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Contacting Me
Feel free to email the author at t.mitchell@uea.ac.uk

Contents
Climate introduced
Climate system
Climate science
Climate change
Climate gases
Climate models
Climate futures
Climate politics
Climate ethics
Climate action
Climate reading

Climate system
Before we search for climate changes, we ought first to understand what it is that might be changing. The climate system is made up of the earth’s atmosphere, oceans, ice, vegetation, and streams.
(Graphic of the climate system. Source: GCIRO)
Each part has its own complex behaviour, and a complex set of relationships with every other part.
(Graphic of ocean currents, illustrating the complexity of just one element of the climate system. Source: NASA)
Humans depend on and affect each part. We see ourselves at our weakest in hurricanes, floods, avalanches, and pests, which are part of the curse inflicted upon the earth following the Fall (Genesis 3:17). We see ourselves at our strongest in predicting the weather, in harnessing the ocean to generate electricity, and in diverting rivers, as we follow God’s command to fill the earth and subdue it (Genesis 1:28). Yet we are neither in control of the climate system, nor certain about the effects of our actions. Control and certainty belong to God alone (Job 38-41). So there is a possibility that our actions may affect the climate system in unexpected ways.

Climate science
Many readers will remember the 1970s, when it was widely suggested that the earth might be about to enter an ice age, and so may be sceptical about the idea of global warming. With the benefit of hindsight, it is easy to criticise the scientists of the 1970s for being alarmist when there was little evidence to support the ice age prediction. Being gifted with hindsight, we should also recognise their valuable contribution in awaking the world to the possibility of climate change. For the decades of painstaking research that have followed the 1970s have unveiled both the natural variability in the climate system, and the dramatic effects of human actions.

Climate change
To assemble a record of global climate changes over the last 150 years we use instrumental records, such as rain gauges and thermometers. Since it is only recently that such instruments have been widely used, to reconstruct climate changes prior to the 19th century we are compelled to use indirect sources of information (‘proxies’), such as tree ring widths and ice core layers. Using this mixture of data, we have assembled global temperature records for the last millennium.
(Time series of global temperature over the last 600 years.)
There is a substantial amount of natural variability throughout the records, but there is a 20th century rise in global temperature that is unprecedented in its magnitude and rate of change.
(Time series of global temperature in the 20th century.)
Is it merely a coincidence that this global warming has come at the same time as the huge expansion in human population and industrialisation that we have seen in the 20th century?

Climate gases
It is conceivable that humans could alter the behaviour of the climate system by polluting it. The more relevant pollutants of the atmosphere may be divided into three groups: greenhouse gases, aerosols, and ozone-destroying chemicals.

Although the destruction of ozone and the ‘ozone holes’ play their part in global warming, it is a comparatively minor part. Ozone holes are more directly important for their potential biological damage to living cells and human skin, which is beyond the scope of this article.
(Graphic showing the thinning of Arctic ozone in November 1999. Source: NASA.)

The role of greenhouse gases in the atmosphere is to absorb energy (in the form of infra-red radiation) that would otherwise be lost from the earth, and so maintain the warmth of the earth.
(Graphic showing how the greenhouse effect works. Source: White House)
Greenhouse gases are well-mixed and stay in the atmosphere for a long time. Greenhouse gases are nothing new, but the amount of carbon dioxide (the principal greenhouse gas) in the atmosphere has increased by 30% since the Industrial Revolution.
(Time series of atmospheric concentrations of carbon dioxide over the last millennium. Source: GCIRO)
The principal reason for the increase in atmospheric concentrations of carbon dioxide is human pollution.
(Time series of human emissions of carbon dioxide over the 20th century.)
The increase is mainly due to land use changes, and the combustion of fossil fuels (oil, natural gas, coal, petrol, diesel) in power stations, transport, homes, and industry.
(Pie-chart showing sources of emissions for Canada, typical for Western nations.)
The vast majority of historical greenhouse gas emissions have come from the West, although the balance is expected to gradually change in the future.
(Pie-chart showing balances of emissions of greenhouse gases at present and in the future.)
It is to be expected that increasing the greenhouse gases in the atmosphere will increase the greenhouse effect, and so warm the earth.

