CBS's Mark Knoller tweets that U.N. Secretary General Ban Ki-moon is asking world leaders, including President Obama, to spend the night in Copenhagen and continue negotiations tomorrow.

So far, the White House won't commit:

WH says it'll consider Ban Ki-moon's request to stay the night, but Obama schedule still calls for him to head home today.  

WH spokesman says "it would have to be really substantive" for Obama to change plans and stay the night in Copenhagen.

Staying an extra day presents a political risk for Obama. If he spends the night and then still fails to reach consensus about emissions targets with China, then he will have lost even more political capital.