Just this morning I saw some tweets about how Global Warming is a "A marketable but mostly inaccurate name for something very very important." I fully agree. I would communicate the problem like this: The climate changes. Which is not a surprise because the climate always changes. Alas, it seems the direction the climate moves have dire consequences on humanity -- some places (affecting hundreds of millions at least) will have severe droughts and other places, like huge cities on ocean coasts might get flooded. While it is doubtful we can stop this, we need to do everything to slow down these changes so there is a chance that we can come up with technology to help. Everyone can do a little, incredibly little but a few billion of those little things do add up.