Slide 26: Future radiative forcings depend on response
Since the current rapid change in climate is understood to be driven by primarily anthropogenic radiative forcing, future climate change is likely to be driven in a similar manner, barring some catastrophic natural event, such as a meteor strike (even the eruption of Mt Pinatubo, which poured vast amounts of light-reflective aerosols into the upper atmosphere only produced a temporary cooling over two years). The outputs of those greenhouse gases that drive radiative forcing (along with other effects such as land transformation) described in the SRES scenarios differ depending on the human political and economic response.
AS can be seen in the diagram on the right, the A1F1, or highly intensity fossil fuel usage scenario (also labelled the "business as usual" scenario) tends to have higher outputs of these gases. The B1 scenario has the lowest predict emissions for carbon dioxide and methane, but in general the A1T scenario, which maintains the global economy but shifts towards clean fuel sources, seems to perform nearly as well. However, the overall likelihood is that emissions are likely to continue to increase at least to the middle of this century, and in many scenarios, even beyond that point.