Naked Science Forum
Life Sciences => The Environment => Topic started by: SkepticSam on 17/09/2009 00:58:35
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When the sun goes quiet Earth shivers
STEPHEN CAUCHI
September 13, 2009
THE sun has gone quiet, with a sharp decline in sunspot numbers in the past couple of years - possibly heralding the start of a solar depression that could lead to cooler weather on Earth.
During the past millennium, whenever the sun experienced long periods of low sunspot numbers, Earth had equally long, cold snaps. The number of sunspots - dark and intensely magnetic blotches on the sun's surface - are at their lowest since 1913.
''This is the quietest sun we've seen in almost a century,'' said NASA solar forecaster David Hathaway.
''Since the space age began in the 1950s, solar activity has been generally high. Five of the most intense solar cycles on record have occurred in the past 50 years. We're just not used to this type of deep calm.''
Sunspots cause other solar activity such as solar flares and coronal mass ejections, radiation from which can interfere with Earth's magnetic field, upper atmosphere and, many scientists believe, Earth's climate.
There have been more than 200 spotless days so far this year and scientists expect the count to reach 290 by year's end. Last year there were 266 spotless days, the previous lowest number recorded since 1913, when there were 311 spotless days.
Sunspot numbers move in regular cycles of 11 years, so the timing of this quiet spell is not unexpected. What is unexpected is the depth and length of the spell. Some scientists believe it may be the start of a long period when the entire cycle is depressed, as it has been several times during the past millennium.
The most famous depression was the Maunder Minimum of 1645 to 1715 in which sunspots nearly vanished for 70 years. It coincided with the coldest period of the Little Ice Age.
''People are wondering about whether we're going into another Maunder Minimum or not,'' said Iver Cairns, from the University of Sydney's school of physics. ''I think the balance of opinion is that it's too early to tell. But it could be very significant.''
Professor Cairns said the fluctuation in sunspot numbers was not fully understood but it was linked to the ''magnetic dynamo of the sun''.
It was equally uncertain how - or indeed if - changes in solar activity affect Earth's climate.
''What some people think is that energetic particles from the sun get into Earth's magnetosphere and some of them get down to the ozone layer - you're talking 40 to 80 kilometres above the surface of Earth. They alter the chemistry of that layer … That changes the chemistry of other layers of the atmosphere, leading to winds and changes in temperature,'' he said.
http://www.smh.com.au/environment/when-the-sun-goes-quiet-earth-shivers-20090912-flhk.html
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I have serious doubts that this will turn into a Maunder type minimum. Low solar activity would have to go on for another 70 years or so. The most likely scenario at this point (from available evidence anyway) is that cycle 24 will pick up sometime next year, but will be pretty mild when compared to 22, 21 and 18 (the REALLY big one).
*IF* (and that is a BIG if) this is the beginning of a Maunder (or even Dalton) type minimum it would be disastrous to the climate system, though it is an absolute worst case scenario.
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I think the problem here si that while sunspots come and go CO2 is "forever".
If we say "It's OK to generate lots of CO2 - the changes in climate are due to sunspot activity" then what happens when the sunspot activity is such that the world warms and the CO2 warms it too?
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Bored Chemist
I think the problem here si that while sunspots come and go CO2 is "forever".
It isn't though. Is it? The atmospheric lifetime of Co2 is between 50 and 200 years.
If we say "It's OK to generate lots of CO2 - the changes in climate are due to sunspot activity" then what happens when the sunspot activity is such that the world warms and the CO2 warms it too?
Who is saying that?
My question is "is sunspot activity more important than co2 levels."
Do we fully understand how sunspot activity affects our climate and is it more important than co2 levels?
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Frethack:
say we are not entering a maunder minimum. But what if we were to continue with low or lower than average activity for the next cycle or two? This would not be the worst case scenario, but would it be bad? Would it make more of an impact on the climate than Co2 levels?
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200>>11
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One number is bigger than the other. But it doesn't answer the question, does it?
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BOULDER--Challenging conventional wisdom, new research finds that the number of sunspots provides an incomplete measure of changes in the Sun's impact on Earth over the course of the 11-year solar cycle. The study, led by scientists at the High Altitude Observatory of the National Center for Atmospheric Research (NCAR) and the University of Michigan, finds that Earth was bombarded last year with high levels of solar energy at a time when the Sun was in an unusually quiet phase and sunspots had virtually disappeared.
