L ater this year, 150 governments led by the US could make an extraordinary breakthrough in the fiendishly complex international politics of global warming. Following the gloomy reports from the recent "earth summit 2" in New York, it will come as a surprise to many people that a dramatic shift could be imminent.
But this is to give readers a glimpse of the d?nouement before even meeting the characters. The chief character in this case is carbon dioxide (CO2), the biggest contributor to climate change induced by the greenhouse effect. CO2 is accompanied by a small family of other greenhouse gases, notably methane, nitrous oxide and industrial gases such as the ozone-destroying CFCs. But CO2 takes centre stage, not only because it is the largest contributor in most projections, but because controlling emissions of CO2 means controlling the scale and mix of the fossil fuel consumption which underpins almost every activity in the modern world, from boiling a kettle to driving and flying.
In an effort to provide authoritative insight and foresight, governments in 1988 established the intergovernmental panel on climate change (IPCC), the most elaborate institution of international analysis and review ever created. By 1995 governments had accepted the IPCC views that global temperatures were rising and that there was a "discernible human influence" on this rise. The IPCC has also produced projections of climate change which range from the relatively benign to the alarming.
The uncertainty of these projections is not surprising; we are far from understanding how planetary biospheric and ecosystems really work. We know that concentrations of CO2 are rising and that this changes the amount of solar radiation trapped near the earth's surface, changing global average surface temperatures. The problem is that changing the temperature even by a very small amount changes lots of other things in complicated ways, such as the hydrological cycle which determines rainfall, cloud cover, ice expanse-which all feed back on the heat balance differently, making firm predictions difficult. The buffer effect of the oceans means also that global temperature change lags behind atmospheric change by several decades; so that even if we stabilise the atmosphere, global average temperature may go on rising for decades and sea levels for centuries.
What we do know is that greenhouse gas emissions interfere with two basic determinants of our planetary system: the radiative heat balance in the lower atmosphere and the global carbon cycle. But we will probably never fully understand the consequences until they are upon us. This makes precautionary action an intrinsic component of a rational response. Most governments have concluded that something does indeed need to be done. The problems are what, how, which, when and by whom.
These problems are not for the faint- hearted. Global emissions of CO2, driven by expanding economies and populations, are projected to double in the first half of the next century. Most scientists say these need to be more than halved to stabilise the atmosphere. The energy sector, dominated by fossil fuel activities, accounts for between 3 per cent and 7 per cent of GDP in most developed economies; energy consumption underpins almost every activity. Although there are many ways of limiting emissions (improved energy efficiency, use of renewable energy) governments may be forced to enact radical changes to the way that consumers make choices about lifestyles and technologies.