Aerosols are microscopic airborne particles that result from burning and the combustion of fossil fuels. They are different from the greenhouse gases in a number of ways: they act to cool the earth; they are short-lived; and they are concentrated in regions. When we combine these different pollutants, it seems very likely that human pollution of the atmosphere has had the overall effect of warming the earth.

Climate models
However, human pollution is not the only conceivable candidate when we try to understand why the earth has warmed in the 20th century. Other possibilities include variability in the oceans, volcanic eruptions, and variations in the sun.
(Pretty picture illustrating where in the world volcanoes can be found. Source: NASA)
We can reconstruct how some of these ‘climate forcings’ have varied over the past centuries, but it is more difficult to evaluate their hidden influence upon climate. Obviously we cannot rewind the history of the earth and adjust these candidates one by one to see how influential they are. However, if we are able to construct a computer model that simulates the behaviour of the climate system, then we can rewind and simulate the last century as many times as we can afford. So the biggest change in climate science since the 1970s has been the exponential increase in computing power. It may be games that drive the computing industry to continually improve power, but science is a major beneficiary.

Equipped with some of the most powerful computers in the world, scientists run climate models time and again with different climate forcings. Each time we look at the magnitudes, rates, and patterns of the changes. We find that although each of the ‘natural’ climate forcings (oceanic, volcanic, and solar) have probably played a role in the historical climate changes, the sum of them is insufficient to explain the global warming of the 20th century.
(Time series of global temperature in the 20th century.)
It is only when we include ‘anthropogenic’ climate forcings (human pollution of the atmosphere) that we can explain the global warming of the 20th century. Consequently the conclusion is that “the balance of evidence suggests that there is a discernible human influence on global climate” (IPCC, 1995).

Climate futures
At present the effect of human pollution on climate is relatively small. However, humans are polluting earth at an ever-increasing rate. So unless substantive positive action is taken soon, the effects of human pollution on climate will become very great. Moreover, due to the time lags in the climate system, even our present actions are having consequences that our grandchildren will still be feeling. We are already committed to seeing global sea levels rise by half a metre during the 21st century.
(Graphic illustrating the likely effect on the Nile Delta of a 1m rise in sea level. Source: UNEP.)
This is quite apart from the unknown risk of a catastrophic collapse of the Antarctic ice sheet. Our best estimate of global warming during the 21st century is 2 degrees Celsius, which makes the record increase of 0.4-0.6 degrees Celsius in the 20th century look almost insignificant.
(Time series of estimated global temperature change in the 21st century.)
The exact climatic effects in any one region will depend strongly on how the global changes affect the circulations of the atmosphere and the oceans, and are difficult to predict.
(Graphic illustrating potential variations in temperature change around the globe. Source: GFDL.)
It is also uncertain how climatic extremes – such as hurricanes – will change.
(Bar chart showing economic losses due to wind storm damage in the past.)
Predicting how climate change will affect economic activities in the environment is even more difficult.
(Graphic illustrating the potential agricultural changes in the 21st century.)
What is certain is that environments and humans will be affected the world over.
(Schematic illustrating some of the potential impacts of climate change. Source: EPA.)
There is no evidence to support tabloid headlines anticipating a Costa del Bognor or the end of the world as we know it, but neither will the impacts be small.
(Potential changes in precipitation in the UK during the 21st century. Source: UKCIP.)
On Radio 4’s ‘Costing the Earth’ in January, the Bangladeshi Environment Minister said that crowded Bangladesh expects to lose around 20% of its land to sea level rises. She noted that this would make 20 million people homeless, and stated that it would be the responsibility of the rich of the world to find room for them. Since it is the rich of the world – such as ourselves - who are primarily responsible for atmospheric pollution, morally she has a strong case. Bangladesh is an extreme example, but there is an abundance of difficult consequences of climate  change.

