Skeptics are wont to say that the climate always changes, which is true but not helpful in the AGW debates. It does always change, but it changes for a variety of reasons.
What science needs to do is present compelling evidence that we’ve added some new reasons for climate to change. And science needs to convince enough skeptics to enlarge the consensus. Right now, about two-thirds of climate scientists, a large majority of politicians and a simple majority of citizens agrees that is the case. That is not enough.
Most skeptics would agree more or less with the following statements:
- Global surface temperatures have warmed about 0.8C over the course of the past century or so.
- Humans have the capacity to change the climate through our actions.
- Scientists have identified ways in which human activity can change the climate: Deforestation, pollution, changes in land use / land cover and emissions of greenhouse gases.
- Conventional physics accurately describes how greenhouse gas concentrations can contribute to warming.
- Emissions of greenhouse gases have grown dramatically over the past two centuries, as have concentrations of CO2 in the atmosphere
In fact, I think that every skeptic I know would agree with the above statements, which is why I think using the term ‘denier’ is cheap agitprop and an insult that defines the user more than the target. At any rate, I intend to ask some of the better-known skeptics to sign off on those. Feel free to join them or oppose them in the comments.