Melbourne Unitarian Peace Memorial Church

Presentation by Chris Mardon, Victorian Greens spokesperson on Energy & Greenhouse, September 1, 2002 to the Melbourne Unitarian Peace Memorial Church

You may have heard the increasingly strident warnings about global warming and climate change over the past few years. Our federal government still seems to be in denial, but scientific bodies such as the CSIRO and Intergovernmental Panel on Climate Change are certainly not. Global temperature records have been kept since the 1860s and they show that temperatures have been rising since the early 1900s, and the 1990s were the warmest decade on record.

It is often suggested that it would be ruinously expensive to reduce our greenhouse gas emissions because the economy is so dependent on energy.

Must we choose between reducing our use of energy or accepting that climate change is inevitable?
Can renewable energy provide a realistic alternative to fossil fuels?
Is it really so expensive to reduce our consumption of energy?
If not, what barriers stand in the way of reducing it?
Do we have a choice, and who will make it?
These are some of the issues that I would like to cover in this talk.

Global-average surface temperatures are projected to increase by 1-6°C over the next 100 years, depending on what we do to reduce emissions. Hence, if we do nothing, the temperature increase over the next century could be an order of magnitude higher than the increase over the past century!

The threat of climate change is not just very serious – it is potentially catastrophic and could lead to the extinction of all life on this planet.

The current concentration of carbon dioxide in the atmosphere is about 360 ppm. The fossil record suggests that the concentration of carbon dioxide in the atmosphere has been below 400 ppm for the last 23 million years. Also, air bubbles trapped in Antarctic ice have shown that apart from the last 100 years, the concentration has cycled between 200 and 300 ppm for the past 420,000 years. Hence, it is only now that ecosystems are faced with really rapid changes in climate and both animals and plants must try to adapt to those changes as best they can. Even if greenhouse gas emissions ceased tomorrow, the time lags and sheer momentum of the physical processes involved in the climate system are such that the concentration would continue to rise for some years, so climate change and sea level rises would also continue for 200-300 years!

In order to stabilise the atmospheric carbon dioxide concentration at current levels within 150 years, we would have to completely eliminate the burning of fossil fuels within 60 years and then plant more forests to suck carbon dioxide out of the atmosphere so as to bring it back to 350 ppm. This means that not only do we need to take very drastic action to reduce emissions at source – we also need to reserve forests for the absorption of historical emissions, not to absorb new emissions.

There have been furious arguments about why global warming is happening, and there are still some sceptics who even deny that it is happening at all. It is generally agreed that the reason why we do not suffer the extreme temperatures experienced by other planets such as Mars and Venus is because we are protected by our atmosphere. Unlike other planets, our atmosphere is 100 km thick and it contains a number of gases that act as a thermal blanket. The lower atmosphere is about 8-10 km thick and contains about 90% of the total mass of the atmosphere. Within that layer, our daily weather occurs – winds, clouds, rain and snow. Without the replenishing actions of life on Earth, the distinctive composition of our atmosphere would not be sustainable.

The atmosphere's role in regulating the earth's temperature and weather is very complex. The atmosphere freely admits solar radiation to the Earth's surface, but then traps some of that energy when it is re-radiated outwards as heat. This is what causes the so-called greenhouse effect. Naturally occurring greenhouse gases – mostly water vapour, carbon dioxide and methane – each absorb part of the heat radiation. It is the retention of this radiant energy in the lower atmosphere that keeps us warm. The average global surface temperature, 15°C, is about 34°C warmer than it would be if all of the re-radiated heat escaped back into space. Without this atmospheric heat blanket, water would freeze and life would not be possible. The greater the concentration of these greenhouse gases, the bigger the warming effect within the lower atmosphere.

Over the past 160,000 years, atmospheric concentrations have been fairly stable, and fluctuations in the atmospheric concentrations of carbon dioxide and methane have been closely correlated with changes in the average global temperature. The correlation suggests that that variations in atmospheric carbon dioxide contributed to variations in global temperature.

This theory of the greenhouse effect is actually not new. The Swedish scientist Arrhenius published a paper in 1896 in which he calculated that a doubling of the atmospheric concentration of carbon dioxide would lead to an average increase in global temperatures of 4-6°C. This estimate was remarkably close to current estimates based on sophisticated mathematical models, but at the time, there was no evidence of any actual global warming. He lived during the early industrial revolution when fossil fuels such as coal were being used for the first time. Fossil fuels contain carbon, and this forms carbon dioxide when it is burnt. The consumption of fossil fuels is now so great that it is having noticeable effects on our climate. The atmospheric concentration of carbon dioxide has risen from its pre-industrial level of 280 ppm to about 360 ppm, and the rate of growth of this concentration is accelerating.

One consequence of global warming is that the oceans expand and sea levels will rise. Glaciers are already starting to melt, but if the great ice sheets in the polar regions start to melt, then much greater rises in sea level will occur. Low-lying countries such as Holland, Bangladesh and the small island states in the Pacific and elsewhere, are all threatened by this rise in sea level. The incidence and strength of hurricanes and other extreme weather events will increase as global warming continues. In northern Australia, we are likely to see a shift of tropical monsoons further south, and drier conditions in southern Australia. The Great Barrier Reef is already being damaged by coral bleaching, which is caused by warming of the surface of the ocean. It could be destroyed completely within 30 years.