problem though is that the interpretation of proxies is almost a comedy of errors.
Our observations of the earthshine take the ratio of the earthshine to moonshine, so they are insensitive variations of the solar irradiance. The 5 +/-2% change in our observed reflectance translates to …. Solar and terrestrial changes are in phase and contribute to a greater power going into the climate system at activity maximum. However, the effect of the albedo is more than an order of magnitude greater. Our simulations suggest a surface average forcing at the top of the atmosphere, coming only from changes in the albedo from 1994/1995 to 1999/2001, of 2.7 +/- 1.4 W/m2 Pall e et al., 2003), while observations give 7.5 +/-2.4 W/m2. The Intergovernmental Panel on Climate Change (IPCC, 1995) argues for a comparably sized 2.4 W/m2 increase in forcing, which is attributed to greenhouse gas forcing since 1850.
Still, whether the Earth’s reflectance varies with the solar cycle is a matter of controversy, but regardless of its origin, if it were real, such a change in the net sunlight reaching the Earth would be very significant for the climate system.
The underlying causes of late-Holocene climate variability in the tropics are incompletely understood. Here we report a 1,500-year reconstruction of climate history and glaciation in the Venezuelan Andes using lake sediments. Four glacial advances occurred between anno Domini (A.D.) 1250 and 1810, coincident with solar activity minima. Temperature declines of approx. 3.2 +/- 1.4°C and precipitation increases of approx. 20% are required to produce the observed glacial responses.