The Earth's temperature is determined by a number of things including the composition of its atmosphere. Over the past 150 years, the balance between the production and consumption of carbon dioxide has changed. Principally, the burning of fossil fuels (coal, oil and gas) to derive energy to power transport, factories manufacture and modern lifestyles have begun to build up in the atmosphere. In addition to the changes arising from the burning of fossil fuels, the rapid change in the amount of land used for agriculture has also changed the concentration of other greenhouse gases such as methane. These changes in the atmosphere have increased the amount of energy (heat) that the atmosphere traps leading to the "enhanced greenhouse effect". Global temperatures have increased by 0.7°C since the late 19th century.
While it seems a very small amount, this increase in average global temperature has had a profound effect on the earth's climate as well as on the acidity of its oceans. The recent Intergovernmental Panel on Climate Change fourth assessment report clearly outlines the changes that have already occurred on the planet. These include changes to our natural ecosystems (e.g. coral reefs, rainforests), water and food production, sea level and storm intensity. These changes are of great concern, especially with the projected rise in the concentration of greenhouse gases such as carbon dioxide and methane over the next few decades and century.
It is very clear that we need to find out more about these changes. This project focuses on one of the signature natural ecosystems that is most susceptible to global climate change. For almost three decades, coral reefs have been registering increasing impact from global warming. As the earth's temperatures have risen, the temperatures of tropical oceans have increased to a point where warm summer temperatures exceed the tolerance of corals and the reefs they built. Corals that experience warm temperatures undergo a process known as coral bleaching, which occurs when the symbiosis that exists between corals (an animal) and tiny plants, known as zooxanthellae, breaks down. Corals are normally brown colour (due to the zooxanthellae) and when the symbiosis breaks down they go stark white (hence bleaching). There have been six major episodes of coral bleaching since 1979, before which they were unknown. In 1998, a major cycle of coral bleaching occurred as global temperatures soared and approximately 16 percent of all corals on the planet died. Because corals provide the habitat for the many thousands of other reef creatures, the impact of this cycle of thermal stress goes far beyond that of corals.
Corals also face another problem with respect to the rising concentration of carbon dioxide in the atmosphere. This is the problem of “ocean acidification”, which occurs when carbon dioxide enters the ocean and combines with water to produce a weak acid known as carbonic acid (approximately 25 percent of carbon dioxide omitted into the atmosphere ends up in the ocean). The carbonic acid that is produced releases a proton which combines with carbonate ions to form bicarbonate. A number of studies have shown that the decline in the concentration of carbonate ions is enough to slow and potentially stop the production of calcium carbonate, the principal compound in coral skeletons. There is growing evidence that relatively small increases in atmospheric carbon dioxide will lead to a rapid reduction of the ability of coral reefs to grow.
There are now many questions that we need to answer with respect to ocean acidification. The first of these is to understand how acidification affects a wide variety of corals, given that studies so far have only concentrated on one or two species. The second set of questions is to look at the effect of acidification on other organisms that also produce calcium carbonate through the process of calcification. Organisms such as red coralline algae are very important on coral reefs because they glue together the dead skeletons of corals to produce the reefs. Other organisms such as sea urchins, snails and crabs have larval stages which produce small skeletons of calcium carbonate as well. Without these skeletons, these organisms are likely not to be able to survive. The impacts of these changes need to be understood if we are to anticipate the conservation challenges that lie ahead.