Global temperature response to radiative forcing: Solar cycle versus volcanic eruptions

I show that the peak‐to‐peak amplitude of the global mean surface temperature response to the 11‐year cyclic total irradiance forcing is an order of magnitude less than the amplitude of a cyclic component roughly in phase with the solar forcing which has been observed in the temperature record in the period 1959–2004. If this cyclic temperature component were a response to the solar forcing, it would imply the existence of strong amplifying feedbacks which operate exclusively for solar forcing, such as top‐down mechanisms responding to the large variability in the ultraviolet part of the solar spectrum. I demonstrate, however, that the apparent cyclic component in the temperature record is dominated by the response to five major volcanic eruptions some of which incidentally took place a few years before solar minimum in four consecutive solar cycles, and hence that the correlation with the solar cycle is coincidental. A temperature rise of approximately 0.15 K over the 20th century ascribed to an increasing trend in solar forcing is more than offset by a cooling trend of about 0.3 K due to stratospheric aerosols from volcanic eruptions.