Is the National Academy of Sciences wrong about the Medieval Warm Period?

Question

They say it was not as warm as at present.

http://dels.nas.edu/dels/rpt_briefs/climate_change_2008_final.pdf

Page 5.

"Skeptics" claim that it was.

Who do you believe?

Note that most of the members of the Academy do NOT receive funding for global warming work.

They were established over 100 years ago, and their record is excellent. One of their jobs is to act as a kind of Supreme Court for scientific issues.

Answer 1

Do we trust scientists or people who aren't scientists to display scientific data and principles?

I say we trust the scientists.  I don't go to a dentist to fix my car... and I sure wouldn't ask the bum on the street, which is roughly analogous to trusting these so-called "skeptics".

Answer 2

my call the scientists have my vote !

Answer 3

I can't imagine how the Medieval Warm Period is relevant in any way.  It was not 6 degrees Celsius warmer, so it does not prove that humans can survive the changes that we're setting in motion.

Although some people seem to be lulled into a false sense of security by the PR slogan "the climate has changed naturally in the past", the evidence of past climate change associated with CO2 increases confirms that we can't take the risk lightly:

http://www.aip.org/history/climate/co2.h...

It was less reassuring to notice what the climate had looked like in certain ancient times when CO2 had stood at a high level... a level that humanity would eventually reach if we went on burning all available oil and coal. The Earth had been virtually a different planet, with tropical forests near the poles and sea levels a hundred meters higher. Worse, as one group pointed out, unchecked emissions seemed bound to bring not only "a warming unprecedented in the past million years," but changes "much faster than previously experienced by natural ecosystems..."(57)

There are dozens of scientific papers that indicate that climate change is linked to greenhouse gas increases:

Climate sensitivity constrained by CO2 concentrations over the past 420 million years

http://www.nature.com/nature/journal/v44...

"A firm understanding of the relationship between atmospheric carbon dioxide concentration and temperature is critical for interpreting past climate change and for predicting future climate change1. A recent synthesis2 suggests that the increase in global-mean surface temperature in response to a doubling of the atmospheric carbon dioxide concentration, termed 'climate sensitivity', is between 1.5 and 6.2 °C..."

Yes, those studies use "proxy data," also the basis for the "climate has changed in the past" arguments.  Ironically people here make conflicting arguments that both accept and reject the same data.  

I suppose that in the absence of any coherent alternate theory to explain the past 120 years of warming corresponding with the past 150 years of greenhouse gas emissions, it makes sense to throw out distractions from the topic.

I'd love to see a solid case casting doubt on global warming theory.  I'd find the discussions about the MWP (or any of the other side topics bought up by skeptics) a lot more credible if they weren't frequently backed by links to extremist blogs and others who gladly accept ExxonMobil and coal industry donations.

Answer 4

Don't know about you, but I'd prefer to stick with statements of professional peer-reviewed scientific organisations, namely NAS and AAAS.

Many civilisations have died in the past due to being wiped out by climate, one of the most powerful sources affecting us.

And have you considered population? In the medieval days, there was a much smaller population to support, and they had ample food supplies to do it. We have too large a population for our own good.

Answer 5

Looking back at the data 160 years, I wonder why anyone would doubt that it was warmer than it is now.

http://environmentaldefenseblogs.org/cli...

Currently we are only 0.5 degrees above average after being 0.5 degrees below average for 130 years.

Surly a +/- 1 deg change is within normal, and if it was colder for 130 years, then it had to be warmer sometime prior to the start of the graph to get an average higher then most of the data.

Frankly, I can't even see where there is any "global warming".

Answer 6

I believe the historical evidence that say it was warmer.  No unbiased scientists believes proxies over real data.

Answer 7

My vote goes to the National Academy of Sciences! To not trust their judgment suggests conspiracy theory, and that is irrational.

Answer 8

I don't believe the Hockey Stick.

Weather changes over time. The medieval period was warm. Isn't that proof enough that we can and have survived climate changes?

WOLF WOLF WOLF!!!

Answer 9

big corporate polluters (aka republicans) have everything to lose if the facts about global warming are accepted and real changes are enacted to combat it in a meaningful way (as opposed to the posturing Bush admin has done, like saying we must get 35 mpg by 2020 - WHAT? we can do better than that NOW!)

It is real. Next thing you know we'll be paying for breathable air. We already pay for drinkable water. Remember when that was a joke?

Answer 10

propaganda....whatever

Answer 11

I'm going to put my money on the majority of Scientists. Sure I could believe the small minority of crackpots who have shadowy links to energy companies, but then again I not Republican.

Answer 12

Why did Lake Naivasha, which despite water use for irrigation has not dried up in the present warm period, dry up for 200 years if it was not warmer then than it is now?

We know of droughts in the American Southwest over the 20th century - how did more severe droughts cause the demise of the Anasazi culture in the 1200s if it was not warmer then than it is now?

How is it that glacial retreat in the Alps is revealing tools and other artefacts from Medieval and Roman times?

Why do ice cores from Antartica show the MWP?

Why do sea sediment records show the MWP?

In fact why do studies that don't rely on bristlecone pine tree rings show the MWP?

How were the Vikings able to have small and almost self-sufficient dairy farms in parts of Greenland? How is it that analysis of their teeth and bones shows that their diet was 80% land-based until the late 1300s when it abruptly became 80% sea-based?  

How were tree lines 300 feet higher in the Sierra Nevadas and the Alps during the MWP than they are today?

How was lower England a wine-producing region?   Mann and Schmidt's explanation is that they now again grow wine grapes in that region..... right, after 900 years of breeding new varieties of grapes, and advances to growing techniques, both mainly to promote cold-hardiness.   That answer doesn't sound very "scientific."

