Read here. French scientists, J.-L. Le Mouël et al., determine that solar activity has major impact on temperatures across the world. Both major global warming and global cooling periods can be attributed to associated solar activity.
"We find that the resulting curves correlate remarkably well at the longer periods, within and between regions. The secular trend of all of these curves is similar (an S-shaped pattern), with a rise from 1900 to 1950, a decrease from 1950 to 1975, and a subsequent (small) increase. This trend is the same as that found for a number of solar indices, such as sunspot number or magnetic field components in any observatory. We conclude that significant solar forcing is present in temperature disturbances in the areas we analyzed and conjecture that this should be a global feature." [Jean-Louis Le Mouël, Vincent Courtillot, Elena Blanter, Mikhail Shnirman 2008; C.R. Geoscience, 340: 421-430]