How might solar variations affect projections of global greenhouse warming?
What has happened in the past can help us assess the relative importance of solar and anthropogenic changes in the climate of the future. It seems likely that changes in solar radiation, linked to long-term variations in solar activity, may have been the dominant climate driver in the period between about AD 1600 and 1850. As discussed earlier, the explanation of trends in global surface temperature since that time is not as simple, when both the positive and negative impacts of fossil fuel consumption are added to the picture. Since 1850, variations in global surface temperature appear to track changes in the level of solar activity at least as well as they track increasing greenhouse gas concentrations. At the same time, when probable energy inputs are taken into account (as in Fig. 4), solar effects can account for only a fourth of the net change in climate forcing in this 140 year period. It could be that the climate system is more sensitive than we think to changes in solar energy
