Measurements of temperature taken by instruments all over the world, on land and at sea have revealed that during the last 100 years the Earth's surface and lowest part of the atmosphere have warmed up on average by about 0.6°C. During this period, man-made emissions of greenhouse gases, including carbon dioxide, methane and nitrous oxide have increased, largely as a result of the burning of fossil fuels for energy and transportation, and land use changes, for food. In the last 20 years, concern has grown that these two phenomena are, at least in part, associated with each other. That is to say, the cause of the observed increase in global average surface temperature is now considered most probably to be due to the increases in greenhouse gas emissions and concurrent increases in atmospheric greenhouse gas concentrations. Whilst other natural causes of climate change, including changes in energy from the Sun, volcanic eruptions, and ocean circulation, can cause global climate to change over similar periods of time, computer models, which simulate the climatic effects of increasing atmospheric greenhouse gas concentrations, suggest that the balance of evidence now indicates that there is a discernible human influence on the global climate. In light of the most recent evidence, and taking into account the remaining uncertainties, most of the observed warming in the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.
If the climate changes as current computer models have projected, global average surface temperature could be anywhere between 1.4 and 5.8°C higher than in 1990 by 2100. To put this temperature change into context, the increase in global average surface temperature which brought the Earth out of the last major ice age 14,000 years ago was of the order of 4 to 5°C. If computer models are correct, the Earth could, within a few generations, be warmer than at any time during the last 50 million years. Such a rapid change in climate will probably be too great to allow many ecosystems to suitably adapt, and the rate of species extinction will most likely increase. In addition to impacts on wildlife and species biodiversity, human agriculture, forestry, water resources and health will all be affected. Such impacts will be related to changes in precipitation (rainfall and snowfall), sea level, and the frequency and intensity of extreme weather events, resulting from global warming. It is expected that the societies currently experiencing existing social, economic and climatic stresses will be both worst affected and least able to adapt. These will include many in the developing world, low-lying islands and coastal regions, and the urban poor.
The Framework Convention on Climate Change (1992) and the Kyoto Protocol (1997) represent the first steps taken by the international community to protect the climate system from dangerous man-made interference. Currently, nations have agreed to reduce greenhouse gas emissions by about 5% by 2008 to 2012. Additional commitments for further greenhouse gas emission reduction will need to be negotiated during the early part of the 21st century, if levels of greenhouse gas concentrations in the atmosphere are to be stabilised at reasonable levels. Existing and future targets can be achieved by embracing the concept of sustainable development - development today that does not compromise the development needs of future generations. In practical terms, this means using resources, particularly fossil-fuel-derived energy, more efficiently, re-using and recycling products where possible, and developing renewable forms of energy which are inexhaustible and do not pollute the atmosphere. Sustainability will impact upon the energy, transport and waste management sectors; the challenge facing society today and in the future is to manage the transition from unsustainable to sustainable practices in these areas in a manner which does not adversely affect human welfare and standards of living.