In-class thought questions: 1. Suppose the tilt of Earth’s axis increased to 25° (it is currently approximately 23.5). Would you expect winters in Boston to be warmer or colder? Explain your reasoning. 2. Suppose that for some reason the rotation of the Earth slowed down so that the length of the day doubled. Would you expect the current mid-latitude deserts to move to higher or lower latitudes? Give reasons for your answer.
Radiative Forcing See note 9, p59 of text for detailed definition. Simple definition: change in net energy balance of earth resulting from a specified change in composition of the atmosphere. Radiative forcing of 1 W/m 2 is predicted to result in a globally averaged increase in surface temperature by 0.75±0.375 0 C ( Charney et al, 1979). Instantaneous doubling of CO2 concentration (280-> 560 ppm) predicted to result in an increase in global averaged surface temperature of between 2.5 0 C and 3.5 0 C.
Globally averaged vertical temperature profile
Concentrations and contribution to radiative forcing over the past 20,000 years for (a) CO 2 , (b) CH 4 , and (c) N 2 O: From IPCC (2007).
Radiative forcing IPCC AR4
- Fall '10