There’s something seductive about manicured green grass. Collectively, however, the chemicals sprayed on lawns, parks, and golf courses represent an urgent threat to human health, pet health, and the health of our ecosystem. Lawns also use a lot of water, and storm water runs off typical lawns almost as fast as from concrete—in part because lawns usually grow on ground as dead as dirt. The irony is that our lawns could be a secret weapon in the fight to balance Earth’s climate. We’ll get to this possibility in a moment, but first some background. Lawns represent America’s largest irrigated crop. According to studies funded by NASA, lawns, parks, and golf courses take up more area than the state of Georgia—so changing our lawns is potentially a huge change to our landscape. An average lawn also requires about 200 gallons of water per day. Thus, lawns slurp up a lot of the more than 8 billion gallons of water used for irrigation each day in America. And then there are the chemicals. In nature, no species exists alone. Healthy ecosystems require a dynamic collaboration of many species excha …