"The Sun continues to surprise us," says NCAR scientist Sarah Gibson, the lead author. "The solar wind can hit Earth like a fire hose even when there are virtually no sunspots."
The study, also written by scientists at NOAA and NASA, is being published today in the Journal of Geophysical Research - Space Physics. It was funded by NASA and by the National Science Foundation, NCAR's sponsor.
Scientists for centuries have used sunspots, which are areas of concentrated magnetic fields that appear as dark patches on the solar surface, to determine the approximately 11-year solar cycle. At solar maximum, the number of sunspots peaks. During this time, intense solar flares occur daily and geomagnetic storms frequently buffet Earth, knocking out satellites and disrupting communications networks. solar diagram
When the solar cycle was at a minimum level in 1996, the Sun sprayed Earth with relatively few, weak high-speed streams containing turbulent magnetic fields (left). In contrast, the Sun bombarded Earth with stronger and longer-lasting streams last year (right) even though the solar cycle was again at a minimum level. The streams affected Earth's outer radiation belt, posing a threat to earth-orbiting satellites, and triggered space weather disturbances, lighting up auroras in the sky at higher latitudes. [ENLARGE] (Illustration by Janet Kozyra with images from NASA, courtesy Journal of Geophysical Research - Space Physics.)
Gibson and her colleagues focused instead on another process by which the Sun discharges energy. The team analyzed high-speed streams within the solar wind that carry turbulent magnetic fields out into the solar system.
When those streams blow by Earth, they intensify the energy of the planet's outer radiation belt. This can create serious hazards for weather, navigation, and communications satellites that travel at high altitudes within the outer radiation belts, while also threatening astronauts in the International Space Station. Auroral storms light up the night sky repeatedly at high latitudes as the streams move past, driving mega-ampere electrical currents about 75 miles above Earth's surface. All that energy heats and expands the upper atmosphere. This expansion pushes denser air higher, slowing down satellites and causing them to drop to lower altitudes.
Scientists previously thought that the streams largely disappeared as the solar cycle approached minimum. But when the study team compared measurements within the current solar minimum interval, taken in 2008, with measurements of the last solar minimum in 1996, they found that Earth in 2008 was continuing to resonate with the effects of the streams. Although the current solar minimum has fewer sunspots than any minimum in 75 years, the Sun's effect on Earth's outer radiation belt, as measured by electron fluxes, was more than three times greater last year than in 1996.
Gibson said that observations this year show that the winds have finally slowed, almost two years after sunspots reached the levels of last cycle's minimum.
The authors note that more research is needed to understand the impacts of these high-speed streams on the planet. The study raises questions about how the streams might have affected Earth in the past when the Sun went through extended periods of low sunspot activity, such as a period known as the Maunder minimum that lasted from about 1645 to 1715.
"The fact that Earth can continue to ring with solar energy has implications for satellites and sensitive technological systems," Gibson says. "This will keep scientists busy bringing all the pieces together."
For the new study, the scientists analyzed information gathered from an array of space- and ground-based instruments during two international scientific projects: the Whole Sun Month in the late summer of 1996 and the Whole Heliosphere Interval in the early spring of 2008. The solar cycle was at a minimal stage during both the study periods, with few sunspots in 1996 and even fewer in 2008.
The team found that strong, long, and recurring high-speed streams of charged particles buffeted Earth in 2008. In contrast, Earth encountered weaker and more sporadic streams in 1996. As a result, the planet was more affected by the Sun in 2008 than in 1996, as measured by such variables as the strength of electron fluxes in the outer radiation belt, the velocity of the solar wind in the vicinity of Earth, and the periodic behavior of auroras (the Northern and Southern Lights) as they responded to repeated high-speed streams.
The prevalence of high-speed streams during this solar minimum appears to be related to the current structure of the Sun. As sunspots became less common over the last few years, large coronal holes lingered in the surface of the Sun near its equator. The high-speed streams that blow out of those holes engulfed Earth during 55 percent of the study period in 2008, compared to 31 percent of the study period in 1996. A single stream of charged particles can last for as long as 7 to 10 days. At their peak, the accumulated impact of the streams during one year can inject as much energy into Earth's environment as massive eruptions from the Sun's surface can during a year at the peak of a solar cycle, says co-author Janet Kozyra of the University of Michigan.
The streams strike Earth periodically, spraying out in full force like water from a fire hose as the Sun revolves. When the magnetic fields in the solar winds point in a direction opposite to the magnetic lines in Earth's magnetosphere, they have their strongest effect. The strength and speed of the magnetic fields in the high-speed streams can also affect Earth's response.
