For our generation that threat is climate change. Wherever I go in the world, I am struck by the fact that the majority of ordinary people want the same things out of life: to be able to live in safety, to feel in control of their own lives, and to be able to build a better future for their families and children. Climate change endangers every one of those aspirations.

At the end of last week, the Intergovernmental Panel on Climate Change published the first installment of its fourth and latest report.

It deals with the basic science of climate change. As many had feared, it confirms that the threat is even more serious, and even more urgent, than we had previously thought.

Children being born today may see, if we don't take concerted and immediate action, global temperatures rise by 3-5 degrees in their lifetimes. That might not sound a lot, but when average temperatures were just 5 degrees less than they are now the world was in the grip of the last global ice age.

So the effects of that sort of climate change to the world we live in would be catastrophic. So much of our daily lives is based upon the predictability and continuity of our climate.

Take those two things away and you threaten every aspect of modern society.

It will affect our ability to meet basic needs like food, water and health. Studies have suggested that temperature rises of just 2-3 degrees will see crop yields in Africa, the Middle East and South Asia fall by as much as 30 to 40 percent.

As my special representative on climate change in Africa recently found out when he visited the region that is already happening, with some African countries facing increased risks of famine.

Meanwhile, one billion people in South Asia are likely to struggle to get water for themselves and for their crops as the Himalayan glaciers melt and monsoon patterns shift. And, in several parts of the world, we have started to see mosquitoes move into new areas -- including densely populated cities -- bringing with them diseases like malaria.

An unstable climate can also lead to a more unstable world, stoking tensions and feeding conflicts.

The conflict in Darfur had many roots, but among them was a shift in rainfall pattern that exacerbated competition for resources between the region's nomadic herders and settled pastoralists.

As deserts grow and fertile land shrinks, we can expect to see more disputes within and across borders.

In the Middle East five percent of the world's population already has to share only one percent of the world's water. Climate change will mean that there will be even less water to go round.

Current climate models suggest that -- globally -- by the end of the century extreme drought could affect nearly one-third of the world's land mass, ten times more than today.

Saudi Arabia, Iran and Iraq will see some of the biggest reductions in rainfall. Disagreements over water access issues along the Jordan basin have, on several occasions, been a major cause of tension between Israel and its Arab neighbours, notably in the years leading up to the 1967 war.

The water in the Jordan basin has already been heavily overused, and climate change could worsen the situation. Meanwhile, Egypt could suffer a double blow. Drastic loss of Nile flow from the South and rising sea-levels in the North combining to destroy its agricultural heartland across the Nile delta.

One study suggests that a sea-level rise of just 50 cms -- well within current estimates -- would displace two million people from the delta.

So no one should think about climate change as a purely "environmental" issue -- it is as much about poverty, conflict, disease and migration as it is about the environment. But even if the scale of the problem is clear, is there anything we can actually do about it?

The answer is yes if we act now, act decisively and -- perhaps most important of all -- act together, to cut carbon emissions.

Everyone stands to lose out from global warming. This is not a problem any country can solve on its own. There is a global imperative for us to co-operate.

Some of the countries that will be hit hardest will be the poorest in the world. But it is the developed economies which have been responsible for the majority of greenhouse gas emissions.

So they -- we -- must take the lead. We in the UK are so concerned by what climate change will mean for all of us that we have made achieving climate security one of our to strategic international priorities.

Along with Africa it was one of the two key themes of our G8 presidency. And we commissioned a report -- by the former World Bank chief economist, Nick Stern -- which was the most detailed examination yet of the economics of climate change.

It was published at the end of last year, and has helped to bolster the case for immediate action. It shows that the costs of tackling climate change are vastly outweighed by the costs we will face if we don't.

Some oil-producing countries seem to be worried that the response to climate change could threaten their economies. They need not.

For a start there is little sign that the global market for oil will contract in the foreseeable future.

Alternative and renewable energy sources to service rapidly increasing global energy demands are certainly a big part of the picture, but so too are new technologies like clean burning power plants and carbon capture and storage.

Indeed, as Nick Stern has shown, the far greater threat that all of our economies face is from global inaction -- he predicts a possible collapse in global GDP of around 20 percent. One of the world's most successful venture capitalists, John Doerr, has described the global response to climate change as "the largest economic opportunity this century."

And, paradoxically, the current high oil prices mean that countries in the Middle East may be in one of the best positions to take advantage of this opportunity.

They have the capital available now to invest in the technologies of the future: and that offers the chance to diversify economies and to stimulate innovation and entrepreneurship across society.

There are potential political benefits, too. If we get our response to climate change right we can turn the tension over diminishing resources into a spur for regional cross-border co-operation.

The truth is that climate change is real, and it is here. The good news is that we have the technology, the capital and the knowledge to meet this challenge.

Governments need to set the political frameworks to encourage investment, businesses need to take new technologies to the market, consumers and citizens have to make the choices that keep up the momentum for change.

The choice facing the people of the world is whether we recognize our common humanity and join together to tackle this problem; or whether we walk, blindly and separately, into a bleak future. For me, that is no choice at all.

Hon Margaret Beckett is the British Secretary of State for Foreign and Commonwealth Affairs.