  But you know what, I know a lot of really good scientists at NASA, and at NOAA, and at our major universities.   And the best scientists in the world are all telling us that our activities are changing the climate, and if we don't act forcefully, we'll continue to see rising oceans, longer, hotter heat waves, dangerous droughts and floods, and massive disruptions that can trigger greater migration and conflict and hunger around the globe.   The Pentagon says that climate change poses immediate risks to our national security.