Other Answers (8)

• Even the AGW crowd has abandoned the hockey stick for something that looks more like those snow shovels for people with bad backs.
  
  They now accept an MWP but insist that we started to exceed MWP temps in the 1990s.
  
  Of course, that still leaves them with two hundred years of uninterrupted temps at early 1990s levels, and no catastrophe, no runaway warming, etc.... So it%26#039;s kind of irrelevant whether it was warmer than peak 1990s levels or the approximately 0.2 degrees C cooler that they now appear to concede - - - that would make the MWP about even with today%26#039;s temps - - for two centuries straight. Without any of the global catastrophe that they tell us will result at the present temperatures.
  
  But that doesn%26#039;t change the fact that it most certainly WAS warmer, based upon events that occurred that cannot occur now because it is not warm enough, and that since they occurred have been attributed to warmer temperatures, and many of which were attributed at the time to warmer temperatures.
  
  The Hockey Stick controversy has always been a significant issue for me. They can%26#039;t prove their case outright - it relies upon their being given a certain benefit of the doubt. I%26#039;d be a lot more open to giving them that benefit of the doubt if they had more credibility, which was destroyed when they re-wrote the climate history.
  
  The record of what grew when and where, what land and sea passages were iced over for what period of the year, etc... - the tangible evidence - supports a warmer MWP. And that is why the MWP was the accepted climate history from the time it happened until the climate had become a political issue and the skeptics were gaining a lot of headway in the debate by citing recent non-CO2-driven warm periods such as the warmer MWP, the almost-as-warm Roman period and the warmer HM.
  
  The physical evidence is from around the world - from the Sierra Nevadas to the Alps, from the American Southwest to Greenland to England to Germany to China, from the arctic to New Zealand. Not all of the events happened at exactly the same time - but then, we%26#039;re repeatedly told that non-synchronous warming today is actually supportive of global warming today.
  
  Indeed not only is there the physical evidence from around the world, but during the MWP and the ensuing LIA there were written accounts of climate change - in literature such as Chaucer%26#039;s Canterbury Tales and in correspondence, such as when the Pope wrote that he could not send ships to Greenland because of the increased sea ice.
  
  Human behavior changed - the economy changed. People planted crops at higher elevations and colder latitudes. Keep in mind the state of the economy at the time, with its lack of credit - - it was a very expensive endeavor to begin planting a new crop on your land, a crop that hadn%26#039;t been grown on your land before. You risked your fortune to plant a new vineyard in lower England or go to Greenland to start a dairy farm - - this wouldn%26#039;t have been done after only a couple of warm years, rather it would have to have been warm on a sustained basis for a generation to justify such an investment.
  
  How can the physical, tangible and indeed written record be overturned on the basis of scant proxy reconstructions?
  
  But it%26#039;s more than that.
  
  The basis for overturning the MWP is NOT %26quot;reconstructions%26quot; generally - - - the sedimentary records show the MWP as do the ice core records taken together.
  
  The basis for overturning the MWP, for re-writing it out of the climate history, is reconstructions that rely on tree ring proxies - - either tree rings only or a blend of evidence in which tree rings form the only cool medieval signal.
  
  Except that the cool medieval signal from the tree ring data is based on the assumption that tree rings keep getting wider with temperature, no matter how warm it gets.
  
  Most of the tree ring samples used in the studies that purport to override the MWP were taken in 1980.
  
  We know it warmed from 1980-2000.
  
  So, it would be a good idea then to validate the tree ring methodology by updating the samples and comparing the model to the measured temperature record for 1980-2000.
  
  Dr. Mann argued that this would be too expensive - - but it%26#039;s been done with a half dozen samples so far - - and surprise surprise, the tree rings do not get wider from 1980-2000.....
  
  Not that tree rings are good proxies for temperature anyway - - there are several other factors related to growth, such as rainfall, other plants competing for sunlight and soil nutrients, pests, the roots extending to a layer of soil that is less nutrient-rich, etc..... This alone would have been enough to throw out the tree ring data, since in many cases entire centuries for entire continents are reconstructed based upon one or two individual trees.
  
  So to put it bluntly: the best you can say for those who think or thought that the MWP didn%26#039;t actually happen, that %26quot;new science de-bunks it,%26quot; is that they want to believe that. Nobody who doesn%26#039;t already want to come to that conclusion can look at the evidence and come to that conclusion.
  
  Now - do prior, non-CO2-driven warm periods prove that the 20th century warming wasn%26#039;t man-made?
  
  No.
  
  But they do mean that we can%26#039;t just infer that the 20th century warming was man-made, and they also prove that we can%26#039;t just automatically assign validity to the %26quot;runaway warming from methane release%26quot; theory, since it%26#039;s been warmer than it is today, for centuries at a time, and no such massive methane release occurred. What it means for the polar bears is unclear, since their population is now recovering from overhunting, which wasn%26#039;t the case hundreds or thousands of years ago.
  
  But to bring the discussion full-circle, the MWP denial (ironically, by those who call everyone else %26quot;denialists%26quot;) is a severe blow to the credibility of the AGW proponents.
  
  They still do not seem to realize this - that most objective, open-minded people are likely to become MORE skeptical, are LESS likely to believe in AGW, as a result of this historical revision.
  
  As for their explanation of the mid-20th century cooling (and it was a cooling), it does make sense that dark particulates would refract some sunlight back into space. Though, with the development of the third world, we%26#039;ll probably see more dark particulates in the atmosphere than we had in the 1950s. But making intuitive sense does not prove that that theory is correct - - based on lab experiments we concluded that CFCs were the cause of the ozone hole. We banned CFCs 20 years ago, most countries comply, CFC levels are down precipitously, yet the ozone hole is bigger now than it was then.
  
  EDIT - the MWP was NOT a %26quot;regional event in Europe.%26quot; For example, tree lines were higher in the Sierra Nevadas, the Anasazi suffered through droughts much more severe than the droughts now seen in the American Southwest and had to abandon their homes, and Lake Naivasha dried up for 200 years. Lake Naivasha is in Kenya, which is not in Europe...... Lake Naivasha is lower than it was a century ago but still exists in the 21st century despite much greater water drainage for irrigation and other uses than was the case during the MWP.
  
  This is what I mean - - the statement below about %26quot;limited to Europe%26quot; is palpably untrue. It%26#039;s just factually false. There%26#039;s no open debate on this issue - it%26#039;s like saying the Diamond Backs beat the Red Sox last night. It%26#039;s just a flat out untruth. Yet they run with it. Why do they think this will cause more people to believe them? Why don%26#039;t they think that so obviously lying about one issue will cause people who haven%26#039;t yet made up their minds to ask, I wonder what else they%26#039;re lying about?
  
  Why do some of them try to dismiss the larger issue of credibility, to relegate this and other similar issues by labeling them %26quot;side issues?%26quot;
  
  This is how we decide things that cannot be proven either way - we consider the logic of the arguments and the credibility of those making them. People are convicted of murder not always because the evidence that they committed the murder is so overwhelming but because they took the stand and lied about some other issue, and as a result the jury doesn%26#039;t believe them.