Global Warming is forecast to have major impacts all around the world affecting human life and world wide biodiversity.  What is causing it and some of the things that will probably happen are described below:

The greenhouse effect

The Earth is heated by the sun; solar radiation passes through the atmosphere and isalt text here absorbed at the Earth's surface (except for a small portion that is reflected back into space). This heat is readily lost; it is emitted from the surface as infra-red radiation. Fortunately, this infra-red radiation cannot escape the atmosphere as easily as the solar radiation can enter. Instead, some of it is 'trapped' by a number of gases; these gases act in a similar, yet different, way to the glass in a greenhouse - heat is allowed in but cannot get out - hence we have the 'Greenhouse Effect'. Were it not for this natural greenhouse effect the Earth would be at least 30°C cooler and life as we know it would not exist.The greenhouse effect (DoE) 

The problem

Unfortunately, recent human activities are enhancing the natural greenhouse effect. The concentrations of certain greenhouse gases in the atmosphere are increasing, therefore more of the infra-red radiation emitted by the Earth's surface is being trapped. The planet is losing less heat and as a result we are beginning to experience 'Global Warming'. Going back to the greenhouse analogy, it is as if the panes of glass are gradually becoming thicker.

The way global temperature is linked to the concentration of CO2  can be seen in the graph below:

temp follows co2

The greenhouse gases

The major greenhouse gases are: water vapour, carbon dioxide, methane, nitrous oxide, CFCs (and their replacements), and ozone. Some of these occur naturally, some result only from human activity, while others occur both naturally and as a result of human activity. The contribution of each gas to the greenhouse effect is a function of three factors:
  • Atmospheric lifetime - simply, how many years the gas remains active in the atmosphere.
  • Global warming potential (GWP) - a relative measure of how effective the gas is at preventing the passage of infra-red radiation (i.e. the Earth's heat). The GWP of CO2 is 1; methane, molecule for molecule, is eleven times as effective as CO2, therefore it has a GWP of 11.
  • Atmospheric concentration - usually measured in parts per million (ppm).
Water Vapour Water vapour is the most important greenhouse gas, although its concentration in the atmosphere is not directly influenced by human activity. However, any increase in global temperatures will increase concentrations, because, as air gets warmer it can hold more water vapour. Hence, any enhanced greenhouse effect caused by other greenhouse gases will increase the global warming effect of water vapour. Carbon dioxide Carbon dioxide (CO2) exists naturally in the atmosphere; however, its concentration is increasing sharply as a result of human activities:
  • Fossil fuel burning: oil, gas, and coal are stores of carbon; when these are burnt, this carbon is released directly into the atmosphere as CO2
  • Deforestation: trees absorb CO2 from the atmosphere; if these trees are cut down they can no longer do this, therefore CO2 levels rise.
Since the beginning of the Industrial Revolution, atmospheric concentrations of CO2 have risen by almost 30%. This rise currently accounts for most of the enhanced greenhouse effect. CO2 has an atmospheric lifetime of about 100 years. Methane About a third of the current atmospheric methane is from natural sources, such as bogs and swamps. The remainder exists as a result of human activities such as cattle rearing, waste disposal, fossil fuel mining, and sewage treatment. It has a higher GWP than CO2, but remains in the atmosphere for less time - just 11 years. Nitrous Oxide A powerful and long-lived greenhouse gas, it occurs naturally in the environment, but concentrations are now rising, mainly as a result of fertiliser use. Nitrous oxide (N2O) should not be confused with nitrogen oxides (NOx) - see section on acid rain. CFCs and their replacements (see section on the ozone layer) CFCs and their replacements are synthetic; their contribution to global warming is entirely due to human activity. All are powerful greenhouse gases. CFCs and HCFCs are being phased out of use as a result of their effect on the ozone layer. They are likely to be replaced with HFC - a similar compound, but one which does not affect the ozone layer. Unfortunately HFC is still a very powerful (GWP 1500), albeit fairly short-lived, greenhouse gas. Ozone (see section on the ozone layer) Ozone is an important greenhouse gas, it occurs both at ground level and in the stratosphere. Ground-level ozone concentrations are increasing as a result of some industrial processes and spiralling transport use. Higher up in the atmosphere, the ozone layer is being depleted; the contribution of stratospheric ozone to the greenhouse effect, therefore, is diminishing. Unfortunately, depletion of the ozone layer is not a good thing. Also, any reduction in the greenhouse effect of the ozone layer is likely to be offset by the global warming effect of the CFCs and other gases responsible for depleting it in the first place. Sulphate aerosols These actually have a 'global cooling' effect. Sulphate aerosols are formed from sulphur-containing gases in the atmosphere; they reflect sunlight away from the Earth. The most recent evidence of this was following the eruption of the volcano Mt. Pinatabu in 1991, which spewed sulphur clouds into the upper reaches of the atmosphere. The following three years were cooler as a direct result. Unfortunately, the most important gas from which the sulphate aerosols are formed - sulphur dioxide - is also responsible for acid rain. In addition, sulphate aerosols have been linked to ozone layer depletion.

