Climate Change and the Quiet Sun

Something strange, very strange, is happening on the sun. On October 8th, NOAA’s Solar Cycle Progression monthly update report came out.

Sunspot activity has dropped off to its lowest point in over 100 years, perhaps to its lowest since the Dalton Minimum of the early 1800s.

The sun is headed into a quiet phase. The evidence is mounting. Sunspot activity is down. Solar flux is down. The sun’s magnetic field is decreasing linearly toward zero by 2026. The long term trend points towards a less active sun.

Solar physicists believe a prolonged period of low solar activity lasting more than one cycle is coming.

This change in the sun’s behavior could have profound long-term implications for climate change over the next several decades.

What’s Happening on the Sun?

2012 Solar Sunspot Activity through September highlighted in Yellow

The trend for 2012 is set. According to NOAA, September’s sunspot number was 61.5.  After a giant hiccup in solar activity late last year the sunspot number for 2012, so far, has settled down to only 59.5.

By international standard, the sunspot number is a measure of the average number of sunspots over time, usually a year. Monthly averages are also published during the year. That is what NOAA just reported. See 2012’s sunspot numbers highlight in yellow above.

Magnetic Field Trend Line

Its certainly possible sunspot activity could pick up. The sun is prone to wild fluctuations, but unlikely to go up much this time. The peak of sunspot activity this cycle has already passed for the sun’s northern hemisphere.

Even if 2013’s forecast high of 75 is reached it would still be among the lowest on record. It doesn’t look like even that will be reached.

The last sunspot cycle, cycle 23, had an unexpectedly long minimum extended nearly two years. Solar sunspot activity this cycle is half what it was last cycle.

The Great Solar Divide

Reporting on the Japanese Hinode mission to the sun, NASA says an asymmetry has developed between the sun’s northern and southern hemispheres.

During every solar cycle sunspot activity begins at its equator and advances toward the poles until it peaks at about 76º north and south. What is different about this cycle is the northern progression has already peaked and turned around. The south still has a ways to go before it peaks. Its flattening out solar maximum.

This flattening asymmetry is turning the world of solar physics upside down. The current model will have to change. Space weather forecasting, an infant science, is evolving rapidly.

As recently as August 2004, NASA’s David Hathaway forecast the current solar cycle would peak at 145 in 2010! Every time since then he (and others) have lowered the peak and pushed it further out. Hathaway’s current prediction is down to 75 that peaks in late 2013.

Its exciting! Hinode and other instruments are studying the current solar cycle, cycle 24, to a deeper level of detail than ever before. That promises to increase our understanding of solar physics and greatly advance the ability to predict the sun’s future behavior.

Trends in Solar Activity

Yellow highlight shows current solar cycle (24) near solar max as of October 2012

In 1700 the sun was just coming out of the longest period of sunspot inactivity known. It is called the Maunder Minimum. The Dalton Minimum followed closely on its heels. It lasted for two solar cycles in the early 1800s.

That was followed by the Modern Maximum that peaked the middle of last century. That maximum is among the highest periods of solar activity of the last 11,500 years going back to the last ice age.

Solar activity has been on the decline ever since.

Now solar physicists tell us to expect another minimum lasting more than one cycle.

Solar Activity and Climate Change

The Maunder and Dalton minimums share something in common. Both are associated with cold periods in Earth’s climate history. The time of the Maunder Minimum is often referred to as the “Little Ice Age“.

It is probably not entirely by chance that the Modern Maximum and another earlier period of high solar activity, the Medieval Warm Period, both correspond to warmer temperatures in Earth’s recent climate history.

In the satellite era it has been found the sun varies in radiant energy from 0.1% to 0.2% over a solar cycle. It is hottest during maximum solar activity. That could be a forcing mechanism driving historical climate change, just like the IPCC says CO2 is today.

It is unknown what the cooling effect of a prolonged period of inactivity might be. Physics cannot yet answer that question, but a long history of anecdotal empirical evidence suggests it does.

Conclusions

There is little doubt that human CO2 emissions have played a significant role in Earth’s current warm period. The Earth is about 1°C warmer than it was in 1880.

The IPCC has considered but rejected solar activity as a cause. The IPCC has rejected all possible causes of current global warming except AGW – Anthropogenic (human caused) Global Warming.

Times are a changin’! The impact of solar variation is becoming clearer.

The amount of irradiance change so far directly measured on the sun is insufficient to explain the global warming observed. But direct radiant energy variations have only been measurable since about 1975, a period covering three of the highest solar cycles ever seen.

It is completely unknown how much cooling happens during prolonged periods of inactivity like we are entering now. That has yet to be measured. The lesson of history teaches us there will be a noticeable effect.

Here is the $100 trillion question:
Will AGW or solar variation dominate climate change in the coming decades?