Earth Sciences 240A - Lecture 34 - Climate III
The Younger Dryas
Event: 13,000-11,700 ya
Most pronounced around
Dramatic cooling because of ‘Lid’
of cold, fresh melt water over sea; Density effect; After
mixing, recovery rapid
The Little Ice Age
(1400-1900 A.D.)
Followed ‘The Medieval Climatic
Optimum’: (1000-1300)
Likely the ‘top’ of the
interglacial event
Dramatic worsening in Europe/N.A.
by 1400; Global T drop of 1 to 1.5oC
1810-19 coldest
in
Gradual warming began mid-1800s; Initial rise of CO2 above long-term base:
~1800
Possible Factors
Milankovitch factors: Too simple
alone (doesn’t account for variations)
Millennial oscillations (Example:
Younger Dryas Event)
The sum of effects
from:
Volcanic dust
and/or CO2; changes in sedimentation rates; temporary ocean current changes;
solar radiation variations; El Niňo; etc.
Observed short-term (as short as 1000 years) climate changes for which
causes are not necessarily defined
Volcanic?
Laki: 1783; Mayon:
1814; Tamboro: 1815
Certainly didn’t
start it! [1-2 year effects?]
Solar radiation
variation?
Too short for
Milankovitch cycle
Sun spot cycle: 11
years; too short
El Niňo?
Cycles roughly 2-7
years, but vary
9 v. severe event
between 1525-1980; also 1983 and 1998
Zero correlation
with Little Ice Age
Humans and the Greenhouse
First human-induced changes:
mid-1800s
Atmospheric CO2: land-clearing
added little
Industrial Revolution: added hugely
Warmed air means faster
decomposition
Increased CO2 and methane CH4
Is it this factor
which ended the Little Ice Age?
Climate in the Next
100-1000 Years
Natural Climate Variation
Short-term
Little Ice Age
marked beginning of natural down-trend (…probably…)
Human intervention
gives us the ‘superinterglacial’
End: final fossil
fuel use + lag time
Long-term:
Glacial period
will continue
Next interglacial
peak:~100,000 years
It will be (much)
smaller than present one (?)
Projected Changes
(short-term)
Models
2xCO2 of preindustrial
Previously: at
least 7 mya
4xCO2 of preindustrial
Previously: at
least 100 mya
Forcing will be too short to reach eq’m.
Only fast-response systems will adjust quickly
Continental ice sheets are
‘slow-response’
Sea ice and vegetation are
‘fast-response’
Likely Impact
Peak T should last 100 years
Preindustrial levels should last
1000 years
Bulk of Greenland/Antarctic ice
will survive (but margins go)
Climate of 2100 will be ~ to 5-10
mya
Catastrophic effects on
Although seas will warm and
evaporation increase, interiors of continents will get less precipitation
Coastal areas flooded (seas up 50
cm)
Gone:
Most of
Large sections of
Seasons will change, Especially at high latitudes
Fresh water: Most continental
interior users must be more inventive in recycling
With warming tropical seas hurricanes/typhoons
will increase in strength and possibly in number
Coastal erosion will be dramatic
High latitude winters will be less
harsh
Time for adaptation for sea life
and land life will be too short
Expect a huge extinction rate
unless we attempt to save species in artificial preserves
Please read the Appendix: The Mackenzie Basin Impact Study
See you in the final exam