Rutherford Appleton Laboratory, Chilton, Didcot, OX11 ODQ, UK, m.lockwood@rl.ac.uk
"The variation in solar brightness since 1868 and its effects on global temperatures"
We have developed a method which derives the magnetic field in the sun's atmosphere from observations of Earth's magnetic field. Application to a homogeneous data series from 1868 shows that this field has risen by 140% since 1900 and by 40% since 1963. The latter is a good test of the method is it is in excellent agreement with observations from interplanetary space. We find a highly significant correlation with total solar irradiance (I) measurements from which we can use the coronal magnetic field as a proxy to extrapolate back over the last 130 years. This reveals that about 50% of the rise in global average temperature at the Earth's surface can be attributed to a rise in I for 1900-1998, although this figure falls to less than 30% for 1970-1998.
However, the toroidal field in the sun's atmosphere may not be the most
appropriate proxy to employ, as both sunspot darkening and facular brightening are influenced by the poloidal field at and below the photosphere. However, we find highly significant correlations between these two regions and, for example, very similar results are obtained if we employ the spread of sunspot latitudes in the photosphere as a proxy with which to extrapolate.