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Effects of Climate Change

Teachers' Information Sheet

Introduction

The driving force behind man-made global climate change is an enhancement in the natural greenhouse effect due to an increase in the atmospheric concentration of greenhouse gases. As a direct consequence of this we will see an increase in global temperatures, but there will probably be many other indirect effects as a result of such a relatively rapid rise in temperature.

The theory of, and gases involved with, global warming have already been discussed in lessons one and two. The causes and effects of ozone depletion are covered in lesson three. The scope of this lesson is therefore restricted to the possible effects of climate change.

The lesson begins by discussing climate modelling, the cornerstone of atmospheric science. The discussion is not included in the pupils' notes and so it is up to the discretion of the teacher whether or not it is mentioned. The lesson then goes on to consider a number of different subject areas which may be affected by a change in world climate.

The consequences of climate change are discussed with particular reference to the following topics.

  • How will temperatures change around the world?
  • What will happen to the oceans?
  • Will there be more or less freshwater?
  • Will we be able to grow enough food?
  • Are any species at risk from global warming?
  • How will some people be affected?

Also included is an experiment illustrating the effect of the melting of ice on sea level.

Climate Modelling

In order to assess the extent and impacts of climate change, complex computer simulations or 'models' are constructed. These models attempt to describe the interactions between the atmosphere, oceans and land. In such models the Earth is described as many homogeneous 'cells'. These cells represent the highest level of detail of the model, in much the same way as one pixel is the highest level of detail on a computer screen.

Even the best climate models have a very coarse resolution, with cells hundreds of kilometres square. Consequently, on a regional scale these models become very crude approximations to real climate systems. Modellers of climate therefore have decreasing confidence in their projections of climate change as the scale of the projection diminishes; this is analogous to the clarity of a photograph decreasing if it is enlarged. Assessments of the local effects of climate change are therefore highly speculative, and will remain so until the resolution of the models, and the understanding of the processes involved, improves dramatically.

How will temperatures change around the world?

The work of the Inter-governmental Panel on Climate Change (IPCC) represents the scientific consensus on issues of climate change. They estimate that average global temperatures will rise by 1.4 to 5.8C over the next century (with a best estimate of 3C) due to an increase in the concentration of the greenhouse gases in the atmosphere. So far there has been an estimated 0.6C rise in global temperatures over the last 100 years.

One of the most serious threats posed by global warming is that these increases in temperature will not be uniformly distributed across the world. Consequently some regions will undergo warming much greater than the quoted average, while other parts of the world may even cool. In addition, extreme weather conditions, such as hurricanes and floods, may show increases both in frequency and magnitude. This may have knock-on effects such as the increasing unwillingness of underwriters to insure against such 'natural' disasters and an increase in the number of environmental refugees.

What will happen to the oceans?

The best current projections by the IPCC anticipate a 9 to 88cm rise in sea level by 2100. This rise will be mainly from two sources: the thermal expansion of water, and the melting of ice-sheets and glaciers. It should be emphasised that the melting of sea ice will not have any effect on sea levels since the volume of water produced from the melting of an iceberg is equal to the volume of water it displaces (see experiment).

Coastal regions are obviously the most vulnerable to changing sea levels. Some very low-lying land may be at risk of permanent submergence, and elsewhere coastlines may be subjected to increased rates of erosion. As the sea rises there will be an increased frequency of flooding, unless costly additional sea-defences are constructed. These floods would cause disruption to populations, damage to infrastructure, and threaten coastal ecosystems. In the UK, two notable examples which would suffer badly from sea-level rise are the coast of East Anglia and the Thames Estuary.

It is also thought that the warming of the oceans may change ocean currents. This could have important consequences for regional climates. The Gulf Stream is responsible for moderating climate in coastal northwest Europe; its disruption would have serious implications for the UK. Fisheries and ocean productivity for important species such as cod could be affected as a result of changing migratory patterns. This could have implications for food stocks.

Will there be more or less freshwater?

Many areas in the world rely on groundwater for much of their water supply. An increase in sea level may lead to increased salination of groundwater, contaminating water supplies. An rise in global temperatures would increase the rates of evaporation and transpiration, but may also increase precipitation. On the whole, however, it is thought that warming would reduce the availability of water resources.

