«The solar and volcanic forcings we use are derived from reconstructions based on proxy data and are therefore also subject to considerable uncertainties, although recent explosive volcanic eruptions are likely to have cooled climate, and independent records
of solar activity levels inferred from the cosmogenic isotope 10Be (43) and geomagnetic records (44) provide support to reconstructions (22, 45) that show generally increasing solar activity during the 20th century (12).»
The past studies have found the
highest solar activity levels in (since) the 1940's based on proxy data, but modern instrumental measurements do not show any trend since 1950's.
However,
solar activity leveled off after 1940 and the net influence from sun and volcano since 1940 has been slight cooling.