claim: About 60% of the warming observed from 1970 to 2000 was very likely caused by this natural 60-year climatic cycle during its warming phase...
evidence: Given that records of solar activity are accurate, solar activity may have contributed to part of the modern warming that peaked in the 1930s, in addition to the 60-year temperature cycles that result in roughly 0.5 °C of warming during the increasing temperature phase.