"We need to treat climate change not as a long term threat to our environment but as an immediate threat to our security and prosperity The first priority of any government is to provide the conditions necessary for security and prosperity in return for the taxes that citizens pay.
Climate change is potentially the most serious threat there has ever been to this most fundamental of social contracts.
On 28 August 2005, New Orleans was a prosperous, stable and relatively harmonious city. By the next evening, most of its population had been driven from their homes and lacked access to electricity, food, fresh water and medical services.
Within a week, gunmen roamed the streets as law and order broke down; simmering racial and political tensions exploded as the buck for dealing with the catastrophe - as well as preventing it - was hurled about. For months, neighbouring cities and states were inundated with refugees as the political and racial stresses spilled across the country. New Orleans is unlikely ever fully to recover.
Hurricane Katrina hit a city in the world's richest nation. If anywhere should have been resilient enough to deal with the force of nature, it was the United States.
The economic and security impacts of extreme climatic events in more vulnerable regions, such as Africa and South Asia, or more strategically important regions, like the Middle East, will be more dramatic.
We can see this already in Africa. A major contributing factor to the conflict in Darfur has been a shift in rainfall that has put nomadic herders and settled pastoralists into conflict with each other.
You cannot use military force to make everyone else on the planet reduce their carbon emissions
Conflict always has multiple causes, but a changing climate amplifies all the other factors. Katrina and Darfur illustrate how an unstable climate will make it harder to deliver security unless we act more effectively now to neutralise the threat.
Our prosperity is also at stake. Europe's economic health increasingly depends on a thriving Chinese economy. Should China falter as we progress through this century, European pension funds would struggle to earn the returns necessary to pay our pensions. As Europe's population ages, the drag on our economies would be immense.
China's economy is one of the most vulnerable to a changing climate. China is already planning to divert water hundreds of kilometres from the south, where it is currently abundant, to the arid but populous north, in order to maintain economic stability. But that plan will fail if the Himalayan glaciers that feed China's southern rivers continue to melt at an accelerating rate because of a rising temperature.
Last week, Professor John Holdren, the newly elected president of the American Association for the Advancement of Science and a distinguished scientist not noted for sensational pronouncements, told the BBC: "We are not talking any more about what climate models say might happen in the future. We are experiencing dangerous human disruption of the global climate and we are going to experience more."
What this means is that we need to treat climate change not as a long-term threat to our environment but as an immediate threat to our security and prosperity.
We need to see a stable climate as a public good without which it will become increasingly difficult to deliver the other public goods that citizens rightly expect from those who govern them.
We need to see the pursuit of a stable climate as an imperative to be secured whatever it costs through the urgent construction of a low carbon global economy, because the cost of not securing it will be far greater.
Military might is not an option in the war on climate, says Mr Ashton
This poses a challenge. Governments have traditionally invested in instruments of hard power as a backstop against the consequences of political and diplomatic failure.
But there is no hard power option either for mitigating climate change or for dealing with its direct impacts. You cannot use military force to make everyone else on the planet reduce their carbon emissions. No weapon system can halt the advance of a hurricane bearing down on a city, or stem the rising sea, or stop the glaciers melting.
If we want to achieve climate security, governments will need to invest more resources in the emerging techniques of soft power. There is no backstop: the politics and diplomacy have to work.
Governments will need, as a matter of security, to build the avenues of trust and opportunity that will divert investment from high carbon to low carbon infrastructure.
They will need to negotiate the agreements that will enable us to do that cost-effectively and without divisive market distortions. They will need to design and mobilise coalitions of mutual interest across sectoral and cultural boundaries to transform the way we supply and consume energy, achieve mobility, and use land.
And they will need to do all of this very fast. It is now becoming increasingly clear that it is what we do in the next 15 years that matters most.
The technologies to avoid an even more unstable climate are already available. Deploying them rapidly is well within what we can afford. What is needed is an investment internationally of political imagination backed up by public resources on the scale that publics routinely expect for the more traditional aspects of national security.
But, as scientists like John Holdren are warning with mounting urgency, the window of opportunity is rapidly closing.
If we fail to see this threat to security very soon for what it is and make our dispositions accordingly, we will end up paying far more and experiencing more insecurity."
John Ashton is the UK foreign secretary's special representative for climate change and a visiting professor at Imperial College London. This article reflects his personal views
The Green Room is a series of opinion pieces on environmental issues running weekly on the BBC News website