Why we must act now to reduce greenhouse gas emissions
Each year humans emit more greenhouse gases than the previous year. Australia needs to help turn this around if we don't want to bear the brunt of climate change, says Chief Scientist Professor Penny Sackett.
The world is at a crossroads.
We must contain and then reduce our greenhouse gas emissions so that our farmers, graziers and fishermen have the best chance to feed the world, and our industries have the best opportunities for sustainable growth and new green markets.
So that we — along with the rest of Earth's inhabitants — are best able to flourish in good health, and the world's poorest have the best opportunity for hope.
The leading climate scientists from the world over warn that we have about five years to avoid the dangerous climate change that would be generated if average global temperatures increase by more than 2°C above pre-industrial levels.
Australia will be one of the most affected regions in the world if we exceed this 'guardrail' temperature.
For example, regional climate change projections indicate that we are likely to see an increase in the frequency and intensity of wildfires (predominately in south-eastern Australia), an increase in the severity of cyclones, decreased rainfall (except in the far north), increased incidence of drought, and an increase in extreme temperatures.
To avoid hitting the guardrail, annual global emissions must reverse from increasing every year, as they do now, to decreasing every year.
The globe has warmed by nearly 0.8°C over pre-industrial levels. Global temperatures will increase by another 0.5°C as the Earth continues to react to the emissions that we have already emitted in the atmosphere, much of which lingers there for a century or more.
Taken together, this means that climate change corresponding to a 1.3°C temperature rise is now 'locked in'. Our previous actions have already placed us more than half way to the 2°C guardrail, and yet rather than putting our foot on the brake, we have it on the accelerator.
The greenhouse effect
The sun continuously bathes the Earth with energy in the form of sunlight. Much of this energy is absorbed by the Earth, and then emitted as infrared radiation, or heat. Greenhouse gases prevent the Earth from discarding as much of this heat as it otherwise would back into space.
Without naturally occurring greenhouse gases, the Earth would be a much colder place, inhospitable to modern human existence. But by the same token, the additional greenhouse gases added to this store by humans is slowly increasing the average temperature of the Earth system.
Due to the quantity in which it is emitted by humans, its longevity in the atmosphere, and its effects in trapping heat, carbon dioxide is the most important of the greenhouse gases currently causing changes in the Earth's climate.
While the growth of human carbon dioxide emissions slowed in 2008, a slight reprieve attributed to the global financial crisis, they are still tracking above the worst-case scenario considered by the Intergovernmental Panel on Climate Change (IPCC) in their 2007 report.
In fact, atmospheric levels of the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are higher now than at any time since modern humans have evolved.
Too much energy
This growing store of greenhouse gases, is leading to extremes in our weather and changing the long-term climate. Summers are becoming hotter, and droughts are longer and drier. The oceans are becoming more acidic. Sea levels are rising as glaciers melt and the warmer water expands.
If we do not act now, the newest and best science indicates that the average global sea level in 2100 will be 75 to 190 centimetres above 1990 levels, and continue to rise thereafter.
In Australia, extreme fire danger days are already becoming more numerous in many parts of the country, and floods and cyclones more intense.
Research by the CSIRO indicates that the frequency of days with very high and extreme Forest Fire Danger Index ratings is likely to increase by 15 to 70 per cent by 2050 in southeast Australia.
With much of Earth's biosphere already 'feeling the heat', the Great Barrier Reef ecosystem is in grave danger both due to increased water temperatures, and increased acidification as the ocean absorbs some of the additional carbon we have placed in the atmosphere.
Changes have been observed in the breeding and migratory patterns of birds, fish and animals; and plant species have spread into latitudes that were previously too cold for them.
Reaching a limit
Why is limiting the average global temperature rise to 2°C so important?
The primary answer is it will be very difficult to adapt to and thrive in temperatures any higher.
As a single example, an increase of surface wind speed of 5 metres per second, made possible with a 1°C rise in ocean temperature, would double the frequency of Category 5 tropical cyclones.
In 2006 Cyclone Larry, a marginal Category 5 cyclone, devastated approximately 12,500 square kilometres around the far north Queensland town of Innisfail and destroyed the region's banana industry.
Exceeding the 2°C guardrail will also reduce Earth's limited ability to counteract some of the effects of climate change. If the temperature rise is 2.5°C or more, land ecosystems may emit carbon rather than absorb it, contributing to rather than acting as a buffer against climate change.
Already, the fraction of anthropogenic carbon dioxide that is absorbed by the ocean 'sink' (a form of 'free' climate change mitigation) has decreased in last 50 years, for reasons that scientists are still studying.
Time is short
And why must we act quickly?
Calculations catalogued by the 2007 IPCC report tell us that if global temperature rise is to be kept between 2.0 and 2.4°C, then the 'CO2 equivalent' concentration, which is used as a combined measure of all Kyoto greenhouse gases, must not be allowed to exceed the range between 445 and 490 parts per million (ppm).
Current CO2 equivalent emissions are 455 ppm and rising.
To meet the 2°C guardrail target, we must halt increases in global CO2 equivalent emissions by about 2015, and then decrease them dramatically and steadily thereafter.
Around the world, individuals, communities and nations are implementing effective strategies to do their part to effect this change. Australians have a leading part to play in demonstrating how this can be done even in a society known for having the highest carbon emissions per capita. But we need more shoulders at the wheel, because time is short and the clock is ticking - loudly.
Professor Penny D Sackett began her appointment as Chief Scientist for Australia in November 2008. She is an accomplished cross-disciplinary scientist with a record of academic excellence on three continents.
Published 25 November 2009