Peer reviewed science: breakthroughs about the sun’s impact on Earth’s climate

Solar cycle 24 remains missing in action, as NASA reports today:  “Are Sunspots Disappearing?” — Excerpt:

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. The quiet has dragged out for more than 2 years, prompting some observers to wonder, are sunspots disappearing?

“Personally, I’m betting that sunspots are coming back,” says researcher Matt Penn of the National Solar Observatory (NSO) in Tucson, Arizona. But, he allows, “there is some evidence that they won’t. … Sunspot magnetic fields are dropping by about 50 gauss per year … If we extrapolate this trend into the future, sunspots could completely vanish around the year 2015.”

… If sunspots do go away, it wouldn’t be the first time. In the 17th century, the sun plunged into a 70-year period of spotlessness known as the Maunder Minimum that still baffles scientists. The sunspot drought began in 1645 and lasted until 1715; during that time, some of the best astronomers in history (e.g., Cassini) monitored the sun and failed to count more than a few dozen sunspots per year, compared to the usual thousands.

“Whether [the current downturn] is an omen of long-term sunspot decline, analogous to the Maunder Minimum, remains to be seen,” Livingston and Penn caution in a recent issue of EOS. “Other indications of solar activity suggest that sunspots must return in earnest within the next year.”

The famous and controversial Livingston – Penn appears below as article #1; their new EOS article is #2.

Possible implications of a quiet sun for Earth

What does an quiet sun do to Earth’s climate?  The historical record suggests global cooling.  For example, the Maunder Minimum overlapped the Little Ice Age. But scientists had both little evidence and fewer explanations.  That’s slowly changing, with an accellerating drumbeat of research results in recent years.  Slowly they begin to understand the mechanisms at work.

Here are several articles.   The first two look at the solar cycle, the rest at its effects on Earth.  No answers yet, just cutting-edge science.  For each is a summary for laypeople, then the abstract of the article.  At the end are links to previous articles about the solar cycle and us.

Previous articles like this provoked firestorms, as pro-global warming zealots mocking these scientists.  For examples see High school science facts prove global warming! Skeptical scientists humiliated by this revelation!  As before, I suggest that folks with such urges directly contact these scientists.

Excerpts

(1-a)  “New Solar Cycle Not Packing Much Punch“, The Arizona Daily Star, 19 May 2008 — Description of the controversial Livingston and Penn paper predicating a “small” solar cycle, probably meaning a cold cycle.  Excerpt:

The paper, rejected in peer review, was never published by Science. Livingston said he’s OK with the rejection.  “I accept what the reviewers said,” Livingston said. “‘If you are going to make such statement, you had better have strong evidence.’ “  Livingston said their projections were based on observations of a trend in decreasingly powerful sunspots but reviewers felt it was merely a statistical argument. 

“We may have to wait. We may be wrong. (But) the sun is going to entertain us one way or another,” he said.

(1-b)  “Sunspots may vanish by 2015“, William Livingston and Matthew Penn, National Solar Observatory, 2006 — Unpublished, 10 pages.  Abstract:

We have observed spectroscopic changes in temperature sensitive molecular lines, in the magnetic splitting of an Fe I line, and in the continuum brightness of over 1000 sunspot umbrae from 1990-2005. All three measurements show consistent trends in which the darkest parts of the sunspot umbra have become warmer (45K per year) and their magnetic field strengths have decreased (77 Gauss per year), independently of the normal 11-year sunspot cycle. A linear extrapolation of these trends suggests that few sunspots will be visible after 2015.

(2)  “Are Sunspots Different During This Solar Minimum?“, William Livingston and Matthew Penn, EOS (of the American Geophystical Union), 28 July 2009 — Note that I cannot find a copy of this at the EOS website.

(3-a)  “Solar Cycle Linked To Global Climate“, ScienceDaily, 17 July 2009 — Excerpt:

Establishing a key link between the solar cycle and global climate, research led by scientists at the National Science Foundation (NSF)-funded National Center for Atmospheric Research (NCAR) in Boulder, Colo., shows that maximum solar activity and its aftermath have impacts on Earth that resemble La Niña and El Niño events in the tropical Pacific Ocean.

… “These results are striking in that they point to a scientifically feasible series of events that link the 11-year solar cycle with ENSO, the tropical Pacific phenomenon that so strongly influences climate variability around the world,” says Jay Fein, program director in NSF’sDivision of Atmospheric Sciences. “The next step is to confirm or dispute these intriguing model results with observational data analyses and targeted new observations.”

