On the edge of global calamity

Professor Kurt Lambeck
President, Australian Academy of Science

Much already has been said about the fourth and latest Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). It has been reported upon, discussed and analysed endlessly by a procession of journalists, scientists, politicians and commentators.

But the basic facts are undeniable, indisputable and confirmed by the best minds the world can bring to bear on the subject: human release of greenhouse gases into the atmosphere has and will continue to cause global warming for many decades.

These central conclusions of the report, announced last Friday, further strengthen the assessments of the previous three IPCC Reports in 1990, 1996 and 2001.

This is a gloomy prospect, to say the least, made even more emphatic by the fact that this confirmation comes from an intensive review of the past five years’ scientific evidence by hundreds of scientists worldwide.

And painful though it may be for our politicians, industrialists and other business people, wouldn’t it have been good if they had sat up and taken notice five years ago. The planet was suffering badly then: five years on, we have lost that precious time, five years that could have been used in implementing remedial action.

While continued climatic change now seems inevitable, the Australian Academy of Science believes that it is important to reduce the pace of that change as much as possible, to give extra time for societies and ecosystems to adapt as smoothly as possible.

To get a sense of perspective, let’s look at some of the figures which, seen in human terms, are downright daunting: the concentration of carbon dioxide (CO2) in the atmosphere is now over 380 parts per million — 35 per cent above the pre-industrial concentration — and increasing faster than ever due to rapidly expanding emissions from the combustion of fossil fuels.

Our seas and oceans aren’t coping well either: the fraction of annually emitted CO2 absorbed by the oceans is declining and is now down to 37 per cent.

The global average surface air temperature has increased by more than 0.7°C over the past century and 10 of the 11 warmest years since measurements started around 1850 have occurred since 1995.

Other changes to the climate system include increasing global ocean temperature down to several hundred metres, accelerating sea-level rise, cooling of the stratosphere and significant decreases in the extent of Arctic sea-ice and of northern hemisphere seasonal snow cover.

Then there’s the retreat of most glaciers; and changes to the characteristics of extreme events like frost, heat wave and drought frequency and of intense rainfall events and cyclones.

The changes cannot be explained by normal climate variability or by any alternative ‘climate-forcing agents’ like solar intensity variation or volcanic eruptions, which are known to play a role in normal climatic variability from decade to decade.

The worldwide extent of these changes shows fingerprints of human-induced forcing and matches the predictions from the best models of the climate system.

The good news about the bad news is that many improvements have been made to the computer-models of the climate system used to project future change.

These include better understanding of feedbacks in the climate system, higher spatial resolution and extensive international testing and model comparisons. However, there is still some uncertainty in the projections and best estimates of global average surface air temperature in 2050 range from 1.3°C to 1.7°C above the present value.

Even if atmospheric CO2 concentration were to be stabilised immediately at today’s concentration, time-lags and inertia in the climate system would produce continued warming.

This would initially be at a rate of 0.1°C per decade and would total 0.5°C over the 21st Century. Given the time needed to develop technology to replace carbon based energy — and the socio-political inertia to change policies, aspirations, behaviour and demand — much greater ultimate global warming than a further 0.5°C is virtually certain.

So, what does it all mean for Australia? A significant common prediction of the various models is that there will be a pole-ward shift in the mid-latitude westerly winds and their associated storm track, leading to more frequent droughts in southern Australia.

Whether the sudden and persistent decline in annual rainfall in the south-west of Western Australia in the 1970s and recent prolonged current drought in eastern Australia are early expressions of that prediction cannot yet be stated with any certainty.

But they are, without a doubt, consistent with the predicted changes due to increased greenhouse gas concentrations.

Droughts and floods will come and go in Australia as always. But with global warming causing a southward shift of storm tracks across southern Australia it’s expected that in future they will occur within a background of gradually declining rainfall in that area during this century.

Other areas of the country and the world will experience increased rainfall.

However, it is important to remember that annual rainfall is not the only thing that is expected to change with global warming.

Accelerated sea level rise, changing seasonal weather patterns and unanticipated repercussions of the collective policies by governments, NGOs, companies and individuals to try to do something about it, will also have substantial socio-economic effects.

Let’s hope there’s a change in the weather soon on accountability and action for the Earth’s climate. Otherwise, our children will be living in a world that would be well-nigh unrecognisable to us.

Published in The Australian, 7 February 2007