How Well Do Scientists Understand Earth Orbit
Changes and Climate Trends
ScienceDaily.com
Saturday, February 6th 2010
How Well Do Scientists
Understand How Changes in Earth's Orbit Affect Long-Term Natural Climate
Trends?
ScienceDaily — The notion that
scientists understand how changes in Earth's orbit affect climate well enough
for estimating long-term natural climate trends that underlie any anthropogenic
climate change is challenged by findings just published.
The new
research was conducted by a team led by Professor Eelco Rohling of the
"Understanding how climate has responded to
past change should help reveal how human activities may have affected, or will
affect, Earth's climate. One approach for this is to study past interglacials,
the warm periods between glacial periods within an ice age," said Rohling.
He continued:
"Note that we have here focused on
the long-term natural climate trends that are related to changes in Earth's
orbit around the Sun. Our study is therefore relevant to the long-term climate
future, and not so much for the next decades or century."
The team, which
included scientists from the Universities of Tuebingen (Germany) and Bristol,
compared the current warm interglacial period with one 400,000 years ago
(marine isotope stage 11, or MIS-11).
Many aspects of
the Earth-Sun orbital configuration during MIS-11 were similar to those of the
current interglacial. For this reason, MIS-11 is often considered as a
potential analogue for future climate development in the absence of human
influence.
Previous
studies had used the analogy to suggest that the current interglacial should have
ended 2-2.5 thousand years ago. So
why has it remained so warm?
According to
the 'anthropogenic hypothesis', long-term climate impacts of man's
deforestation activities and early methane and carbon dioxide emissions have
artificially held us in warm interglacial conditions, which have persisted
since the end of the Pleistocene, about 11,400 years ago.
To address this
issue, the researchers used a new high-resolution record of sea levels, which
reflect ice volume. This record, which is continuous through both
interglacials, is based on the '
Water passes
between the
By analysing
oxygen isotope ratios in tiny marine creatures called foraminiferans preserved
in sediments that were deposited at the bottom of the
The researchers found that the current
interglacial has indeed lasted some 2.0-2.5 millennia longer than predicted by
the currently dominant theory for the way in which orbital changes control
the ice-age cycles. This theory is based on the intensity of solar radiation
reaching the Earth at latitude 65 degrees North on 21 June, the northern hemisphere
Summer solstice.
But the anomaly
vanished when the researchers considered a rival theory, which looks at the
amount of solar energy reaching the Earth the same latitude during the summer
months. Under this theory, sea levels could remain high for another two
thousand years or so, even without greenhouse warming.
"Future
research should more precisely narrow down the influence of orbital changes on
climate," said Rohling: "This is crucial for a better understanding
of underlying natural climate trends over long, millennial timescales. And that
is essential for a better understanding of any potential long-term impacts on
climate due to man's activities."
The study was
funded by the