What's the right age to start teaching students about climate change?

Let's face it: Climate change can be a scary topic. Lessons about its impact on the planet -- food and water shortages, catastrophic natural disasters, animal extinctions -- are appropriate causes for alarm. Add to that the guilt factor that comes from humanity's complicity in global warming, and teaching this subject to young students can be a daunting task. Yet in some schools, students as young as kindergartners are getting an introduction to the costs of climate change (such as endangered plant life) and ways they can help (conserving water, for instance). A proposed bill in California calls for the mandatory inclusion of climate change in the science curriculum of all state public schools, though it does not say in which grade these lessons must start. Is it ever too early to teach children about climate change, or is the sooner the better? Tell us what you think!