Although many examples of environmental changes that are forced by variations in solar energy input have been documented, the solar influence on climate need not be a direct relationship. For example, climate variability can be caused by forcing from internal modes of ocean circulation, ice sheet growth and decay, solar effects induced in different regions and propagated across time and distance, or changes in the biosphere, all of which could recur at frequencies independent of solar input. And even if direct, solar forcing can be nonlinear, which may obscure the driving force of changes at any particular location.
Turney et al. investigate the links between solar forcing and regional climate in the North Atlantic during the Holocene by comparing the solar component, recorded in the 14C record of tree rings, with surface moisture, derived from fluctuations in the populations of oaks and pines in Irish bogs. They find that climate change in the North Atlantic, on centennial to millennial time scales, is not a direct, linear response to changes in solar input. -- HJS
J. Quaternary Sci. 20, 511 (2005).
