Don't take my word for it; listen to a tree-hugging environmentalist pressure group called the Pentagon. The US security agency issued a report earlier this year admitting that imminent and catastrophic climate change is now "a plausible scenario" and a greater threat to US national security than terrorism. They forecast wars to secure dwindling food, water and energy supplies, and tens of millions of environmental refugees.

The Pentagon's predictions - ignored by the Bush administration - are coming true faster than anybody could have expected. The genocide unfolding in Darfur is in fact the first global warming war. The tribes of western Sudan have been awkwardly sharing the region's resources for the past 40 years. But - as the International Crisis Group has documented - massive ecological damage to Sudan has caused those resources to shrivel over the past few years. With less and less to go around, the Arab tribe has turned murderously on black Darfurians. They are raping and hacking them off the land because the region's resources are no longer enough for everyone.

Tony Blair's speech yesterday was an honest acknowledgement of this encroaching dystopia. He admitted he was "scared" when his top scientists explained the situation to him. But were his practical proposals enough? He's right that Kyoto - which merely pledges to restore greenhouse gas emissions to 1990 levels - can only be a first step. He advocated a "green industrial revolution" as a way both to meet our Kyoto commitments and then realise a second phase of environmentalism. This would require us to develop renewable energies - such as wave and tidal power or hydrogen fuel cells - and phase out our current dirty energy sources.

Blair's commitment to this is more than just rhetorical blather: the Government has invested such large sums in wind power that the market analysts Ernst & Young describe Britain as "the number one market for wind power suppliers in the world". (You can find out how to make your own transition to wind power sources at home at http:// www.ukgreenpower.co.uk).

Yet this one positive aspect to Blair's environmental record is seriously undermined by many of his other actions. Wind power has a low political cost - few people oppose it - but when it comes to taking environmental decisions that would require him to face down serious opposition, Blair's record is lousy.

British drivers are increasingly turning to SUVs - monstrous gas- guzzlers that none of us, save a tiny number of farmers, actually need. The French are introducing whacking great taxes to drive these big-league pollutants off the road, but Blair has refused to do the same here.

On air travel, he's even worse. A single three-hour air flight releases more polluting gasses than the average motorist racks up in a year. Yet Blair has authorised a fifth terminal for Heathrow airport against the opposition of environmentalists. He could have explained to the British people that - at a time of global crisis - we have to make sacrifices. Yes, it's inconvenient to fly less - but it's considerably more inconvenient to face catastrophic floods and (according to the Pentagon) the possibility of Britain's climate becoming "Siberian". Blair didn't; he chose the propane- scented path that pleased the airlines instead.

So Britain's current policy is to develop wind power for a fraction of our future energy needs, while piling on the pollutants elsewhere. Is this really a proportionate response to the biggest threat to human security today? Is this the way a society that really understood what we are facing would behave?

The ideal solution is a drastic reduction in carbon emissions immediately across the world, and a rapid transfer to renewable energy - far faster than the one envisaged by Blair. This is not going to happen; we cannot expect the poorest countries in the world to resist the prosperity that accompanies industrialisation, or to postpone economic development until we have cleaner technologies. Nor can we wait for the Americans to wake up to climate change and drive less; by that time, it may be too late.

So it is time to consider other drastic solutions. The idea of developing carbon sinks to drain the gas from the atmosphere is popular among environmentalists. One radical type of carbon sink has been discussed by environmental scientists for more than a decade now, but it has yet to break through into the wider public debate. In the early 1990s, the world's leading oceanographer - a man called Dr John Martin - made a suggestion that has become known as "the iron hypothesis".

Dr Martin discovered that adding iron to the surface of an ocean creates tiny marine plants called phytoplankton. These plants absorb carbon faster than any forest.

Once Martin had discovered this, he publicly proposed that seeding the world's oceans with iron could provide a solution to climate change. Sounds mad? Extensive tests were carried out off the coast of Miami in 1991 and off the Galapagos Islands in 1993, and they found that the iron hypothesis worked. Phytoplankton are the most efficient carbon-eaters we know of. Many distinguished scientists now take the idea seriously.

Dr Martin knew that his proposal was imperfect. "I agree that the idea would be to have the average American get out of his car; have the Chinese not develop his coal resources; have the Brazilians not cut down the rainforest," he said. "But we don't live in that world yet." And, he might have added, he wants us to survive until we get there. If we cannot prevent carbon emissions right now, we urgently need to do something to reduce the amount of carbon in the atmosphere. This idea might sound like science fiction today, but so did global warming itself just a few decades ago.

Giving in to despair is not a luxury we can afford; last year, the Greenland ice shelf thawed so quickly that the meltwater running off it was equivalent in volume to the River Nile. If we don't deal with climate change fast, climate change will come to deal with us.

j.hari@independent.co.uk