No-one doubts that carbon dioxide has increased in the earth’s atmosphere profoundly over the last hundred years. Almost everything else, however, is in doubt. Do greenhouse gasses make the earth warmer? It’s hard to say because eighty percent of the increase in carbon dioxide in the atmosphere followed, but did not precede the increase in the surface temperature that has been measured over the last hundred years. If it caused the increase in temperature, it’s an odd pattern of causality, where the cause follows the effect.