Nature constantly adjusts the atmospheric carbon level  An increase in the level causes the atmosphere to hold more heat, which causes more water to evaporate from the oceans, which causes increased rain  Rain washes some carbon from the air into the oceans, where it eventually becomes part of the seabed  A decrease in atmospheric carbon causes the atmosphere to hold less heat, which causes decreased evaporation from the oceans, which causes less rain, and thus less carbon is washed into the oceans  Yet some environmentalists worry that burning fossil fuels may raise atmospheric carbon to a dangerous level  It is true that a sustained increase would threaten human life
But the environmentalists should relax -- nature will continually adjust the carbon level
A decrease in the level of carbon in the atmosphere causes decreased evaporation of ocean water.