“It is generally accepted that the climate warms during periods of strong solar activity (e.g., the Medieval Warm Period) and cools during periods of low solar activity (e.g., the Little Ice Age).” —Lyu et al., 2016
Within the last 1,000 years, global-scale surface temperatures underwent a warm period during Medieval times, centennial-scale cooling during the 14th to 19th centuries, and another warm period since the early 20th century.
According to scientists publishing in the peer-reviewed scientific literature within the last several months (2016), these long-term thermal changes are well correlated with long-term variations in solar activity, namely the Medieval Solar Maximum (Medieval Warm Period), Spörer, Maunder and Dalton Minimums (Little Ice Age), and Modern Grand Maximum (20th Century).
Scientists Zharkova and colleagues (2015) provide a cogent summary with a user-friendly graphic denoting the solar changes and their correspondence with warming and cooling trends.
“The longest direct observation of solar activity is the 400-year sunspot-number series, which depicts a dramatic contrast between the almost spotless Maunder and Dalton minima, andthe period of very high activity in the most recent 5 cycles [1950s – 2000s], prior to cycle 24. … The records show that solar activity in the current cycle 24 is much lower than in the previous three cycles 21–23 revealing more than a two-year minimum period between cycles 23 and 24. This reduced activity in cycle 24 was very surprising because the previous five cycles were extremely active and sunspot productive forming the Modern Maximum. … We predict correctly many features from the past, such as: 1) an increase in solar activity during the Medieval Warm period; 2) a clear decrease in the activity during the Little Ice Age, the Maunder Minimum and the Dalton Minimum; 3) an increase in solar activity during a modern maximum in 20th century.”
“The corrected series is provided as supplementary material in electronic form and displays secular minima around 1800 (Dalton Minimum) and 1900 (Gleissberg Minimum), as well as the Modern Grand Maximum of [solar] activity in the second half of the twentieth century. The uniqueness of the grand maximum is confirmed for the last 250 years.”
“[T]he modern Grand maximum (which occurred during solar cycles 19–23, i.e., 1950–2009) was a rare or even unique event, in both magnitude and duration, in the past three millennia. Except for these extreme cases, our reconstruction otherwise reveals that solar activity is well confined within a relatively narrow range.”
Below is a list of 18 peer-reviewed papers published in 2016 that support the position that changes in solar activity are well correlated with warming and cooling periods for the last millennium.