Rising sea surface temperatures will affect every aspect of the Great Barrier Reef. Gradual overall increases in sea surface temperatures are expected as a result of climate change.

Temperature is a key environmental factor controlling the distribution and diversity of marine life. It is critical to reef building and controls the rate of coral reef growth.

All animals and plants have temperature limits and when these are reached, natural processes may break down. On coral reefs, temperature changes can affect the relationship of mutual dependence between some animals and the algae which live within their tissues.

Atmospheric temperatures, lack of cloud cover and freshwater run-off all contribute to rising sea surface temperatures.

The temperature gradient along the Great Barrier Reef has shifted markedly over the last century. When averaged across the last 30 years, sea surface temperature in the Great Barrier Reef has increased by about 0.4^oC, compared to records averaged across 30 years in the late 1800s.

The two warmest five-year average sea surface temperatures have been recorded in the last decade. Analysis of coral cores in centuries-old corals suggests that current temperatures are warmer now than over the last three centuries. The summer of 2010 saw the highest recorded sea surface temperatures in Australia.

Projections

The average annual sea surface temperature on the Great Barrier Reef is likely to continue to rise over the coming century and could be as much as 1°C to 3°C warmer than the present average temperatures by 2100.

Whatever climate scenario is used, it is predicted that by 2035, the average sea surface temperature will be warmer than any previously recorded.

It is likely that sea surface temperatures might warm more in winter and in the southern Great Barrier Reef. Projected increases in average sea surface temperatures indicate that by 2020 it could be 0.5°C warmer and greater than 1°C warmer by 2050.