President Barack Obama arrives in Denmark today, either just in time to save the Copenhagen talks, or just in time to watch this "last best hope for mankind" die.

The president softened the turf before he landed, sending in Secretary of State Hillary Clinton with an offer to contribute to an annual $100 billion fund for developing nations to produce cleaner energy.

"We're running out of time," Clinton said Thursday. "Without the accord, the opportunity to mobilize significant resources to assist developing countries with mitigation and adaptation will be lost."

The $100 billion offer is both generous and appropriate. If past international funds are an indication, the United States would begin paying out about $20 billion by 2020. It’s an expensive but necessary commitment.

However, the United States cannot be expected to bear any greater share of this fund. Developed European nations readily acknowledge as much as $150 billion a year could be needed. Yet, they haven’t actually stepped forward with long-term commitments. They must do so now.

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