In the climate chance course video of week two we saw a graph showing the medieval warming
quite lower than the modern warm period. Also in the video from the end of week
two the professor draw a graph like this and explained, that the
medieval warming was just locally. Other sources say that it was
global and the temperatures even higher than today.
Even in Germany now the media talk about this. Here is a graph from ARD
Television (similar to the BBC):
http://wetter.tagesschau.de/wetterthema/2013/12/27/klima-macht-geschichte.html
According to this graph there have been various times before as warm
or warmer than today.
So I looked for science papers about that topic and found a lot, e.g.
one in science:
http://www.sciencemag.org/content/342/6158/617
Here
the editors description:
Global
warming is popularly viewed only as an atmospheric process, when, as
shown by marine temperature records covering the last several
decades, most heat uptake occurs in the ocean. How did subsurface
ocean temperatures vary during past warm and cold
intervals? Rosenthal et
al. (p. 617)
present a temperature record of western equatorial Pacific subsurface
and intermediate water masses over the past 10,000 years that shows
that heat content varied in step with both northern and southern
high-latitude oceans. The findings support the view that the Holocene
Thermal Maximum, the Medieval Warm Period, and the Little Ice Age
were global events, and they provide a long-term perspective for
evaluating the role of ocean heat content in various warming
scenarios for the future.
And here another one:
http://scienceandpublicpolicy.org/images/stories/papers/originals/medieval_warm_period_russia.pdf
The description:
Excerpts:
The
Medieval Warm Period (MWP) was a global climatic anomaly that
encompassed a few centuries on either side of AD 1000, when
temperatures in many parts of the world were even warmer than they
are currently. The degree of warmth and associated changes in
precipitation, however, varied from region to region and from time to
time; and, therefore, the MWP was manifest differently in different
parts of the world. How it behaved in Russia is the subject of this
Summary.
In
contradiction of another of Mann
et al.'s contentions,
Krenke and Chernavskaya went on to unequivocally state - on the basis
of the results of their comprehensive study of the relevant
scientific literature - that “the Medieval Warm Period and the
Little Ice Age existed globally.”
The
fact that the warming that brought the world the Current Warm Period
began around 1750 AD, or nearly 100 years before the modern rise in
atmospheric CO2 concentration, should be evidence enough to argue
that the planet's current warmth is the result of nothing more than
the most recent and expected upward swing of this natural climatic
oscillation.
From
approximately AD 1200 to 1410, they concluded that temperatures in
the region of their study were “probably higher than today,”
providing yet another example of times and places when and where
low-CO2 Medieval Warm Period temperatures were likely higher than
high-CO2 Current Warm Period temperatures.
In
conclusion, and considering the full spectrum of studies included in
this Summary, it would appear that a goodly portion of the Medieval
Warm Period throughout Russia was somewhat warmer than what has so
far been experienced there during the Current Warm Period. And since
the MWP held sway when the atmosphere's CO2 concentration was
something on the order of 285 ppm, as compared to the 400 ppm of
today, it would appear that the air's CO2 content has had essentially
nothing to do with earth's near-surface air temperature throughout
the entire Holocene, when the air's CO2 concentration at times
dropped as low as 250 ppm. Other factors have clearly totally
dominated.
The
number of papers about that topic appear to be about 100, but I have not checked them
all. Seems an interesting area for further search.
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