Four Australian scientists have their say on climate change issues

The Daily Telegraph 8 Dec 09;

HERE, four Australian scientists give their opinions on coastline erosion, melting ice, carbon emissions and the fate of the Great Barrier Reef. Do you agree with their findings?

Bottom line: The Reef will slowly die
By Ove Hoegh-Guldbe

THE Great Barrier Reef is one of the most spectacular places on Earth. Stretching over 2000km along the northeast coast of Australia, it is the largest continuous coral reef ecosystem in the world. From orbiting spacecraft, it is one of the few signs of life on our planet.

Home to thousands of unique species, the Reef is important to the Australian economy, bringing in over $6.5 billion each year in tourist and fishing income. It is valuable and robust and has been a persistent feature of Australia for thousands of years.

So, why are the majority of coral reef scientists telling us that its days are numbered?

Coral reefs all over the world have faced challenges from human activities such as poor farming practice along adjacent coastlines, pollution and overfishing. This has led to the large-scale loss of reef-building corals, which lie at the heart of these complex and important ecosystems. In Australia, this has led to an increased attention to solving these problems from governments. Beginning in the early 1980s, however, mass coral bleaching began to occur on the Great Barrier Reef. Coral bleaching occurs when the relationship between corals and tiny plant-like organisms falls apart across thousands of square kilometres of coral reef. Corals then tend to get diseased and die.

The increase in the death rate of corals can be enormous. In 1998, for example, 16 per cent of the world's reef-building corals died in a single year.

These massive events coincided with small increases (1-2C) in sea temperature above the long-term maximums. In 1998 and 2002, our Reef experienced the worst episodes of coral bleaching, with over 60 per cent affected.

Scientific investigations indicate that coral reefs are extremely sensitive to small increases in sea temperature. Sea temperatures on the Reef are slowly increasing, and projections of ocean temperatures from 2030 onwards indicate they will be too warm for reef-building corals.

Without corals, the habitat for unique species will cease to exist.

Ove Hoegh-Guldberg is Professor of Marine Studies and Director of the Global Change Institute at the University of Queensland

Immediate action pivotal on emissions
By Dr Michael Raupach

CARBON dioxide (CO2) is the most important greenhouse gas directly influenced by human activities. Its concentration has increased from about 280 parts per million (ppm) at the start of the industrial revolution to 386ppm today, and is now rising at nearly 2ppm per year. This is happening because global CO2 emissions, mostly from fossil fuel combustion, are climbing rapidly. Emissions increased by over 3 per cent per year since 2000. Most of the recent and future growth in CO2 emissions is occurring in developing countries, which now account for 55 per cent of the fossil fuel emissions. However, emissions per person from the developing world are still only about a quarter of those from developed (OECD) nations.

Where does all this CO2 eventually end up? At present, worldwide emissions from fossil fuel burning add 4ppm worth of CO2 to the atmosphere each year, with a further 0.6 ppm from deforestation. That adds up to nearly 5ppm entering the atmosphere each year - but only 2ppm stays there. The rest is removed from the atmosphere by land and ocean "CO2 sinks", through net uptake into growing vegetation and into the surface layers of the ocean. These sinks are great planetary stabilisers, discounting the greenhouse impact of CO2 emissions by about 55 per cent. If emissions continue to rise rapidly, the sinks will not be able to keep up and will not continue to offset emissions.

If we are to avoid dangerous climate change (a temperature increase of over 2C above preindustrial temperatures), then the total amount of CO2 that can be emitted by the human race is limited. On our present course, without rapid reductions in emissions, this limit will be reached in under 35 years. We must decarbonise our energy systems in a shorter time than this.

Michael Raupach is a research scientist in CSIRO Marine and Atmospheric Research and a Fellow of the Australian Academy of Technological Sciences and Engineering

Melting ice is pushing up sea levels
By Dr Ian Allison

POLAR regions will continue to heat up more over the coming century than the rest of the earth.

Already major changes are occurring to ice and snow in both Antarctica and the Arctic.

These changes affect the rest of our planet in several ways. When the reflecting and insulating cover of seasonal sea ice decreases, the ocean absorbs more heat and warming increases and when ice is lost from the ice sheets, global sea level rises. A decrease in the summer minimum Arctic sea ice extent has occurred since accurate records began. The last three years were the lowest on record, with an average of 2 million sq km less ice than the 1979-1999 average. The average winter thickness of Arctic sea ice has decreased by 1.75m (48 per cent) since 1980.

In Antarctica there has been a small increase in winter sea-ice extent due to changes in Southern Ocean winds. There is considerable regional variability, with some regions showing significant decrease in winter ice and in the length of the ice season.

Both the Antarctic and Greenland ice sheets are now losing ice and contributing to sea level rise. Evidence of this comes from three different satellite-based technologies. Measurements show the ice sheet surface is thinning. The net loss from Antarctica and Greenland is about the same and this contributes about 12cm per century to sea level rise. But the rate of loss has increased from near zero in the mid 1990s, and is accelerating.

Much of the loss is occurring because the flow of large glaciers has increased. This is probably a result of reduced "buttressing" of the flow from floating ice shelves around the coast, which have thinned and in some cases collapsed completely.  If the rate of discharge continues to increase, the ice sheet contribution to sea level rise by the end of the century will be considerably more than 12cm.

Dr Ian Allison is a glaciologist at the Australian Antarctic Division and the Antarctic Climate and Ecosystems CRC

Erosion of coastline is inevitable
By Dr John Church

GLOBALLY, the sea level has risen by about 20cm since 1870 and is continuing to rise.

Its rate of rise has accelerated and, since the early 1990s, is almost double the average rate for the 20th century.

The evidence is clear and comes from coastal sea level observations around the world.

There are two main reasons for recent sea-level rise. Firstly, observations show the oceans have absorbed vast amounts of heat. As the oceans warm, they expand and sea level rises. Secondly, as a result of warmer temperatures, many mountain glaciers in Alaska and elsewhere are melting and contributing to rising sea level.

The Greenland and Antarctic ice sheets have the greatest potential to contribute to sea-level rise. Recent satellite observations of the height of these ice sheets, the speed at which ice is flowing into oceans, and their mass, all indicate an accelerating contribution to sea-level rise.

Current models project a sea-level rise of about 20 to 80cm above 1990 levels by 2100, including an allowance for the poorly understood ice sheet contributions. Sea level is currently tracking near the upper limit of these projections and some studies have suggested a rise of well over a metre is possible.

Because of the long time scales of ocean and ice sheet processes, sea level will continue to rise for centuries after greenhouse gas concentrations are stabilised. Substantial reductions of global greenhouse gas emissions now will result in a lower future rise.

Rising sea levels will increase the frequency and severity of coastal inundation and erosion.

Without significant reduction of emissions, temperatures could pass a threshold during the 21st century that is likely to result in an ongoing decay of the Greenland ice sheet and a sea-level rise of metres.

Dr John Church is from the CSIRO's Marine and Atmospheric Research unit