO2 emissions due to burning of fossil fuels over the last 250 years, thus reducing the amount remaining in the atmosphere.
  • Continued acidification will reduce the ability of the ocean to take up CO2 from the atmosphere, which will have feedbacks to future climate change, further accelerating the accumulation of CO2 in the atmosphere.
  • Future increases in ocean acidity will have major negative impacts on some shell/skeleton-forming organisms within this century.

The uptake of anthropogenicA change within part of the climate system that can be attributed to human action, rather than natural causes. carbon since 1750 has led to the oceans becoming more acidic with an average decrease in pH of 0.1 units. Surface ocean and UK coastal water pH will continue to rapidly decline in the future as they take up more atmospheric CO2.

Although the effects of the current reduction in pH on the marine biosphere are as yet undocumented this is due, in part, to lack of research in this area. However, unless we substantially and urgently reduce CO2 emissions, experiments, observations and modelling indicate that future reductions in ocean acidity will have major negative impacts on aragonitic and calciticOrganisms that use the aragonite or calcite form of calcium carbonate to form their mineral parts, such as shells. (shell/skeleton) forming organisms this century and their dependent species. There is growing evidence that the physiology (e.g. growth and reproduction) of adults, larvae and juveniles of some species are sensitive to acidification. Impacts of decreasing pH on key biogeochemical processes other than calcification is theoretically possible and serious (e.g. impact on nutrient speciationHow the main element is contained within a nutrient molecule e.g. Nitrogen may be in nitrate, nitrite or other forms., primary production and nutrient, carbon and sulphur cycling,) but there has been little research on this. The knock-on effects of ocean acidification on marine ecosystems, Are cycles that transfer energy and chemicals around marine ecosystems through life (bio) and its environment (geo).biogeochemical cycles, food webs and biodiversity could be considerable but difficult to quantify. Reducing CO2 emissions is the only way of reducing ocean acidification.

Nearly half of the CO2 derived from burning fossil fuel has already been absorbed by the surfaces of our seas and oceans and more will be absorbed in the future as we continue to increase our CO2 emissions to the atmosphere. The ocean uptake of CO2 is effectively buffering even more serious climate change than that predicted by clear evidence-based scientific consensus.  Continued acidification will reduce the ability of the ocean to take up CO2  from the atmosphere, which will have feedbacks to future climate change, further accelerating the accumulation of CO2 in the atmosphere.

What is happening now - High

The uptake of anthropogenicA change within part of the climate system that can be attributed to human action, rather than natural causes. carbon since 1750 has led to the oceans becoming more acidic with an average decrease in ph of 0.1 units (IPCC, 2007a) (High certainty). However, the effects of current, observed ocean acidification on the marine biosphere are as yet undocumented (IPCC, 2007b) due, in part, to lack of research in this area and long term time series.

High confidence, that ocean pH is changing and will change in the future and unless we substantially and urgently reduce CO2 emissions that these will have major impacts on aragonitic organismsOrganisms that use the aragonite or calcite form of calcium carbonate to form their mineral parts, such as shells. this century.

What could happen in the future - Medium

We have a moderate level of confidence that this will have a knock-on effect on marine ecosystems and foodwebs, according to evidence from modelling and experimental observations.

Impacts of pH on other organisms than aragonitic and calcitic organisms is theoretically serious (e.g. impact on nutrient speciationHow the main element is contained within a nutrient molecule e.g. Nitrogen may be in nitrate, nitrite or other forms. and therefore primary production and biodiversity) but there has been little research on this.

We have a high degree of confidence that reducing emissions is the only way of reducing ocean acidification.

Many, and in all areas, as this field is very much still emerging, they are mentioned briefly in the text above and more specifically in Royal Society, 2005; JGR, 2005; Haugen et al., 2006; Kleypas et al., 2006; Blackford et al., 2007.

Potentially fisheries will be impacted through changes to marine productivity and biodiversity and shell fisheries through reduced physiological functioning such as growth rate, reproduction and survival/recruitment of larvae and juveniles.

Carol Turley
Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH, UK