KEY POINTS:
No one has worked harder than former American Vice-President Al Gore to raise awareness of the threat of climate change, and on Saturday he takes it to the next level with Live Earth, a series of concerts around the world that will be watched or heard by as
many as two billion people.
But many millions of us don't need Gore to tell us something is up with the weather. Not if you have been driven from your home in recent days by cyclones in Pakistan, by raging floods in Texas or Yorkshire, by forest fires in California or have sweltered in intense heat in southern Europe.
Linking a single meteorological event, however dramatic, to global warming may be tricky. (Yes, there have been protracted rain delays at Wimbledon before this year.) The planet has forever undergone cycles of droughts, floods and fires.
Yet, few scientists now say those cycles are not becoming more extreme and frequent or that global warming is not a major factor.
Each new scientific paper seems to carry a message grimmer than the last. This year, a United Nations panel on climate change, with 2500 leading experts, officially endorsed the notion that the rising temperatures are the result of human activity, especially the burning of fossil fuels.
The warmest 10 years of the past 150 have all been since 1990. And without action to curb it, the temperature climb is not going to stop.
The "best estimate" of the UN panel is that the planet's surface temperatures will rise 1.8C to 4C by the end of this century.
People are getting the message all over the world that the planet is ailing. Results last week from a poll conducted in 46 countries by the American Pew Research Centre showed environmental degradation was the number one concern of people around the world.
"It's going to get worse before it gets better," says David Masur, director of PennEnvironment, a Pennsylvania environmental advocacy group.
"We're not even at the tipping point yet, in terms of the worst of the worst."
Salvano Briceno, who shapes UN policy for responding to natural disasters, agrees, saying: "Severe events are going to be more frequent."
He says governments must come up with plans to protect people from dangerous events such as drought, famine and flooding.
"We need to reduce all the underlying risk factors, such as by moving communities out of hazard-prone areas," he says.
"We now have a clearer picture of what is going to happen, and it's urgent that governments give this higher priority."
In broad terms, rising temperatures result in faster evaporation of surface moisture. This in turn produces more frequent and more serious droughts for some.
But it also increases the amount of moisture entering the atmosphere, meaning it has eventually to fall as rain, sometimes in extreme events such as last week's flooding in Britain and cyclones in Asia.
Even the devastating forest fires in Tahoe, California, last week seem to be connected to global warming.
The western US had four times more major wildfires between 1986 and 2004 than it did between 1970 and 1986.
As spring and summer temperatures have risen, mountain snow cover has shrunk, flow in streams and rivers has decreased and so humidity in forest areas has fallen. This year, the snow cover above Tahoe was just 15 per cent of the average.
Last week, EU Environment Commissioner Stavros Dimas unveiled new plans to protect Europeans from weather disasters.
He said: "In Britain, there is bad flooding and destruction on a scale rarely seen before, and more bad weather is on the way. For some people in Europe it will be a case of adapt or die."
Europe
To fly from the UK to Italy last week was like crossing continents: Britain's cold rain gave way to suffocating heat and a ferocious sirocco, the hot Saharan wind, in Sicily. The Fiat car plant was closed after employees refused to work in the heat. Fires were burning in southern Italy, with Calabria (24 blazes) and Puglia (22) worst affected. In Greece, seven people have died. Firefighters and soldiers are battling a fire that has destroyed much of Mt Arnitha National Park, and threatens Athens.
Australia
From the worst drought in a century to the worst floods in decades, Australians are wondering what will come next. Severe storms have battered the east coast, causing flooding in New South Wales. In the low-lying Gippsland region of Victoria, hundreds of people had to abandon homes and businesses at the weekend after rivers burst their banks. Helicopters rescued residents as floods engulfed houses, barns and paddocks, leaving cattle stranded. Floods have also hit the Newcastle area leaving nine people dead. Another attempt is being made to refloat the Pasha Bulker, a coal freighter swept on to a sandbank just off a Newcastle beach three weeks ago.
America
The first days of summer in the United States have seen fire and water combine with devastating effect. Wildfires around Lake Tahoe, California, have consumed more than 250 homes. Fire chiefs predict that the week-old fire will be finally brought under control by tomorrow. Boston broke high temperature records on Wednesday while blackouts in a sweltering New York City stranded a quarter of a million commuters. Meanwhile Texas and Oklahoma, until recently struggling with drought, have been hit with record rains and widespread flooding. Storms in the southern plains left 11 people dead.
Asia
Fresh floods struck Pakistan this weekend, killing at least 100 people and forcing another 10,000 from their homes, just days after Cyclone Yemyin left 1.5 million people without shelter. The latest floods roared through six villages in the country's Baluchistan province. Troops and emergency crews are struggling to help the homeless and those stranded by the floodwaters. The province had already been reeling from floods caused by the cyclone and persistent rain only aggravated the situation.
Africa
Freak weather turned Joburg into "Snowburg" last week, the city's first snowfall since 1981. A massive cold front has swept across South Africa, pushing temperatures well below zero, closing roads and cutting electricity. In the Eastern Cape, motorists were dug out of metre-high snowdrifts. Further north, the Horn of Africa is battling its persistent drought. UN statistics show rainfall in Sudan down 40 per cent in the past 20 years.
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