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FAQs & Facts
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The following FAQs & FACTS have been compiled by Dr Julian Wright of the Environment Agency and UKCIP and also take account of the IPPC 4th Assessment report 2007:
A few basic facts about climate change:
What is the greenhouse effect?
The Sun's warmth heats the surface of the Earth, which in turn radiates energy back to space. Some of this radiation, which is nearly all in the infrared spectrum, is trapped in the atmosphere by greenhouse gases. For instance, water vapour strongly absorbs radiation with wavelengths between 4 and 7 micrometres, and carbon dioxide (CO2) absorbs radiation with wavelengths between 13 and 19 micrometres.
The trapped radiation warms the lower atmosphere, or troposphere. Some heat then finds its way back down to the Earth's surface, making it hotter than it would otherwise be. This is the greenhouse effect.
What are greenhouse gases?
Greenhouse gases are gases in the atmosphere that have the capacity to absorb long-wave radiation emanating from the Earth's surface. By absorbing this energy and re-radiating it, the gases cause the temperature of the Earth's lower atmosphere and surface to increase. The most common greenhouse gases are water vapour and carbon dioxide.
Are water vapour and carbon dioxide all we have to worry about?
No. Other gases can absorb infrared radiation and contribute to greenhouse warming. These include methane, ozone, CFCs (chlorofluorocarbons) and nitrous oxide (released by fertilisers). Methane is the most important of these. Its atmospheric concentration has more than doubled since pre-industrial times. Methane sources include bacteria in paddy fields, cattle guts and natural gas from landfills and rotting vegetation. Molecule for molecule, other substances are even more potent greenhouse gases. A single molecule of either of the two most common CFCs has the same greenhouse warming effect as 10,000 CO2 molecules.
Is the greenhouse effect a thoroughly bad thing?
Not quite. Without it, the average tempearature of the earth would be about -18°C, i.e. too cold to support life as we know it. The problem is that pre-industrial greenhouse gas levels are being boosted by burning fossil fuels. If nothing is done to curb emissions, the amount of CO2 in the atmosphere will probably be more than double pre-industrial levels by the end of this century.
What is climate change?
Climate refers to the average weather experienced in a region over a long period, typically 30 years. This includes temperature, wind and rainfall patterns. The climate of the Earth is not static, and has changed many times in the past in response to a variety of natural causes. The term 'climate change' usually refers to recent changes in climate that have been observed since the early 1900's.
The earth is kept warm by the greenhouse effect. Certain gases in the atmosphere (so-called greenhouse gases) absorb energy that is radiated from the Earth's surface, and so warm the atmosphere. The greenhouse effect is a natural phenomenon without which life on Earth as we know it would not be possible, as the Earth would be approximately 30°C cooler. However, our modern lifestyles have resulted in us releasing large amounts of greenhouse gases - like carbon dioxide and methane - into the atmosphere, enhancing the greenhouse effect and so pushing up temperatures globally.
What's the difference between global warming and climate change?
Global warming refers to the increase in the average temperature of the earth's atmosphere. Climate change refers to the changes in climate that might accompany the warming of the atmosphere, such as changes in the frequency and intensity of extreme weather and sea level rise. Many people use these expressions interchangeably. However, the word 'warming' may be misleading, as it doesn't suggest the range of changes that could result.
What evidence is there that climate change is happening?
Most climate scientists agree that the world is going to get warmer. The Intergovernmental Panel on Climate Change (IPCC) was set up by the World Meteorological Organization and the United Nations Environment Programme in 1988 to assess scientific and socio-economic information on climate change and its impacts and to the advise the United Nations Framework Convention on Climate Change. In its Fourth Assessment Report (involving over 2,500 scientific expert reviewers, 800 authors with 450 lead authors from over 130 countries) it projects that global temperatures could rise by between 1.1 and 6.4°C by the end of this century.
The range of temperatures reflects a number of uncertainties, as many aspects of the weather are not fully understood, such as the impact of clouds, which can have both warming and cooling effects. Also unclear is the role of ocean currents, and role of the carbon cycle in oceans and forests.
Central England has one of the longest temperature records dating back to 1659. This record shows that temperatures have increased by 0.7°C in the UK since 1659. Of that, a rise of 0.5°C occurred in the 20th century. Globally, average temperatures have increased by 0.6°C since 1860. At the same time global sea level has shown a consistent and measurable rise and the majority of the world's glaciers have been in retreat (i.e. melting - see World Glacier Monitoring Service).
