Global climate change

In the past, global climate has changed due to a variety of causes. Increasing amounts of greenhouse gases in the atmosphere as a result of human activity since the industrial revolution has added a new, relatively rapid source of climate change. The most significant greenhouse gas is carbon dioxide, which has increased in concentration by more than a third in the last 200 years due to burning of fossil fuels and to deforestation. The concentrations of other gases, such as methane and nitrous oxide, and the ozone-depleting halocarbon gases have also greatly increased over the same period. Enhanced greenhouse gases in the atmosphere warm the air by trapping heat from the Sun that would otherwise radiate from Earth back towards space. The warming that results is similar to that which occurs inside a greenhouse.

Bleached reefs can be seen from the air. Photo by GBRMPA.

Complex computer models are used to project climate change due to enhanced greenhouse gases. Models have to take into account that atmospheric temperature rises with increasing carbon dioxide but is decreased by other gases such as aerosols, and also by the reduction in ozone. Importantly, the longevity of different gases in the atmosphere varies. Carbon dioxide
is particularly long-lived and likely to persist at elevated levels for centuries. About 30% of the increased carbon dioxide in the atmosphere has been absorbed by the oceans and is changing ocean chemistry. There is concern that the oceans are becoming more acidic which will negatively affect the ability of corals to deposit carbon from the oceans into their skeletons and form reefs. Some carbon dioxide has also been taken up by plants and will only be released when the plant decomposes, is eaten or is burnt.

Since the end of the 19th century (for which there are instrumental climate records), the average global temperature has warmed by 0.6°C. During the same time, average water temperatures of the Great Barrier Reef have warmed by 0.4°C. According to a recent international study, global average temperatures are projected to warm by another 1.4-5.8°C over the next 100 years. This average warming is greatest at higher latitudes. Tropical ocean temperatures where coral reefs live are likely to warm between 1-3°C by the end of this century. Warmer global temperatures will have dramatic effects on current global climate patterns. These include changes in ocean circulation patterns; increased frequency of storm events; and rising sea level due to expansion of warmed oceanic water and loss of land ice.

CRC Reef Research Centre Ltd was established and is supported under the Australian Government’s Cooperative Research Centres Program. Its mission is to plan, fund and manage world-leading science for the sustainable use of the Great Barrier Reef World Heritage Area. CRC Reef is a joint venture between Association of Marine Park Tourism Operators, Australian Institute of Marine Science, Great Barrier Reef Marine Park Authority, Great Barrier Reef Research Foundation, James Cook University, Queensland Department of Primary Industries and Fisheries, Queensland Seafood Industry Association, Sunfish Queensland Inc. The University of Queensland is an associate member.