  The climate change attribution problem is addressed using empirical
decomposition. Cycles in solar motion and activity of 60 and 20 years were used
to develop an empirical model of Earth temperature variations. The model was
fit to the Hadley global temperature data up to 1950 (time period before
anthropogenic emissions became the dominant forcing mechanism), and then
extrapolated from 1951 to 2009. After subtraction of the model, the residuals
showed an approximate linear upward trend after 1942. Herein we assume that the
residual upward warming observed during the second half of the 20th century has
been mostly induced by a worldwide rapid increase of anthropogenic emissions,
urbanization and land use change. The warming observed before 1942 is
relatively small and it is assumed to have been mostly naturally induced by a
climatic recovery since the Little Ice Age of the 17th century and the Dalton
Minimum at the beginning of the 19th century. The resulting full natural plus
anthropogenic model fits the entire 160 year record very well. Residual
analysis does not provide any evidence for a substantial cooling effect due to
sulfate aerosols from 1940 to 1970. The cooling observed during that period may
be due to a natural 60-year cycle, which is visible in the global temperature
since 1850 and has been observed also in numerous multisecular climatic
records. New solar activity proxy models are developed that suggest a mechanism
for both the 60-year climate cycle and a portion of the long-term warming
trend. Our results suggest that because current models underestimate the
strength of natural multidecadal cycles in the temperature records, the
anthropogenic contribution to climate change since 1970 should be around half
of that previously claimed by the IPCC [2007]. A 21st Century forecast suggests
that climate may warm less than 1^{\circ}C by 2100.
