9 May 2005

The world is now warmer than it has been at any point in the last two millennia

An excellent feature New Yorker article series on climate change by Elizabeth Colbert. All need to read this.
There is a very broad consensus in the scientific community that global warming is under way. To the extent that there are conflicting views, they are usually over how exactly the process will play out. This is understandable. The climate affects just about every natural system on earth, and these systems in turn affect the climate. So making predictions is very complicated. Meanwhile, we have only one planet, so it’s impossible to run a controlled experiment. To focus on the degree of disagreement, rather than on the degree of consensus, is, I think, fundamentally misguided. If ten people told you your house was on fire, you would call the fire department. You wouldn’t really care whether some of them thought that the place would be incinerated in an hour and some of them thought it would take a whole day.


Global warming can cause global cooling
Jeff Poling


Scientists announced in the July 21, 1999, edition of the journal Nature findings that suggest that global warming can sometimes lead to cold weather or even a worldwide freeze.

Scientists have long known that a severe cold spell occurred after the end of the Pleistocene glaciation, approximately 8,200 years ago. The cause, however, has been a mystery. The authors of the Nature article write that the centuries long cold spell might have been caused by meltwater from the disappearing glaciers, cooling the North Atlantic.

The Laurentide Ice Sheet covered parts of North America with ice up to two miles thick for more than a million years. When the Earth began to warm 10,000 years ago, it retreated back toward the poles. The ice sheet left in its wake at least two lakes containing more water than the Great Lakes combined.

In the Hudson Bay, ice held the water in place like a plug in a bathtub. When the plug finally melted, trillions of gallons gushed into the Labrador Sea, flowing out at 100 times the rate water leaves the Mississippi.

The conclusions of the authors are the result of a study by University of Colorado and Canadian researchers who examined evidence of this huge flood in the Hudson Bay region of Quebec and Ontario.

Independent research showed that global temperatures dropped significantly within several hundred years of the flood. Until this study, nobody could pinpoint if these two events were connected, said the study's lead author, University of Colorado geologist Don Barber. The scientists used radiocarbon dating of clams in the flood sediment, and other evidence, to correlate the two events.

The Atlantic Gulf Stream normally acts like a conveyor belt to deliver warm tropical water to temperate regions. By adding so much cold fresh water in such a short time, the flood shut down the Gulf Stream, said Richard Alley, a climate expert at Penn State University.

Temperatures in Greenland and Europe dropped by 6 to 15 degrees for at least 200 years, according to ice core data.

The authors conclusions demonstrate how global warming can, paradoxically, provoke a global freeze. If a modern glacier such as the Greenland Ice Sheet melts as a result of rising temperatures in the next century, it could trigger a similar flood and climate fluctuation, the researchers said.
Source: University Of California - Berkeley
Date: 2004-06-03
17th Century Solar Oddity Believed Linked To Global Cooling Is Rare Among Nearby Stars
Berkeley - A mysterious 17th century solar funk that some have linked to Europe's Little Ice Age and to global climate change, becomes even more of an enigma as a result of new observations by University of California, Berkeley, astronomers.

For 70 years, from 1645 until 1714, early astronomers reported almost no sunspot activity. The number of sunspots - cooler areas on the sun that appear dark against the brighter surroundings - dropped a thousandfold, according to some estimates. Though activity on the sun ebbs and flows today in an 11-year cycle, it has not been that quiet since.

Since 1976, when it was pointed out that this lengthy period of low sunspot activity, the so-called Maunder minimum, coincided with the coldest part of the Little Ice Age in Europe and North America, astronomers have been searching nearby sun-like stars for examples of stellar minima. They have hoped to determine how common such minima are and to predict the next solar minimum - and perhaps the next period of global cooling.

Now, data from a group of UC Berkeley astronomers cast doubt on the hundreds of stars thought to be examples of stellar minima analogous to the quiet period the sun experienced 300 years ago.