The father of climate science, Hubert Lamb, who died in 1997 - a year before the IPCC abandoned his climate history for the Hockey Stick - found "multifarious evidence.... from the arctic to New Zealand" of a warmer MWP.

Has any of this evidence been explained away?  No - not a single example.

Or alternatively, is there new evidence from the non-contiguous regions from which Lamb didn't have any evidence either way that shows an equal and opposite local cooling, by which we could argue that overall the MWP was on a global scale cooler?     There is one "isolated region" in the Pacific where there was a prolonged La Nina - anything else?  To paraphrase Lindzen: indeed, if the global mean temperature did not change while Europe and the North Atlantic and the other regions Lamb covered, some of which I mention above, underwent very substantial warming, this would imply a major change in the geographic pattern of temperature. However, a major assumption in the hockey stick is that the patterns remain fixed. One is then left with the paradoxical conclusion that if the hockey results are right, the hockey stick analysis is wrong.

Prior to the climate becoming a political issue it was universally accepted that the MWP existed and was warmer than it is today.   Not "consensus with a few skeptics" but universally accepted.  Not a single climatologist anywhere questioned it.   When some skeptics of AGW today started overplaying the importance of the natural MWP, one member of the IPCC noted to John Daly that "we have to get rid of the MWP."  

And in 1998 they did....

....but without ever explaining a single example of Lamb's direct evidence - rather, just dismissing it as "anecdotal" and "regional" - - but evidence is evidence, and tangible, direct evidence has to trump indirect evidence plugged into a computer model, and what is the global climate if not the sum of the regional climates?

Sometimes the evidence is dismissed as being "largely from Europe" or "the North Atlantic."

Kenya is in neither Europe nor the North Atlantic.

A glacier retreats and advances.   As it retreats it reveals artefacts from known, separate periods in human history.   How did that happen if it wasn't warmer during those periods than it is today?

Please just explain how that happened.

Or explain how Sen. Inhofe and Rush Limbaugh and everyone else you claim the skeptics follow forged that evidence, and forged the evidence of the Viking settlement in Greenland, and the higher tree lines in the Sierra Nevadas, and the drying-up of Lake Naivasha in Kenya, and all the other evidence.

I go with the tangible evidence.   To do otherwise suggests a conspiracy on the grandest scale, spanning the globe and time itself.

And that would not be rational.

And note, why do the studies now relied upon by Bradley et al, while they still show a weaker MWP, show a prolonged period of more than 200 years with temperatures equal to those reached in the first half of the 20th century?    Even using the AGW proponents' version of it, we had temperatures sustained for over two centuries that were within 0.2 degrees of the average global temperature for January 2008, the most recent month published.

As for what "we've set in motion" - I think the last few years has made it clear that we don't know what will happen within the next couple of months, much less the next couple of centuries or millenia.

EDIT - voting "thumbs down" is not the same thing as explaining any of these events which, since they occurred, have been attributed to warmer temperatures.    You can't "vote down" the facts any more than you can make them disappear with bristlecone pine tree ring widths plugged into a computer model.    

Trees growing then where it's too cold for them to grow now are stronger evidence than the rates of growth of trees that grow now where they grew then.

And "skeptics claim it was warmer" is disingenuous - until the climate had become a political issue and until Hubert Lamb died, EVERYONE claimed it was warmer, including the NAS, the IPCC.....

Answer 13

I believe the NAS.  The 'skeptics' argument is based purely on anecdotal evidence from a few isolated locations (i.e. wine grapes in England).  Scientific studies are based on scientific evidence (i.e. various proxies which are in agreement that the MWP was cooler than today).

http://globalwarmingart.com/wiki/Image:2...

Even if the MWP were as warm as today it wouldn't prove anything, but the fact is that it almost certainly wasn't.

Answer 14

Reid A. Bryson holds the 30th PhD in Meteorology granted in the history of American education. Emeritus Professor and founding chairman of the University of Wisconsin Department of Meteorology—now the Department of Oceanic and Atmospheric Sciences—in the 1970s he became the first director of what’s now the UW’s Gaylord Nelson Institute of Environmental Studies. He’s a member of the United Nations Global 500 Roll of Honor—created, the U.N. says, to recognize “outstanding achievements in the protection and improvement of the environment.” He has authored five books and more than 230 other publications and was identified by the British Institute of Geographers as the most frequently cited climatologist in the world.

“All this argument is the temperature going up or not, it’s absurd,” Bryson continues. “Of course it’s going up. It has gone up since the early 1800s, before the Industrial Revolution, because we’re coming out of the Little Ice Age, not because we’re putting more carbon dioxide into the air.”

Little Ice Age? That’s what chased the Vikings out of Greenland after they’d farmed there for a few hundred years during the Mediaeval Warm Period, an earlier run of a few centuries when the planet was very likely warmer than it is now, without any help from industrial activity in making it that way. What’s called “proxy evidence”—assorted clues extrapolated from marine sediment cores, pollen specimens, and tree-ring data—helps reconstruct the climate in those times before instrumental temperature records existed.

We ask about that evidence, but Bryson says it’s second-tier stuff. “Don’t talk about proxies,” he says. “We have written evidence, eyeball evidence. When Eric the Red went to Greenland, how did he get there? It’s all written down.”

Bryson describes the navigational instructions provided for Norse mariners making their way from Europe to their settlements in Greenland. The place was named for a reason: The Norse farmed there from the 10th century to the 13th, a somewhat longer period than the United States has existed. But around 1200 the mariners’ instructions changed in a big way. Ice became a major navigational reference. Today, old Viking farmsteads are covered by glaciers."

I concur with Bryson