How Well Do Scientists Understand Earth Orbit
Changes and Climate Trends
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.
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 '
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