The authors speculate that the high number of low-latitude coronal holes during this solar minimum may be related to a weakness in the Sun's overall magnetic field. The Sun in 2008 had smaller polar coronal holes than in 1996, but high-speed streams that escape from the Sun's poles do not travel in the direction of Earth.
"The Sun-Earth interaction is complex, and we haven't yet discovered all the consequences for the Earth's environment of the unusual solar winds this cycle," Kozyra says. "The intensity of magnetic activity at Earth in this extremely quiet solar minimum surprised us all. The new observations from last year are changing our understanding of how solar quiet intervals affect the Earth and how and why this might change from cycle to cycle." About the article
Title: "If the Sun is so quiet, why is the Earth ringing? A comparison of two solar minimum intervals"
Authors: Sarah Gibson, Janet Kozyra, Giuliana de Toma, Barbara Emory, Terry Onsager, and Barbara Thompson
Publication: Journal of Geophysical Research - Space Physics
http://www.earthtoday.net/news/viewpr.rss.html?pid=29191
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One number is bigger than the other. But it doesn't answer the question, does it?
Actually that's the symbol for "is much bigger"
On the timescale of the sunspot cycle CO2 is "forever".
That's what answers the question.
If the CO2 keeps rising (as it has for decades) but the sunspots come and go then eventually the CO2 will have more effect.
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Frethack:
say we are not entering a maunder minimum. But what if we were to continue with low or lower than average activity for the next cycle or two? This would not be the worst case scenario, but would it be bad? Would it make more of an impact on the climate than Co2 levels?
Thats kind of a loaded question. It depends on how low solar activity goes and for how long. During the 1970's, solar cycle 20 was comparatively small cycle (when compared to the 20th century average), and there was a decline in global temperatures, though historically it was not much of a decline. The same with the very deep solar minimum around 1913 (between cycles 14 and 15). The year without a summer occurred during the Dalton Minimum, a very short minima (15 years I think), but was also aided by the eruption of Mt Tambora. In short...its a very difficult question to answer with any degree of certainty until more is understood about the physical mechanisms that link solar activity and climate. I have my own hypothesis, and am gathering data and resources, but until there is a large body of evidence to show an actual physical mechanism within the climate system, it is just that...a hypothesis.
200>>11
The eleven year cycle is one of the short solar cycles. There are others.
~11yr - Schwabe cycle
~22yr - Hale cycle
~87yr - Gleissberg cycle
~210yr - deVries/Suess cycle
~400yr - unnamed
~1500yr - unnamed and has a range of error of about 500 years. This one is controversial, but has been linked to Dansgaard/Oeschger events(warming) and Heinrich events (ice rafted debris events) during the last ice age. It also could be linked to millennial scale climate variability during the Holocene, but this is again only hypothesis for now.
Solar cycles are much broader in length than CO2 residence times.
Another bothersome thing is that there have been many periods in geologic time where CO2 has been MUCH higher than it is today. It has only been this low once that I know of for any extended period of time, and that was during the Carboniferous (~350 - 290 ma) when the earth was extremely humid and hot. This may have had much to do with arrangement of the continents as well. Also, during the Ordovician/Silurian ice age, CO2 estimates range from 3000 to 5000 ppm...much higher than the 385ppm of today. The Cretaceous averaged around 1000ppm and was generally very hot and humid as well.
There are a multitude of controls on the climate system, and I am not arguing that CO2 is not one of them. I do believe, though, that a LOT more research is necessary before we will understand the even the basics.
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One number is bigger than the other. But it doesn't answer the question, does it?
Actually that's the symbol for "is much bigger"
I thought it was the symbol for greater than.
Why do you feel the need to write replies that attempt to belittle people? The question is valid and should not be so easily dismissed.even if the question was stupid you do not have to treat the person asking thecquestion like they are. A little respect is not too much to ask, is it?
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Thanks for the reply Frethack.
Thats kind of a loaded question. It depends on how low solar activity goes and for how long. During the 1970's, solar cycle 20 was comparatively small cycle (when compared to the 20th century average), and there was a decline in global temperatures, though historically it was not much of a decline. The same with the very deep solar minimum around 1913 (between cycles 14 and 15). The year without a summer occurred during the Dalton Minimum, a very short minima (15 years I think), but was also aided by the eruption of Mt Tambora. In short...its a very difficult question to answer with any degree of certainty until more is understood about the physical mechanisms that link solar activity and climate. I have my own hypothesis, and am gathering data and resources, but until there is a large body of evidence to show an actual physical mechanism within the climate system, it is just that...a hypothesis.
