CLIMATE CHANGE

What is Climate Change?

Climate change (or global warming) refers to the increase in average world temperature, especially over the last 50 years. There is broad agreement among climate scientists that this temperature increase is almost certainly due to an enhanced greenhouse effect resulting mostly from human activity.

What is the enhanced greenhouse effect?

Gases in the earth’s atmosphere trap heat from the sun, thus creating the conditions for life as we know it on earth. Without this natural greenhouse effect, temperatures on earth would be of the order of 30 degrees Celsius colder. Over the last 200 years (and particularly since the mid 20^th century), the release of carbon dioxide and other gases (predominantly from burning coal, oil and gas) has increased the levels of greenhouse gases in the atmosphere.

Pre-industrial levels of greenhouse gases are estimated to have been equivalent to about 280 parts per million (ppm) of carbon dioxide (CO2-e). Today levels are about 430 ppm CO2-e and increasing by about 2 ppm CO2-e per year. Climate scientists generally accept that the release of greenhouse gases from human activity is the main cause of the higher average world temperatures.

Why is climate change a problem?

Scientists forecast that an increase in average world temperature of only a few degrees Celsius is very likely to cause major changes to the earth’s ecosystems and natural processes. The most significant of these changes are:

Rising sea levels (caused by melting ice and snow on land and expansion of ocean water as it warms) displacing hundreds of millions of people - rises could be more than a metre by 2050, with some probability of rises in the tens of metres if significant portions of the Greenland and West Antarctic ice sheets melt or break up and slide into the sea;
Disappearance of glaciers in the Himalayas and the Andes, threatening hundreds of millions of people currently dependent on water from these glaciers;
Destruction of rainforests like the Amazon, which are a stabilising influence on climate;
Triggering ‘positive feedback’ processes such as the release of carbon dioxide and methane stored in the Siberian permafrost, which would further amplify temperature increases.

How do positive feedbacks create further temperature rises?

Global temperature rises can create the conditions for even greater rises (positive feedbacks).

Examples of these positive feedbacks are:

o warming results in significantly more water vapour (the main greenhouse gas) evaporating into the atmosphere;

o as ice melts, the land or water now below the ice (being less reflective than ice) absorbs more solar heat;

o the warming and thawing of permafrost in Siberia and elsewhere are expected to release very large amounts of stored greenhouse gases (carbon dioxide and methane) into the atmosphere.

All these positive feedbacks will create further temperature rises. There is a serious risk that if the average global temperature exceeds a ‘tipping point’, natural processes will cause even greater temperature rises, resulting in large sea level rises affecting the Australian coastline as well as major cities like London and New York.

How can we avoid reaching a tipping point?

A broad consensus is growing that there is a tipping point at about 2 degrees Celsius above pre-industrial temperature levels, beyond which the impacts may be very difficult to manage. The European Union for example, has adopted 2 degrees C as a target for the maximum temperature rise.

Climate modelling suggests that to limit the risk of average global temperature rise exceeding 2 degrees C, we will need to stabilise the level of atmospheric greenhouse gases below 450 ppm CO2-e. The Intergovernmental Panel on Climate Change (IPCC) in its Fourth Assessment Report indicates that a CO2-e level of 445-490ppm is likely to produce an average temperature rise of 2.0-2.4 degrees C (see http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_SPM.pdf).

What will be required to limit greenhouse gases to 450 ppm CO2-e?

Greenhouse gas emissions from both human and natural sources are more than the earth can absorb and excess greenhouse gases ‘spill over’ into the atmosphere. With greenhouse emissions currently increasing by about 2 ppm CO2-e each year, levels in the atmosphere are likely to reach 450 ppm CO2-e within about 10 years. The IPCC Fourth Assessment Report suggests that greenhouse gas emissions would need to peak and start to decline before 2015.

There is a very urgent need to reduce the rate of growth in emissions so that there is enough time to move towards a ‘low-carbon’ society.

Why is effective action on climate change urgently needed?

With global greenhouse gas emissions continuing to rise, climate modelling suggests that there is significant risk that the global temperature will pass a tipping point before 2020 unless the rate of emissions growth is urgently cut back.

While both the Government and the Opposition in Australia are supporting some action on climate change, there is little indication that the major political parties understand the scale of what is required or the urgent need for effective action to prevent dangerous climate change.

What is the scale of the task to prevent dangerous climate change?

Effective action must be based on the best scientific analysis and forecasts, not on what may be considered politically acceptable. There is a growing consensus that the task must be to prevent average global temperatures exceeding 2 degrees above pre-industrial levels.

A long-term target (e.g. 60% reduction by 2050) for greenhouse gas reductions is likely to be irrelevant if the tipping point of 450 ppm CO2-e level is exceeded by 2020 and the rapid melting or breaking up of the Greenland or West Antarctic ice sheets, or significant melting of permafrost is set in train. Immediate effective action to rapidly slow greenhouse gas emissions within the next 5 years is what is needed.

An example of the scale of the response required has been proposed by James Hanson (NASA climate scientist and one of the earliest to sound a warning on dangerous climate change). In Hansen’s view, we urgently need to promote energy efficiency and renewable energy so that construction of new coal, gas or oil fired power stations can be delayed until the viability of large-scale carbon capture and storage technology has been proven (or alternatively, found to be impractical) (see http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_1.pdf). In Australia, promoting energy efficiency is likely to require phasing out the billions of dollars of subsidies that are paid by governments to coal and oil companies (see http://www.isf.uts.edu.au/publications/ISFsubsidiesreport2007.pdf).

Click on the Effective Solutions tab for other effective responses.