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ARE SUNSPOTS DISAPPEARING?
The sun is in the pits of the deepest solar minimum in nearly a
century. Weeks and sometimes whole months go by without even a single
tiny sunspot. Are sunspots disappearing? Experts discuss the question
in today's
story from Science@NASA.
SOLAR MINIMUM VS.
GLOBAL WARMING: From 2002 to 2008, decreasing
solar irradiance has countered much anthropogenic warming of Earth's
surface. That's the conclusion of researchers Judith Lean (NRL)
and David Rind (NASA/GISS), who have just published a new analysis
of global temperatures in the Geophysical Research Letters.
Lean and Rind considered four drivers of climate change: solar activity,
volcanic eruptions, ENSO (El Nino), and the accumulation of greenhouse
gases. The following plot shows how much each has contributed to
the changing temperature of Earth's surface since 1980:
Volcanic aerosols are a source of cooling; ENSO and greenhouse
gases cause heating; the solar cycle can go either way. When added
together, these factors can account for 76% of the variance in Earth's
surface temperature over the past ~30 years, according to the analysis
of Lean and Rind.
Several aspects of their model attract attention: "The warmest
year on record, 1998, coincides with the 'super-El Nino' of 1997-98,"
points out Lean. "The ESNO is capable of producing significant
spikes in the temperature record." Solar minimum has the opposite
effect: "A 0.1% decrease in the sun's irradiance has counteracted
some of the warming action of greenhouse gases from 2002 - 2008,"
she notes. "This is the reason for the well-known 'flat' temperature
trend of recent years."
What's next? Ultimately, the authors say, temperatures will begin
rising again as greenhouse gases accumulate and solar activity resumes
with the coming of the next solar cycle. Of couse, the solar cycle
could be out
of whack; if solar minimum deepens and persists, no one is certain
what will happen. Lean and Rind reveal their predictions
for the future here.
Reference: Lean, J. L., and D. H. Rind (2009),
How will Earth's surface temperature change in future decades?,
Geophys. Res. Lett., 36, L15708
FAITH FULL MOON:
"I'm spending the Labor Day weekend up in Yellowstone National
Park," reports astronomy professor Jimmy
Westlake of Colorado Mountain College. "I took the opportunity
to capture an eruption of the Old
Faithful geyser in front of the beautiful full Moon." He
calls this snapshot Faith Full Moon:
"The Moon is visible through the top of Old Faithful's steamy
plume," he points out. "I took the picture using a Fuji
Finepix S2 digital camera set at ISO 800 for a 4-second exposure."
Readers in Yellowstone should note that this scene will repeat
itself about every
two hours throughout the night. Grab your camera!
August
2009 Aurora Gallery
[previous Augusts: 2008,
2007, 2006,
2005, 2004,
2003, 2002,
2001]
Explore
the Sunspot Cycle
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