The United States and China are the two largest emitters of greenhouse gases. They seem unable to co-operate even though it would be beneficial for both of them - as well as for everybody else - if they did so. Realizing those benefits requires a level of trust that does not exist. Without that trust, the United States, China, and other major emitters of greenhouse gases will not take sufficient action to avoid catastrophic climate change.

The United States and China are locked in a classic "prisoners' dilemma," a fundamental problem in game theory that demonstrates why two parties might not cooperate even if it is in both their best interests to do so. As long as this impasse lasts, the future climate for everyone is held hostage.

Fortunately, the strategy for escaping from a prisoners' dilemma, called "tit-for-tat," has been known for sixty years. Each party must make and reciprocate small, confidence-building measures. Each may also punish, but then forgive, any minor transgressions. This wisdom has kept nuclear war at bay and served as the basis for nuclear disarmament treaties that have been neither ratified nor flouted.

In order to make small, confidence-building measures on climate change, it is necessary to unbundle the components of the Copenhagen Accord reached by world leaders last December. It provided for emission reduction commitments by developed economies including the United States, emission reduction activities by rapidly developing countries including China, and substantial funding for emission reductions and adaptation to climate change in other developing countries.

The United States has insisted that the Copenhagen Accord forms an indivisible "take it or leave it" package and has expressed concern that ceding on some points would not be reciprocated by China. Perhaps not, but failing to offer small confidence-building measures ensures that negotiations remain deadlocked or deliver token outcomes at best. As a confidence-building measure, funding for developing nations to adapt to climate change should be separated from the other Copenhagen Accord components.

The countries put most at risk by climate change are also those who have contributed least to the problem. Their need for funding to cope with climate change also provides a unique opportunity to establish new, additional and reliable approaches to economic development as the Obama administration has already proposed. Those approaches are critical to the welfare of millions of people who are failing to cope with existing climate-related floods, droughts and crop failures, let alone inevitable, additional ones. Delay simply makes the future cost of funding adaptation greater.

The president's Council on Environmental Quality has recommended federal policies and programs to better prepare the United States for inevitable impacts of climate change. The United States should not deny the poorest, most vulnerable nations the same opportunity. Other developed nations have not.

At the Major Economies Forum, the United States should offer unconditional adaptation funding for the most vulnerable nations and invite China to reciprocate on other parts of the Copenhagen Accord. That would be a classic "tit-for-tat" strategy - and one that could go a long way toward slowing global climate change.

Earl C. Saxon, Ph.D., is a senior fellow for global climate change at AED. Lisa M. Schenck, J.S.D, is associate dean for academic affairs and professorial lecturer in law at the George Washington University Law School.