Wednesday, July 22, 2015

The Ice Age Cometh?

Recent media reports have claimed that a drop in solar activity will lead to a mini-Ice Age within the next 15 years.  Unfortunately, even press reports from science-related media such as Science Daily, have been riddled with errors.

Let's get the biggest one out of the way first.  Zharkova et al. (2015) did not predict a new Little Ice Age (LIA).  What they did was use principle component analysis to detect and model magnetic waves within the sun.  They found that there were two such waves, each with an 11-year cycle, that either interfered with each other when sunspot activity was low or magnified each other when sunspot activity was high.  They then ran their statistical model ahead to make a prediction for the next solar cycle and found that their model predicts that the waves should cancel each other out, resulting in their subsequent prediction that solar activity should drop to levels not seen since the Maunder Minimum.  That bit about the Maunder Minimum is what set off the media, as the Maunder Minimum coincided with the coldest time period of the Little Ice Age.

Unfortunately for the journalists and editors who made that connection and then made the claim that a new Little Ice Age would begin within 15 years, they are dead wrong.  First, multiple research papers have found that a new Maunder Minimum would shave a maximum of 0.3ºC off the expected rise in global temperatures by AD 2100 (Feulner and Rahmstorf 2010, Jones et al. 2012, Anet et al. 2013, Meehl et al. 2013).  So the world would warm by "only" 3.7ºC rather than 4ºC.  Furthermore, the impacts would be largely regional, not global, and temporary.  Ineson et al. (2015) found that the greatest cooling would fall on Europe and the eastern US during winter but that global temperature as a whole could be largely unchanged.  Once the new minimum ended, regional temperatures would warm back up.

Second, solar activity decoupled from global temperature in the 1970s.  Solar activity peaked in the late 1950s and then again around 1980 and has declined sharply since whereas global temperatures rose.  In short, global temperatures are controlled by something other than solar activity now.

Third, research shows that the Little Ice Age began and was sustained by volcanic eruptions, not solar activity (Miller et al. 2012).  And contrary to the Science Daily article, the LIA began in AD 1300, not AD 1645 as that article wrongly claimed.  The timing of the Maunder Minimum, coinciding with the coldest part of the LIA, gave the false appearance of a link between the two.

Fourth, there is a lot more CO2 and other greenhouse gases in the atmosphere now than there was during the Maunder Minimum.  The 12-month moving average for CO2 is now 399.34 ppmv.  Pre-industrial CO2 levels were around 280 ppmv, which means that there is now 1.89 W/m2 of extra energy being trapped by Earth's atmosphere that wasn't there during the Maunder Minimum.  That translates into a temperature rise of 1.53ºC, greater than the drop the Earth experienced during the Maunder Minimum.

Last, the Little Ice Age was just that—little on the global scale.  Using the global data from Marcott et al. (2013), the Little Ice Age was a mere blip compared to how temperatures have risen since.


Global temperatures over the LIA declined by about 0.2ºC over 550 years.  Temperatures have risen by 0.8ºC in the 160 years since the LIA ended.  Even if we did have another LIA, then all it would do is return global temperatures to about where they were around 1980, which is a far cry from where they were during the Maunder Minimum.

To sum all of this up, there is no new ice age coming, even if the sun does repeat the Maunder Minimum.  Instead, we can expect temperatures to continue rising as CO2 levels increase due to the 30+ billion metric tons of CO2 we spew into the atmosphere each year. 

Likely global temperature rise in the near future. The thick dashed line represents the continuation of the trend. The thinner dashed lines mark one standard deviation and two standard deviations from the trend, respectively.

Abraham Lincoln once quipped that his opponents "had their facts absolutely right but were drawing the wrong conclusion."  Those journalists who wrote that another mini-Ice Age was coming not only drew the wrong conclusion—they also got their facts absolutely wrong.

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