Workshop Presentations - The Effects of Solar Variability on Earth's Climate - page 18

Climate Response at Earth's Surface to Cyclic and Secular Solar Forcing
Ka-Kit Tung, University of Washington
One overriding problem in all studies that attempt to relate past changes in climate to solar
forcing involves the complications of other forcing factors operating on similar timescales. Volcanic
forcing is of particular significance, especially during recent centuries (including the Maunder and Dalton
Minima) when explosive eruptions were common (Figure 2.5). In addition, internal modes of circulation,
such as the Atlantic Multidecadal Oscillation (AMO), further complicate signal detection at certain
frequencies. Ka-Kit Tung examined this matter by focusing on the longest instrumental temperature
record, from central England, which extends back over 350 years, as well as estimates of the global
surface temperature instrument record since 1850 to help define a component of these records due to
unforced internal variability likely associated with the AMO. This analysis suggests that >90 percent of
the variance in temperatures can be accounted for by non-solar forcing factors and internal modes of
variability.
Using the central England temperature record to help define AMO cycles in earlier centuries,
Tung also estimated that roughly half of the warming at the end of the Maunder Minimum period could
be due to AMO variability and that, more generally, internal variability combined with volcanic forcing
can explain a significant part of the variability commonly attributed to solar variations.
FIGURE 2.5 The low-frequency portion of the Central England temperature record, which could represent the
Northern Hemisphere mean, is plotted along with the solar TSI index and the occurrence of known large volcanic
explosions. The figure indicates that the warming at the end of the Maunder Minimum around 1700 leads the
increase in TSI by about 20-30 years and suggests that the warming may instead be a recovery from the cooling
produced by the aerosols from a series of large volcanic eruptions between 1660 and 1680. SOURCE: Courtesy of
K.K. Tung and J. Zhou, University of Washington, “Climate Response at Earth's Surface to Cyclic and Secular
Forcing,” presentation to the Workshop on the Effects of Solar Variability on Earth's Climate, September 9, 2011.