Ice Age predictions are premature

A Scene on the Ice

A Scene on the Ice

The internet has been full of speculation about the late start of Solar Cycle 24, with some voices predicting an abrupt drop in global average temperatures associated with a prolonged sun spot minimum, like one that affected temperatures in the early nineteenth century.

While it was quickly rebutted within the mainstream scientific community, the speculation has continued to provide a source of comfort for those who remain skeptical about global warming.

The case for a predicted drop in global average temperatures triggered by sunspots was put by Phil Chapman in an opinion piece, “Sorry to ruin the fun, but an ice age cometh” in The Australian.  Chapman, born in Melbourne and raised in Paramatta, is a former American astronaut and has a long history as an adviser to the US government on space research, and he has also worked in some commercial space programs.  In the piece, Chapman argues that a 0.7C drop in global temperature from January 2007 to January 2008, and the scarcity of sun spots from the new Solar Cycle 24, point to an abrupt change in the global weather.  He says, “If the temperature does not soon recover, we will have to conclude that global warming is over.”

The link to the Little Ice Age is a phenomenon known as the Dalton Minimum, named after its discoverer John Dalton.  A Cumbrian-born Quaker best known as the inventer of the modern atomic theory, Dalton was also a pioneer of meteorology who kept a meteorological diary comprising about 200,000 observations from 1787 until his death in 1844, encompassing a minimum in solar activity roughly from 1790 to 1830 that coincided with a marked drop in global temperature (at least in the Northern hemisphere).  It isn’t the only such minimum, the Maunder Minimum (1645 to 1715) and the Spörer Minimum (1420 to 1570), and all three seem to have coincided with lower than average global temperatures.  Because of the apparent correlations, there are some suggestions that such sunspot activity may have an effect on the global weather, but at present there is considerable skepticism about this because of the failure to find a possible mechanism.

Nevertheless, Chapman claims that the expected increasing solar activity hasn’t materialized.  “The sunspot number follows a cycle of somewhat variable length, averaging 11 years. The most recent minimum was in March last year. The new cycle, No.24, was supposed to start soon after that, with a gradual build-up in sunspot numbers.”  On this basis, he speculates that “the odds are at least 50-50 that we will see significant cooling rather than warming in coming decades”.

Chapman also raises the possibility of an imminent end of the present interglacial and a return to the status quo (in which most of Europe is covered by glaciers).  It’s certain that this will occur, it’s just a matter of when.  Chapman estimates the chance that the 0.7K drop is a sign of the end of the interglacial as “perhaps one in 500, but not totally negligible.” If he’s right then we have a real live Ice Age on our hands.

A rebuttal, “Warming trend has not reversed“, was published in April 29 in the same newspaper by Australian climatologist David Karoly.  Karoly is a leading member of the Intergovernmental Panel on Climate Change (IPCC).

Karoly says that the 0.7K drop is not unprecedented, and that “similar dramatic falls occurred from 1998 to 1999, and from 1973 to 1974” when each coincided with a “rapid change from El Nino to La Nina conditions, from warm temperatures in the eastern equatorial Pacific Ocean to cold temperatures in the same region, which has a significant effect on global climate patterns and global average temperature.”  As a consequence of this shift, he says, “2008 is likely to be about 0.3C cooler than the average of the previous few years.”  Moreover, “the annual average temperature for 2007 was within 0.1C of the average temperature in 2006 and 2005; no dramatic cooling there.”

Karoly also refutes Chapman’s sunspot claims, citing two well respected data sources to conclude that “the average number of sunspots a day last January was 3.4, followed by 2.1 in February and 9.3 in March. The minimum was in October 2007.”  He also notes that any correlation between sunspot numbers and global temperatures is not evident on a monthly timescale, and the effect on a yearly timescale “is very small, as can be found by correlating the variations of global average temperature on monthly or annual timescales with the sunspot numbers.”  Karoly also criticizes Chapman for “[making] conclusions about long-term climate trends from inter-annual climate variations,”  He restates the conclusion of the IPCC that “Most of the increase in global average temperature over the past 50 years is due to the increase in greenhouse gases in the atmosphere” and the trend is set to continue through the 21st century.  An ice age,” he says, “is definitely not going to occur in the 21st century.”

Despite this, Chapman’s message was picked up by Lawrence Solomon, columnist for the conservative Canadian daily, the National Post, in his series The Deniers in which he highlights scientists who dissent from the consensus on climate change.  On May 31, he highlighted Chapman’s article in “The Deniers: Our spotless sun“.  He does not mention Karoly’s April 29 rebuttal.

In July, NASA issued a feature, “What’s Wrong with the Sun? (Nothing)” in which it reports NASA solar physicist David Hathaway as saying: “There have been some reports lately that Solar Minimum is lasting longer than it should. That’s not true. The ongoing lull in sunspot number is well within historic norms for the solar cycle…It does seem like it’s taking a long time, but I think we’re just forgetting how long a solar minimum can last.”  There are records from the early twentieth century of periods of low sunspot activity lasting twice the length of the current minimum.”

Hathaway continues: “The average period of a solar cycle is 131 months with a standard deviation of 14 months. Decaying solar cycle 23 (the one we are experiencing now) has so far lasted 142 months–well within the first standard deviation and thus not at all abnormal. The last available 13-month smoothed sunspot number was 5.70. This is bigger than 12 of the last 23 solar minimum values…the current minimum is not abnormally low or long…We have already observed a few sunspots from the next solar cycle.  This suggests the solar cycle is progressing normally.”

Sunspots from a new cycle appear at high latitudes, and with reversed magnetic polarity, those from an older cycle tend to appear near the solar equator.  The first sunspot of the new cycle, Cycle 24, appeared in January, 2008.

To forestall cries of “Global Warming is a Hoax”, I’ll link to this blog by Tim Lambert.  That isn’t what this article is about.

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2 Responses

  1. […] space exploration, sunspots, the sun, ulysses, unmanned spaceflight A week or so ago, in “Ice Age Predictions are premature“, I discussed some speculation resulting from observations of the current solar cycle end.  […]

  2. […] a comment » A couple of months ago, in “Ice Age predictions are premature”,  I discussed an alternative climate theory that has been exciting anthropogenic climate change […]

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