With global temperatures seeing no real increase in the last 10 years and suggestions that we may be entering a period of 10 to 20 years of cooling I think sunspots may be a larger factor than Co2 levels, even if it's only for this "short" period.
There are also predictions that Co2 levels will begin to drop due to the global recession. I'm not sure how that will play out but if we do have 20 years of cooling and a drop in Co2 levels then I would expect to see more research in to sunspot activity and impacts.
There is talk that a prolonged quiet sun is going to be a "saviour" and retard the warming.
Sceptics seize on climate cooling model (http://m.guardian.co.uk/?id=102202&story=http://www.guardian.co.uk/environment/georgemonbiot/2009/sep/16/global-temperature-cooling)
Climate myths: Any cooling disproves global warming (http://www.newscientist.com/article/dn17808-climate-myths-any-cooling-disproves-global-warming.html)
CO2 emissions tumble; leaders to meet on climate (http://www.ibtimes.com/articles/20090921/co2-emissions-tumble-leaders-meet-on-climate.htm)
Don't you find it strange how a possible 10 years of cooling confirms that global warming is happening? And how skeptics are wrong to "sieze" on cooling to show that AGW is not happening. It would seem that AGW proponents have all the bases covered.
Average global temperatures rising proves AGW
Average global temperatures staying static proves AGW
Average global temperatures dropping for 10 to 20 years proves AGW
AGW will cause more and stronger hurricanes, hurricane activity drops and this proves AGW
just what doesn't prove AGW?
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> <> >>
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While it is true that average temperatures have declined slightly in the past decade, it does not indicate the certainty of another 20 years of cooling. As for myself, I believe that there is at least a decent chance that this could be the case, but there is nothing concrete and conclusive to allow me (or anyone else) to make such a statement with absolute certainty.
As for CO2 dropping due to a global recession...that is fundamentally untrue. Even with the slight CO2 decrease that would accompany a global economic contraction, there would still be a significant increase of CO2 above and beyond the natural CO2 output. Though elevated temperatures cause oceanic outgassing, permafrost outgassing, and increased bioproductivity, which all increase CO2 (even during historically warm periods before the Industrial Revolution), human activity and industrialization still produces a pretty significant amount. CO2 will continue to rise.
As for low solar activity being our savior...people should be careful what they wish for. I would direct those people to a few papers...among them Zhang et al. 2008 "A Test of Climate, Sun, and Culture Relationships from an 1810-Year Chinese Cave Record". The rise and fall of Chinese dynasties (as well as the fall of Mayan civilization in South America) can be traced to monsoonal variability and fluctuations in the Intertropical Convergence Zone that appear to be controlled almost exclusively by solar variability. A new Little Ice Age would not be fun...especially for Europeans, as the Gulf Stream looks to be very susceptible to this same mechanism.
Please remember that there are very few climatologists who would fudge their data to benefit their careers. Most of the doom and gloom rhetoric has come since politicians have become involvled...science and politics do not mix. Even the IPCC itself is as much a political body as it is a scientific body. Thats why I decided to pursue climatology as a career...to save the world from Al Gore :)
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Fret,
I continuosly baffled by the very idea climate cooling is a good thing. I suggest anyone who wishes to cool the planet take a February vacation to Chicago. Or the North Slope of Alaska. All humor aside, it is not funny.
If you really really wish for an Ice Fair on the Thames, I suggest you hire a local refridgeration company to do so, and keep it local. The last time we had icebergs on the Delaware, George Washington was deploying a successful attack on Heshians on the other side. We all know how that ended up....
Warm is Good, Cold is Bad. Just ask the Salem Witches who were hanged, perhaps as the result of Ergot induced psychosis. [There is a dirct correlation between the families of witches and marginal, cool damp crop fields.]
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"I continuosly baffled by the very idea climate cooling is a good thing. "
Did anyone say it was?
Stabillity is a good thing. Warming or cooling would be bad. There's not a lot we can do about natural vairation but at least we can stop pissing in our own pool.
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Bored
I don't have my referces redily at hand, but my recolection is the Jurasic had about 3000ppm and was about 20 degrees (FC?) warmer. CO2 has subsequently declined and has been less then 300ppm for a very long time.