Effects of global warming

There is still much uncertainty over the degree by which temperatures will actually rise and what the effects of these rises will be. What is not in doubt is that the Earth's temperature has risen by 0.5°C over the past century, and that recent years have been among the hottest on record. The likely effects of global warming have serious implications for the environment: Sea level - a 20cm rise by 2030 is expected to result from glacial melting and from the thermal expansion of the oceans as water temperatures rise. This may inundate some coastal regions, and increase the risk of serious flooding in many more. Internationally, populations throughout much of China, Egypt, Denmark and South-East Asia are most at risk - millions could lose their homes and livelihoods. In the UK, south-east England is most vulnerable to inundation, although floods, such as that which occurred in Towyn, mid-Wales, in 1990, are likely to increase in both frequency and severity throughout the country. Agriculture and forestry - crop failure and famine will ensue throughout marginally productive regions of the world. In the UK, agricultural practices will need to adapt; milder weather will benefit some crops at the expense of others. Forestry will be affected: in Wales, native broadleaf trees could suffer as a result of droughts, whereas conifer plantations are likely to become more productive. More conifers will exacerbate some of the problems associated with acid-rain, and, simultaneously, have serious implications for the biodiversity of our woodlands. Water resources - global rainfall patterns will change and the water management strategies of different regions will need to adapt. This will have serious global security implications, conflict over water resources could well follow. In the UK, droughts and floods will become more common, while rising temperatures will increase domestic water demand. Water quality may suffer owing to an increase in the incidence of algal blooms. Terrestrial ecosystems - many plant and animal species will have problems adapting, others will not; this will influence the mix of species at different locations. Many will be at risk from extinction, whereas more tolerant varieties (often including weeds and pests) will thrive. Human health - over the long term there is likely to be an increase in the spread of certain diseases; malaria, for instance, could reach parts of Europe, including the UK. Urban air pollution is likely to get worse and its associated ill-health effects exacerbated. Heat-induced deaths are likely to increase, especially among the elderly. Adverse weather conditions, such as storms and floods, will exact their own costs, both human and economic: lives will be lost, insurance premiums will rise.

Measures to curb global warming

The most important contributor to global warming is the increase in atmospheric CO2 levels due to human activity. To remedy the situation, the increase will not only need to be halted, but also reversed:
  • CO2emissions can be cut by reducing the use of fossil fuels: cutting back on car use, investing in energy efficiency, implementing energy conservation measures, and utilising renewable resources such as wind, solar, and hydro power. Reducing fossil fuel use will, coincidentally, also reduce emissions of methane, nitrous oxide, and ozone
  • CO2 is consumed by plants and trees (known as 'carbon-sinks') as they grow, therefore levels in the atmosphere may be reduced by reversing deforestation and implementing reforestation programmes.
The need to take such measures was first recognised at the Rio Climate Change Convention in 1992, after which over 160 countries pledged to limit emissions of CO2 and to protect and enhance natural 'sinks' of CO2.

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