Medieval warm period

[David Hall]

I just finished reading this interesting NYT article about a warming period that happened around 1000 years ago. It doesn't go into any detail as to the causes, but at the end it suggests it was due to a brightening of the Sun.

http://nytimes.com/2002/03/26/science/earth/26TREE.html

So how accurate is this? The article says that warming in the early 1900's was caused by solar brightening. Is this a confirmed observation or just a hypothesis? And if so, does it have anything to do with the mini-ice-age that followed in the 1400's as well?

[Silas]

I couldn't read the article... Was it referring to "Maunder" periods? This was covered in the last earth-sciences class I took -- but in the intervening years, I'll bet that a lot has been discovered...

(For instance, there's an island continent south of Malaysia!)

Silas

[DStahl]

I am not registered for the NY Times webpage either. On the same subject, Oregon's State Climatologist George Taylor has noted that during the Medieval Warm Period sea levels were higher than they are now, implying that the current warming is well within the range of normal terrestrial climate variation. He also notes, however, that the CO₂ level is currently much higher than during the Medieval climatic optimum. This page explores some of the hypotheses about causes--if the page is up-to-date then it seems there may not be a clear single cause identifiable at this time. (Scroll to the bottom of the page and find the link labelled "Possible Causes").

Incidentally, some researchers suggest that the MWP was limited to northern Europe and was not a global phenomenon. Other researchers assert that Argentine glaciers showed a pattern of retreat consistent with climatic warming during the MWP, so the episode was global...I dunno the evidence or the issue in enough detail to come down on one side or the other, personally.

--Don Stahl

<font size=-1>[ This Message was edited by: DStahl on 2002-03-31 14:21 ]</font>

[Jigsaw]

Selections from the article.

March 26, 2002

Tree Rings Show a Period of Widespread Warming in Medieval Age
By KENNETH CHANG

A new study of old tree rings shows that 1,000 years ago, long before power plants and sport utility vehicles, temperatures across North America, Europe and Asia rose in a period of unusual warmth.

Temperatures were known to be warm in Europe between 900 and 1100, what is known as the Medieval Warm Period. Collecting wood samples in 14 locations that cover a swath of the globe from New Orleans north to the top of Alaska, researchers from Columbia University's Lamont-Doherty Earth Observatory and the Swiss Federal Research Institute found evidence that the warm temperatures extended to much of the Northern Hemisphere.

Writing in the current issue of the journal Science, the scientists say the data demonstrate that temperatures naturally rise and fall over the centuries. The scientists, however, add that their data do not argue against the view that artificial emissions — so-called greenhouse gases — have set off the global warming of recent decades.

"I never intended or meant to imply that that's the case," said Dr. Edward R. Cook, an author of the Science paper and an expert at Lamont-Doherty on reconstructing climate from tree rings.

So, tree rings and another argument about global warming.

[jrkeller]

Global warming is one topic that gets discussed quite frequently here at the Johnson Space Center espeically in our thermal group (at least during those times of friendly discussions). One of the reasons that this topic comes up quite frequently is that we need to know the amount of solar heating so that we can design our thermal control systems. We have spent years and years and many experiment trying to figure out what the solar constant is. Our conclusion, is that it's variable even over short times like a year or two.

When it comes to global warming, most of us feel that while CO2 does have an impact, the variation in the solar output seems to be ignored, or least it doesn't get much press.

[Kaptain K]

It seems to me that the "greens" try to blame all of the recent warming on CO2 build-up and their opponents say that it is just solar variability. If solar variability is/was enough to make Greenland truly green a thousand years ago and industrial emissions have doubled the CO2 content of the atmosphere in the past century, a rise in solar output now or in the near future has frightening implications.

[David Hall]

Hey guys, if you are interested, why don't you just sign up for the Times? It's easy and free to do, and they have a great science section.

I know it can sometimes be risky to put your name and email up, but come on, this is a venerable and trusted company here, not some fly-by-night organization. [img]/phpBB/images/smiles/icon_smile.gif[/img]

Anyway, so what is the extent of observed fluctuations in solar brightness? I mean in percentage terms or the like. And for example, how would a 1% change affect the amount of energy flooding the Earth?

[jrkeller]

I don't know how much of a change in temperature occurs with a 1% variation in solar output, but I can tell you that amount of energy the Earth receives from the sun varies by as much as 8%. This is based on extreme measurements, which may only last for a short period. About 3% of this variation is due to the eccentricity of the Earth's orbit.

I also don't know the accuracy of our measuring instruments.

[John Kierein]

Don't forget that the arctic and antarctic circles are retreating. This has a lot to do with the breakup of ice shelves and tundra melting near there.
http://earth.agu.org/sci_soc/eischao.html

This has a bigger effect at the south pole than at the north because perihelion occurs when the sun is almost at its southernmost. So not only is the sun shining further south and north, due to the changing angle to the ecliptic, it also is brighter at the south because it's nearer. This may be why there seems to more dramatic devastation to the Larsen Ice Shelf.

