Monday, May 9, 2011

New paper: Increased solar activity caused far more global warming than assumed by the IPCC

A recent peer-reviewed paper published in Astronomy & Astrophysics finds that solar activity has increased since the Little Ice Age by far more than previously assumed by the IPCC. The paper finds that the Total Solar Irradiance (TSI) has increased since the end of the Little Ice Age (around 1850) by up to 6 times more than assumed by the IPCC. Thus, much of the global warming observed since 1850 may instead be attributable to the Sun (called "solar forcing"), rather than man-made CO2 as assumed by the IPCC.
Total Solar Irradiance (TSI)
Astronomy & Astrophysics 529, A67 (2011)   

A new approach to the long-term reconstruction of the solar irradiance leads to large historical solar forcing

A. I. Shapiro, W. Schmutz1, E. Rozanov, M. Schoell, M. Haberreiter1, A. V. Shapiro and S. Nyeki

1 Physikalisch-Meteorologishes Observatorium Davos, World Radiation Center, 7260 Davos Dorf, Switzerland
2 Institute for Atmospheric and Climate science ETH, Zurich, Switzerland
3 Institute for Astronomy ETH, Zurich, Switzerland

Received: 19 November 2010 Accepted: 22 February 2011

Context. The variable Sun is the most likely candidate for the natural forcing of past climate changes on time scales of 50 to 1000 years. Evidence for this understanding is that the terrestrial climate correlates positively with the solar activity. During the past 10 000 years, the Sun has experienced the substantial variations in activity and there have been numerous attempts to reconstruct solar irradiance. While there is general agreement on how solar forcing varied during the last several hundred years – all reconstructions are proportional to the solar activity – there is scientific controversy on the magnitude of solar forcing. Aims. We present a reconstruction of the total and spectral solar irradiance covering 130 nm–10 μm from 1610 to the present with an annual resolution and for the Holocene with a 22-year resolution. Methods. We assume that the minimum state of the quiet Sun in time corresponds to the observed quietest area on the present Sun. Then we use available long-term proxies of the solar activity, which are 10Be isotope concentrations in ice cores and 22-year smoothed neutron monitor data, to interpolate between the present quiet Sun and the minimum state of the quiet Sun. This determines the long-term trend in the solar variability, which is then superposed with the 11-year activity cycle calculated from the sunspot number. The time-dependent solar spectral irradiance from about 7000 BC to the present is then derived using a state-of-the-art radiation code. Results. We derive a total and spectral solar irradiance that was substantially lower during the Maunder minimum than the one observed today. The difference is remarkably larger than other estimations published in the recent literature. The magnitude of the solar UV variability, which indirectly affects the climate, is also found to exceed previous estimates. We discuss in detail the assumptions that lead us to this conclusion.


  1. Interesting, however I'd ask a question.

    this study seems to use proxy linked primarily to galactic cosmic rays. it is linked to solar magnetic fiels, thus to solar activity thus to TSI, but maybe sometime is it less correlated.

    however the correlation with GCR is maybe the true data. some solarist theory attribute some effect to GCR on climate...
    is another proxy, related to TSI and not GCR does not show this evolution, maybe we have a new data...

    could someone precise if my reasoning is right or wrong.

  2. "We assume that the minimum state of the quiet Sun in time corresponds to the observed quietest area on the present Sun." - Is that in any way a fair assumption? (I'm not being snide - it just seems quite arbitrary to me)

  3. Be careful about the implications of this. A larger solar TSI variability, in combination with a fixed temprature variation over the same period, implies a lower climate sensitivity to TSI variation.

  4. not necessarily - there is likely to be a considerable lag time during which heat accumulates in the ocean.

    the "sunspot integral" + ocean oscillations track temps almost perfectly

  5. @benedict It's not. Well, not really, but it is an upper estimate. So lowering this value would increase the variability

  6. Full paper:

    Shapiro et al Be10 reconstruction cited in this paper Table 4 showing solar forcing in Wm-2 over 400 times greater than estimated from sunspot reconstructions [Wang et al 2005]

  7. subsequent posts based on this post: