The melting of the planet's ice due to climate change will be the central theme of World Environment Day, celebrated annually on June 5 and this year hosted by the Arctic town of Tromsoe in Norway.
Melting ice offers some of the clearest evidence of global warming, and this year's choice of host city was no coincidence, with the picturesque Norwegian town nestled in the Arctic, a region which is heating up twice as fast as the rest of the planet and where the effects are already visible. "The Arctic and Antarctica may be the Earth's climate early warning system - feeling the heat first - but we know it does not end there," the head of the United Nations Environment Program (UNEP), Achim Steiner, said.
The melting is both a consequence and a cause of global warming: ice reflects heat, as opposed to water which absorbs it and warms up the climate, thus causing more glaciers and snow to melt.
The gradual disappearance of ice and snow has already affected the four million inhabitants of the Arctic region.
With ice sheets gradually receding, Inuits have seen their seal and polar bear hunting grounds shrink and their traditional way of life threatened.
Accidents are believed to be on the rise among the far north communities as hunters fall through the once-thick but now thinning ice, and they are increasingly swapping their dogsleds for motor boats.
Meanwhile, polar bears risk becoming extinct over the next decades as their natural habitat melts away.
On the positive side, the shrinking ice sheet will open up two new maritime routes between the Atlantic and Pacific Oceans off Canada and Russia, shortening shipping times considerably.
And for better or worse, the ice melt will also open up the Arctic for oil and gas drilling.
The region is believed to be home to one-quarter of the world's remaining reserves, the US Geological Survey says, though that could also heighten tensions among bordering countries.
The melting ice will also affect parts of the world much further afield than the polar regions.
"What happens in the Arctic and the Antarctica as a result of climate change is of direct interest to us all - from someone living in the Congo River Basin, the Australian outback and in rural China, to suburban dwellers in Berlin, New Delhi, Rio de Janeiro or Washington DC," Mr Steiner said.
Climate refugees
Canadian researchers say the melting of the Greenland ice cap, the planet's second-largest source of freshwater after Antarctica, could cause ocean levels to rise by seven metres, drowning coastal regions and islands, including several countries in the Pacific.
Indonesia alone could lose 2,000 islands by 2030, its Environment Ministry says.
That would lead to tens of millions of "climate refugees," in addition to the masses that would undoubtedly have to flee droughts and flooding brought on elsewhere by the warming of the planet.
The Intergovernmental Panel on Climate Change says a stabilisation of carbon dioxide (CO2) concentrations in the atmosphere at today's levels would make it possible to limit the temperature rise to around two degrees Celsius and would cost only 0.12 per cent of global gross domestic product.
But despite US President George W Bush's announcement last week of an "initiative" to cap greenhouse gas emissions, the United States, the biggest CO2 polluter, has refused to commit to binding targets.
The issue is expected to be one of the main bones of contention between the United States and its western allies at the G8 summit to open in Germany on Wednesday, the day after World Environment Day.
A slew of activities are being held around the world to mark World Environment Day.
In the Arctic town of Tromsoe events will last three days, running from June 3 to June 5.
South Africa's former Anglican archbishop Desmond Tutu will hold a religious service on Sunday, and an international scientific report on melting glaciers will be presented on Monday.
A two-day conference on the melting ice cap will also be held, while the UNEP will launch a book on sustainable tourism in the polar regions.
On its website, the UNEP has listed 77 suggestions for how to celebrate World Environment Day, including planting trees, bicycle parades and rickshaw races.