The oceans absorb much of the carbon dioxide we emit, but have they reached breaking point? asks ecologist Alan Jones.
Everyone has heard of the greenhouse effect, or global warming, caused by emissions of greenhouse gases into the atmosphere, particularly the 30 billion tonnes of carbon dioxide generated annually by human activity. But not everyone knows that the oceans absorb about one-third of this carbon dioxide, which combines with water to produce carbonic acid.
Measurements show that surface water acidity has increased in the last 150 years, overwhelming the natural buffering that helps maintain a relatively constant pH level. Scientists estimate that seawater could become 150% more acidic by 2100 – a larger change than any in the last 20 million years.
According to the Stockholm Resilience Centre, oceanic acidification has the potential to cause catastrophic environmental damage.And the Royal Society has warned that it is essentially irreversible, and it would take tens of thousands of years for ocean chemistry to return to pre-industrial conditions.
Changes in water chemistry pose a threat to the great diversity of species that live and grow in seawater.
Increasing acidity reduces growth in many species, including mussels, oysters, sea urchins and gastropods. It reduces the development and survival of sea urchins, brittle stars and corals. It also reduces the ability of calcifying species – such as corals, crustaceans, echinoderms, molluscs and some phytoplankton – to build shells and skeletons. In turn, these changes threaten the marine food webs of fish, seabirds and marine mammals.
Coral reefs – already under stress from warming water, excess sediments and nutrients, and stronger storms – face increasing acidification, which reduces their structural integrity and biological diversity. These changes will directly affect people because reefs protect stretches of coastline and beaches and, on the Great Barrier Reef alone, support tourism and fishing industries worth $5.4 billion annually and employing 63,000 people.
Unfortunately, research on oceanic acidification is in its infancy and we cannot be conclusive about its effects on complex marine ecosystems. But scientists have produced plausible scenarios, supported by theory and measurements, that have serious implications for future human generations and their planetary life support systems.
So what can be done? First, fundamental change is needed to reduce the rate at which carbon dioxide is increasing in the atmosphere. We need to use economic instruments to limit carbon emissions, to develop green technologies and to conserve energy.
Second, we need to better understand the effects of acidification. Such knowledge will help us make choices towards achieving overarching public goals such as quality survival of humans and the protection of nature in general.
Finally, we will need wisdom as well as knowledge – the communal wisdom to act and restore harmonious relations among elements of the world. The capacity for wisdom is, after all, a human trait that our Latin name, Homo sapiens, embodies.
Can we pass the acid test?
Dr Alan Jones, Senior Research Fellow
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Pandolfi, JM, SR Connell, DJ Marshall and AL Cohen, 2011. Projecting coral reef futures under global warming and ocean acidification. Science 333:418–22.
Schiermeier, Q, 2011. Earth’s acid test. Nature 471:154–6.