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Copenhagen climate summit: Science Q&A
Politicians, activists and civil servants from around the world have descended on Copenhagen for the UN conference. Delegates from the 192 countries represented are aiming to reach at new treaty on climate change at the end of two weeks of arguing and horse-trading. But why are the talks happening and are they really necessary? Environment editor David Derbyshire examines the issues at stake
IS THE WORLD WARMING?
The vast majority of climate scientists say yes. The average global temperature increased by 0.74C or 1.33 F in the 20th century and by 0.6C in the century before that. Central England temperatures have gone up by 1C since the early 1970s. According to the Met Office, the ten warmest years since records began in 1850 have occurred since 1997.
DOESN'T CLIMATE ALWAYS CHANGE?
Yes. Temperatures have risen and fallen throughout history. Natural variations in temperature are caused by changes in the Earth’s orbit, changes in the Sun’s intensity, volcanic eruptions which fill the atmosphere with dust and natural weather cycles such as El Nino.
SO WHY DO SCIENTISTS BLAME MANKIND FOR GLOBAL WARMING?
They argue that natural variations can only account for some of the recent warming. The orbit of the Earth should be propelling us to a cooler spell, not a hotter one. And solar cycles cannot explain warming since the 1960s. The Met Office says the warmth of the last half century is 'unprecedented' in the last 1,300 years.
Computer climate models can only explain warming of the last half century if human activity is included. The most recent report from the United National Intergovernmental Panel on Climate Change (IPCC) 2007 says human activity is 'very, very likely' to be contributing to global warming - and that burning of fossil fuels is contributing to the 'greenhouse effect'.
WHAT'S THE 'GREENHOUSE EFFECT'?
Since the early 19th century, scientists have known that the Earth is kept warm by a blanket of gases in the atmosphere. Without these greenhouse gases to trap heat from the sun, the world would be a much cooler place. The most important is carbon dioxide - or CO2. Others include methane and water vapour.
WHERE DO GREENHOUSE GASES COME FROM?
They are released from volcanoes, from evaporating oceans and burning forests. They are removed from the air by plankton, seawater , the weathering of rocks and the creation of fossil fuels.
Climate scientists say the burning of coal, oil and gas since the industrial revolution has released CO2 that has been locked away for millions of years. These higher levels of CO2 have enhanced the greenhouse effect.
IS THERE EVIDENCE THE CO2 LEVELS HAVE GONE UP?
Studies of ice cores (where bubbles of prehistoric air are trapped in ice) show the concentration of CO2 in the air has gone up sharply over the last 150 years.
Since 1880 the concentration of CO2 in the atmosphere has risen from around 270 parts per million (ppm) to 370ppm today, scientists say. That level is thought to be the highest for 650,000 years.
A cloud of dust engulfs a group of Chinese workers shoveling coal at a coal mine. China is the world's leader of sulphur dioxide emissions, up to 90 per cent of which are as a result of coal use
DO CO2 LEVELS VARY NATURALLY?
Yes. At the end of the last Ice Age, levels of CO2 rose by 50 per cent. Millions of years ago levels were far higher than today. However, climate scientists say the current rise in CO2 mirrors the advent of the industrial age, and is unprecedented in recent history.
Confusingly, historical CO2 levels don't just appear to cause warming, warming also increases levels of CO2. So a natural warming of climate caused by a wobble in the Earth's orbit leads to more CO2 which leads to more warming. A wobble that triggers an ice age reduces CO2 which leads to more cooling. This feedback effect is thought to have speeded up natural global warming and cooling in the past.
WHAT HAS HAPPENED TO TEMPERATURES OVER THE LAST 10 YEARS?
The warmest year since records began was 1998, according to the Met Office. It was unusually hot because of a natural weather event called El Nino. Since then temperatures have been stable, but remain historically high. The Met Office points out that the last ten years are still among the hottest on record and says there is no sign of global cooling.
IS IT THE END OF GLOBAL WARMING?
Probably not. Throughout the last 150 years, temperatures have ebbed and flowed. Between 1940 and 1970s temperatures fell even though the long-term trend was up. (The post-war cooling has been linked to a rise in soot in the atmosphere released from factories and power stations which ended with clean air legislation.) A decade of stable or falling temperatures doesn’t necessarily mean the upward trend has stalled.
WHAT WILL HAPPEN IN THE FUTURE?
The U.N.'s IPCC has set out a range of scenarios based on the latest climate models. Any prediction of the future has to be taken with a pinch of salt. They show a rise in temperatures of between 1.1C and 6.4C by the end of the century.
A climate change protestor in London yesterday. The aim of the demonstration was to draw attention to the UN conference starting tomorrow
WHAT TO DO THE SCEPTICS ARGUE?
There are many different types of sceptics - from those who dismiss the science completely - to those who accept the science, but disagree with the 'hair shirt' response of the green movement.
It is fairly uncontroversial to argue that burning fossil fuels releases CO2 - or that CO2 in the atmosphere retains heat from the sun.
However, some sceptics challenge the historical temperature records, particularly when it is compiled using data from tree rings or ice cores. Others say the climate models are inaccurate.
WHO IS RIGHT?
On the science, the sceptics are hugely outweighed by scientists. The pro-lobby says the evidence is overwhelming and is getting stronger all the time. The sceptics say dissenting voices are suppressed because they don’t get the funding or support from universities. Challenging the climate change orthodoxy can be career suicide for a young scientists, they say.
WHAT ARE THE UNCERTAINTIES?
Sceptics say the models don’t take into account the effects of clouds which are more likely in a warmer world. Others say the higher atmosphere is not warming in line with the computer models. Some question the historical records that appear to show a warming world, others say the warming is natural - and that climate scientists underplay the role of the Sun and even cosmic rays.
IS THERE EVIDENCE OF GLOBAL WARMING NOW?
No single events can be linked to climate change - despite the attempts of environmentalists and politicians to make capital out of disasters. Hurricane Katrina, droughts in Australia, the vanishing snow on Kilimanjaro are not necessarily caused by climate change - although they make good pictures for TV news.
A RISE OF A FEW DEGREES DOESN'T SEEM THAT SERIOUS?
It depends where you live. If temperatures go up, seas become warmer and the volume of water in the oceans expands. Warmer seas will melt ice sheets in the Antarctic and speed up the flow of ice from the Antarctic into the oceans. The latest forecasts are for a 4.5ft ise in sea levels by 2100 - enough to drown London, huge areas of Bangladesh and New York.
Global warming could turn fertile farmland into deserts, and frozen tundra into farmland. Water and food shortages could cause mass migration and armed conflicts. Higher CO2 levels could make the oceans more acidic, killing off coral reefs and wiping out fish.
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