The mood outside the formal negotiations in Copenhagen — among the tens of thousands of business leaders, entrepreneurs, NGO representatives, and clean tech curiosity-seekers in town — has been overwhelmingly optimistic, celebratory even. But the moment talk turns to the latest news emanating from the Bella Center (where the actual negotiations are taking place), the festival mood considerably darkens. The gap between developed and developing nations seems as wide as ever. The “cost” of funding the effort to address the challenge seems to keep going up.