Most scientists and governments accept that increased atmospheric carbon dioxide (CO2) caused by burning fossil fuels is warming our planet with potentially dangerous results. That same manmade CO2 that we observe to be causing climate change is also altering the chemical balance of the oceans. This – “the other CO2 problem” – has received little attention until quite recently, but it may turn out to be as serious as the more familiar one.
The world’s oceans currently absorb about one metric tonne of CO2 produced by each person each year. It is estimated that the oceans have taken up approximately one hundred and twenty thousand million (120 billion) tonnes of carbon, about half of all that generated by human activities since 1800 ( see this article in the journal Science).
By absorbing all this additional CO2 the oceans have buffered the effects of atmospheric climate change. But there is a cost. CO2 reacts with seawater to form carbonic acid and this results in a greater acidity (that is, a lower pH). If this trend continues, and we burn all available fossil-fuel reserves, ocean pH could fall (and acidity increase) by as much as 0.4 units from its current level of pH8 by the year 2100 and 0.77 by 2300 if we burn all the fossil-fuel reserves.
This may not seem much, but such an increase in acidity (and reduction in pH) is far greater than the annual variation that organisms currently experience through the uptake and production cycles that occur naturally in our surface oceans. Further, such changes have not occurred for the tens of millions of years during which existing marine organisms have evolved.
Past (from Pearson and Palmer, 2000) and predicted variability of marine pH. Future predictions are model derived values based on IPCC mean scenarios. The error bars indicate the likely seasonal scale variability in pH.
Research is in its infancy, but scientists are concerned that increasing acidification could have a particularly detrimental effect on corals and other marine organisms with calcium carbonate shells (see: Katherine Richardson).
Increased acidity may also directly affect the growth and reproduction of fish as well as the plankton on which they rely on for food. The consequences for marine food webs are not yet well understood, but could be catastrophic.
At present rates of acidification and bleaching induced by warming, virtually all corals in the oceans could be wiped out by 2065. Another important group of microscopic plants called coccolithophorids, are also under threat. These organisms may be tiny but their blooms are so extensive that you can see them from space and they annually cover about 1.4 million square kilometres of the ocean. When they die, their platelets – known as liths – rain down to the ocean floor, where they are buried. This locks away carbon in the sediment, which in time can form vast structures such as the white cliffs of Dover. This “biological pump” helps to control the exchange of carbon between the oceans, atmosphere and sediment. Without it, there could be large changes in the Earth system.
A coccolithophores bloom off the SW coast of England captured by satellite remote sensing. The calcium carbonate liths produced by these microscopic algae make the sea look milky.
Ocean acidification is a mainstream scientific concern for the majority of international marine scientific research associations and organisations. The International Geosphere-Biosphere Programme (IGBP), the Scientific Committee on Oceanic Research (Scor), the Commission on Atmospheric Chemistry and Global Pollution (CACGP), the International Council for Science (ICSU), and the Intergovernmental Oceanographic Commission (IOC, part of Unesco) are all sponsoring research programmes or have called for more research (see, for example, Priorities for Research on the Ocean in a High-CO2 World). Britain’s Royal Society reports on this matter in June 2005.
We at the Plymouth Marine Laboratory have reviewed the potential impact of increasing CO2-driven acidification on marine ecosystems and its potential consequences for climate change and the whole Earth system (see here and here). We conclude that the likely changes are severe in the extreme. Avoiding further ocean acidification is a powerful additional argument to that of climate change for reducing global CO2 emissions.
Surface ocean acidification is happening now. It is happening at the same time that the oceans are warming. Organisms and ecosystems are going to have to deal with two major rapid changes at once – unless we urgently introduce effective ways to reduce CO2 emissions. The United Kingdom government, which seeks to lead on climate change as it hosts the G8 summit in July 2005 and during its presidency of the European Union in the second half of 2005, should take this very seriously indeed. And so should all of us.
|
This article appears as part of openDemocracy‘s online debate on the politics of climate change. The debate was developed in partnership with the British Council as part of their ZeroCarbonCity initiative – a two year global campaign to raise awareness and stimulate debate around the challenges of climate change. |
