The greenhouse signature is missing. We have been looking and measuring for years, and cannot find it.
Each possible cause of global warming has a different pattern of where in the planet the warming occurs first and the most. The signature of an increased greenhouse effect is a hot spot about 10km up in the atmosphere over the tropics. We have been measuring the atmosphere for decades using radiosondes: weather balloons with thermometers that radio back the temperature as the balloon ascends through the atmosphere. They show no hot spot. Whatsoever.If there is no hot spot then an increased greenhouse effect is not the cause of global warming. So we know for sure that carbon emissions are not a significant cause of the global warming.
Which, in turn, suggests that recent global warming originated in nature, rather than in our activities...and that any reductions in carbon emissions we make--no matter how drastic--will not have a significant effect on global temperatures.