July 31, 2014

Climate modelling

While lower total solar irradiance during the Maunder minimum explains the order of magnitude of the variation in observed temperatures (due to the direct radiative effect), we still don’t know why such effects can manifest themselves rapidly, since the climate system exhibits a certain degree of inertia due to the oceans. Non-linear positive feedback mechanisms are one possible explanation, the most likely candidate being solar ultraviolet radiation. Over a complete solar cycle of 11 years, the variation in UV radiation at the wavelength of 200 nm is 8%, whereas total solar irradiance in the same conditions only varies by 0.1%. UV variations affect the thermal and dynamic structure of the stratosphere, which by coupling leads to variations that reach into the troposphere (Haigh, 1994; Soon et al., 1996; Haigh, 1996; 2004; Shindell et al., 1999; Schlesinger and Andronova, 2004; Egorova et al., 2004). Scientists are therefore now factoring solar variability into their models.