Is the warming a consequence of human activities?
In 1995, the IPCC concluded that the balance of evidence suggested that the recent observed warming of the Earth's atmosphere was due to human activities. In 2001 (and again in 2007), it concluded that "most of the warming observed over the last 50 years is likely to be attributable to human activities."
Recent temperature rises can only be explained by human activities - computer models that simulate climate demonstrate that it other variations, such as the sun's output and changes in volcanoes cannot account for all the warming. Only when human activities are included in the models do they correlate with observed changes.
Can we prevent climate change by reducing emissions of greenhouse gases?
Experiments run on global climate models show us that when we reduce emissions of carbon dioxide, we reduce the rate of rise of average global temperatures and so lessen the rate and impacts of climate change. We can therefore slow the rate of warming by changing our behaviour. However, once released into the atmosphere, carbon dioxide remains there for about 100 years. So even if we were to reduce emissions, we are committed to a certain amount of warming and are likely to see a global rise in temperature of 2°C by the end of the century (or sooner) owing to greenhouse gases currently in the atmosphere. We may need to reduce emissions by 60-80% to stabilise the climate completely.
Isn't there a chance that Northern Europe could get much colder? What about the Gulf Stream switching off?
The UK's climate is affected by the Gulf Stream, which brings warm water from the Gulf of Mexico across the Atlantic Ocean to north west Europe. This warm water keeps the climate of the UK warmer than continental locations at similar latitudes. Some scenarios of climate change suggest that with further climate change, the North Atlantic Thermohaline Circulation (THC), of which the Gulf Stream is a part, could 'shut down'. If this were to happen, average temperatures in the UK would drop by some 4°C. Research at the Met Office shows that global warming could reduce the strength of the THC circulation by 25% by 2100. However, the direct heating of global warming would be greater than any cooling effect from reduced activity of the THC. A cold future is therefore very unlikely.
Why do sea levels rise as it gets warmer?
Oceans absorb heat from the atmosphere. As the atmosphere warms, so too do the oceans. When water is warmed, it expands, causing sea levels to rise. In addition, as the temperature of the oceans and atmosphere increases, so glaciers and small ice sheets melt, releasing water into the oceans and contributing to sea level rise.
In addition, the UK and northern Europe are still responding to the melting of ice sheets that covered the land during the last Ice Age. Mainland Britain is slowly tilting, with South and East England slowly sinking into the sea and the North West and Scotland rising. Sea level rises around the UK would increase the risk of flooding and coastal erosion.
Why think about how climate change will affect us now, when its effects won't be felt for many years?
The earlier you find out the likely impacts, the more options you have for adapting, including taking advantage of opportunities. This is particularly important when it comes to major investment decisions and decisions that may affect whole sectors, or communities. In addition, the sooner we take action to reduce emissions, the greater the chance of stabilising the climate. In adapting to climate change there is much potential for "win-win" and "no regrets" action.
Isn't the UK a winner in terms of climate change? If so, why worry so much?
The UK will be warmer and this will certainly bring advantages. However, we are also likely to experience more extreme weather and we need to start planning now to deal with the consequences, such as additional flooding, drought and sea level rise. There are also likely to be serious implications for other parts of the world, for example, our trading partners, that will have effects for the UK. It's in our interest to be prepared. In addition we have an ethical responsibility in the developed world (which has emitted the majority of greenhouse gases leading to man-made climate change) to help those less-developed countries in which the impacts will be most felt.
Are there scientists out there who do not believe in the greenhouse effect or global warming?
No, this is a myth. All scientists believe in the greenhouse effect. Without it the planet would be frozen. And all climate scientists accept that if humans put more greenhouse gases into the atmosphere then it will warm the planet. The only disagreement is over precisely how much the warming will be amplified by planetary feedbacks.
However, there is scientific consensus that the average global warming of 0.6°C seen in the twentieth century - and particularly the pronounced warming of the past three decades - is due to the greenhouse effect.
How do we know what pre-industrial greenhouse gas levels were?
The most informative measurements have come from air bubbles trapped in Antarctic ice. These show that, for at least 400,000 years, CO2 levels in the atmosphere have closely followed the global temperatures as recorded in ice cores, tree rings and elsewhere.
