Comparing the spatial patterns of climate change in the 9th and 5th millennia BP from TRACE-21 model simulations
<p>The spatial patterns of global temperature and precipitation changes, as well as corresponding large-scale circulation patterns during the latter part of the 9th and 5th millennia BP (4800–4500 versus 4500–4000 BP and 9200–8800 versus 8800–8000 BP) are compa...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-01-01
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| Series: | Climate of the Past |
| Online Access: | https://www.clim-past.net/15/41/2019/cp-15-41-2019.pdf |
| Summary: | <p>The spatial patterns of global temperature and precipitation changes, as well
as corresponding large-scale circulation patterns during the latter part of
the 9th and 5th millennia BP (4800–4500 versus 4500–4000 BP and
9200–8800 versus 8800–8000 BP) are compared through a group of transient
simulations using the Community Climate System Model version 3 (CCSM3). Both
periods are characterized by significant sea surface temperature (SST)
decreases over the North Atlantic, south of Iceland. Temperatures were also
colder across the Northern Hemisphere but warmer in the Southern Hemisphere.
Significant precipitation decreases are seen over most of the Northern
Hemisphere, especially over Eurasia and the Asian monsoon regions, indicating
a weaker summer monsoon. Large precipitation anomalies over northern South
America and adjacent ocean regions are related to a southward displacement of
the Intertropical Convergence Zone (ITCZ) in that region. Climate changes in
the late 9th millennium BP (the “8.2 ka event”) are widely considered to have been caused by a large freshwater
discharge into the northern Atlantic, which is confirmed in a meltwater
forcing sensitivity experiment, but this was not the cause of changes
occurring between the early and latter halves of the 5th millennium BP.
Model simulations suggest that a combination of factors, led by long-term
changes in insolation, drove a steady decline in SSTs across the North
Atlantic and a reduction in the North Atlantic Meridional Overturning
Circulation (AMOC), over the past 4500 years, with associated teleconnections
across the globe, leading to drought in some areas. Multi-century-scale
fluctuations in SSTs and AMOC strength were superimposed on this decline.
This helps explain the onset of neoglaciation around 5000–4500 BP, followed
by a series of neoglacial advances and retreats during recent millennia. The
“4.2 ka BP Event” appears to have been one of several late Holocene
multi-century fluctuations that were embedded in the long-term, low-frequency
change in climate that occurred after <span class="inline-formula">∼4.8</span> ka. Whether these
multi-century fluctuations were a response to internal centennial-scale
ocean–atmosphere variability or external forcing (such as explosive volcanic
eruptions and associated feedbacks) or a combination of such conditions is
not known and requires further study.</p> |
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| ISSN: | 1814-9324 1814-9332 |