Total Solar Irradiance Composites and the Empirical Analysis of the Solar Contribution to
Global Mean Air Surface Temperature Change
Nicola Scafetta, ACRIM, Jet Propulsion Laboratory, Pasadena, California
We discuss the Total Solar Irradiance satellite composites and show that the
ACRIM/PMOD controversy is still open to further investigation. In particular we show that
TSI proxy models based on solar surface magnetic field disprove the alterations made by
PMOD of the Nimbus record during the ACRIM gap (1989-1992). This suggests that the
TSI may have increased from 1980 to 2000 as ACRIM science team has proposed. By using
alternative TSI model we evaluate the solar contribution to global mean air surface
temperature change by using an empirical bi-scale climate model characterized by both fast
and slow characteristic time responses to solar forcing: T1 = 0.4 +/- 0.1 yr, and T2 = 8 +/- 2
yr or T2 = 12 +/- 3 yr. Since 1980 the solar contribution to climate change is uncertain
because of the severe uncertainty of the total solar irradiance satellite composites. The sun
may have caused from a slight cooling, if PMOD TSI composite is used, to a significant
warming (up to 65% of the total observed warming) if ACRIM, or other TSI composites are
used. The model is calibrated only on the empirical 11-year solar cycle signature on the
instrumental global surface temperature since 1980. The model reconstructs the major
temperature patterns covering 400 years of solar induced temperature changes, as shown in
recent paleoclimate global temperature records.