Following is a factfile on climate change:
WHAT IS CLIMATE CHANGE? Climate change is the phenomenon caused by global warming. Natural cycles of warming and cooling have occurred many times in Earth's history, and indeed the rise of Homo sapiens is attributed to the end of the last Ice Age some 11,000 years ago. What worries scientists is man-made global warming -- when carbon-rich fuels stored for aeons beneath the ground are extracted and burned, releasing billions of tonnes of carbon dioxideeach year. CO2 is a "greenhouse gas": it traps the Sun's heat in the atmosphere instead of letting it radiate out to space. As a result the Earth's surface is warming, disrupting the planet's delicate climate system.
HOW CERTAIN IS THE EVIDENCE? Global warming appeared on scientists' radar a quarter-century ago, but evidence was sketchy and the tools to explore it were so poor that for nearly two decades there was no consensus that rising temperatures were natural or man-made. That all changed in 2001, when the UN's top authority on global warming, the Intergovernmental Panel on Climate Change (IPCC), declared the evidence for man-made warming was incontrovertible. Today, there are still gaps in knowledge, but these are shrinking fast -- as is the skeptics' camp, whose cause is backed by some oil majors.
WHAT DO SCIENTISTS SAY? The IPCC predicted a temperature rise of 1.4 to 5.8 C (2.5 to 10.4 F) from 1990-2100, according to scenarios of CO2 levels ranging from 540 to 970 parts per million (ppm). That compares with 280ppm for pre-industrial times and around 380ppm today, which is already the highest concentration of CO2 for 650,000 years. But that prediction was made more than four years ago, and the science has made many leaps forward since then. New aspects about global warming are being uncovered almost every month, but the new is almost always bad. In recent weeks, new studies have pointed to accelerated melting of glaciers in the Himalayas and Alps and worrying movement in part of the Greenland ice sheet.
HOW BAD WILL CLIMATE CHANGE BE? The more CO2, the higher the temperature; and the higher temperature, the bigger the impact. At the lower range of the IPCC estimates, there will be a tiny increase in global sea levels and some increased water stress, and some cold regions in higher latitudes may in fact benefit for farming and human settlement. At the higher temperature range, droughts, floods and storms will become more violent and more frequent, mean sea levels could rise by up to 88 centimetres (2.9 feet) by 2100, creating an exodus of "climate refugees". Almost all of the world's population will be affected, but poor tropical countries -- the nations least to blame for the problem -- will be hit worst.
DOOMSDAY SCENARIOS: A lot of research is being done on a phenomenon called positive feedback, in essence a vicious circle in which rising temperatures release more stored carbon, which thus adds to global warming, which frees up more CO2 and so on. Among these scenarios, gigatonnes of CO2 could be released from melted permafrost in Canada and Russia; the oceans could become so acidic from absorbing atmospheric CO2 that their biodiversity shrivels; Western Europe could be plunged back into an Ice Age by the stopping of the balmy Gulf Stream; and the Western Antarctic icesheet could melt, drowning coastal cities around the world. There is no evidence that any of these nightmare events is taking place. They exist only as computer models, and in some cases, the timeframe for disaster would span several hundred years. The concern, though, is real: positive feedback could make global warming unstoppable.
HOW MUCH TIME IS LEFT FOR ACTION? Not much. In February, a top science conference in Britain declared that climate change is already underway, visible through glacier shrinkage, melting of polar ice, shifts in rainfall patterns and bad heatwaves. Experts generally say that if the world wants to keep to the bottom end of the IPCC temperature estimates, global emissions of CO2 will have to peak in 2020 and then fall to half of today's levels by 2095 -- a tall order, given that developing countries and the United States are gobbling up fossil fuels. The International Energy Agency (IEA) predicts that on current trends CO2 emissions will surge by 63 percent over 2002 levels by
WHAT ARE THE SOLUTIONS? The obvious answer: to stop using fossil fuels and use clean energy sources such as wind, solar, hydro and hydrogen. But this is far easier said than done. Oil, gas and coal are the world's long-established energies. They have big advantages in cost and efficiency over technologies that are still in their infancy and need tax breaks or regulatory help to make headway. And the fossil-fuel lobby is fighting a fierce rearguard action to keep its crown, particularly in Washington. Over the next couple of decades, the best hopes may lie in interim solutions such as better fuel efficiency, promoting hybrid cars and storing CO2 underground from coal as the fuel is burned rather than letting the damaging gas escape into the air. Mitigation costs should not be expensive -- just 1-2 percent of gross domestic product (GDP) if launched today -- but the cost will multiply if the effort is delayed.
WHAT'S THE KYOTO PROTOCOL? The UN treaty is the only global deal that specifies cuts in greenhouse gases. It requires industrialised countries that have ratified it to limit their emissions of greenhouse gases by a 2012 timeframe as compared to a 1990 benchmark. The accord took effect last February, surviving abandonment by the US, which opposed binding targets as too expensive for its economy, and footdragging by Russia. But Kyoto remains in a bad way. Even its European champions are having big problems meeting their pledges. The treaty is criticised for making only timid cuts (just one or two percent at best, after the US walkout), for being absurdly complex and for not including India and China, now big polluters, in commitments on emissions cuts. Talks on the post-2012 Kyoto period start in Montreal on Monday.
