LONDON — The July 9 Major Economics Forum (MEF) meeting in L'Aquila, Italy, where the leaders of the world's largest economies have gathered to discuss progress toward a new global climate agreement, comes at a vital moment just six months before a deal is supposed to be struck in Copenhagen. When many of the same leaders met in April to address the economic crisis, they rightly pledged to do "whatever is necessary." The same spirit needs to animate the L'Aquila meeting.

There is enormous good will to do so. The new U.S. administration is supporting strong American action. China is setting ambitious targets for reducing energy intensity and making massive investments in renewable energy. India has put forward its own action plan. Europe has set a goal of cutting emissions by 30 percent below 1990 levels by 2020 if there is an ambitious global agreement. Japan has published its proposals for major carbon reductions. Across the world, commitments are forthcoming.

But practical challenges remain. What is being asked is that global emissions be less than half their 1990 levels by 2050, having peaked before 2020. Since emissions from the developing countries are on the whole lower than those of the developed world — and will need to continue to rise in the short-term as they maintain economic growth and address poverty — it has been proposed that developed countries cut emissions by at least 80 percent relative to 1990 by 2050, with major steps toward this goal over the next decade.