Imagine for a moment a war between Japan, Vietnam, Taiwan, Russia, China and the Philippines, each laying claim to the oil-rich Spratley Islands in the South China Sea as economic prosperity increases the demand for energy.
Or picture a Sars-type virus that is impossible to contain because of civil unrest prompted by a lack of vaccines as biotechnology firms set prices too high.
These may seem like nightmare scenarios, but in fact they are not far removed from certain realities in the world today. In numerous cases, the conditions for catastrophe already exist and the worst situations can be averted only with concerted international action.
In the UK, the Government has already ordered security exercises on a large scale to prepare for "dirty bomb" attacks by terrorists using chemical or radiological weapons - possibly made from unguarded Cold-War leftovers in the Ukraine.
Meanwhile, an early-warning system is being sought in case tidal waves become more frequent, but children's organisations fear that the massive surge in child-trafficking in the aftermath of Indonesia's tsunami disaster could be repeated as violent gangs take advantage of displaced people in the wake of similar catastrophes in future.
If lives are to be saved, the world must be prepared. But too often it is not, as the tsunami cruelly demonstrated. In the worst possible case, if some or all of these disasters occur at the same time, coupled with global terrorism and international crime, organisations such as the United Nations will not be able to cope, and could collapse under the strain.
"Some threats are just beginning to emerge, such as cloning and biotechnology," says Mats Berdal, professor of security and development at King's College, University of London. "But there are many other threats that have been there for a long time but are not addressed by the United Nations system."
The UN's multilateralism is under attack from neo-Conservatives in President Bush's administration. This, alongside the wrangling of major powers in the UN Security Council in the run-up to the Iraq war, prompted UN Secretary-General Kofi Annan to assemble a "high-level panel" on Threats, Challenges and Change, which compiled the report "A More Secure World: Our Shared Responsibility" in 2004.
"The world is changing, and the UN needs to change with it," said Mark Malloch Brown, Annan's chief of staff, when he presented the report in January. "And if we miss this opportunity for lasting reform, there may not be another one."
The report's most raked-over section is the review of the Security Council so that it can be made more "democratic" and less likely to be hijacked by superpower interests.
For the 60 years since the end of the Second World War, seats have been taken by the victors - Britain, France, the United States, Russia and China, all of them with the power of veto. Last year, Brazil, Germany, India and Japan launched a joint effort to seek permanent membership of the Security Council. South Africa has also been proposed.
"A More Secure World" offers two very different ideas for expansion of the Security Council, and a vague time line for change. But wrangling over a new Security Council configuration risks dominating the reform process and reopening wounds over Iraq.
Diplomats agree that new approaches to world security are needed - especially since the end of the Cold War. Now, more wars are fought within states than between them, and poor countries, no longer propped up by the superpowers, are failing and destabilising whole regions. And terrorism, while not new, has taken on a more global character and is stoked by religious fervour. It is in the light of such "new" global threats that "A More Secure World" sets out to offer a much broader definition of global security.
But not everyone is convinced. For example, the international campaign group Social Watch maintains that the debate must "shift towards what humanity really wants, rather than what a few states and their specialised security bodies are interested in or perceive".
The emphasis, the group says, should be on "human security", rather than state security. Inequality and poverty - particularly if seen as the result of injustice - have long been major factors in conflict and social unrest.
With its focus on economic development, the world body argues that this is already within its ambit. But countries such as Japan, Norway and Canada, which have strongly embraced theidea of human security in their foreign policies, are also the most vocal on a host of "new" international security issues, including the prohibition of anti-personnel mines, control of light arms, preventing recruitment of child soldiers, and promotion of international humanitarian law.
Jens Martens of Social Watch says: "It is a narrow approach to regard security as military and state security - dangers to people's security include situations that are not always classified as threats to state security."
In the organisation's latest annual report, an Algerian non-governmental organisation lists the main threats to human security in that country as "widespread and increasing poverty, frequent terrorist attacks and natural disasters". Yet only one of these - terrorism - is really tackled in "A More Secure World".
"Environmental threats and social justice are very important, but they are simply not in the UN picture," says Martens.
It is a sentiment echoed by certain voluntary relief organisations in the UK that believe global warming is now a much more significant threat to humanity than terrorism. They criticise the UN for placing too much emphasis on terrorism and international crime and pandering to the US agenda.
James Paul, executive director of the Global Policy Forum, which monitors the UN in New York, says: "Governments have developed national security plans as part of the global fight against terrorism, but this has not alleviated political insecurity in many countries.
"The report did not handle the problem of natural resource management at all. The UN would sooner it were hidden than discussed."
A case in point is that the UN has been reluctant to get involved in the management of the headwaters of the Tigris and Euphrates rivers - potential flashpoints between Turkey- Syria and Syria-Iraq - in an already unstable region, and military experts have already warned that future wars in the Middle East might be fought over water, not oil.
James Paul provocatively points out that the world has not changed in the way the UN would have us believe. Trafficking of children and women are hardly new problems, and mass migration has gone on for two centuries, but it is the sheer scale of such phenomena that has changed. Now, it is their root causes, rather than their manifestations such as terrorism, that must be tackled.
Members of the UN panel on threats, challenges and change say they were careful not to construct "a hierarchy of threats". But James Paul fears a stress on new threats could mean that existing, growing threats are not addressed adequately.
"Without more money for the UN, any reform is a joke," he says. "It will just be a financial shell game in which money is moved from here to there to tackle supposedly new threats, while ignoring other aspects such as the economic conditions that cause instability."