Never has the challenge of saving the world felt as simple as it does right now. Sitting on the sofa in front of me, Jeffrey Sachs is leaning back, gingerly sipping his coffee and sweeping away some of the most intractable problems facing our planet with the barest waft of his palm.

Poverty and a billion starving people in Africa? Whisked away like dust. Overpopulation and water shortages? Waft, waft. Global warming and climate change? A little brush and they’re gone.

It would all seem rather utopian did Mr. Sachs not share that Clinton/Blair-style knack of making almost anything seem completely do-able. Unlike so many economists, who tend dismally to explain why things will fail and why good intentions almost invariably go to waste; Mr. Sachs, the director of the Earth Institute at Columbia University and the head of United Nations’s Millennium Project, is Professor Optimism. For evidence look no further than the title of his first book, “The End of Poverty,” or the fact that he has become the poster boy for can-do economics, or witness the adulation he inspires in everyone from undergraduates to film and rock stars.

This is not to say he in any way plays down the magnitude of the threats the world is facing. In fact, along with other renowned economists such as Nobel prize winner Joseph Stiglitz, he fears the combined set of economic crises facing us right now are more severe than perhaps any in recent history. We’re not talking about the credit crunch here, though that could prove a dangerous distraction and impediment.

The Sachs thesis, laid out in his latest book, “Common Wealth,” is that the world could stumble blindly towards further conflict unless it addresses some key problems: global warming; the population explosion in the developing world, and poverty in Africa and central Asia being chief among them.

“This is not an argument about doom — it’s an argument about changing course,” he said. “You can be pessimistic about the current trajectory, but also optimistic about the solutions.”

Though, while we’re on the subject of doom, his fears about the worst-case scenario are terrifying — particularly coming from an eternal optimist.

“For me, the nightmare concept of the modern era is 1914, when an age of globalization slips away — not only into a disastrous bloody war but also into 75 years of consequences to that — the Bolshevik revolution, the Great Depression, World War II. It takes generations to surmount that disaster and tens of millions of deaths in between. “If I were a grim novelist of an Orwellian bent, my novel would be called 2014. That’s possible still: in an age of globalization, where everything seems inevitable — scientific progress, nanotechnology, the information age, breakthroughs in neuroscience — we could blow it all.”

For swirling beneath our feet is a potent cocktail of threats — everything from massive income inequality to rising food prices — which could erupt with violent consequences. “What I am trying to say as an economist is: if we choose the bad course, let’s be clear it’s not because the good course would break the bank. It’s because we failed to take them.” When it comes to climate change his argument is quite simple: most scientists are now agreed there is a problem, and that levels of carbon dioxide in the atmosphere need to be contained, if not fall. However, no one in government has actually provided a simple instruction manual of what to do about it.

Green taxes and markets for carbon are “secondary issues” behind the question of developing new green tools, he insists, convinced that there could be “silver bullet” technologies — if only the Government would invest the cash in researching them.

In case you hadn’t realized, Mr. Sachs is firmly of the view that these solutions won’t be produced by the free market. The leading research projects into one of these technologies, carbon capture and sequestration, have been scrapped on both sides of the Atlantic, while he bemoans the lack of progress in developing decent, cheap solar thermal power plants. “I believe we also need safe nuclear,” he said, running through his ministerial instruction manual.

“We need carbon capture and sequestration; long distance automobiles like plug-in hybrids. I believe we need to examine the potential for biofuels which do not compete directly with foodstuffs.” The problem is that many of the new technologies may not work. For the past quarter century, for instance, nuclear fusion has been held up as the pollution-free power source of the near future but its development has taken decades longer than anyone anticipated and it is still generations from completion.

And even if these technologies do exist, so do intractable barriers at every level from between different disciplines of science and squabbling government departments on the minute scale to, on the global level, a system of multilateral institutions which is at its lowest ever ebb — not to mention the war on terror which is “a disastrous distraction from real problems.”

“It’s an American habit,” he concludes. “We seem to move from defining an enemy to defining an enemy. The idea of my book is that we all have common interests and common problems, and it’s trying to surmount them for future generations.”