global warming
atmospheric carbon dioxide levels more or less track global temperature. the recent warming trend started 10,000 years ago when people developed agriculture. forests and wild lands generally absorb co2 from the atmosphere and sequester it in dirt. agriculture generally removes carbon from the ground and eventually releases it into the air. qualitatively, that's common sense. quantitatively, we've been arguing about the exact numerical rates for decades. we can't really stop farming. 6 billion people eat a whole lot of food. the ideal solution would be a power plant whose "waste" product is fertilizer instead of co2.