3.4 Climate change

Climate change tutorial

Earth from spaceThere is now little doubt that the Earth's climate is warming. In this tutorial we will explore the facts about climate change, and what effects a change in climate may have.

What is climate change?

Earlier we said that climate is the average weather experienced by a place over a long time period (say 30 years). For any given place on the Earth, climate varies over timescales ranging from tens of years to thousands of years. Such changes are due to natural causes such as changes in solar activity and long-term changes in the tilt of the earth and its orbit around the sun. However, the term climate change generally refers to changes since the early 1900s.

We've seen already that both natural and human factors affect the Earth's climate. The IPCC is the Intergovernmental Panel on Climate Change. In its 2007 report, the IPCC stated that: 'There is very high confidence that the net effect of human activities since 1750 has been one of warming' (IPCC 4th Assessment Report, 2007).

In fact the IPCC concluded that most of the observed increase in global temperature since the middle of the 20th Century is very likely due to an increase in man-made greenhouse gas emissions.

We may well be seeing the effects already, though it is hard to say for certain that any single 'event' (a drought, a flood or the spread of an invasive species, for example) is the result of climate change.

How is the climate changing?

The global average temperature has risen by about 0.89°C over the period 1901 to 2012 (source: UK Met Office). In the UK, temperatures have risen by about 0.7°C since 1659 (source: UKCIP website).


Rothamsted mean temperatures from 1878 - 2005

The graph above shows data from the ECN Rothamsted site in Hertfordshire, England. The points are 5-yearly averages of annual average (mean) air temperatures recorded at Rothamsted. The data are from 1878 to 2010. Temperatures were relatively stable over the period up to the late 1980s. Since then temperatures have generally been higher than the long-term mean (the red line, which is the mean for 1878-1990). The data suggest progressive warming over the period, and particularly in the last 30 years. (Data courtesy of Rothamsted Research Ltd.).

You can see a version of this graph showing the annual mean temperature data on the Rothamsted website.

It doesn't sound like much: what's the problem?

Warming of less than 1°C doesn't sound like a lot, but even a 2°C temperature rise could lead to rising sea levels and more extreme events like droughts and heavy rain. In fact, the IPCC reports '... widespread melting of snow and ice and rising global average sea level ...' (source: IPCC 4th Assessment Report, 2007). Such changes will affect many millions of people. Communities living in low lying coastal areas, or in parts of the world which are already prone to droughts or flooding could be the worst affected.

In the UK, the direct effects are likely to be less severe (and some people may even welcome a warmer climate). We may experience more frequent extremes of weather such as storms, heatwaves and heavy snow. We are also all vulnerable to the indirect effects of climate change, such impacts on food harvests, pressure on water resources, human migration or the movement of pests and disease-carrying organisms.

Sources of information

In this tutorial on climate change we have drawn mainly on the following sources of information: