4 The effects of global warming

4.1 What are the global effects of climate change?

There are three main global effects of climate change:

• increasing global mean surface temperature

• rising sea level (initially mainly as a result of thermal expansion of warmer seawater)

• changing ocean water chemistry (increasing acidity as CO₂ concentrations rise in the oceans).

The effects vary with increasing temperature. On the face of it the differences in temperature sound quite small (1 or 2°C or 3°C or more). But it is important to remember that these figures are for global mean surface temperature. They incorporate everything from the average temperature in the coldest parts of the Earth (e.g. Vostok in Antarctica with average monthly winter temperatures of less than −50°C) to average summer temperatures in the hottest places on Earth (+40 or 50°C). So, the global mean average incorporates a range of about 100°C, and the changes will be much more marked in some places than in others. In general, we expect to find much greater change at high latitudes (the polar regions) and low latitudes (the desert belts), while temperate latitudes will be slower to change.

Similarly, the impacts of sea level rise will be different in different parts of the world, depending on, for example, regional variations in the rise and fall of continents.

Changes in climate will interact with regional or local factors, including management of the land and sea to produce different effects in different places. It is often difficult to disentangle these factors to say how much is definitively attributable to a changing climate and how much is due to other factors. But a major conclusion of the IPCC Fourth Assessment Report is unequivocal evidence for climate change caused by human activity.

Additional information can be found in these web-based resources

• Slideshow from the BBC entitled ‘How the world is changing’

• Glacial Retreat 2009 BBC Film.

• IPCC Fourth Assessment Report, Working Group III, Adaptation, Impacts and Vulnerability – Summary for Policy Makers

• Red Cross Red Crescent Climate Guide .