However, what is of huge concern and of global significance both short-term and increasingly long-term is enhanced levels of greenhouse gases caused by human activity. The greenhouse gases which are being produced in vast quantities by human activity are carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulphur hexaflouride and these are the six major gases restricted by the Kyoto Protocol. These gases are produced by a vast array of human activities but there is no doubt that the current global dependence on fossil fuels whether for electricity generation, heating and motorised vehicle use is the biggest contributor. In Ireland there is an additional significant contribution to methane levels due to the enormous number of cattle and sheep in the country.

The clearest way of showing how much change has been caused to the atmosphere is take a brief look at the levels of carbon dioxide. In 1600 the level of carbon dioxide in the atmosphere was around 275 parts per million by volume (ppmv). From then until now this level has been rising at a faster and faster rate to the current level of over 360 ppmv. This is a higher level than has been experienced by the Earth for at least 200,000 years and the rate of increase is probably faster than at any time in the Earth's history. It is estimated that this change represents the release into the atmosphere of over 210 billion tons of carbon dioxide cause by human activities over the last 400 years. Along with increases in the other greenhouse gases humans are in effect carrying out a massive global scale experiment on the atmosphere of the planet with up until recently no idea of the short and long term impact of this experiment. As we are learning you cannot significantly alter the composition of the atmosphere without having a significant climate effect.

This significant climate effect is global warming and is caused by the enhanced levels of these greenhouse gases due to human activity. Basically, these gases allow incoming short-wave radiation from the sun and prevent some of the reflected outgoing long-wave radiation from leaving the atmosphere. The difference between the two is what keeps the Earth warmer than its astronomical position would dictate. As the level of these gases have increased in the atmosphere due to human activity more and more of the long-wave radiation is being trapped leading to the heating up effect called global warming.

If you were to ask climate scientists 25 years ago what was the most likely change to the climate then it would be cooling as naturally based on the last 1.6 million years of climate history we should be drifting back into the next ice age. This has changed dramatically over the last 25 years with a realisation that the opposite effect is occurring and the obvious causal agent is human activity. As people and governments became increasingly concerned a world organisation was set up to examine and report on this problem. This body is the Intergovernmental Panel on Climate Change (IPCC).

The third major report the IPCC was published in 2001 and is based on the work of thousands of climate scientists throughout the planet and it makes for very grim reading. Based on a series of scenarios calculated using the most up-to-date understanding of the global climate system and human impact and using the latest supercomputers they predict global warming of between 1.6oC and 5.8oC between 1990 and 2100. The lower end would be more likely if humans get control of greenhouse gas emissions and stop further increases in the rate of emissions and the latter end represents the likely outcome if greenhouse gas emissions are not controlled and are allowed to continue rising. However, they warn that because of imperfect knowledge of the world climate system and future likely human impact that these estimates may not represent the extremes. Either way we are committed to global warming whether we like it or not and that is simply because these gases take anything from years to decades to centuries to cycle out of the atmosphere.
The implications of this warming are global in scale and include for example sea-level rise. For Ireland this could be the most significant aspect as most of our major cities and towns are on the coast or on estuaries and as recent tidal flooding in Cork Waterford and Dublin has shown are already vulnerable to coastal flooding.

Other threats would include increased desertification and shortages of water, changes in vegetation and animal distributions, changes in agricultural crops and productivity to name but a few. In fact, it is very difficult to identify any aspect of the planet, its inhabitants including ourselves and any of our activities that would not be affected by global warming and its knock-on effects and all because we have altered the composition of our atmosphere by pumping vast quantities of greenhouse gases into it without any thought of the consequences until recently.