On Tuesday, two of the world’s most important men—U.S. President Barack Obama and Chinese President Hu Jintao—shared the spotlight at the UN Summit on Climate Change to speak about taking steps to combat climate change. The headliners of a group of over 100 leaders, both presidents spoke of the importance of the upcoming Intergovernmental Panel on Climate Change’s December meeting in Copenhagen. While the message of both men was a step in the right direction, we call on the leaders to translate promises into concrete action.

Representing the world’s largest emitter of greenhouse gases, Hu took a fateful step in announcing China would cut carbon dioxide emissions by 2020. Several of the measures that Hu unveiled will have a dramatic impact, such as making 15 percent of China’s fuel come from non-fossil sources by that target date, while planting enough trees to cover what the Los Angeles Times calculated to be the entire size of Norway.

UN climate chief Yvo de Boer reacted to Hu’s speech by saying that China could become the “front-runner” on climate change with these steps, depending on the U.S. government’s response. But this lofty aspiration depends on China reaching these targets and proving it has substance to match appealing words.

For its part, the U.S. does face an important challenge as well. The substance of Obama’s speech was positive and indicated that he recognizes the importance of climate-change efforts, though he could not provide much substance. While the Waxman-Markey bill would make the U.S. the clear leader in climate-change reform, the bill remains stalled in the Senate after passing through the House. While we do not agree with the Los Angeles Times that this situation renders Obama’s words meaningless and the U.S. position “woefully weak,” we do recognize the importance of passing this legislation promptly.

The IPCC meeting in Copenhagen to replace the ineffective 1997 Kyoto Protocol will be critical for the world’s future, and the U.S. must show initiative in helping to develop a system of short- and middle-term targets and emission reductions for all nations, including developing nations. In such a system, the massively growing nations of China and India will play a critical role. Just as the United States doomed the Kyoto Protocol by rejecting it, the non-participation of any nation in the upcoming Copenhagen talks will sap it of its significance.

We recognize that developed nations will have to play a larger role in any plan, aiding countries with greater need through shared green technology and general support. We call on Obama and Hu to take leading roles in making such plans a reality. Speeches and declarations of intent are important, but now must come the transition to action.