Please Note: This website is out of date. The Steward Community Woodland sustainable living project ended in 2018 for legal and planning permission reasons. The contents have been left here as a historical archive.

Global Warming

Human activities and the 'green house' effect

While the 'greenhouse effect' has only become an issue during the last decade or two, it is infact a natural phenomenon and responsible for keeping the earth's climate warm enough to sustain life. Naturally occurring gases (such as carbon dioxide (CO2), water vapour and methane (CH4)), trap some of the suns radiation that is reflected back skywards from the earths surface. These gases make up only a very small fraction of the earth's atmosphere. They act as an insulating blanket around the earth and without them the planet's surface temperatures would average about 33°C colder than they do now.

Evidence from glacial ice shows that there is a close correlation between atmospheric levels of greenhouse gases and global temperatures. Over the past 160,000 years, the concentration of CO2, the most important greenhouse gas, has varied between levels of 180 to 300 parts per million by volume (ppmv). During this time, there have been temperature swings of up to 10°C, resulting in several ice-ages separated by warmer, inter-glacial periods. These changes were initiated by periodic changes in the earth's orbit, variations in the sun's output, or periods of intense volcanic activity.

These temperature variations and changes in greenhouse gas concentrations are part of the planet's natural cycles. They occur gradually over periods of thousands of years, allowing life on earth time to adapt to the changing conditions. However, during the past 150 years, human activities (such as the burning of fossil fuels) have drastically increased atmospheric concentrations of CO2 and other greenhouse gases. Prior to industrialisation concentrations of CO2 was about 280 ppmv compared to over 350 ppmv now. Other greenhouse gases associated with human activity add to the total build up. It is quite possible that the rate of climate change caused by this build-up will be too great to allow for various ecosystems to adapt. The concentration of greenhouse gases is now far higher than anything the earth has experienced over the last 160,000 years.

Records show that the earth's surface air temperatures have increased by over 0.5°C in the 90 years. Such a rise need not necessarily be a result of human activity. Temperatures have naturally fluctuated by about 1°C during the last 1000 years. However the current rate of change is very fast in comparision and the evidence is that human activities are responsible.

Computer models predict that global temperatures could increae a further 4 degrees within the next 100 years. Such significant rises would result in sea level rises, changes to patterns of precipitation, and increasingly extreme weather. A variety of other devastating consequences would follow: flooding, drought, loss of agricultural production, the spread of diseases like malaria. Furthermore, long term changes to habitat may cause mass species extinction and even the collapse of entire ecosystems.

In response to world wide concern about the impact of global warming, many governments signed a 'Climate Change Convention' in 1992 at Rio. By doing so they pledged to adopt policies which would stabilise their emissions of 'greenhouse gases' and in 1997, at Kyoto, the industrialised nations went on to agree to cut their emissions (although only by 5%).

The production and use of energy is responsible for 60% of the human contribution to global warming. Other activities which increase the level of greenhouse gases in the atmosphere are the use of chemicals (such as CFCs), modern agriculture and changes in land-use. Despite governmental pledges, the rate of world-wide greenhouse gas emissions is increasing every year.

In order to minimize the magnitude of future warming these emissions must begin to decrease. Reducing the consumption of fossil fuels such as coal, oil and natural gas, especially in the industrialized world, is the single most important factor in controlling global warming.

Predicting Future Temperatures

There is little disagreement that the increased levels of greenhouse gases in the atmosphere will lead to a warming of the earth's surface. There is disagreement over the magnitude and rate of warming. Predictions are complicated by the hundreds of factors which can influence the climate. Some operate independently of the greenhouse effect, while others are 'feedbacks' which are influenced by climatic changes.

An example of a control mechanism which is largely unaffected by global warming is the amount of particulate matter in the atmosphere which reflect incoming solar radiation, and therefore have a cooling effect on the earth's temperature. These tiny particles of dust are released by natural processes such as volcanoes, as well as human activities such as burning wood or coal, or engaging in nuclear warfare.

Several positive and negative feedback mechanisms have also been identified that have the potential to greatly influence future temperatures and make prediction difficult. Methane trapped in frozen permafrost could be released by warmer arctic climates causing even more warming. This 'positive feedback' would act to reinforce any initial warming. Changes in cloud cover is one potential feedback mechanism, but there is disagreement whether this would be a positive or negative factor. A warming of the atmosphere would result in the increased evaporation of sea water, creating more cloud cover over the planet. Clouds are composed of water vapour, a greenhouse gas which traps outgoing heat, but clouds also reflect incoming solar radiation, thus acting to offset the warming. The overall effects of the cloud feedback mechanism are therefore difficult to estimate.

