[Vision2020] Questioning the MWP & LIA as Global Climate Periods

[Ted Moffett]

One of the most common theories to question anthropogenic climate change is
to reference the Medieval Warm Period and Little Ice Age during the past
1100 years,
http://www.ncdc.noaa.gov/paleo/ctl/resource1000.html
as recent examples of natural climate variability, then to assert the
warming of global average temperatures over the past 100 years is mostly a
natural recovery from the LIA.

Some climate scientists have questioned whether indeed there was a truly
global climate shift that defined a MWP or LIA, pointing out these climate
periods were more a regional phenomenon.

A just published online April 21, 2013 peer reviewed study in Nature
Geoscience supports a more skeptical view of a truly global MWP or LIA, if
I read the this paper correctly:

http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo1797.html

Nature Geoscience | Progress Article
Continental-scale temperature variability during the past two millenniaNature
Geoscience(2013)doi:10.1038/ngeo1797 Received 09 December 2012 Accepted 11
March 2013 Published online 21 April 2013Abstract

   - Abstract•
   - Author information<http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo1797.html#author-information>
   •
   - Supplementary
information<http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo1797.html#supplementary-information>

Past global climate changes had strong regional expression. To elucidate
their spatio-temporal pattern, we reconstructed past temperatures for seven
continental-scale regions during the past one to two millennia. The most
coherent feature in nearly all of the regional temperature reconstructions
is a long-term cooling trend, which ended late in the nineteenth century.
At multi-decadal to centennial scales, temperature variability shows
distinctly different regional patterns, with more similarity within each
hemisphere than between them. There were no globally synchronous
multi-decadal warm or cold intervals that define a worldwide Medieval Warm
Period or Little Ice Age, but all reconstructions show generally cold
conditions between ad 1580 and 1880, punctuated in some regions by warm
decades during the eighteenth century. The transition to these colder
conditions occurred earlier in the Arctic, Europe and Asia than in North
America or the Southern Hemisphere regions. Recent warming reversed the
long-term cooling; during the period ad 1971–2000, the area-weighted
average reconstructed temperature was higher than any other time in nearly
1,400 years.

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Vision2020 Post: Ted Moffett
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