In addition, I had a whole host of proxy matterial that showed Roman times as much as 6 degrees warmer. Then the climate started to cool, then got warmer then today dring The Midieval era, followed by the Little Ice age which only ended in the middle of the 1800's.
One of the biggest mistakes the climatistas ever made was to invent the "Hocky" stick graph. Anyone who believes the climate was flat for the last 2,000 years then started to warm suddenly during the industrial era has placed themselves flat in the flat earth society. Hocky sticks and forlorn Polar Bears.
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Bored
I don't have my referces redily at hand, but my recolection is the Jurasic had about 3000ppm and was about 20 degrees (FC?) warmer. CO2 has subsequently declined and has been less then 300ppm for a very long time.
In addition, I had a whole host of proxy matterial that showed Roman times as much as 6 degrees warmer. Then the climate started to cool, then got warmer then today dring The Midieval era, followed by the Little Ice age which only ended in the middle of the 1800's.
One of the biggest mistakes the climatistas ever made was to invent the "Hocky" stick graph. Anyone who believes the climate was flat for the last 2,000 years then started to warm suddenly during the industrial era has placed themselves flat in the flat earth society. Hocky sticks and forlorn Polar Bears.
Jurassic estimates are around 800ppm, increasing to about 1000ppm during the Cretaceous with an average temp of around 22C...still much higher than today, but not 20C/F warmer. Of course, these are from incomplete records with large error bars, and like most paleoenvironmental proxies, are subject to constant refinement.
Ive never seen compelling evidence that the Roman Warm Period was substantially warmer than today, especially by six degrees, though records indicate that it could have been warmer in some regions. The same holds for the Medieval Warm Period, which may *possibly* have been warmer than today, but so far nothing is conclusive. The MWP appears to have been substantially warmer than the RWP. Many of these temperature reconstructions are from Mg/Ca records from oceanic sediment cores which tend to overstate temperature, or from tree ring data which suffer from a lack of robustness before the Little Ice Age.
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Fret - All this just adds to the gumbolia mix of data, fact, and fiction. I will attempt to reconstruct my GW evidence on the Roman Era Warming. In the mean time, however, decades ago I studied Latin as a member of "The Young Classical League". We took it for granted Britain exported wine to Europe. At the time it was considered nothing more then a curiosity.
To this day vinticulture in Britain has been, shall we say, a mixed bag.
See You Later Alligator!
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Fret - This is weird! Looking for Roman Era Warming I ran accross this Dutch site extolling the newly revived vinticulture of The Netherlands! I am not yet ready to concede Netherland Pinot Noir to be world class. However, as a proxy for Roman Era warming it is something of a nifty proxy!
http://www.digitaljournal.com/article/272124
I have been negligent in recent years and have not kept up with the latest data. Here is another recent find in my work to establish Roman Era Warming. It is incidental, but pertinent.
http://planetgore.nationalreview.com/post/?q=YmFmMDg0NThjZGIyZmRkNmRlNjA2ODJkYTRiOTI2NWE=
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Bored
I don't have my referces redily at hand, but my recolection is the Jurasic had about 3000ppm and was about 20 degrees (FC?) warmer. CO2 has subsequently declined and has been less then 300ppm for a very long time.
In addition, I had a whole host of proxy matterial that showed Roman times as much as 6 degrees warmer. Then the climate started to cool, then got warmer then today dring The Midieval era, followed by the Little Ice age which only ended in the middle of the 1800's.
One of the biggest mistakes the climatistas ever made was to invent the "Hocky" stick graph. Anyone who believes the climate was flat for the last 2,000 years then started to warm suddenly during the industrial era has placed themselves flat in the flat earth society. Hocky sticks and forlorn Polar Bears.
That doesn't seem to have had anything much to do with the point I made.
Change is bad.
More change is worse.
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skeptic - I found that old Time Magazine article on Global Cooling. I will post the entire thing here. I hope that does not break the rules, but you gotta get a load of this thing.... "Telltale signs [of a comming ice age] are everywhere..."
