Up to now it has been generally assumed that global warming will be a linear process. However evidence from the geological past linked with climate modelling that takes into account the global warming that is already locked into the system indicates that there may not be a linear response to rising CO2 levels. There is a danger that at some point we will cross a threshhold when global warming accelerates. By continuing to increase the amount of CO2 in the atmosphere we are getting closer to that point.
From the analysis of the bubbles of air trapped in ice cores taken from the Greenland icecap that are up to 500,000 years old it has been shown that the temperature of the Earth's atmosphere and the CO2 content has followed a regular 100,000 year cycle of change with the CO2 content and temperature closely linked and following the same graph line. Within this regular cycle there are some recently discovered very short periods of approximately only a few hundred years duration when temperatures rise dramatically by 8 degrees centigrade above the slower rises of up to 7 degrees centigrade. This gives a total range of 15 degrees centigrade from peak to trough. These records show natural processes at work before the impact of man's activities. We are currently in the lower temperature part of the cycle.
During the period covered by the ice core research the CO2 content of the atmosphere has varied between 170 and 280 ppm. (parts per million). From 1850 to today with the added input from the burning of fossil fuels the CO2 content has risen to 350 ppm. So we are now well outside of the historic range of values and CO2 levels are going to continue to rise for a long time yet and temperatures will follow.
Recent research has shown that the Amazon rain forest is not a stable mature forest with growth and decay in balance but is in fact an expanding forest that is being fertilised by the excess atmospheric CO2. The trees are getting bigger and there is a net take up of 5000 kg of carbon per hectare per year (1 hectare = 100 x 100 metres). The total area of forest is 400 million hectares so the whole forest could be absorbing 2 billion tons of carbon per year.
Research in the savanah lands to the east of the Amazon Basin has established that the crucial factor determining the development of the rain forest is the length of the dry season. The savanah to the east of the Amazon Basin and the eastern Amazon rain forest both receive about the same amount of rainfall, 1500 mm per year. However in the savanah the dry season lasts 6 months but in the rainforest the dry season only lasts 4 months.
As a result of the longer dry season the savanah catches fire an average of twice in ten years whereas the rainforest with the shorter dry season does not dry out and remains damp enough to prevent fire. In the savanah the fires destroy most of the vegetation and this prevents the savanah developing into a rainforest. If the dry season in the rainforest was extended to 6 months by climate change effects then the rainforest would dry out and burn and could not then re-establish itself. If the rainforest burnt this would release the CO2 currently being absorbed year by year. So the forest would change from being a buffer which for a hundred years has absorbed our excess CO2 into a major source of CO2 releasing tens of years build up of CO2 in a matter of weeks.
It is accepted by all, including climate change sceptics, that increasing the amount of CO2 in the atmosphere will lead to increased global warming and many computer models have been constructed giving a rise in average atmospheric temperature of between 2 and 6 degrees centigrade by the end of the century i.e. by 2100.
But only now are models being constructed that incorporate a feed-back into the model of the effects of changes in world climate due to the changes in temperature that are predicted by the model as the model programme runs. One of the most important effects of climate change is the release of carbon dioxide from natural processes as atmospheric temperature rises.
Because of the "above normal" level of CO2 already in the atmosphere we are already committed to a certain amount of global warming because the excess CO2 will remain effective for many years. In addition the continued burning of fossil fuels will continue to add to the atmospheric burden of CO2. This warming will inevitably cause some climate change.
The area of the world most vulnerable to the effects of global warming induced climate change is the Amazon basin. The climate change models show that rising sea temperatures in the Pacific Ocean result in less rainfall and a longer dry season in the Amazon Basin. As described above this could lead to a reversal of the Amazon basin acting as a CO2 sink and it becoming a major source of CO2 returning the billions of tons of carbon to the atmosphere that have been stored there.
If the Amazon rainforest burns and releases billions of tons of CO2 into the atmosphere in a short period then this will be a further boost to global warming that will result in significantly higher end of century temperatures.
The climate change model with climate change induced feedbacks indicates that on present trends the date for the change from CO2 sink to source for the Amazon rainforest is about 2050. So we have not got much time to get CO2 under control before that might happen. The Amazon rainforest is at present still acting as a buffer and is protecting us from the full effect of the global warming that would be created if all the CO2 we produce remained in the atmosphere.
If temperatures rise too high then there could be another natural phenomenon which would lead to the release of methane into the atmosphere. Methane is a very powerful greenhouse gas
Current research based on the analysis of ancient sediments from Vladivostock and fossil evidence from Wyoming indicates that runaway methane global warming events have occurred in the past and the conditions prevailing on Earth now are suitable for it to happen again.
James Nash is a climate scientist with Greatest Planet (www.greatestplanet.org). Greatest Planet is a non-profit environmental organization specialising in carbon offset investments.
James Nash is solely responsible for the contents of this article.