Ever since the 1750s, when the writer, satirist, statesman and inventor Benjamin Franklin put political cartooning on the map by publishing the first cartoon of the genre in America, artists have combined their talent, wit and political beliefs to create cartoons that enrage, enlighten or simply engage the viewer.

A picture may paint a thousand words, but a cartoon provokes, protests and entertains – all at once. It is this that makes cartoonists so valuable and influential in times of crisis. Today, that crisis is climate change, and clever imagery can give new impetus to our struggle to combat global warming. The organisers of Earthworks 2008, a global cartoon competition, believe that art and humour are simple ways to get the environmental message across.

"We set up the competition to give cartoonists around the world a platform on which to express themselves," says John Renard, one of the Earthworks organisers. "We hoped that the competition would stimulate cartoonists to use their pens and wit to help combat environmental devastation and give new impetus to our desperate fight to stop global warming," he says. "After all, humour is often a valuable key in the struggle to win hearts and minds."

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But despite the sharp wit that pervades the cartoons, climate change is no laughing matter for their creators. The 50 or so countries from which the 600 competition entries were sent are all suffering the effects of global warming, some more dramatically than others. Two cartoons were sent from Burma, where in May this year a cyclone tore through five regions along the western coast, killing at least 100,000 people, and leaving millions more without shelter, food, or clean water.

And although governments around the world are reluctant to suggest, officially, that the disaster in Burma is a direct result of global warming, there's little doubt that it will have added to the cyclone's destructive power.

Studies published in the journals Nature and Science have demonstrated a link between rising sea temperatures and increased wind-speed of cyclones and hurricanes, and even US-government-funded organisations such as the National Oceanic and Atmospheric Administration admit that a warming of the global climate will affect the severity of storms. "Experiencing first-hand the catastrophic effects of climate change allowed these artists to give their cartoons a special poignancy," says Renard. "And it brought home to us the burden of responsibility to do our utmost to prevent such devastation becoming more common."

But dramatic weather changes aren't the only consequences of global warming and the cartoons reflected this, with some artists focusing on species loss or coral reef degradation, others on rising seas or water wars.

Certain effects of global warming, such as shortages of food and clean water, for example, clearly resonated with cartoonists from places like Yemen and Syria, where increases in average temperatures have already exposed the population, particularly children and the elderly, to potentially life-threatening diarrhoea and malnutrition.

Predictably, water scarcity and desertification were common themes among the entries, with many images showing parched landscapes, dry oceans and dying animals. These cartoons illustrate what is already occurring in hotter parts of the world such as Africa, Australia and South America, but dwindling supplies of fresh water potentially affect everyone.

Even in Britain's supposedly wet climate, summer hosepipe bans have become routine. And, according to the Food and Agriculture Organisation of the United Nations, every continent is suffering, with water scarcity already affecting 40 per cent of the world's population.

Receiving competition entries from individuals who have had to endure the adverse effects of climate change is, you could argue, to be expected, but entries also came in from those countries most often accused of halting progress towards cutting greenhouse emissions.

There were several entries from China, the world's second biggest producer of greenhouse gases, which also continues to build, on average, one new coal-fired power plant every week and has no intention of stopping or slowing production. There were also entries from the United States, whose government has stubbornly refused to acknowledge the impact of human activity on global warming and remains one of the few countries not to have ratified the Kyoto Protocol on climate change.

Brazilian cartoonists, too, felt the urge to illustrate their disappointment with a government that failed to prevent the terrifying pace of deforestation in their country, where 1,250 square miles of Amazon forest were lost in the latter half of last year.

Many of the competition entries showed passion and were exceptionally well drawn, but the winner, "Coat Star" by Mikhail Zlatkovsky from Russia, held a particularly poignant message, the judges felt, showing humanity in the form of a man indecently exposing himself to a pristine universe.

"It says, 'This is the disdain we've shown our world'," says Renard. "And we felt the sleaziness was appropriate to the topic." Second prize went to Constantin Ciosu, from Romania, for his illustration of a man holding a flower being chased by hundreds of butterflies, a humorous and unusual take on the world's dwindling natural resources. Finally, "The Hand" by Tawan Chuntraskawvong, from Thailand, was chosen for its immediate impact.

The judging panel, which included cartoonists Martin Rowson and Morten Morland and Green Party principal speaker Dr Derek Wall, among others, had a tough job choosing the three winners.

"We were quite taken aback by the enormous response this year," says Renard. "And the entries were simply outstanding. Some cartoons were bitingly satirical, others outrageously funny or bitter and even fatalistic, but none were neutral or indifferent."

The panel made their choices, ultimately, on the basis of the clarity of the message. "Language should be unnecessary, the imagery should transcend the need for words," says Renard.

"And the judges felt the winning cartoons sent a message that could be understood internationally, across cultural, religious or political barriers and boundaries."

Powerful, uncompromi-sing and uncomfortable, the cartoons bring home what global warming will mean: not a Costa Brava on the south coast but desertification, widespread hunger and, ultimately, our own destruction.

But the allow us a wry smile as we interpret each artist's take on global warming. And if it's true, as George Orwell stated, that "every joke is a tiny revolution", these cartoons should get the wheel turning.

A selection of the best cartoons will go on tour over the next year, details and information on the next biennial competition will be announced on www.kenspraguefund.org. The Ken Sprague Fund was set up to commemorate the work and ideas of the cartoonist and graphic artist, Ken Sprague, who died in 2004