In a poster to be presented Monday, May 31, at the Denver meeting of the American Astronomical Society, UC Berkeley graduate student Jason Wright shows that nearly all the supposedly sun-like stars displaying minimal activity are, in fact, much brighter than and significantly different from the sun and therefore not examples of Maunder minima. The findings throw into question all studies using these stars to make inferences about the sun's own activity and future minima, Wright said.

"Star surveys typically find that 10 to 15 percent of all sun-like stars are in an inactive state like the Maunder minimum, which would indicate that the sun spends about 10 percent of its time in this state," Wright said. "But our study shows that the vast majority of stars identified as Maunder minimum stars are well above the main sequence, which means they're not sun-like at all, but are either evolved stars or stars rich in metals like iron and nickel. To date, we've found no star that is unambiguously a Maunder minimum star."

"We thought we knew how to detect Maunder minimum stars, but we don't," he said.

The main sequence is a region where normal, steady-burning stars cluster when plotted on a chart of color versus brightness. As stars age, however, they get redder and brighter - becoming what are called subgiant stars - and move upward off the main sequence. The sun has been on the main sequence for about 5 billion years, ever since it settled down after igniting hydrogen fusion in its core, and will remain there for another 5 billion years until it starts to swell and become a subgiant.

"The fact is, we still don't understand what's going on in our sun, how magnetic fields generate the 11-year solar cycle, or what caused the magnetic Maunder minimum," said Wright's advisor, Geoffrey Marcy, professor of astronomy at UC Berkeley. "In particular, we don't know how often a sun-like star falls into a Maunder minimum, or when the next minimum will occur. It could be tomorrow."

The drop in solar activity in the late 17th and early 18th centuries was drawn to the world's attention in 1893 by English astronomer Edward Walter Maunder, who also noted a dip during the same period in the intensity and frequency of the northern lights, which are caused by storms on the sun. Again, in 1976, astronomer John Eddy reviewed various pieces of evidence for the Maunder minimum and concluded not only that it was real, but cited a 1961 paper linking the minimum with a contemporaneous period of cooling throughout Europe, perhaps due to decreased energy output from the sun. The sun, and stars like the sun, are dimmer when inactive.

The idea of a Maunder minimum is controversial, however, because no one really knows how closely people were observing the sun in the mid-1600s, a mere 40 years after the invention of the telescope. No record of solar activity exists before the Maunder minimum, though a surge in activity signaled its end in 1714.

Uncertainty also surrounds the cause of the Little Ice Age, which began around 1300 A.D. and lasted for several hundred years. Characterized by colder than normal winters and cool summers throughout the Northern Hemisphere, it may have been caused by greenhouse gases and particulates spewed into the atmosphere by volcanoes, or by fluctuations in the sun's output.


Many climate experts take the Maunder minimum seriously, however, and astronomers have put together a long list of stars supposedly exhibiting the same dip in activity, as evidenced by decreased emission from the element calcium in the star's atmosphere. Solar activity is characterized by strong magnetic fields that heat the sun's upper atmosphere, or chromosphere, to some 8,000 to 10,000 degrees Kelvin, exciting calcium to emit blue light.

The question, Wright said, is whether the cause of decreased calcium emission is a stellar Maunder minimum or something else, like age - stars spin more slowly as they age, lose their magnetic dynamo and no longer produce magnetic fields or spots - or high metal content. "We've now found that it's not from Maunder minima," he said.

"What astronomers have assumed is that sun-like stars going through a stellar funk are actually very, very old stars whose magnetic fields have turned off forever. They are not in a temporary Maunder minimum, but a permanent one. They're dead," Marcy said. "The sun will be in that state in 4 billion years or so."

"This implies that if other stars do undergo Maunder minima of their own, then it is either a rare occurrence nearly undetected in activity surveys or it is not necessarily indicated by low calcium ... emission levels," Wright wrote. Therefore, he added, some other criterion is needed to discern those stars in a stellar downturn.

The problem with stars thought to be in a Maunder minimum went unnoticed because it wasn't until 1998 that the Hipparcos satellite was launched and began determining the precise distances to many nearby stars. It then became possible to calculate the absolute brightness of these stars, and to place them precisely on a color-brightness plot, known as a Hertzsprung-Russell diagram.

