Nature News: Two lines of evidence nearly brought down the last-minute climate agreement brokered last week in Copenhagen by US President Barack Obama: studies indicating that the impacts of global warming could be more severe than previously thought, and that rich countries could do more to counter the problem without breaking the bank.Now, negotiators are seeing whether they can strengthen a deal nearly universally acknowledged as weak âmdash; or whether even the mounting scientific evidence on the most dire effects of climate change will be enough to forge a more meaningful deal.