Several different computer models have been developed in an effort to make climate predictions. These 'Global Circulation Models' (GCMs) are complex computer programs that attempt to take into account the thousands of interactions to determine future climates. Depending upon the assumptions made about future population growth, energy use and the various feedback mechanisms, the models predict a global mean temperature change of between 1.5 and 4°C by the end of the century. A global mean temperature increase of 1.5-4 degrees would not be distributed evenly around the planet. Temperatures at the poles would increase more than those near the equator and winter temperatures would rise more than those in the summer.

Impacts of Global Warming

To some people, a winter warming of 10 degrees might not seem like a problem. It is not the absolute magnitude of the warming which is a problem, so much as the rate of the warming. A global mean temperature rise of 1.5-4 degrees in the next century would have widespread and complex impacts on the world's already strained ecosystems many of which are very difficult to predict. All the climate models agree that an increase in the global mean temperature will result in increases in both evaporation and precipitation (rain). Rain fall would not increase everywhere and in some places it would actually decrease. This could mean that formerly fertile agricultural areas could become decertified and barren.

The rate of temperature increase predicted would force ecosystems to migrate quickly in order to survive. Some types of plants and animals are able to migrate more quickly than others and this could also cause problems. Insect pests are likely to migrate faster than their predators, and this could cause plagues of insects further damaging threatened ecosystems.

Water expands as it warms. The expansion of the world's oceans in addition to the melting of glacial ice masses would result in sea levels rising. Some calculate increases of 0.5-1.0 m which would displace hundreds of millions of people worldwide who live near existing coastlines. Worldwide agricultural production would be effected. Some low lying countries such as Bangladesh and the Maldive Islands would virtually disapear under water. Coastal wetlands which play important ecological roles and provide homes for large numbers of species would also be destroyed.

Curbing Global Warming

Human emissions of greenhouse gases are still increasing. To prevent a warming of more than a couple of degrees, atmospheric scientists say that we would need to reduce our current level of emissions by about 60%. The nations that signed the Climate Convention at the Earth Summit in Rio only pledged to work towards stabilizing future emissions at current levels. At Kyoto, in 1997, agreements were made to make some reductions however three years on there had been no significant progress towards even those tiny targets. In 2000 at the Hague, governments met again to agree a set of rules to govern how to make the reductions they had agreed to. Even before the conference started, it was clear that the USA planned to block any agreement that might threaten economic prosperity. Not surprisingly, vested interests prevented the 182 countries represented from making any significant progress and the talks were suspended without an agreement.

If the world's scientists are correct, the tiny reductions promised (but not delivered) by the industrialised nations will not be enough anyway. Especially if countries such as India and China use their vast reserves of coal to power their own industrialisation. Minimising the potential warming will require worldwide cooperation and quick action to improve energy efficiency, develop renewable (non fossil fuel) sources of energy, stop the destruction of tropical forest and develop alternatives to CFCs.

According to the UN scientific advisory group on climate change, delaying action to curb global warming would leave an even tougher battle for future generations and risk devastating and chaotic long term climate changes. Business leaders and oil companies argue that the cost of cutting CO2 emissions could have a negative impact on economic growth and jobs. But the longer we avoid acting, the higher the costs of climate change: floods, droughts, and sea-level rise - costs measured in hunger, misery and lost lives, not in dollars.

While governments talk but do nothing, corporate public relations departments are lobbying and applying 'green washing' techniques to avoid being forced to make effective changes. Immediate emission reductions are called for - cuts in energy use, greater efficiency and a switch to renewables. We can't wait for science and new technologies to save us, there is no time. Existing sustainable technologies already provide part of the solution. By making some changes to the way we live, we can begin to build a sustainable future.

For further information contact the UK Climate Action Network Tel. 020 7251 9199

Things we can do every day to cut C02 emissions NOW!

  1. Use local shops and services
  2. Reduce food miles, buy local produce.
  3. Walk, cycle or use public transport.
  4. Turn off lights and other mains electrical devices.
  5. Turn down central heating.
  6. Improve house insulation and cut draughts.
  7. Avoid packaging, buy less, re-use more.
  8. Reduce waste, compost and recycle.
Last updated: 2009-04-22

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