All politics are local, goes the old aphorism. Yet today, we can say that all problems are global. As world leaders meet at the G-8 Summit in Italy, they will have to update their politics to grapple with problems that none of them can solve alone.

The last two years have witnessed a cascade of interconnected crises: financial panic, rising food and oil prices, climate shocks, a flu pandemic, and more. Political cooperation to address these problems is not a mere nicety. It has become a global necessity.

The intensity of global interconnectedness is stunning. The H1N1 influenza virus was identified in a Mexican village in April. By now it has reached more than 100 countries. The effects of the collapse of Lehman Brothers last September were transmitted worldwide within days: soon even the most remote villages in Africa, Asia, and Latin America were feeling the shock of reduced remittance income, canceled investment projects, and falling export prices. In the same way, climate shocks in parts of Europe, Australia, Asia, and the Americas in recent years contributed to soaring food prices that hit the poor and created instability and hardships in dozens of countries.

No nation or world leader can solve these problems alone. True, politicians answer to local voters. But those voters want solutions that can't be achieved within any country's own borders. Every country faces worsening climate shocks that result from worldwide greenhouse-gas emissions, not just those within national borders. A recent report by the United States government, to pick but one example, warns that “business as usual” in climate policy will result in severe droughts in the American southwest, intense storms and flooding in the Gulf of Mexico, and torrential rains in the northeast. America's politicians will be answerable, but heading off these dire effects requires a global agreement.

This is the reason why I am calling on the G-8 to act on a set of crucial issues over the coming 12 months. Some are within the purview of the G-8 countries; others require global agreements by all members of the United Nations. Either way, given their past commitments, the size of their economies, their countries' disproportionate share of greenhouse-gas emissions, and their responsibilities as donor countries, the G-8 leaders have a special obligation to lead.

First, the G-8 and other major emitters of greenhouse gases must intensify their work to seal a deal at the UN climate change conference in Copenhagen in December. That agreement must be scientifically rigorous, equitable, ambitious, and exact. Achieving the goal of limiting the global mean temperature increase to two degrees Celsius will require nations to cut carbon emissions by 50% by 2050. The G-8 and other industrialized countries must take the lead by committing to emissions cuts of at least 80% from 1990 levels.

Any effective accord must help vulnerable countries – especially the poorest of the poor and the highly vulnerable arid and island nations – adapt to climate change. It must provide promised financing to poor countries to build sustainable energy systems and climate-resilient economies, and it must create a system for developing and then transferring green technologies for worldwide benefit.

If the Copenhagen negotiations are to be a success, world leaders must do more than talk about leadership. They must show it. That is why I am calling all world leaders to the UN on September 22 for a global summit on climate change. I expect them to be there. Our future is at stake.

Second, the G-8 should take specific steps needed to honor long-standing but unfilled pledges of support to poor countries to help them achieve the Millennium Development Goals. Back in 2005, the G-8 itself promised to double aid to Africa by 2010. It is now more than $20 billion per year short of that pledge, with just one year to go. The very credibility of the G-8 is on the line, as the world's poorest nations are squeezed by financial crisis, climate shocks, and unfulfilled aid promises, all beyond their control.

Third, the G-8 should focus urgent attention on the intensifying global hunger crisis. The UN estimates that the number of chronically hungry people has recently increased by around 150 million people, and that the world's hungry now stand at one billion.

This shocking reversal of progress on food security is the result of many factors: climate shocks, crop failures, and, of course, the global financial crisis itself. Scientists have sent the world's leaders a powerful message: the poor and food-deficit regions can grow much more food if their smallholder farmers get the improved seeds, fertilizers, and irrigation they need to boost productivity. Food aid is vital in the midst of the current disaster; growing more food in Africa, particularly, is vital for next year and beyond.

Global cooperation was decisive in arresting last year's financial meltdown. While the world's economic situation remains difficult, the benefits of monetary and fiscal cooperation among the major economies is clear. We saw a similarly effective collective response to the H1N1 pandemic. Cooperation works, but we've only just gotten started.

Let us now bring the power of global partnership to bear on climate change, poverty reduction, and food production. Let us begin an economic recovery that is not only robust, but also just, inclusive, and sustainable – lifting the entire world. For if we do not do it now, at a moment of crisis, when will we?