Michael
Bastasch
If you think
the Earth is hot now, try wearing plate armor in the Middle Ages.
A Swedish study found that the planet was warmer in ancient
Roman times and the Middle Ages than today, challenging the mainstream idea
that man-made greenhouse gas emissions are the main drivers of global warming.
The study, by scientist Leif Kullman, analyzed 455
“radiocarbon-dated mega-fossils” in the Scandes mountains and found that tree
lines for different species of trees were higher during the Roman and Medieval
times than they are today. Not only that, but the temperatures were higher as
well.
“Historical tree
line positions are viewed in relation to early 21st century equivalents, and
indicate that tree line elevations attained during the past century and in
association with modern climate warming are highly unusual, but not unique,
phenomena from the perspective of the past 4,800 years,” Kullman found. “Prior
to that, the pine tree line (and summer temperatures) was consistently higher
than present, as it was also during the Roman and Medieval periods.”
Kullman also
wrote that “summer temperatures during the early Holocene thermal optimum may
have been 2.3°C higher than present.” The “Holocene thermal optimum was a warm
period that occurred between 9,000 and 5,000 years ago. This warm period was
followed by a gradual cooling period.”
According to
Kullman, the temperature spikes were during the Roman and Medieval warming
periods “were succeeded by a distinct tree line/temperature dip, broadly
corresponding to the Little Ice Age.”
For many years
now, there was an alleged scientific consensus that the Earth was warming due
to humans releasing greenhouse gases into the air — primarily through burning
fossil fuels. However, temperatures stopped rising after 1998, leaving
scientists scrambling to find an explanation to the hiatus in warming.
Increasingly,
scientists are looking away from human causes and looking at
solar activity and natural climate variability for explanations of why the
planet warms and cools.
“All other
things being equal, adding more greenhouse gases to the atmosphere will have a
warming effect on the planet,” Judith Curry, a climatologist at the Georgia
Institute of Technology, told the Los Angeles Times. “However, all things
are never equal, and what we are seeing is natural climate variability
dominating over human impact.”
The Kullman
study points to mounting evidence that climate is largely out of human control,
as humans were not burning large amounts fossil fuels during Roman and Medieval
times.
Some
scientists have pointed to solar activity as the predictor of where global
temperatures are headed. Researchers have pointed to falling sunspot activity
as evidence that the planet will cool off in the coming decades.
“By looking
back at certain isotopes in ice cores, [Professor Mike Lockwood of Reading
University] has been able to determine how active the sun has been over
thousands of years,” the BBC reports. “Following analysis of the data,
Professor Lockwood believes solar activity is now falling more rapidly than at
any time in the last 10,000 years.”
Others have
looked to natural climate systems for explanations for answers to the 15-year
pause in global warming.
A study by Dr. Roy Spencer from the University of
Alabama, Huntsville found that about half the warming that occurred since the
1970s can be attributed to El Niño weather events, which had a warming effect
on the planet.
The Pacific
Ocean’s natural warming and cooling cycles last about 30 years, with La Niña
cooling being dominant from the 1950s to the 1970s and El Niño warming events
dominating late 1970s to the late 1990s. Spencer suggests that the world may be
in a La Niña cooling period.
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