Abrupt Tropical Climate Change: Past and Present

Abrupt Tropical Climate
Change: Past and Present
Lonnie Thompson, E Mosley-Thompson, H Brecher, M Davis, B Leon, D Les, P
Lin, T Mashiotta, K Mountain
David Chauvaux
Atmos Sci
An examination of three lines of
evidence that point to multiple
events of abrupt climate change
in the last ~5000 years, possibly
including now
1) δ18O averages and net mass-balance histories
determined from ice cores covering the last 400 and 2000
years show that current warming of high elevations in the
tropics is unprecedented in at least 2 millennia
2) The retreat of mid- to low-latitude glaciers (which had been
doing just fine for thousands of years) signals a recent, abrupt
change in Earth's climate
3) Carbon dating of preserved plants recently exposed along
the margin of the Quelccaya ice cap as it recedes, along with
widespread proxy evidence, point to an abrupt cooling event
marking the transition from early to late Holocene ~5200
years ago
Data distribution
Where Oh Where Has My Glacier
 Qori Kalis, outlet of
Quelccaya, has been
monitored since 1963
 Avg retreat rate 19631978: ~6m/yr
 Avg retreat rate 19912005: ~60m/yr
 10X faster in only 30
 Graph shows about
equal rates of retreat
across numerous
Peruvian glaciers
 Avg retreat rates
1980-1995: ~20m/yr
400 years ago to now: Everybody
Loves Ice Cores
2 sets of cores were takes from Quelccaya, in
1983 and 2003
Annual avg δ18O values were compared
across the cores and found to be virtually
Double significance
 confirms time scale for 1983 core
 shows that δ18O record well-preserved
despite 20 yrs of surface warming
7 cores compared from Andes,
Himalayas, and Tibetan Plateau
to build a climate profile
Comparison of δ18O and
An fluctuations 1600-2000
2000 years ago to now
The Holocene: Distiwho muscowha?
Distichia muscoides (Juncaceae)
Yet another graph...
But hey, pretty picture
More evidence of abrupt cooling
~5200 years ago
Otzi the Iceman
You made a mess o' potamia
Closer to home
Little Salt Spring, FL
Closer to home 2
South Cascade Glacier
Back South
The current accelerating glacial retreat across the
world suggests the increase in the globally
averaged temperature may have prematurely
interrupted the natural progression of cooling.
Observations suggest that a century of human
activity may have kicked the global climate closer
to what it had been like before 5000 years ago. If
so, the retreat of the glaciers may indicate the
passing of a threshold and tropical glaciers may
soon disappear.
Movie time!

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