What is climate change?

 

When we use the term 'climate' what we actually mean is the average weather experienced in a region over a long period of time.  Meterological variables other than temperature, such as wind and rainfall patterns are constituents of climate. The climate on earth has undergone many changes in the past and this is entirely natural. However, the rate at which the climate has been changing over the past 50 years has led to a consensus amongst scientists that this recent change is likely to be as a result of man's activities. This is what we refer to as 'Climate Change'. Other related terms are the 'greenhouse effect' and 'global warming'.

What is the greenhouse effect?

Certain gases – mainly carbon dioxide (CO2), but also methane (CH4), nitrous oxide (N20), and volatile organic compounds (VOCs) – play an important role in regulating the temperature of the earth’s atmosphere. These are known collectively as the greenhouse gases. Most visible and ultraviolet light coming from the sun is able to reach the Earth’s surface by passing through the atmosphere. Some of this energy is re-radiated back to space in the form of long-wave or infra-red radiation. Natural amounts of greenhouse gases maintain the earth’s temperature at a habitable level by absorbing some of this energy – the ‘greenhouse effect’. However, human activities are increasing the concentrations of greenhouse gases in the atmosphere, leading to a gradual warming of the earth’s atmosphere. It is this enhanced greenhouse effect that is generally referred to as global warming.

Why is climate change occurring?

Human activities, such as deforestation and the burning of fossil fuels, have resulted in an increase in the concentrations of ‘greenhouse gases’ in the atmosphere. The most important of these gases is carbon dioxide (CO2), which has risen from a concentration of 275 parts per million (ppm) prior to 1850 to the current value of 370 ppm. Levels of CO2 are expected to continue rising, and current estimates predict a concentration of 525-950 ppm by the end of this century. The enhancement of the ‘greenhouse effect’ by rising concentrations of these greenhouse gases is largely responsible for the issue of global warming. However, rising temperatures are only one consequence of the enhanced greenhouse effect, with changes to weather patterns and many aspects of the climate such as rainfall and humidity predicted. Collectively, these are referred to as ‘climate change’.

The Intergovernmental Panel on Climate Change (IPCC) concluded in their Third Assessment Report that, " .. most of the warming observed over the last 50 years is likely to have been due to increasing concentrations of greenhouse gases."

What are the predictions for the future climate?

In May 2002 climate change scenarios for the UK were produced by the Tyndall and Hadley Centers on behalf of The Department for Environment Food and Rural Affairs (DEFRA).

The UK Climate Impact Programme (UKCIP02) scenarios provide predictions of mean climate and an indication of annual variability over thirty year time slices centred on the 2020s, 2050s and 2080s. For each time-slice, data are presented for four different emissions scenarios.

Average temperatures are predicted to rise by between 2 and 5 degress C by the end of this century with warming greater in summer than in winter, and in the south and east compared to the north and west. Rainfal patterns will also change, with winter rainfall increasing and summer rainfall decreasing, across the whole country. These changes are predicted to be most extreme in the Southeast, with a reduction in summer rainfall of up to 60% and increases in winter rainfall of up to 25% predicted. Relative humidity will fall and absolute humidity, rise, in both cases most markedly in the summer months. Snowfall is likely to become a thing of the past across much of the lowlands. Predictions of changes to the wind climate are uncertain, but indicate that the storm track may move southwards, with more deep winter winter depressions crossing the southern UK; as a consequence, the largest increases in windspeed are predicted for the the Southeast and in the winter months. Finally, as a result of the changes in absolute and relative humidity, cloud cover is predicted to fall, particularly in the south and in summer and autumn. Futher details are available from the individual pages on temperature, rainfall and wind and the UKCIP website. 

The Gulf Stream - will it switch off?

The Gulf stream is part of the North Atlantic Thermohaline circulation (THC) and is the flow of warm equatorial waters past the west coast of Ireland and Scotland. The Gulf Stream is responsible for our climate being wamer, particularly the mild winters typical of Britain, in comparison with other regions at similar latitudes. It is driven by cold, dense seawater sinking in the North Atlantic.

There are concerns that climatic warming will increase the flow of less dense meltwater from the polar icecap, and that the driving force of the Gulf Stream and, the Gulf Stream itself, will switch off. Most climate models do predict a weakening of the Gulf Stream as climate change progresses; however, none predict a shut-down of the Gulf Stream.

The UKCIP02 climate change scenarios do take this into account, and make allowances for a weakening of the Gulf Stream. However, it is thought that over the coming century, the effects of climatic warming will outweigh any weakening of the Gulf Stream. The following statement was made in the scientific report (chapter 7) accompanying the UKCIP02 climate change scenarios, and this position has not changed:

'We state with medium-to-high confidence that although the strength of the Gulf Stream may weaken in the next 100 years, it is unlikely that this would lead to a cooling of UK climate over this time-scale.'