418 Engineering Response to Climate Change
Accord that it would be dangerous to society and the environment for the
global average temperature to exceed 2°C above its preindustrial level.
With so much important environmental change occurring at 0.8°C, a
growing number of scientists are suggesting that avoiding a high likelihood
of signicant environmental and societal consequences may well require
the increase in global average temperature be no more than 0.5°C above
preindustrial, a level that has already been exceeded (e.g., see Hansen et al.
2008). IPCC’s Fourth Working Group 2 assessment (IPCC 2007b) describes
the impacts to be expected at various levels of global average warming and
the potential for building resilience to and adapting ...