The Climate has always been changing. I suppose the current hypothesis is that it is changing faster than ever before. Where is the proof for that? What I disagree with is that the change in atmospheric concentration of CO2 from 280 ppm in preindustrial times to 390 ppm in todays times is responsible for the increase in global temperatures since that time. Other factors could produce such a change and nobody has proven what the climate sensitivity is to a doubling in CO2 concentration.