<font size=-1>[ This Message was edited by: John Kierein on 2002-04-02 13:23 ]</font>

[Jigsaw]

Ditto on going ahead and registering--I've been registered there for a long time now and I've never had any spam that I could trace back to them, at the e-mail address I used.

It's worth it to be able to read the articles.

[dgruss23]

There is a lot of compelling evidence for the Sun's role in climate changes on Earth. Here are a few links:

http://pubs.usgs.gov/fs/fs-0095-00/fs-0095-00.pdf

http://www.eurekalert.org/pub_releas...c-1c060602.php

http://www.geotimes.org/june02/WebExtra0621.html

http://www.co2science.org/edit/v4_edit/v4n48edit.htm

http://www.fraserinstitute.ca/admin/...e-Baliunas.pdf

http://www.news.harvard.edu/gazette/...eningSuni.html

[Colt]

The Viking's settling down at the beginning of the warm period was significant to history in Europe. It reminds me of the Ender series' pygmies (?) culture and life cycle being determined by the temperature. -Colt

[g99]

From what i have heard the little ice age around the time of the Vikings was the reason why they left greenland and North America. (along with the Native Americans). It just got to dang cold for them.

[RafaelAustin]

And also the intense drought about that time brought the fall of the Mayan civilization.

[Argos]

Ditto on going ahead and registering--I've been registered there for a long time now and I've never had any spam that I could trace back to them, at the e-mail address I used.

True. Now that the American press lost much of its credibility, NYtimes remains as an island of high quality, in a sea of mystification.

[edited for fixing grammar]

[irony]

At least we're past the phase when blaming global warming on anything but human activities is considered politically incorrect. I had to slog through the stupid environmental propaganda unit in grade five science. For our exam at the end of the unit, we were told to 'write an essay on whether or not you believe global warming is a problem and support your position with evidence.' I'm pretty sure those were the exact words, because I heard them quoted a lot when my parents went in to yell at the teacher after she gave me an 'f' on the thing. I was an astronomy geek even back then, so I was able to suggest a long list of things besides human activity that might account for global warming... I did it basically just to play devil's advocate, because I knew that everybody else in the class was going to tow the party line. Excuse me for thinking for myself. :roll:

Er... sorry. ops: That's just something I like to rant about now and then.

[dgruss23]

I asked my environmental science class to carefully read the textbook and list all evidence cited for global warming. They found nothing because the book skips from the greenhouse effect and the increase in CO2 right to what should be done about it. So then I asked them to go on-line and find evidence. They found this remarkably difficult. "Evidence" in the minds of global warming advocates constitutes the global warming theory itself and anything computer models spit out.

In the 1970's they were concerned about the coming ice ages (contributed to by pollution of course). Then in the 1980's it was catastrophic global warming. Yet despite the hysteria the actual evidence for global warming is scant.
In the meantime there is a growing body of evidence for a strong connection between the Sun and changes in the Earth's climate - from the Maunder Minimum, medieval maximum to the evidence uncovered by Sharma and Baliunas in the links above.

Instead of asking for equal time for creationism, how about equal time for the Sun-climate connection.

[crazy4space]

[quote="dgruss23"] Yet despite the hysteria the actual evidence for global warming is scant.

First, how long have we been tracking this? Not so long I think. Second - most of the data that I have seen shows less than 2 degrees flux over the last 75-100 years. My gut feeling is that the sun could more than account for this. I am also glad to know that there are still some science teachers out there with open minds and willing to look at the emperical data.

My initials are on the moon because Gene Cernan put them there.

[dgruss23]

crazy4space wrote: First, how long have we been tracking this? Not so long I think.

That's an important point. Think about it. They went from catastrophic ice ages in the mid-70's to catastrophic warming in the mid-80's - about as long as a sunspot cycle. Meanwhile researchers are finding evidence for Sun-climate links over time spans of hundreds of years on up to hundreds of thousands of years. One also has to wonder why the planet was cooling between 1940 and 1970 if carbon dioxide increases are supposed to be causing a warming - a point made by Sallie Baliunas and Willie Soon in the December 1996 Sky&Telescope.

[aurorae]

One also has to wonder why the planet was cooling between 1940 and 1970 if carbon dioxide increases are supposed to be causing a warming - a point made by Sallie Baliunas and Willie Soon in the December 1996 Sky&Telescope.

There are many factors that influence the earth's climate, as you know.

CO2 levels is only one.

But, if CO2 increases high enough... Venus.

[dgruss23]

One also has to wonder why the planet was cooling between 1940 and 1970 if carbon dioxide increases are supposed to be causing a warming - a point made by Sallie Baliunas and Willie Soon in the December 1996 Sky&Telescope.

There are many factors that influence the earth's climate, as you know.

CO2 levels is only one.

But, if CO2 increases high enough... Venus.

The atmosphere of Venus is 96% Carbon dioxide and the pressure of the atmosphere is 98x the Earth's atmospheric pressure. Venus does not have weathering processes like those on Earth or life that we know of to trap the CO2 in rocks. Even the most radical estimates of global warming computer models don't leave us with something that looks like Venus.