Water scarcity will be exacerbated in areas where it is already a problem, such as semi-arid regions or where water supplies are contaminated. Drought risk is thought to be one of the most serious threats to agriculture. In England, where climate change may lead to hotter, drier summers, the southeast will be increasingly at risk from drought.

Will we be able to grow enough food?

In order to grow, plants must convert CO2 into organic compounds by photosynthesis, and climate change is associated with increased atmospheric concentrations of CO2. Therefore crops may be expected to respond to increased CO2 concentrations by enhanced growth rates. In fact this is true for a group called the C3 plants (so-called because the first product of photosynthesis contains three carbon atoms) including wheat, rice and soya beans. Another group called the C4 plants, which includes maize, sorghum, sugarcane and millet do not demonstrate any increased productivity. C3 crops may be favoured both biologically and economically, since C4 crops will prove to be less competitive, which may, in turn, lead to a world shortage of some crops.

An increase in temperature has the effect of prolonging the growing season. This may push the climatic limits for certain crops northwards. For example, the current geographical boundary (in terms of temperature) for ripening maize excludes virtually the whole of the UK. If temperatures were to increase by just 0.5C, its cultivation would be feasible across most of southern England. However an increase in temperature would also extend the range of temperature limited pests, causing more damage to crops. Realistically, increased crop productivity would be offset by lower soil moisture, evaporation from irrigation systems, and increases in pest populations.

Globally there is doubt whether agricultural productivity will increase or decrease. Since the local patterns of climate change are hard to predict, and given that relatively small areas grow the bulk of the world's food resources, assessments of the change in food supplies have an inherently low degree of confidence.

As with other impacts, some areas are more sensitive to change than others. Brazil, Peru, the Sahel region of Africa, south-east Asia and China are thought to be at considerable risk. In general, crops are at their most vulnerable where they are grown close to their limits in terms of conditions such as temperature or soil moisture.

Are any species at risk from global warming?

Generally, climate zones would move poleward and to higher elevations. In the next fifty years this shift could be hundreds of kilometres. Some species may find themselves in climatic conditions to which they are no longer well adapted. Flora and fauna will tend to migrate as the climate changes, but at a slower rate limited by how quickly a given species can respond. This could lead to extinction of local, or even global, populations.

Species particularly at risk from climate change are those which exist at the edge of their optimal range, are geographically localised (for example in montane ecosystems or reservations), and occupy highly specialised niches.

How will some people be affected?

Many of the impacts (especially on agriculture and sea-level) so far discussed will be of relevance to humans. It is within the means of developed countries to counteract these effects, but other countries may not have sufficient resources. In areas with extensive, highly populated coastal flood-plains such as Bangladesh, Egypt, or China, this could lead to the displacement of whole populations. Wide-scale, environmentally induced migrations would then increase pressure on land and resources elsewhere, and lead to less tangible effects such as increases in socio-economic instability.

Questions and sample solutions

1. Can you think of any parts of the UK that could be affected by sea-level rise?

Sample solution: Any low-lying area will be at risk from flooding if sea levels do rise, for example East Anglia and the Norfolk Broads and London (through the Thames Estuary)

2. How do you think people in very dry areas could manage with even less water?

This question is intended to make the pupils aware of the fact of environmental refugees and to test their ingenuity as far as water storage and collection is concerned.

3. Can you think of any species that might be affected by global warming?

Sample answer: Any animal which has a highly specific habitat with a small range of dietary foodstuffs will be affected by global warming, for example the panda, polar bear.

4. What might life be like in the UK if the climate was much hotter?

This could be turned into an essay type question where the pupils could write 'a day in the life...' type answer describing the UK as a Mediterranean-type holiday resort.

5. Assuming the average summertime temperature in the UK is currently 15C, and assuming the IPCC estimated rate of increase in global temperatures, what would be the new average summertime temperature in the UK in a) 2010, b) 2050, c)2100 ?

Answer: (Taking the average warming per decade to be 0.3C )

a) 15.3, b) 16.5 and c) 18.0C


Glossary

ecosystem: a system involving the interactions between a community and its non-living environment.

groundwater: water that has seeped from the surface, and is held underground in porous and permeable rocks.

pixel: the smallest element which goes to make up an image on a computer screen.

salination: to make salty

sorghum: a kind of grass cultivated for grain.