Global growth is the leitmotif of our era. The great economic expansion, now in its fifth decade, has raised living standards worldwide and lifted billions out of poverty.

Yet today, many wonder how long it can last. The reason: plenty comes at an increasingly high price. We see it daily in the rising cost of fuel, food and commodities. Consumers in developed countries fear the return of "stagflation" – inflation coupled with slowing growth or outright recession—while the poorest of the world's poor no longer can afford to eat.

Meanwhile, climate change and environmental degradation threaten the very future of our planet. Growing populations and rising wealth place unprecedented stress on the earth's resources. Malthus is back in vogue. Everything seems suddenly in short supply: energy, clean air and fresh water, all that nourishes us and supports our modern ways of life.

As the leaders of the Group of 8 gather in Hokkaido Toyako, we know that these issues affect us all: north and south, large nations and small, rich and poor. And we know we must find new ways to extend the benefits of the global boom to those who have been left behind, the so-called "bottom billion". In dealing with problems of such dimension and complexity, there is only one possible approach: to see them for what they are – as parts of a whole, susceptible to a comprehensive solution.

A big part of that solution should be a "global supply-side response", as some economists put it, grounded in sustainable development – nations, international financial institutions, the United Nations and its various agencies, working together as one.

Begin with the global food crisis. It has many causes, among them a failure to give agricultural development the importance it deserves. What's needed, in effect, is a second green revolution of the sort than once transformed south-east Asia, this time with a special focus on small farmers in Africa. With the right mix of programs, there is no reason why productivity cannot be doubled within a relatively short span, easing scarcity worldwide. We've seen it happen in Malawi, which with international assistance has gone in a few years from famine to become a food exporter.

In Hokkaido, I will call on G8 nations to triple official assistance for agricultural research and development over the next three to five years. We must act immediately to get seeds, fertilizers and other agricultural inputs to farmers in vulnerable countries in time for the coming harvests. And we must encourage nations to eliminate the export restrictions that many placed on foodstuffs this spring, as well as the more long-standing subsidies that many developed nations provide their farmers. Such artificial barriers distort trade patterns and drive up prices, deepening the immediate crisis and jeopardising global growth.

With climate change, as well, sustainable development figures large in the solution. Most experts agree that we are nearing the end of cheap energy. Among our best hopes for cleaner, affordable power is alternative technologies. Here, too, a new green revolution is underway. According to a new report by the United Nations Environment Programme, $148bn in new funding went into sustainable energy last year, up 60 per cent from 2006 and accounting for 23 per cent of all new power-generating capacity.

Our job, as national and international leaders, is to help guide and accelerate this nascent economic transformation. We need to change social behavior and consumption patterns throughout the developed world. And we must help developing countries green their economies by spreading climate-friendly technologies as broadly as possible.

We can take a big step forward in Hokkaido. Mindful of our responsibilities to the poorest nations most vulnerable to climate change, we must fully fund and operationalise the global Adaptation Fund. Looking forward to the December climate change summit in Poznan – and beyond that to Copenhagen in 2009 – we must push ahead with negotiations for a comprehensive agreement limiting greenhouse gases. Above all, we need to inject a sense of urgency and real leadership into this quest. It is not enough to set goals for 2050, far down the road. We also need a middle-term timeline to 2020 if we are serious about promoting change now.

Lastly, Hokkaido will test our commitment to the Millennium Development Goals. For Africa alone, donors have pledged $62bn a year by 2010. Those we must help have faces: mothers who die needlessly in childbirth, infants stunted through life because they do not receive adequate nutrition during their first two years. We promised to help. Now is the time to do so.

Not in recent memory has the global economy been under such stress. More than ever, this is the moment to prove that we can cooperate globally to deliver results: in meeting the needs of the hungry and the poor, in promoting sustainable energy technologies for all, in saving the world from climate change – and in keeping the global economy growing.

These are the ties that bind us. We must act, in Hokkaido and beyond -– not merely because it is the right thing to do, though it is, but because it is in all of our enlightened self-interest.

Ban Ki-moon is secretary general of the UN.