The concept of global warming is more than 100 years old, but confusion still reigns about the solution. John Houghton explains his blueprint for survival.

Global warming is firmly on the national and international agenda. Politicians make speeches about it, scientists argue about it, the international Earth Summit at Rio in 1992 agreed action should be taken to counter it. But many people are sure neither of the facts of climate change due to global warming nor of what action really needs to be taken.

Global warming is a pollution issue concerning the whole planet. Any solution demands the involvement of every polluter, however small his contribution may seem to be. Yet we are still uncertain about the facts of global warming and its likely effects. What is the appropriate action to take and how much will it cost? Moreover, how can there be an equitable arrangement between countries, in particular between developing countries (which have rapidly increasing energy demands because of their entirely reasonable aspirations for industrial growth).

The principles have been known for a long time; the first "global warming" calculation was made in 1896 by Swedish chemist, Svante Arrhenius. Gases such as water vapour and carbon dioxide which have been in the atmosphere for many millions of years act as a thermal blanket and keep the earth's surface 20 to 30oC higher than it would otherwise be because they absorb infrared radiation emitted by the earth's surface; without their presence most of the world would be covered with ice. These "greenhouse gases" are increasing because of human activities; the most important is carbon dioxide; methane and nitrous oxide also have significant effects. Over the past 200 to 300 years - mostly due to the burning of fossil fuels, coal, oil and gas, but due also to the effects of deforestation - carbon dioxide in the atmosphere has risen by nearly 30 per cent and is still rising. This adds to the "blanketing" of the outgoing radiation from the earth's surface.

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According to the 1996 assessment of the Intergovernmental Panel on Climate Change, if no action is taken to curb the rise in "greenhouse gases", the global average temperature would rise by about 2.5oC by the year 2100. In terms of local temperature change this may seem a small amount but in terms of global average temperature it is very large; the global average temperature has only changed by 5 to 6oC between the middle of an ice age and the warm periods in between.

Expressing climate change in terms of the increase in global average temperature is not very meaningful for most people. What means more is how our local climate may change.

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Recently the increasing vulnerability of our crowded world has been amply demonstrated as different places have experienced extreme temperatures, record floods, droughts and windstorms. The impact of these events has made more relevant the question of whether human activities are likely to lead to damaging future climate change.

The sea level is expected to rise about 0.5 metres by the year 2100, mostly from the expansion of water in the oceans because of the increased temperature and from the melting of glaciers. It will continue to rise for many centuries, even if the greenhouse gas concentrations are stabilised. Adaptation, at a cost, to a rise of a metre or less will be possible in many coastal regions. However, adaptation will be extremely difficult, if not impossible, in the delta regions of large rivers in Bangladesh, Egypt and Southern China and the low lying islands in the Indian and Pacific oceans. Substantial loss of land will occur here and many millions of people (for instance, six million live below the one metre contour in Bangladesh) are likely to be displaced.

There is also likely to be a greater tendency to heavy rainfall in some places, leading to an increasing possibility of floods. Other places, by extension, will see longer periods of drought. Those most likely to be strongly affected are places with particularly heavy rainfall (eg the regions of the Asian summer monsoon) and those with marginal rainfall. In these areas, droughts and floods - the most damaging natural disasters we experience - are likely to become more frequent.

Demand for water has been growing in nearly every country and especially in those where it is extensively used for irrigation. There are already significant tensions, especially in countries where the water from major river systems is shared between nations. It is not surprising that the secretary general of the UN has suggested that wars in the future are likely to be about water rather than oil.

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At the Earth Summit in 1992, the governments of the world agreed that action needed to be taken now to reduce the emissions of greenhouse gases and signed the Framework Convention on Climate Change (FCCC). This framework acknowledges that developed countries should take the first steps, urging them to reduce the growth of carbon dioxide emissions so that by the year 2000 they should be no greater than they were in 1990. The convention also laid the foundation for longer-term action, issuing an "objective" which says that action should be taken to stabilise the concentrations of greenhouse gases in the atmosphere at levels which "avoid dangerous interference with the climate system" and which also "enables economic development to proceed in a sustainable manner".

Unfortunately, few countries (among them the UK) are likely to achieve the first goal - of reducing emissions to 1990 levels by the year 2000. However, the FCCC is now addressing proposals for reductions after the year 2000, the aim being that developed countries should have agreed binding targets at the third Conference of Parties which was held at Kyoto, Japan this week.

For this conference, the European Union proposed reductions of 15 per cent below 1990 levels by 2010 - which is the sort of rate likely to be required of developed countries if the objective of the climate convention is to be met. Much of the reduction initially needed can be achieved by using appliances which use energy more efficiently. Improvements in insulation and control of energy production is also needed together with a switching to renewable energy as the possibilities arise. The cost to most country's economies need not be large (1 per cent of GDP or less) and is estimated to be much less than the cost on average to the world economies of the damage due to climate change if no action is taken.

Since about 1988, when the problem of global warming first began to be appreciated by politicians and policy makers, international bodies and others have come a long way in identifying the problem and in spelling out the sort of action which is needed. But, as Sir Crispin Tickell has said in his Domesday Letters on Radio 4, "we know what to do, but we lack the will to do it". Both governments and industry throughout the world need to see the problem of climate change not as a threat but as an opportunity and in so doing turn the talk into appropriate action.

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John Houghton is chairman of the Royal Commission on Environmental pollution and chairman of the scientific assessment working group of the IPCC.