At Tuesday’s United Nations Climate Summit, high-wattage guests from both the developing and developed worlds delivered their nations’ commitment and promises to fight global warming.

Eyes were especially focused on what the world’s leading polluters had to say, including China which is the world’s largest source of carbon emissions.

Addressing the assembly, Chinese Vice Premier Zhang Gaoli cited a World Bank’s study showing that in 2013, China cut its carbon dioxide emissions by nearly 30 percent from 2005 levels. That’s the equivalent of saving the world of 2.5 billion tons of carbon dioxide. The vice premier also expressed China’s commitment to meeting its carbon reduction targets and setting new ones.

The United States, the world’s second largest emitter of greenhouse gases, continues to take big steps to change this. U.S. President Barack Obama said the U.S. has made great strides in clean energy investments and carbon reduction, harnessing three times as much electricity from wind energy and ten times as much from the sun as the country did when he took office.

Little coincidence that the world’ two largest producers of greenhouse gas emissions are also the world’s two largest economies, which is why, according to Obama, both countries need to lead the climate fight. This was a message he repeated to the Chinese vice premier in a separate meeting earlier in the session. He also called on all countries to join this effort, saying that no nation can meet this global threat alone.

For more insight, we talked with Angel Hsu from New Haven, Connecticut. She’s a research scientist and lecturer at the Yale School of Forestry and Environmental Studies.

Some environmental activists are optimistic about how the U.N. Climate Summit has addressed the issue of climate change. We spoke with Jennifer Morgan, Director of the Climate and Energy Program at the World Resources Institute.