Wright decided to look systematically at Maunder minimum stars after he and Marcy noticed that many seemingly inactive nearby stars were actually brighter than main sequence stars. They have collected spectra of more than 1,000 nearby stars to look for evidence of planets.

In his analysis, Wright used Hipparcos data on distance to determine the absolute brightness of several thousand nearby stars surveyed not only by Marcy's California and Carnegie Planet Search Program but also by other projects, such as the Mount Wilson H-K Project and Project Phoenix. He noted that some of the stars previously identified as Maunder minimum stars may be metal-rich stars, which also burn brighter than our sun and show less activity. Further analysis of nearby stars is needed to characterize these quiet stars.

The findings, which have been submitted to Astrophysical Journal, resulted from work supported by Sun Microsystems, the National Aeronautics and Space Administration, and the National Science Foundation.

"Global warming -- the gradual increase in planet-wide temperatures -- is accepted by most scientists now as a fact. Generally, this warming is attributed to the increase of green-house gases, i.e. chemical pollutants, being spewed into the Earth's atmosphere.

However, some solar scientists are considering whether the warming might be caused, in part, by a periodic but small increase in the Sun's energy output. An increase of just 0.2% in the solar output could have the same affect as doubling the carbon dioxide in the Earth's atmosphere."


"Climatologists and astronomers speaking at the American Association for the Advancement of Science meeting in Philadelphia say the present warming may be unusual - but a mini ice age could soon follow."

"Careful studies over the last 20 years show that its overall brightness and energy output increases slightly as sunspot activity rises to the peak of its 11-year cycle.

And individual cycles can be more or less active.

The sun is currently at its most active for 300 years.

That, say scientists in Philadelphia, could be a more significant cause of global warming than the emissions of greenhouse gases that are most often blamed.

The researchers point out that much of the half-a-degree rise in global temperature over the last 120 years occurred before 1940 - earlier than the biggest rise in greenhouse gas emissions."

"Using ancient tree rings, they show that 17 out of 19 warm spells in the last 10,000 years coincided with peaks in solar activity.

They have also studied other sun-like stars and found that they spend significant periods without sunspots at all, so perhaps cool spells should be feared more than global warming.

The scientists do not pretend they can explain everything, nor do they say that attempts to reduce greenhouse gas emissions should be abandoned. But they do feel that understanding of our nearest star must be increased if the climate is to be understood."


"Global warming may not be caused by humanity's fossil fuel emissions, but could be due to changes in the Sun.

Research suggests that the magnetic flux from the Sun more than doubled this century. As solar magnetism is closely linked with sunspot activity and the strength of sunlight reaching Earth, the increase could have produced warming in the global climate.The evidence for an increasingly energetic Sun comes from a new analysis of the magnetic field between the planets, carried out by scientists at the Rutherford Appleton Laboratory, near Oxford, UK. "




"The most common global warming theories attribute temperature increases to increases in the greenhouse effect caused primarily by anthropogenic (human-generated) carbon dioxide and to possible increases in solar activity."


"Objectively speaking, any environmental change should have both positive benefits and negative effects. For example, theory predicts and observations confirm that human-induced warming takes place primarily in winter, lengthening the growing season. Satellite measurements now show that the planet is greener than it was before it warmed. There are literally thousands of experiments reported in the scientific literature demonstrating that higher atmospheric carbon dioxide concentrations -- cause by human activity -- dramatically increase food production. So why do we only hear one side about global warming?"


"It is really quite amazing by what margins competent but conservative scientists and engineers can miss the mark, when they start with the preconceived idea that what they are investigating is impossible. When this happens, the most well-informed men become blinded by their prejudices and are unable to see what lies directly ahead of them. "

Arthur C. Clarke - Science Writer

Note: portions of the above articles are based on opinions, those opinions, may or may not be the opinion of the poster. These postings are posed solely for informational purposes and may or may not inspire reflection.

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