What about feedback mechanisms? Can't the earth sort itself out naturally?
One of the easiest to estimate is the "ice-albedo" feedback. As the world warms, ice caps will melt, to be replaced by water or land. Ice is very efficient at reflecting solar radiation, whereas water and land are less so. Therefore, the Earth's surface will trap more heat, increasing warming - a positive feedback.
Less clear-cut is the impact of the extra water vapour likely to enter the atmosphere because of higher evaporation rates. This added water vapour itself contributes to the greenhouse effect, another positive feedback. But it may also increase cloud cover, shrouding and cooling the Earth - a negative feedback.
Disputes about how water vapour and clouds will influence global warming are at the heart of disputes between mainstream scientists and the handful of greenhouse sceptics. Most believe that positive feedbacks could amplify the warming effect by between two and five times. But some sceptics believe the feedback effect could be neutral or negative.
Are there other greenhouse gas complications?
Yes. A whole series of other feedbacks will influence the concentration of greenhouse gases in the atmosphere. Not all the CO2 that we put into the atmosphere stays there. Some is absorbed by vegetation and a lot is taken up by the oceans. If CO2 absorption rate changes, then the rate of build-up in the atmosphere will also change, potentially speeding up, or slowing down, global warming.
One way to increase the build-up of CO2 would be to chop down all the tropical forests. Another could be the impact of warming on ocean currents, particularly the global "conveyor belt" that begins in the North Atlantic. This water carries dissolved CO2 with it on a centuries-long journey across the ocean floor.
Most oceanographers believe that as warming takes hold, and ice formation is reduced, these currents - which lock CO2 up in the depths - could slow down or carry less water, meaning that less CO2 is removed from the atmosphere.
Is there any evidence of a speed-up in the accumulation of CO2 in the atmosphere?
Yes. Since the start of the 21st century, the rate of accumulation has accelerated. It is now at twice the 1990s level. Nobody is sure why. It is not because emissions have accelerated. It could be temporary natural variability. Or it could be that the forests and oceans are losing the ability to absorb our pollution. If so, then global warming could shortly gather pace.
Will a warmer planet absorb more carbon dioxide?
That is correct. Warmer temperatures and the fertilising effect of CO2 in the air will stimulate faster plant growth, which in turn will soak up some of the CO2. But plants need other things too. They need water, which could be in short supply as greater evaporation will dry out soils, and space, which urbanisation is taking up.
How do organisms in the oceans affect global warming?
Once dissolved in surface waters, a great amount of CO2 is absorbed by plankton and other marine organisms and turned into organic compounds. Most of this eventually falls to the ocean floor. The strength of this sink for carbon depends on how much life the ocean is producing. It is not clear to what extent global warming will affect the oceans' biological productivity - it could rise or fall.
Is there anything else that could shield us from global warming?
Yes, volcanoes. When Mount Pinatubo erupted in 1991, it threw masses of sulphate particles and dust into the stratosphere that partially shielded the Earth from solar energy. Computer models successfully predicted that the debris would temporarily cool the Earth's atmosphere. The models also predicted that as the volcanic debris cleared in 1992 and 1993, average temperatures would swiftly return first to the level of the 1980s, and then, by the mid-1990s, to the higher levels expected with the ongoing build-up of greenhouse gases.
Volcanoes produce cooling sulphate particles, but do we make them, too? What about Global Dimming?
Yes we do. Ironically, burning fossil fuels produces sulphate particles. These particles - which make acid rain - help to shield industrialised countries from global warming's full impact. In some places, such as central Europe and parts of China, they may have even produced a net cooling effect. Dust from soil erosion and desertification can also curb local warming effects.
But even if you are comfortable with the idea of using one form of pollution to protect us from another, there is a problem. Whereas the average CO2 molecule in the atmosphere lasts for about a century, sulphates and their like persist for only a few days. If you turned down the power stations, the world would get much hotter within a few days. So sulphates are not a solution.
Are there any cataclysmic events in the offing? What about the West Antarctic ice sheet?
One fear is that the entire West Antarctic and Greenland ice sheets might disappear into the oceans. According to projections by the UK's Hadley Center for Climate Prediction, before the end of the century a warming of at least 3°C would probably trigger the eventual melting of the entire Greenland ice sheet. The glacial collapse could raise sea levels by 7 metres.
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