Climate gets hot’ and cruel
Legislators, scientists and conservationists meet again under the gathering clouds of species extinction. The meeting in Nagoya, Japan, to discuss the state of Earth’s biodiversity at the Tenth Conference of Parties for the Convention on Biological Diversity (CBD) takes place amidst discouraging news.
The convention’s Global Biodiversity Outlook 3 reports that the target, set in 2002, to achieve significant reduction in the rate of biodiversity loss by 2010 has failed. Underlying causes of continued loss of biodiversity include habitat loss, unsustainable use and overexploitation of biological resources, climate change, invasive species and pollution. There is some good news in this report on localised or partial success in stemming some of these pressures. However, while climate change is viewed as a threat of “increasing significance,” it’s remarkable that this document does not call for international agreement on an effective course of action to tackle climate change with utmost urgency. Without such an agreement, humankind will be the causative agent of a planetary extinction expected to rival the five great extinctions recorded in geological history.
Coral reefs are the most species-rich marine ecosystems on Earth. Despite only comprising about 0.2 per cent of the area of the oceans, coral reefs host a quarter of all marine fish species and perhaps 1 to 3 million marine species in total. In economic terms, they provide goods and services estimated up to $375 billion per annum. Around 500 million to 1 billion people rely on coral reefs for food, and 30 million of the world’s poorest people in coastal communities depend entirely on reefs as their primary means of food production and livelihood.
The impacts of climate change are already apparent on coral reefs. There’s no need to resort to models that forecast the effects of increased global temperatures on coral-reef ecosystems and the species associated with them, the evidence is there.
Mass coral bleaching has increased in frequency as sea-surface temperatures (SSTs) have steadily increased in response to global warming. At the Nagoya conference, news that another large-scale mass coral bleaching event affecting the Indian Ocean, Pacific Ocean and Caribbean has occurred in 2010, potentially rivaling that of 1998 in severity, is particularly unwelcome. By the middle of the century the steady increase in SSTs will make bleaching annual events, laying waste to corals reefs globally.
However, global warming is not the whole story of CO2-induced climate change. The oceans have been absorbing a large proportion of the CO2 produced by humankind. When absorbed by seawater, CO2 forms carbonic acid and reduces pH, a measure of the acidity. So far a pH reduction of 0.1 units has been recorded by long-term ocean monitoring stations around the globe suggesting the oceans are becoming more acidic.
Ocean acidification has been found to have other unexpected effects on the marine animals. For example, clown fish lose their ability to discriminate between the reef on which they were spawned and other reef habitats, possibly less favorable for their growth and survival.
Ocean acidification not only affects the tropics. If CO2 emissions continue to increase at the present rate, parts of the polar-ocean surface become under-saturated with calcium carbonate by the middle of the century. This means they will actually become corrosive to calcium carbonate. The consequences on marine food webs in high latitudes are not understood.
We know that careful management of coral-reef ecosystems helps them to recover from the impacts of a mass-bleaching event. Fishing has a profound influence on reef recovery because the removal of grazing fish species allows algae to smother a damaged reef and prevent re-colonisation of the reef substrata by coral larvae. Sustainable management of fishing and prevention of destructive fishing practices maintain reef health and improve resilience to climate-change impacts. Likewise, the presence of sediments and pollutants can also damage reef health and inhibit reef recovery.
Coral reefs at this point will be in an uncontrolled decline from which recovery will be unlikely. Climate negotiations are currently discussing 450ppm atmospheric CO2 level as a target for stabilisation, not peak emissions. This means that, at best, careful management of coral reef ecosystems will postpone demise by a few decades. This may give human populations some chance of adaptation to the destruction of these ecosystems, but it will not save the biodiversity associated with coral reefs. By the end of the century we will have lost the most beautiful, most diverse and in socioeconomic terms, one of the most valuable marine ecosystems on the planet.
At the Tenth Conference of Parties for the Convention on Biological Diversity, there will be calls for more protected areas, greater action to restore populations of threatened species, more efforts to reduce consumption of biological resources and destruction of habitats.
But the elephant in the room that is climate change cannot be ignored. Beyond direct actions to protect biodiversity the message must be delivered clearly, without compromise, that failure to take action on climate change and curb CO2 emissions immediately and drastically will result in ecological catastrophe. The consequent loss of biodiversity and ecosystem goods and services will significantly impact the Earth and along with it humankind.
Alex David Rogers is a professor with the Department of Zoology, University of Oxford © 2010 Yale Center for the Study of Globalisation
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