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Thursday, December 31, 2009

Joseph Romm: The hottest decade ends and since there’s no Maunder mininum — sorry deniers! — the hottest decade begins

The hottest decade ends and since there’s no Maunder mininum — sorry deniers! — the hottest decade begins

2009 ends with a "sunspot surge" as solar cycle 24 revs up, though the sun is increasingly a bit player in the global warming trend

by Joseph Romm, Climate Progress, December 31, 2009

The figure is from, in its “Sunspot Surge” post.

The 2000s were  the hottest decade in recorded history by far — even though we’re at “the deepest solar minimum in nearly a century.”  The 2000s were a full 0.2 °C warmer than the 1990s, which of course had been the hottest decade on record, 0.14 °C warmer than 1980s (according to the dataset that best tracks planetary warming).  Hmm.  It’s almost like the warming is accelerating.

There’s little doubt the 2010s will be the hottest decade on record, barring multiple supervolcanoes.  Yet when the anti-science crowd isn’t perversely spending their time trying to stop all efforts to cut global warming pollution that might slow warming, they are perversely trying to convince the public and policymakers we’re not warming at all.  That’s why many of them have been rooting for this deep solar minimum to become a Maunder Minimum, to mute the warming signal and hence the motivation for action for a few more years.  Yes, they have a self-destructive streak.

In fact, even if total solar irradiance (TSI) never recovered, we wouldn’t have entered a period of cooling since, “the negative forcing, relative to the mean solar irradiance is equivalent to seven years of CO2 increase at current growth rates,” as NASA noted in January 2009.  Heck, even with a La Niña and an unusually inactive sun, 2008 was almost 0.1 °C warmer than the hot decade of the 1990s as a whole.  And 2009 now seems likely to be the second hottest year on record after 2005.  Changes in the sun just ain’t the big dog anymore when it comes to driving climate change (see below).

When we last looked at the sun [please, don't try that at home], NASA was reporting that the sunspot cycle was about to come out of its depression, if a newly discovered mechanism for predicting solar cycles — a migrating jet stream deep inside the sun — proved accurate (see National Solar Observatory, NASA say no “Maunder Minimum”).

It now appears TSI is well on its way to recovering, as NASA and others had predicted.  Leif Svalgaard recently put up this figure (click to enlarge): says of its sunspot figure at the top of the page:
The dark line is a linear least-squares fit to the data. If the trend continues exactly as shown (prediction: it won’t), sunspots will become a non-stop daily occurrence no later than February 2011. Blank suns would cease and solar minimum would be over.

If the past two years have taught us anything, however, it is that the sun can be tricky and unpredictable. Stay tuned for surprises.
Even as Solar Cycle 24 picks up, it won’t affect global temperatures quickly.  Again, as  NASA explained in January:
Because of the large thermal inertia of the ocean, the surface temperature response to the 10-12 year solar cycle lags the irradiance variation by 1-2 years. Thus, relative to the mean, i.e., the hypothetical case in which the sun had a constant average irradiance, actual solar irradiance will continue to provide a negative anomaly for the next 2-3 years.
Also, Solar Cycle 24 has recently been predicted to be on the wimpy side.

The sun simply isn’t a big player in driving recent warming.  As a major 2009 study found (see Another long-debunked denier talking point is debunked again: Changes in the Sun are not causing global warming):
According to this analysis, solar forcing contributed negligible long-term warming in the past 25 years and 10% of the warming in the past 100 years.
And a major 2007 study concluded:
Here we show that over the past 20 years, all the trends in the Sun that could have had an influence on the Earth’s climate have been in the opposite direction to that required to explain the observed rise in global mean temperatures.
Related scientific studies on the subject can be found on the excellent debunking website, Skeptical Science.  Here’s but a few:
  • Erlykin 2009: “We deduce that the maximum recent increase in the mean surface temperature of the Earth which can be ascribed to solar activity is 14% of the observed global warming”
  • Benestad 2009: “Our analysis shows that the most likely contribution from solar forcing a global warming is 7 ± 1% for the 20th century and is negligible for warming since 1980.”
  • Lockwood 2008: “It is shown that the contribution of solar variability to the temperature trend since 1987 is small and downward; the best estimate is −1.3% and the 2σ confidence level sets the uncertainty range of −0.7 to −1.9%.”
  • Lockwood 2008: “The conclusions of our previous paper, that solar forcing has declined over the past 20 years while surface air temperatures have continued to rise, are shown to apply for the full range of potential time constants for the climate response to the variations in the solar forcings.”
  • Ammann 2007: “Although solar and volcanic effects appear to dominate most of the slow climate variations within the past thousand years, the impacts of greenhouse gases have dominated since the second half of the last century.”
  • Lockwood 2007: “The observed rapid rise in global mean temperatures seen after 1985 cannot be ascribed to solar variability, whichever of the mechanism is invoked and no matter how much the solar variation is amplified.”
  • Foukal 2006 concludes “The variations measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years.”
By one recent estimate, human-caused greenhouse gas emissions are responsible for “80 to 120% of the warming” in recent decades (see “What percentage of global warming is due to human causes vs. natural causes?“)

Human-caused emissions are simply driving climate change to dangerous levels with forcings that dwarf previous natural forcings both in speed and scale (see “Humans boosting CO2 14,000 times faster than nature, overwhelming slow negative feedbacks“).

And that’s why the time to act is now, so every decade this century isn’t the hottest decade on record, with unimaginably catastrophic consequences for the health and well-being of our children and grandchildren and their children and grandchildren.


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