There is now a consensus among the majority of the world’s scientists that the Earth is already experiencing the effects of man-made climate change.

Climate Change is caused by emissions of pollutants which increase the so called ‘greenhouse effect’, by which gases in the atmosphere create a “blanket” or warming effect by limiting the ability of heat to be radiated out in to space. Gases responsible for the greenhouse effect include water vapour, carbon dioxide, methane, ozone and halocarbons, the latter four of which have been affected by human activities over the last 300 years and have increased greatly over this period.

Careful analysis of the historical record of measurements shows the following facts:

• global temperature has risen by about 0.6ºC since the beginning of the twentieth century
• about 0.4ºC of this warming occurring since the 1970s
• 1998 was the warmest in this 142-year record
• 2001 was the third warmest
• globally, the decade of the 1990s was the warmest in the last 100 years

Greenhouse gases are likely to be emitted in large quantities for the foreseeable future. The result will be a substantially altered climate. Sophisticated computer simulation models show that the global mean temperature is likely to rise by between 1.5 and 5.9ºC by 2100. The wide range in this estimate reflects both uncertainties in how the climate will respond to increased concentrations of greenhouse gases and the fact that we simply don’t know how emissions of greenhouse gases will change in the coming decades. How much we do emit will depend on our choices as a global society over the coming years and decades.

What will the effects be?

Around the world, the land is likely to warm more than the ocean, and northern high latitudes will warm the most. Global precipitation is likely to increase by about 2% per degree of warming, but the regional patterns are complicated and not well-understood – many areas will see significant drying while others will get substantially wetter.

One major consequence of climate change will be continuing sea-level rise, and accompanying increase in the occurrence of extreme storm surges. Many millions of people live in areas at risk from inundation. Changing rainfall patterns are likely to increase soil erosion and subsidence, and profoundly affect water availability and quality. Drier soils will change the type and yield of crops, increasing the risk of famine in some areas. Health is likely to be affected, both directly (more summer heat stress but fewer cold deaths in winter) and indirectly (through changes in diseases such as increased food poisoning). Infectious diseases such as malaria are expected to spread.

Evidence is therefore accumulating that climate change is under way and that something needs to be done now if we are to mitigate its future effects. However, carbon dioxide has a very long lifetime in the atmosphere and we have already significantly increased levels of greenhouse gases in the atmosphere above their pre-industrial levels.

We are already committed to a certain amount of climate change over the next 100 years, and we must expect to have to deal with impacts that have yet to be manifested: we need to address adaptation as well as mitigation.