In Katowice, Poland, delegates from around the world have gathered to discuss how to curb emissions of greenhouse gases. The intent is to meet the goals that emerged from the 2015 Paris United Nations Climate Summit. But this year there’s a new top dog at the table. The United States, led by a president who doesn’t believe in climate change or the scientists who study it, will take a back seat at this month's climate summit, known as COP24.