Slowing Down Global Warming

Teachers' Information Sheet


Global warming is already happening. Even stabilisation of greenhouse gas concentrations today would not halt the warming process immediately. We are, in effect, already committed to an uncertain degree of global warming.

The Intergovernmental Panel on Climate Change (IPCC) has attempted to establish a scientific consensus on the effects of, and responses to, global warming. They project that a doubling of atmospheric CO2 concentrations will cause a rise in global temperatures of between 1.4 and 5.8C. Even global warming sceptics concede that, under this scenario, a rise of 0.5C is likely.

Following on from the IPCC reports, governments around the world have accepted the need to implement policies designed to first limit and then reduce greenhouse gas emissions. Ultimately, only national governments have the power to act on this issue, but it is desirable that governments are guided by international agreements, such as the Framework Convention on Climate Change signed by over 150 governments in Rio in 1992. Given the inertia in the world's political and economic system, only by acting now can real benefits be achieved in the future.

This lesson looks at the sectors which emit the most greenhouse gases (especially energy production and consumption), and what options are open to reduce these emissions. The following sectors are discussed.

  • Energy - What has energy got to do with global warming?
  • CFCs - How important are CFCs to the greenhouse effect?
  • Forestry - Can forests help to slow down global warming?
  • Agriculture - Agriculture and the greenhouse effect.
  • Developing countries - Developing countries and their contribution to global warming.

What has energy got to do with global warming?

Harnessing energy is essential to both industrial and agrarian societies, from smelting iron to cooking. About half the enhanced greenhouse effect is caused by our use of energy, especially fossil fuels. Any energy policy must therefore look at both the sources and uses of energy.

On a global scale most of our energy sources release CO2, whether from fossil fuels or biomass burning. Due to the depletion of fossil fuel reserves, the mix of fuels may change substantially in the long term. In the meantime the high relative cost of the alternatives will ensure the continued dominance of fossil fuels. Activities such as coal mining are also responsible for large emissions of methane, another important greenhouse gas.

Energy Sources

Certain sources of energy are not directly responsible for emitting greenhouse gases. These include nuclear power and the renewables: solar, wind, wave, tidal and hydro-electricity. Currently, renewable sources of energy supply only 3% of the UK electricity needs. Although the Government would like to increase this to 10% by 2010, the scope for increasing the proportion of power generated from renewables is thought to be very limited. In the long term, technologies such as producing electricity directly from light by the photo-voltaic effect offer possibilities, though they are uncompetitive at the moment.

A significant proportion of our electricity (approximately 26%) is currently generated from nuclear power, and it would be possible to increase this amount. However there is a strong anti-nuclear lobby, and if electricity from nuclear power were to include de-commissioning costs, it may not be competitive in price.

The fastest growing source of CO2 emissions is the transport sector. One proposed solution to this is the adoption of more so-called zero-emission vehicles which run on electricity. In fact, more often than not, the electricity is first generated by burning fossil fuels in power stations. These vehicles are only useful in combating local pollution hotspots such as Los Angeles.

Energy Efficiency

The UK report under the Framework Convention on Climate Change focuses on energy efficiency as the most applicable strategy to reduce CO2 emissions. In the electricity generating sector, coal and oil fired power stations are very inefficient, and have been superseded by new gas fired stations, which can improve efficiencies by up to 15%.

In the domestic sector, awareness of energy efficiency is primarily driven by the possibilities of saving money. The link between efficiency and global warming is not often made. There are many ways to reduce the domestic consumption of energy, from putting lids on pans, to cavity wall insulation.

Realistically, whether a particular method is used will depend largely on its cost effectiveness. Double glazing, despite its saving on heating bills, is thought to have too long a payback time unless windows are to be replaced anyway.

This highlights another point which limits the rate at which energy efficiency can make an impact. Often there is a considerable capital investment required to improve energy efficiency; this investment will usually have to wait until refurbishment or replacement of the existing system. For example improving the insulating properties of houses is cheaper and easier when new ones are constructed. Thus the improvements in efficiencies in a sector depend on the turnover rates for the existing stock; the housing stock will improve only slowly, whereas household appliances such as washing machines are replaced more frequently by new models with better efficiencies.

Road transport constitutes the fastest growing source of greenhouse gas emissions. Cars are an extremely inefficient method of transport, especially where the car contains only one person. In California measures have been introduced to promote the sharing of car journeys, primarily to reduce congestion and local pollution, though it will also reduce CO2 emissions. Diesel and lean-burn engines are also more efficient.

Though energy efficiency is undoubtedly worthwhile, it is not sufficient. Past experience shows that the number of car journeys grow to fill the roads available. The projected growth in road transport will eventually cancel out the benefits of improved efficiency. For this reason, barring the adoption of clean fuels, bus and rail services may offer the best long-term reduction in greenhouse gas emissions. Persuading car owners to use alternative modes of transport may prove the most significant obstacle to the adoption of this strategy.

