Read here and here. (click on image to enlarge - Solar Activity Events image source here)
The death and destruction of the Little Ice Age (LIA) mercifully came to an end during the mid-1800's as the world began to warm. The LIA occurred during a time when solar activity was extremely low, as evidenced by the Maunder, Spörer and Dalton minimums. Since the absolute solar low point of the Maunder epsiode, solar activity has slowly increased over the last 400 years until it reached its maximum during the modern era.
As the solar activity (total solar irradiance) increased, so did global temperatures [the HADCRU global warming from 1850 to 2000 is .55C] and the warming commenced well before the tremndous increase of CO2 emissions after World War II. Now, a new peer-reveiwed study also identifies a 50% in solar UV striking earth over the last 400 years, which would cause a warming of the oceans. A combination of the increased TSI and UV may explain up to 0.44 degrees of the 0.55 degree HADCRU warming - 80%.
"A peer-reviewed paper [Krivova et al.] published in the Journal of Geophysical Research finds that reconstructions of total solar irradiance (TSI) show a significant increase since the Maunder minimum in the 1600's during the Little Ice Age and shows further increases over the 19th and 20th centuries.....Use of the Stefan-Boltzmann equation indicates that a 1.25 W/m2 increase in solar activity could account for an approximate .44C global temperature increase.....A significant new finding is that portions of the more energetic ultraviolet region of the solar spectrum increased by almost 50% over the 400 years since the Maunder minimum.....This is highly significant because the UV portion of the solar spectrum is the most important for heating of the oceans due to the greatest penetration beyond the surface and highest energy levels. Solar UV is capable of penetrating the ocean to depths of several meters to cause ocean heating." [N. A. Krivova, L. E. A. Vieira, S. K. Solanki 2010: Journal of Geophysical Research, Vol. 115, A12112, 11 PP., 2010 doi:10.1029/2010JA015431]