(3-b)  “A Lagged Warm Event–Like Response to Peaks in Solar Forcing in the Pacific Region“, Gerald A. Meehl et al, Journal of Climate, July 2009 — Abstract:

The forced response coincident with peaks in the 11-yr decadal solar oscillation (DSO) has been shown to resemble a cold event or La Niña–like pattern during December–February (DJF) in the Pacific region in observations and two globalcoupled climate models. Previous studies with filtered observational and model data have indicated that there could be a lagged warm event or El Niño–like response following the peaks in the DSO forcing by a few years. Here, observations and two climate model simulations are examined, and it is shown that dynamical coupled processes initiated by the response in the tropical Pacific to peaks in solar forcing produce wind-forced ocean Rossby waves near 5°N and 5°S. These reflect off the western boundary, producing downwelling equatorial Kelvin waves that contribute to transitioning the tropical Pacific to a warm event or El Niño–like pattern that lags the peaks in solar forcing by a few years.

(4-a)  “New Temperature Reconstruction From Indo-Pacific Warm Pool“, ScienceDaily, 28 August 2009 — Excerpt:

A new 2,000-year-long reconstruction of sea surface temperatures (SST) from the Indo-Pacific warm pool (IPWP) suggests that temperatures in the region may have been as warm during the Medieval Warm Period as they are today.

The IPWP is the largest body of warm water in the world, and, as a result, it is the largest source of heat and moisture to the global atmosphere, and an important component of the planet’s climate. Climate models suggest that global mean temperatures are particularly sensitive to sea surface temperatures in the IPWP. Understanding the past history of the region is of great importance for placing current warming trends in a global context.

(4-b)  “2,000-year-long temperature and hydrology reconstructions from the Indo-Pacific warm pool“, Delia W. Oppo, Nature, 28 August 2009 — Abstract:

Northern Hemisphere surface temperature reconstructions suggest that the late 20thcentury was warmer than any other time during the past 500 years and possibly any time during the past 1,300 years. These temperature reconstructions are based largely on terrestrial records from extra-tropical or high-elevation sites; however, global average surface temperature changes closely follow those of the global tropics3, which are 75% ocean. In particular, the tropical Indo-Pacific warm pool (IPWP) represents a major heat reservoir that both influences global atmospheric circulation and responds to remote northern high-latitude forcings.

Here we present a decadally resolved continuous sea surface temperature (SST) reconstruction from the IPWP that spans the past two millennia and overlaps the instrumentalrecord, enabling both a direct comparison of proxy data to the instrumental record and an evaluation of past changes in the context of 20th century trends.

Our record from the Makassar Strait, Indonesia, exhibits trends that are similar to a recent Northern Hemisphere temperature reconstruction. Reconstructed SST was, however, within error of modern values from about ad 1000 to ad 1250, towards the end of the Medieval Warm Period.

SSTsduring the Little Ice Age (approximately ad 1550–1850) were variable, and 0.5 to 1 °C colder than modern values during the coldest intervals. A companion reconstruction of 18O of sea water — a sea surface salinity and hydrology indicator—indicates a tight coupling with the East Asian monsoon system and remote control of IPWPhydrology on centennial–millennial timescales, rather than a dominant influence from local SST variation.

(5-a)  “Small Fluctuations In Solar Activity, Large Influence On Climate“, ScienceDaily, 17 July 2009 — Excerpt:

Subtle connections between the 11-year solar cycle, the stratosphere, and the tropical Pacific Ocean work in sync to generate periodic weather patterns that affect much of the globe, according to research appearing this week in the journal Science. The study can help scientists get an edge on eventually predicting the intensity of certain climate phenomena, such as the Indian monsoon and tropical Pacific rainfall, years in advance.

An international team of scientists led by the National Center for Atmospheric Research (NCAR) used more than a century of weather observations and three powerful computer models to tackle one of the more difficult questions in meteorology: if the total energy that reaches Earth from the Sun varies by only 0.1 percent across the approximately 11-year solar cycle, how can such a small variation drive major changes in weather patterns on Earth?

The answer, according to the new study, has to do with the Sun’s impact on two seemingly unrelated regions. Chemicals in the stratosphere and sea surface temperatures in the Pacific Ocean respond during solar maximum in a way that amplifies the Sun’s influence on some aspects of air movement. This can intensify winds and rainfall, change sea surface temperatures and cloud cover over certain tropical and subtropical regions, and ultimately influence global weather.

“The Sun, the stratosphere, and the oceans are connected in ways that can influence events such as winter rainfall in North America,” says NCAR scientist Gerald Meehl, the lead author. “Understanding the role of the solar cycle can provide added insight as scientists work toward predicting regional weather patterns for the next couple of decades.”