TIME Magazine Archive Article -- Another Ice Age? -- Jun. 24, 1974
TIME MAGAZINE ^ | June 24, 1974/2006 | Time Magazine
LINK TO 1974 ARTICLE
In Africa, drought continues for the sixth consecutive year, adding terribly to the toll of famine victims. During 1972 record rains in parts of the U.S., Pakistan and Japan caused some of the worst flooding in centuries. In Canada's wheat belt, a particularly chilly and rainy spring has delayed planting and may well bring a disappointingly small harvest. Rainy Britain, on the other hand, has suffered from uncharacteristic dry spells the past few springs. A series of unusually cold winters has gripped the American Far West, while New England and northern Europe have recently experienced the mildest winters within anyone's recollection.
As they review the bizarre and unpredictable weather pattern of the past several years, a growing number of scientists are beginning to suspect that many seemingly contradictory meteorological fluctuations are actually part of a global climatic upheaval. However widely the weather varies from place to place and time to time, when meteorologists take an average of temperatures around the globe they find that the atmosphere has been growing gradually cooler for the past three decades. The trend shows no indication of reversing. Climatological Cassandras are becoming increasingly apprehensive, for the weather aberrations they are studying may be the harbinger of another ice age.
Telltale signs are everywhere —from the unexpected persistence and thickness of pack ice in the waters around Iceland to the southward migration of a warmth-loving creature like the armadillo from the Midwest.Since the 1940s the mean global temperature has dropped about 2.7° F. Although that figure is at best an estimate, it is supported by other convincing data. When Climatologist George J. Kukla of Columbia University's Lamont-Doherty Geological Observatory and his wife Helena analyzed satellite weather data for the Northern Hemisphere, they found that the area of the ice and snow cover had suddenly increased by 12% in 1971 and the increase has persisted ever since. Areas of Baffin Island in the Canadian Arctic, for example, were once totally free of any snow in summer; now they are covered year round.
Scientists have found other indications of global cooling. For one thing there has been a noticeable expansion of the great belt of dry, high-altitude polar winds —the so-called circumpolar vortex—that sweep from west to east around the top and bottom of the world. Indeed it is the widening of this cap of cold air that is the immediate cause of Africa's drought. By blocking moisture-bearing equatorial winds and preventing them from bringing rainfall to the parched sub-Sahara region, as well as other drought-ridden areas stretching all the way from Central America to the Middle East and India, the polar winds have in effect caused the Sahara and other deserts to reach farther to the south. Paradoxically, the same vortex has created quite different weather quirks in the U.S. and other temperate zones. As the winds swirl around the globe, their southerly portions undulate like the bottom of a skirt. Cold air is pulled down across the Western U.S. and warm air is swept up to the Northeast. The collision of air masses of widely differing temperatures and humidity can create violent storms—the Midwest's recent rash of disastrous tornadoes, for example.
Sunspot Cycle. The changing weather is apparently connected with differences in the amount of energy that the earth's surface receives from the sun. Changes in the earth's tilt and distance from the sun could, for instance, significantly increase or decrease the amount of solar radiation falling on either hemisphere—thereby altering the earth's climate. Some observers have tried to connect the eleven-year sunspot cycle with climate patterns, but have so far been unable to provide a satisfactory explanation of how the cycle might be involved.
Man, too, may be somewhat responsible for the cooling trend. The University of Wisconsin's Reid A. Bryson and other climatologists suggest that dust and other particles released into the atmosphere as a result of farming and fuel burning may be blocking more and more sunlight from reaching and heating the surface of the earth.
Climatic Balance. Some scientists like Donald Oilman, chief of the National Weather Service's long-range-prediction group, think that the cooling trend may be only temporary. But all agree that vastly more information is needed about the major influences on the earth's climate. Indeed, it is to gain such knowledge that 38 ships and 13 aircraft, carrying scientists from almost 70 nations, are now assembling in the Atlantic and elsewhere for a massive 100-day study of the effects of the tropical seas and atmosphere on worldwide weather. The study itself is only part of an international scientific effort known acronymically as GARP (for Global Atmospheric Research Program).
Whatever the cause of the cooling trend, its effects could be extremely serious, if not catastrophic. Scientists figure that only a 1% decrease in the amount of sunlight hitting the earth's surface could tip the climatic balance, and cool the planet enough to send it sliding down the road to another ice age within only a few hundred years.
The earth's current climate is something of an anomaly; in the past 700,000 years, there have been at least seven major episodes of glaciers spreading over much of the planet. Temperatures have been as high as they are now only about 5% of the time. But there is a peril more immediate than the prospect of another ice age. Even if temperature and rainfall patterns change only slightly in the near future in one or more of the three major grain-exporting countries—the U.S., Canada and Australia —global food stores would be sharply reduced.