A weakening Sun won’t save us

SOHO satellite image of the Sun, 10 March 2010 @ 00:50 UTC

Observations of decreasing solar activity are argued by some climate change sceptics to point to a fall in temperature during the 21st century. There is even talk of a “Little Ice Age” or “Grand Minimum”, similar to the Maunder Minimum of the late 17th century, that would swamp warming due to anthropogenic greenhouse gas emissions.

This could be wishful thinking, given recent climate modelling results which show that decreasing solar activity will lead to a temperature difference of at most 0.3 degrees until the end of the century. That is less than 10% of the projected business-as-usual scenarios published by the Intergovernmental Panel on Climate Change (IPCC).

In their modelling study Potsdam climatologists Georg Feulner and Stefan Rahmstorf simulated three particular solar scenarios:

  1. a repeat of the last 11-year solar cycle until 2100
  2. a 0.08% reduction in solar activity (1950 baseline)
  3. a 0.25% reduction in solar activity (1950 baseline)

The first of these corresponds to the IPCC’s business-as-usual projections, while the second reproduces the Maunder Minimum. With no Grand Minimum in solar activity the model indicates a 3.7–4.5 degree temperature rise above the 1961 to 1990 average level, which matches other recent global warming projections. For the Maunder Minimum reconstruction the temperatures in 2100 are just 0.1 degrees lower, and with scenario #3 the difference is 0.26 degrees.

Feulner and Rahmstorf say that a new Maunder-type solar activity minimum cannot offset global warming caused by anthropogenic greenhouse gas emissions. They also add that any effect would be temporary, as solar minima tend to last for no more than a few decades.

Further reading: G Feulner and S Rahmstorf, “On the effect of a new grand minimum of solar activity on the future climate on Earth”, Geophys. Res. Lett., 37, L05707 (2010)