Climate change is due to enhancement of the natural greenhouse effect, which is caused by emissions of carbon dioxide and other greenhouse gases that trap heat in the Earth’s atmosphere. Rising atmospheric temperatures alter weather patterns causing intense rainfall, severe storms and drought and disrupt the balance of natural processes (including the carbon cycle).

• What is the greenhouse effect?
• What are the main greenhouse gases?
• What is causing climate change?
• How much warmer could the Earth get?
• What are positive feedback processes?
• What is dangerous climate change?
• Is climate change related to the hole in the ozone layer?
• What is the best source of scientific information on climate change?

What is the greenhouse effect?

The greenhouse effect is a natural phenomenon that keeps Earth within a stable temperature range of 15°C (59°F). Without it, the average surface temperature of our planet would be -18°C (0°F); so cold it would be unable to sustain life.

When the sun’s energy warms the Earth’s surface and its atmosphere, a portion of the heat is absorbed by a delicate balance of heat-trapping greenhouse gases (among them carbon dioxide and water vapour), which create an insulating layer and keep the Earth within its stable temperature range.

Human activities, however, are now causing unnatural enhancement of the Earth’s temperature. Through increased use of fossil fuels, as well as deforestation and other land-use changes, we are adding relatively large amounts of greenhouse gases to the atmosphere and this is having rapid and environmentally-damaging effects.

Whilst climate change has occurred naturally throughout Earth's history (fluctuating between ice-ages and warmer periods) human civilisation has arisen during a period of relative climate stability and we are not yet equipped to cope with dramatic or rapid changes in climate.

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What are the main greenhouse gases?

Greenhouse gases are from natural and artificial sources and can remain in the atmosphere, exerting their effect, for decades or even centuries. Properties of the main greenhouse gases are shown in the table:

Greenhouse Gases

• warming of the climate system is beyond doubt;
• humans are contributing to it; and
• the last half century has been unusually warm compared to at least the previous 1300 years.

Scientists have simulated the climates response to natural causes, such as solar radiation changes and volcanic explosions. They have found that these kinds of natural events alone could not have caused the degree of increased climate change in the latter half of the 20^th century.

Since pre-industrial times, the atmospheric concentration of carbon dioxide, which contributes to climate change, has increased by nearly a third. Over the same period, atmospheric methane has tripled, mostly from agricultural activities.

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How much warmer could the Earth get?

The IPCC's Fourth Assessment Report suggests continued global warming of up to 0.2°C over coming decades. If global emissions were to be maintained at the level they were in 2000, the overall increase would be in the range of 0.3 to 0.9ºC or in the range 1.1 to 6.6ºC, depending on a combination of future social and economic scenarios.  

Even if we stopped emitting greenhouse gases immediately, the climate would not stabilise for many decades because gases already released into the atmosphere will take decades and even centuries to disappear. So, while warming rates will slow if we reduce emissions significantly, global temperatures will not return to today's averages. The faster and higher the temperature rises, the greater are the chances of irreversible climate changes.

An increase of a few degrees does not mean pleasantly warmer temperatures. In the last 10,000 years, the Earth’s average temperature hasn’t varied by more than 1°C, and even a modest rise of 1.1° – 1.7°C could have dramatic effects. Indeed, temperatures only 5° – 9°C cooler than those today prevailed at the end of the last Ice Age, when large parts of the Northern Hemisphere were covered by more than 3,000 feet of ice.

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What are positive feedback processes?

Positive feedback is the increase of a system’s natural output. Global climate change can set-off positive feedback loops in nature, which trigger ecological and chemical responses and amplify warming trends. Warmer oceans, for example, give off more carbon dioxide and warmer soils decompose faster, releasing ever-increasing amounts of carbon dioxide and methane. Of course, it is these greenhouse gases that further exacerbate the problem. Conversely, negative feedback loops can increase cooling trends.

Find out more about natural feedback processes >>>

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What is dangerous climate change?

There is uncertainty about the link between temperature change and atmospheric greenhouse gas concentrations. However, stabilisation in the range of 450 to 550 parts per million (ppm) of carbon dioxide equivalent (CO₂e) gives us a 50:50 chance of limiting global temperature increases to between 2 and 3°C. If temperature rise does exceed 5°C, the Earth’s natural feedback loops (see above) could become unbalanced, and so prompt abrupt and dangerous climatic events. This rise is equivalent to the change in average temperatures from the last ice age to today, but at a rate much faster than previously recorded.

Find out more about dangerous climate change >>>

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Is climate change connected to the hole in the ozone layer?

Climate change and ozone depletion are separate but related threats. Global warming and the greenhouse effect refer to the warming of the lower part of the atmosphere (known as the troposphere), while the ozone hole refers to the loss of ozone in the upper part of the atmosphere (called the stratosphere).

This is of serious concern because the stratospheric ozone blocks incoming ultraviolet radiation from the sun, some of which is harmful to plants, animals, and humans.

How are they related?

• Trapping heat in the lower part of the atmosphere allows less heat to escape into space and leads to cooling of the upper part of the atmosphere. The colder the stratosphere gets, the greater the destruction of the protective ozone layer.
  
  
• Certain ozone-depleting substances, which include gases known as halocarbons, destroy the ozone layer and act as greenhouse gases.
  
  

What needs to be done?

Reducing ozone-depleting gases is crucial to preventing further destruction of the ozone layer, but eliminating these gases alone will not prevent climate change. Only efforts to reduce all types of greenhouse gas emissions will benefit the recovery of the ozone layer.

Working towards this aim, the Montreal Protocol limits the use of the most common ozone-depleting substances. Although their production has largely been phased out in the UK, the long atmospheric life and prevalence in many products demands continued monitoring and controls.

Find out more about ozone-depleting substances here >>>

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What is the best source of scientific information on climate change?

The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by the United Nations Environment Programme and the World Meteorological Organisation. It assesses scientific, technical and socio-economic information relevant to understanding the risks of human-induced climate change, potential impacts and options for adaptation and mitigation.

Scientists from approximately 100 countries review published and peer-reviewed scientific information about global climate, how it changes, what it will mean for people and the environment and what can be done about it. This information is then used to produce the IPCC Assessment Reports, which serve as the basis for international climate negotiations and policy. The Fourth Assessment Report on Climate Change is being released in stages throughout 2007.

Find out more about the IPCC here >>>

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