Myths on the Greenhouse Effect
Here is a list of some of the most common myths about the greenhouse effect, and a brief explanation of why they are wrong.
Ice caps melting
A common myth is that sea level rises will be caused by melting polar icecaps. While this might happen over hundreds or thousands of years, the sea level rises predicted for the next 40 years will be caused by ocean water expanding as it warms and by some melting of non-polar ice.
Is it hotter now?
Another myth is that greenhouse predictions are based on extrapolations of past temperature rises. The global record does in fact show an average warming of about 0.5 degrees Celcius over the past century.Scientists do not regard this as definative and do not base their predictions on this. However, they believe greenhouse warming will become unmistakable over the next two or three decades.
There have been claims that measurements of global temperatures have been distorted because a number were made in cities, with local temperature rises caused by urban development. In fact climatologists have long recognised the "urban heat island effect", and have allowed for it in their assessments. And ocean temperatures, which cannot be affected by the heat island effect, also show global warming.
It's just a theory
Wrong. There is unequivocal evidence that greenhouse gases are increasing in the atmosphere. Since the industrial revolution the level of carbon dioxide alone has risen from 280ppm (parts per million) to 350 ppm. This will have an effect on the world's climate. What is not clear is the magnitude of that effect - predictions now are based on comparing results from the best of the world's computer models.
Greenhouse is part of a natural cycle
No - greenhouse is a natural phenomenon, but the extra gases produced by humanity are making it stronger. If it weren't for the natural greenhouse effect the Earth would be about 33 degrees Celcius cooler than it is. The planet is warm because naturally occurring gases (including carbon dioxide) trap heat which would otherwise escape into space. But now humanity is adding to these gases faster than oceans and plants can absorb them - the greenhouse effect is being unnaturally "enhanced."
Of the estimated seven billion tonnes of carbon from human-generated carbon dioxide going into the atmosphere each year, three billion tonnes stay there. We know the oceans take up about two billion tonnes. The remainder, often referred to as 'the missing sink' must also be going into the ocean or be taken up by living plants. This missing sink does not render the greenhouse theory invalid, as it is the three billion tonnes known to remain in the atmosphere which is of concern.
It's only caused by burning coal
This is not true. The biggest contributor to carbon dioxide emmissions is fossil fuel (coal,oil and gas). But carbon dioxide also comes from the destruction and burning of forests, and there are other gases involved as well - methane, nitrous oxide, ozone and CFCs - generated by many different human activites.
Computerised climate models can't tell us anything
Not so. The most recent climate models are surpisingly good at simulating the broad features of our present climate. Global distribution of surface temperatures, winds and precipitation over the seasons are very similar to what is observed. This shows that, while there is still need for further improvement, the models are not far out in the way they represent the processes at work. It also lends confidence to the general conclusions that are drawn from climate model experiments about the effect of increased levels of greenhouse gases.
Source: CSIRO (Australia) Information Sheet