2001; Hong et al., 2003; Hu et al., 2003; Niggemann et al., 2003; Poore et al., 2003).
It appears from such correlations that the solar-driven nuclide variations impact climate, at least on a regional scale, enough to leave an imprint in the proxy data (Figure 3-6). These results suggest either that the nuclide-solar irradiance connection is more direct and robust than models suggest, that there are amplified responses of the climate to solar irradiance variations, or both. Potentially, such amplifications include solar ultraviolet impacts on stratospheric ozone and associated tropospheric dynamical responses (e.g., Haigh, 2003; Labitzke and Matthes, 2003; Shindell et al., 2001a, 2003), cosmic ray influences on cloud formation (Carslaw et al., 2002), or changes in North Atlantic meridional overturning (Bond et al., 2001).
Recent theoretical modeling studies have evaluated the role of natural and anthropogenic radiative forcing on climate changes over the past one or more centuries. Detailed attribution studies have focused on the appar-