How important are CFCs to the greenhouse effect?

As well as destroying ozone (see lesson 3), CFCs are greenhouse gases, and are thousands of times more effective in terms of contributing to the greenhouse effect than an equivalent mass of CO2. This is due in part to the longer time these gases spend in the atmosphere. Following the discovery of reduced ozone levels over Antarctica, pressure mounted on the international community to act to reduce consumption of CFCs. In 1987 the Montreal Protocol committed its signatories to reducing consumption of CFCs, in order to attempt to restore the ozone layer. Since then the Protocol has been updated several times. The use of CFCs by developed countries was phased out by the end of 1995.

There are two types of substitute for CFCs: HCFCs and HFCs. Both are greenhouse gases, though less effective than CFCs. HCFCs are also ozone-depleting, and are due to be phased out by 2029. This late date is to encourage countries to move away from using the more harmful CFCs. There is no current restriction on HFCs because there is as yet no evidence that they are ozone-depleting.

Can Forests help to slow down global warming?

One major sink for CO2 is its absorption by green plants, especially forests. When forests are chopped down, CO2 is released from the burning of waste products such as roots, undergrowth and small branches, and from the slower decay of timber products. There is therefore an increase in the amount of CO2 produced, and a reduction in the amount absorbed.

One obvious solution is to use fewer timber products, and to use them more efficiently. Timber is a renewable resource, and it is possible to extend forests or plant the same number of trees as are cut down. However, this would increase the price of timber, and there is often pressure for the cleared land to be used for purposes other than forestry.

Agriculture and the greenhouse effect

There are several different agricultural sources of greenhouse gases. Methane (CH4) is produced from flooded rice paddies, and in the stomachs of ruminant livestock. These are natural processes associated with the anaerobic decay of organic compounds, and would be difficult to eliminate without major changes in diet for many millions of people.

Nitrous oxide (N2O) is released by the use of artificial fertilisers, which have been increasingly used to dramatically improve crop yields across the world. Intensive arable farming requires large quantities of these fertilisers to prevent rapid depletion of soil nutrients. It would therefore be difficult to stop using these fertilisers because of the consequent drop in crop yields, though in many cases they could be used more efficiently.

Developing countries and their contribution to global warming

No one country can absolve themselves of responsibility for global warming. While it is true that the industrialised world contributes the bulk of greenhouse gas emissions, such emissions from developing countries are growing extremely quickly.

Understandably, the developing world is reluctant to slow its economic growth by implementing costly measures to reduce greenhouse gas emissions, when other countries have become fully industrialised over the past 100 years without restriction.

Hence the developing world seeks aid from the richer countries in the form of scientific and technological expertise. For example, the Montreal Protocol (see above) gives developing countries an additional 10 year period of grace, extending their deadline for ceasing production of CFCs.

Questions and sample solutions

1. Can you think of ways in which energy could be used more efficiently in your house?

Sample solution: Insulate the loft, reduce temperature of thermostat by 1C, put a full load in the washing machine, only boil as much water as you need at the time.

2. One way of producing energy more efficiently is through a Combined Heat & Power (CHP) plant. Can you find out how these systems work and investigate if they are being used in your area?

Solution: Simply, CHPs work by harnessing the waste heat that is generated through power production and uses it to heat buildings. As a result of its nature it is typically used for small scale ventures. Many hospitals use this type of scheme to heat their buildings.

3. Find out what type of energy is used in your own home and how much it costs to run over a twelve month period.

Most people save their old bills. This exercise is useful to encourage pupils to think about the actual cost of energy.

4. The figure below can be used to show the children what constitutes an inefficient kitchen. The class could then, for example, be asked what measures they would take to make the kitchen more efficient.

An energy inefficient kitchen

Longer term

Since energy use is the principal factor contributing to global warming, pupils could carry out a survey of where energy is used in their home, what fuel is used, and, if possible, how much energy is used (by monitoring gas and electricity meters from week to week).

It may also be possible to monitor energy consumption for one or two weeks, then implement simple energy efficiency measures to see if there is a noticeable decrease in consumption. A weekly monitoring period will be essential, as energy consumption is likely to follow a weekly cycle.


Biomass: organic matter, living or once living matter.

De-commissioning costs: the costs involved in closing down and making safe a nuclear installation.

Photo-voltaic effect: the production of electricity directly from sunlight.

Zero-emission vehicles: vehicles which are not directly responsible for producing exhaust gases. Generally it means vehicles that run on electricity. The generation of that electricity will usually involve the emission of greenhouse gases. Zero-emission vehicles help reduce local pollution levels.