Solar forcings are not too small to explain twentieth century warming. In fact, their effect could be equal to or greater than the effect of CO2 in the atmosphere.
To see the effects of the model response to solar forcing compared to GHG + sulfate, the difference of solar + GHG + sulfate minus GHG + sulfate (solar residual) is shown in Fig. 3c. The increased global-mean warming arising from solar forcing (Fig. 1b) is manifest most markedly at high latitudes of the Northern Hemisphere associated with ice-albedo feedback, with maximum values of about +0.7°C north of 65°N in the late 1940s. Contributions in the Tropics and at high southern latitudes are about +0.1°–+0.2°C. The contribution of the solar forcing to the late twentieth-century warming is again most notable at high northern latitudes between 1985 and 1995 with values of about +0.3°C north of 70°N. The high-latitude warming associated with ice-albedo feedback was noted in the earlier studies with increased solar forcing (e.g., Wetherald and Manabe 1975). Though the impact of sulfate aerosols is greatest in the northern midlatitudes where the emissions are largest (e.g., Kiehl and Briegleb 1993; Meehl et al. 1996), warming is only slightly decreased there in Fig. 3b. The effects of the well-mixed ocean and the consequently large thermal inertia inhibit high-latitude warming in the circumpolar southern regions (e.g., Cubasch et al. 2001).