Evidence mounts that humankind is changing the Earth's energy balance. The change in energy balance is attributable to the build-up in the atmosphere of greenhouse gases (GHGs) that partially trap outgoing long-wave radiation – that is, radiation given off by the Earth as a result of absorbing solar (short-wave) radiation. There is still some debate as to how much of the change in energy balance has shown up to date in the form of changes in climate-related variables such as global average temperature and precipitation–evaporation patterns. But there is overwhelming evidence that some GHG-induced change has occurred, as distinct from changes attributable to natural phenomena (solar or volcanic) or factors affecting long-term variability in the earth's climate (Solomon et al. 2007). We also know that at least some (perhaps half) of the imbalance is temporarily hidden – stored in the oceans (Hansen and Nazarenko 2005). Almost certainly as the twenty-first century progresses the climatological evidence of human-induced change will mount – and so will the impacts on the environment and vulnerable aspects of the economy and society.
There are ongoing attempts to frame a climate policy to succeed the Kyoto Protocol. Unless there is an epiphany in climate policy thinking, the emphasis will be on how much to do in the next period, rather than how to do it.