I guess what it boils down to is whether or not global warming advocates can produce credible evidence that significant warming is happening. But even if they do - Is that warming because of increased CO2 levels or because of increases in solar energy output? Or is it a combination of both along with other factors.

This is part of the problem. The environmental movement is turned global warming into a political movement and effectively brainwashed a generation into believing that every time they turn on their minivan/SUV/whatever they are contributing to catastrophic climate change. So lets say the planet does begin to exhibit convincing warming in the next decade or two. Global warming advocates will say "You see ... we were right." But it is just as possible that the Sun will be the cause of that warming. The links I've pointed to above indicate that it doesn't take a dramatic change in solar irradiance to induce changes in the Earth's climate.

[crazy4space]

[quote="dgruss23"][quote="aurorae"]

I guess what it boils down to is whether or not global warming advocates can produce credible evidence that significant warming is happening. But even if they do - Is that warming because of increased CO2 levels or because of increases in solar energy output? Or is it a combination of both along with other factors.

I would almost bet that a volcano, any old volcano puts more into the atmosphere than all the cars combined. You will be glad to know that 4 years ago all the insulation manufacturers changed their blowing agents from CFC's to HCFC's. What they did was hydragenate the atom so that it breaks down lower in the atmosphere and doest mess up the ozone in addition, the earth naturally creates ozone when sea water runs into limestone cliffs.

My initials are on the moon because Gene Cernan put them there.

[g99]

Right now Global warming is not a problem. If it happens like this for hundreds more years, we might have to really worry.

During much of the Mezozic, the entire earth was warmer and there were no ice caps at the poles and we still lived. The reason was from the intense volcanic and plate tectonic activity back then. It has calmed down now. Well at least for now.

A few degrees warmer will not kill us all instantly. But a few degrees a year for a few hundred years will melt the Ice caps and drown coastal cities (and all of Florida. Yikes!!). Then we will have to worry about all that extra co2 and methane we are putting into the atmosphere. The SUV next door will not do that. Heck the Methane produced by the hundreds of cows in the farm down the road produces much, much more greenhouse gasses than that car nextdoor.

But most likely by the time we really have to worry about significant warming like on Venus, we would have much cleaner ways of making energy and running our cars.

Right now i am more worried about the smog cloud caused by that SUV next door, than anything else.

[Argos]

Right now Global warming is not a problem. If it happens like this for hundreds more years, we might have to really worry.

(...) During much of the Mezozic, the entire earth was warmer and there were no ice caps at the poles and we still lived.

I would say it is not a problem for Russians, Canadians, Brits, Swedish, and anyone who lives upwards of paralel 50, or in other frigid zones. Indeed it can improve living conditions in those regions (maybe England becomes a pleasant resort.). But when you have a summer like the last one here at 23S the things get pretty worrisome.

During the mezozoic there was no man over the Earth. Of course it´s possible for man to survive in a warmer Earth. The question is on what basis; the quality of the survival. Global warming will add further spice to our pot of social problems, since a massive movement of people in search of a shelter from the inclement weather is expected to occur when the problem reaches a certain threshold. The political strains derived from this condition will be of great magnitude.

The irony of destiny: the nations beneficiary of the indiscriminate pollution of the last 250 years are the same to which global warming will be most beneficial.

[snowcelt]

Argos said that "the nations beneficiary of the indiscriminate pollution of the last 250 years are the same to which global warming will be most benefical." I do not think so. Life on the arid western plains of Canada are at best marginal. If I understand the global warming model correctely, a mere couple degree average rise in temperature globally could result in micro- climatic temperature changes of 10+C degrees. A temperature change of this magnitude would be devistating: Canada's south-western plains would be turned into desert. Furthermore, Canada's high artic would be drastically changed, traditional hunting culture would end. These are but a couple cases of global climatic changes that would be experienced in Canada alone. Personnally I think the evidence is not in yet, there is still much work to be done.

[dgruss23]

snowcelt wrote: If I understand the global warming model correctely, a mere couple degree average rise in temperature globally could result in micro- climatic temperature changes of 10+C degrees. A temperature change of this magnitude would be devistating: Canada's south-western plains would be turned into desert. Furthermore, Canada's high artic would be drastically changed, traditional hunting culture would end. These are but a couple cases of global climatic changes that would be experienced in Canada alone.

I wouldn't get too worried about the computer models snowcelt :

http://www.techcentralstation.com/10...D=1051-062802B

[snowcelt]

Thanks dgruss23, I was becoming worried that I would have to change my user name to sweatingcelt!

[g99]

Inland areas would be more effected than coastal areas initially by temp changes. Costal areas are regulated by the oceans. So at first move to the coast, then once the waters start to rise, Kansas here we come.

[Argos]

then once the waters start to rise, Kansas here we come.

I wouldn´t do it. Deep in the heart of the continents is where temperatures will undergo the most extreme variations. My advice: once the oceans start to rise, move some few meters back into the land, but stay close to the sea (always keeping an eye on it). :wink:

[dgruss23]

Has anyone been able to demonstrate that the oceans are rising?