(5-b)  “Amplifying the Pacific Climate System Response to a Small 11-Year Solar Cycle Forcing“,  Gerald A. Meehl et al, Science, 28 August 2009 — Abstract:

One of the mysteries regarding Earth’s climate system response to variations in solar output is how the relatively small fluctuations of the 11-year solar cycle can produce the magnitude of the observed climate signals in the tropical Pacific associated with such solar variability. Two mechanisms, the top-down stratospheric response of ozone to fluctuations of shortwave solar forcing and the bottom-up coupled ocean-atmosphere surface response, are included in versions of three global climate models, with either mechanism acting alone or both acting together. We show that the two mechanisms act together to enhance the climatological off-equatorial tropical precipitation maxima in the Pacific, lower the eastern equatorial Pacific sea surface temperatures during peaks in the 11-year solar cycle, and reduce low-latitude clouds to amplify the solar forcing at the surface.

(6)      Interesting article, but no summary for laypeople; it was not a hot topic last year.

“A Coupled Air–Sea Response Mechanism to Solar Forcing in the Pacific Region“, Gerald A. Meehl et al, Journal of Climate, 15 June 2008 — Abstract:

The 11-yr solar cycle [decadal solar oscillation (DSO)] at its peaks strengthens the climatological precipitation maxima in the tropical Pacific during northern winter. Results from two globalcoupled climate model ensemble simulations of twentieth-century climate that include anthropogenic (greenhouse gases, ozone, and sulfate aerosols, as well as black carbon aerosols in one of the models) and natural (volcano and solar) forcings agree with observations in the Pacific region, though the amplitude of the response in the models is about half the magnitude of the observations. These models have poorly resolved stratospheres and no 11-yr ozone variations, so the mechanism depends almost entirely on the increased solar forcing at peaks in the DSOacting on the ocean surface in clear sky areas of the equatorial and subtropical Pacific.

Mainly due to geometrical considerations and cloud feedbacks, this solar forcing can be nearly an order of magnitude greater in those regions than the globally averaged solar forcing. The mechanism involves the increased solar forcing at the surface being manifested by increased latent heat flux and evaporation. The resulting moisture is carried to the convergence zones by the trade winds, thereby strengthening the intertropical convergence zone (ITCZ) and the South Pacific convergence zone (SPCZ). Once these precipitation regimes begin to intensify, an amplifying set of coupled feedbacks similar to that in cold events (or La Niña events) occurs. There is a strengthening of the trades and greater upwelling of colder water that extends the equatorial cold tongue farther west and reduces precipitation across the equatorial Pacific, while increasing precipitation even more in the ITCZ and SPCZ.

Experiments with the atmosphere component from one of the coupled models are performed in which heating anomalies similar to those observed during DSO peaks are specified in the tropical Pacific. The result is an anomalous Rossby wave response in the atmosphere and consequent positive sea level pressure (SLP) anomalies in the North Pacific extending to western North America. These patterns match features that occur during DSO peak years in observations and the coupled models.

Afterword

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For more information

To read other articles about these things, see the FM reference page on the right side menu bar. Of esp relevance to this topic:

• About Science & Nature – my articles
• About Science & nature – studies & reports (esp section 4 about the solar cycle)
• About Science & Nature – general media articles
• About Science & Nature – the history of climate fears

Posts on the FM site about the solar cycle:

1. Worrying about the Sun and climate change: cycle 24 is late, 10 July 2008
2. Update: is Solar Cycle 24 late (a cooling cycle, with famines, etc)?, 15 July 2008
3. Solar Cycle 24 is still late, perhaps signalling cool weather ahead, 2 September 2008
4. Update on solar cycle 24 – and a possible period of global cooling, 1 October 2008
5. This week’s report on the news in climate science, 7 December 2008
6. Weekend reading recommenations about climate change, 13 December 2008
7. An important new article about climate change, 29 December 2008
8. My “wish list” for the climate sciences in 2009, 2 January 2009
9. About the recent conference ”Solar Activity during the onset of Solar Cycle 24″, 3 January 2009
10. Important new climate science articles, 11 January 2009
11. NASA: Sun undergoing a “deep solar minimum”, 13 April 2009
12. The Unusually Quiet Sun finally gets some attention, 23 April 2009
13. A brief look at the Sun’s influence on Earth’s climate, 4 May 2009
14. An important puzzle from the National Weather Service’s Space Weather Prediction Center, 10 May 2009