Carbon emissions threaten marine species

Abstract

Researchers, increasingly frustrated at the political response to the evidence of climate change as a result of human-derived carbon dioxide emissions, are still reporting new worries. A recent report highlights the impact of the emissions on the acidity of the oceans and the possible consequences. Nigel Williams reports. Researchers, increasingly frustrated at the political response to the evidence of climate change as a result of human-derived carbon dioxide emissions, are still reporting new worries. A recent report highlights the impact of the emissions on the acidity of the oceans and the possible consequences. Nigel Williams reports. No one had great expectations about the outcome of discussions on climate change at the recent G8 summit of the world’s wealthiest nations in Scotland, and the modest resulting statement did little to reassure researchers that the topic is being taken as seriously as many feel it demands. “At the heart of the communique is a disappointing failure by the leaders of the G8 unequivocally to recognise the urgency with which we must be addressing the global threat of climate change,” commented Britain’s science academy, the Royal Society. Just ahead of the meeting, the society produced a report highlighting just one of the consequences of growing human-derived carbon dioxide emissions to the atmosphere: increasing acidity of the oceans as the waters absorb growing volumes of the greenhouse gas. Failure to address the issues “may mean that there is no place in the oceans of the future for many of the species and ecosystems that we know today,” said John Raven, chair of the group that produced the report. The oceans cover two-thirds of the Earth’s surface. They play a vital role in global biogeochemical cycles, contribute enormously to the planet’s biodiversity and provide a livelihood for millions of people. “The oceans are absorbing carbon dioxide from the atmosphere and this is causing chemical changes by making them more acidic, that is decreasing the pH. In the past 200 years the oceans have absorbed approximately half of the carbon dioxide produced by fossil fuel burning and cement production,” the report says. “Ocean acidification is serious and its impact on the climate will be irreversible,” said Raven. Calculations based on measurements of the surface oceans and knowledge of ocean chemistry indicate that this uptake of carbon dioxide has led to a reduction of the pH of surface seawater of 0.1 units, equivalent to a 30 per cent increase in the concentration of hydrogen ions. “If global emissions of carbon dioxide from human activities continue to rise on current trends then the average pH of the oceans could fall by 0.5 units (equivalent to a 3-fold increase in the concentration of hydrogen ions) by the year 2100,” the report warns. This pH is probably lower than has been experienced in hundreds of millennia and critically, this rate of change is probably one hundred times greater than at any time over this period. “Ocean acidification is essentially irreversible during our lifetimes. It will take tens of thousands of years for ocean chemistry to return to a condition similar to that occurring at pre-industrial times about 200 years ago,” the report says. But, as with many other climate change analyses, the exact prospects remain unclear. “The scale of the changes may vary regionally, which will affect the magnitude of the biological effects,” the report says. But it warns that the possibility of changing marine acidity through artificial means is highly unlikely. “Reducing carbon dioxide emissions to the atmosphere appears to be the only practical way to minimize the risk of large-scale and long-term changes to the oceans,” the report says. Such a conclusion is still not embraced by many politicians. The impact of ocean acidification on marine organisms and their ecosystems is much less certain but it is likely that, because of their particular physiological attributes, some organisms will be more affected than others. “Predicting the direction and magnitude of changes in a complex and poorly studied system such as the oceans is very difficult. However, there is convincing evidence to suggest that acidification will affect the process of calcification, by which animals such as corals and mollusks make shells and plates from calcium carbonate,” the report says. The tropical and subtropical corals are expected to be among the worst affected, with implications for the stability and longevity of the reefs that they build and the organisms that depend on them. Cold-water coral reefs are also expected to be adversely affected, before they have been fully explored. Other calcifying organisms that may be affected are components of the phytoplankton and the zooplankton which are a major food source for fish and other animals. Regional variations in pH will mean that by 2100 the process of calcification may have become extremely difficult for these groups of organisms particularly in the Southern Ocean. Some shallow water animals, which play a vital role in releasing nutrients from sediments, also calcify, and may be affected by changes in the chemistry of the oceans. Some studies suggest that growth and reproduction in some calcifying and non-calcifying marine species could be reduced due to the projected changes in ocean chemistry. “From the evidence available it is not certain whether marine species, communities and ecosystems will be able to acclimate or evolve in response to changes in ocean chemistry, or whether ultimately the services that the ocean’s ecosystems provide will be affected,” the report says, adding that “Research into the impacts of high concentrations of carbon dioxide in the oceans is in its infancy and needs to be developed rapidly”. “The impacts of ocean acidification are additional to, and may exacerbate, the effects of climate change. For this reason, the necessary funding should be additional and must not be diverted from research into climate change.” Oceans play a very important role in the global carbon cycle and Earth’s climate system. There are potentially important interactions and feedbacks between changes in the state of the oceans and changes in the global climate and atmospheric chemistry. Changes in the chemistry of the oceans will reduce their ability to absorb additional carbon dioxide from the atmosphere, which will in turn affect the rate and scale of global warming. “The knowledge of these impacts and effects is currently poor and requires urgent consideration,” the report warns. The socioeconomic effects of ocean acidification could also be substantial. Damage to coral reef ecosystems and the fisheries and recreation industries that depend on them could amount to economic losses of many billions of dollars per year in the longer term, changes to the stability of coastal reefs may reduce the protection they offer to coasts. There may be direct and indirect effects on commercially important fish and shellfish species. Marine ecosystems are likely to become less robust as a result of the changes to the ocean chemistry and these will be more vulnerable to other environmental impacts (such as climate change, water quality, coastal deforestation, fisheries and pollution). increased fragility and sensitivity of marine ecosystems needs to be taken into consideration during the development of policies that relate to their conservation, sustainable use and exploitation, or the communities that depend on them,” the report says. “Ocean acidification is a powerful reason, in addition to that of climate change, for reducing global carbon dioxide emissions. Action needs to be taken now to reduce global emissions of carbon dioxide to the atmosphere to avoid the risk of irreversible damage to the oceans. We recommend that all possible approaches be considered to prevent carbon dioxide reaching the atmosphere. No option that can make a significant contribution should be dismissed.” Carol Turley of the Plymouth Marine Laboratory, one of the report’s authors, commented that ocean acidification is a “sister” problem to that of climate change. “The oceans have already taken up about 50 per cent of the carbon dioxide that man has produced over the past 200 years and will continue to do so,” she said. “Essentially, the oceans have been reducing the impact of climate change but at their own expense.”