Democratic senator and former presidential candidate John Kerry writes in the Huffington Post that climate change is more than a threat to the earth's flora and fauna. It will also lead to exacerbated conflicts and instability around the world, he says.

"Make no mistake: catastrophic climate change represents a threat to human security, global stability, and -- yes -- even to American national security," writes Kerry, D-Massachusetts.

"... Former CENTCOM Commander Anthony Zinni, no radical tree-hugger, put it simply: "We will pay for this one way or another. We will pay to reduce greenhouse gas emissions today, and we'll have to take an economic hit of some kind. Or, we will pay the price later in military terms. And that will involve human lives. There will be a human toll."