Climate politics
The issues involved are serious, and they are of global concern. Consequently, in 1988 the IPCC (the Inter-Governmental Panel on Climate Change) was set up to advise all countries of the latest scientific findings. The IPCC produces consensus reports that represent agreement between thousands of scientists worldwide, and that have an authority that individual scientists cannot hold. Motivated by these reports, 180 countries have ratified the UN Framework Convention on Climate Change (UN/FCCC), which has as its aim the “stabilisation of greenhouse gas concentrations at a level that would prevent dangerous anthropogenic interference with the climate system”. In 1997 in Kyoto (Japan), a protocol to the UN/FCCC was signed in which it was agreed that, relative to 1990, there should be a 5% cut in annual emissions of greenhouse gases by the period 2008-2012. This does not mean that all is now well.

1. Thus far the Kyoto protocol has only been signed, not ratified, and there is substantial doubt as to whether the key player (the USA) will ratify it.
2. A 5% cut is a minor cut, not the major cut that is required.
3. The cut is in emissions, not in atmospheric concentrations, and so only slows down the rate at which concentrations are increasing.
4. It is one matter to agree to a cut, it is another matter to implement it.

Climate ethics
There is no perfect level of greenhouse gases in the atmosphere, and there is no perfect global temperature. Both vary naturally. However, the changes we are introducing through our pollution are morally questionable. Put simply, in the rich part of the world we have polluted in order to get rich. The most severe consequences are likely to fall upon the poor, simply because they often cannot afford to adapt to changes in climate.

This introduces two parallel ethical issues for us in the West.

• Now that we know the consequences, should we continue to pollute?
• Given that we may be responsible for hurting our fellow humans, should we help them?

Of course, in practice each part of the world seeks its own material interest. Oil-producing states lobby for unrestricted combustion of fossil fuels. Rich countries lobby for reductions in greenhouse gases that will not hurt their economic interests. Poor countries lobby for free help from the rich. Christians in politics ought not to think in this way.

Climate action
What can individual Christians do? Some, but not many, are called to be scientists and politicians. However, we all have the vote, and environmental issues ought to be among those that we weigh up carefully before casting our vote.

We are also each responsible for a small part of the daily emissions of greenhouse gases.
(Pie-chart showing how a typical Western nation's emissions break down for the man on the street.)
Do we use our energy-intensive cars wisely, or are we guilty of the world’s attitudes to public transport? With domestic heating, do we spend more and pollute more than is necessary? (See the DIY Guide to Combating Global Warming.) The government urges us to reduce our energy usage in order to get wealthier, but we have a higher motive (1 Timothy 6:17-19).

Climate change is another of the birth pangs of creation, as it eagerly awaits being delivered from the bondage of corruption (Romans 8:19-22).
(Graphic to stimulate the imagination. The future of earth lies beyond our imagination. Source: NASA.)
May we look forward to the new heavens and earth in which there will be no more corruption (2 Peter 3:13-14), and be motivated to be diligent while we wait.

Climate reading

• The US Environmental Protection Agency has a global warming site.
• GFDL provide an introduction to the state of science on climate change.
• For a register of the latest articles on climate issues, try Newswatch.
• The Tiempo Climate Cyberlibrary is "an electronic information service covering global warming, climate change, sea-level rise and related issues".
• Tiempo is a quarterly bulletin that "aims to promote communication between the nations of the North and South on the issue of climate change, to promote the interests of developing nations in the climate debate and to provide authoritative and timely information on relevant scientific, technical and policy matters".
• Authoritative reports (including policymakers summaries) on climate change may be obtained from the IPCC Secretariat.
• For environmental scientists, climate data is available from the IPCC Data Distribution Centre.
• Media reports of climate change tend to be unbalanced, due to an all-encompassing desire for argument. This tends to result in 'wacky' and minority opinions being given equal weight to the IPCC consensus. Sceptics are addressed in a number of sources, including this article by James Hansen.