"As is well known, the TSI (Total Solar Irradiance) varies directly with the Sun’s activity level, with an amplitude of about 0.1%. The Sun is about 0.1% brighter at activity maximum than at minimum. SORCE carries an instrument called TIM (Total Irradiance Monitor) that measures just this, but it also includes another intrument called SIM, the Spectral Irradiance Monitor. This instrument measures solar variability in six different wavelength bands, and SIM has turned up something very interesting."
"Part of Figure 1 from the Harder et al. paper. This shows two of the six wavelength regions the SIM observes, from 2004 to 2008. During this time, solar activity has declined to its current minimum between cycles 23 and 24. The key observational point is that while the UV irradiance has decreased (purple line, 201-300 nm), there has been an increase in the visible (green line, 400-691 nm). Other increases in the infrared are offset by declines in the red and near IR (691-972 nm) and near UV (300-400 nm)."
THAT connected me to THIS:
Solar Variability: Striking A Balance With Climate Change
"The fluctuations in the solar cycle impacts Earth's global temperature by about 0.1 degree Celsius, slightly hotter during solar maximum and cooler during solar minimum," said Thomas Woods, solar scientist at the University of Colorado in Boulder. "The sun is currently at its minimum, and the next solar maximum is expected in 2012."
and THIS:
Stronger Evidence For Human Origin Of Global Warming
"Verdes, now at Novartis Pharma, examined data on temperature anomalies, the strength of the radiation emitted from the Sun, and volcanic activity. The relatively recent increases in solar radiation, combined with reduced volcanic activity, contribute to the increase in world temperatures. However, Verdes' analysis demonstrates that these natural causes do not completely explain the observed warming.
Verdes calculated the amount of non-natural influence required to match the increases in temperature observed in the last 150 years. He plotted the influence over time. Then, he compared it to the evolution of greenhouse gasses, taking into account the cooling due to aerosols. With allowances for error, he found that influences attributable to greenhouse gasses mirror the graph of non-natural influence needed to explain the observed temperature increase of recent decades.
Bottom line (supported by several other studies) -- the climate of the 20th and 21st centuries can't be explained without the increasing influence of greenhouse gas concentrations in the atmosphere, particularly CO2 concentrations
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