Download Orbital-Scale Interactions in the Climate System

Chapter 12
Orbital-Scale Interactions in
the Climate System
報告學生:彭炯博
Orbital-Scale Forcing and
Response Revisited
Fast response time.
Slow response time.
Fast response time
One part of the climate system has a
fast response time , measured in
months or years.
Example: monsoon.
No thermal inertia and so easily
influenced by other parts of the climate
system.
Slow response time
One part of the climate system has a
slow response time, measured in many
thousands of years.
Example: ice sheets.
Have a large thermal inertia and
independent from other parts of the
climate system.
Ice-Driven Responses
Ice-Driven Responses in High Northern Latitude
Region of ice-driven responses
North Atlantic surface response to ice
The ice sheets to influence Atmosphere
A clockwise flow of wind occurred
around the central dome of North
American ice sheet.
The presence of a high-albedo ice
surface at latitudes where snow does
not fall today.
The hung ice sheet ???.
Climate in Northern Europe and Asia
France
European vegetation
Surface-ocean sensitivity test
Responses of windblown debris in East Asia to ice colume
In summary the ice volume signal can
be transferred far from the immediate
proximity.
Orbital Cycles in Regions Remote
from Northern Hemisphere Ice
N. African monsoon ~ 23,000 years, a summer season
phenomenon
Ice-sheet signals ~ 41,000 and 100,000 years , a winter
season phenomena
So, no significant effect may be felt across the eq.
Yet, ice sheet signal shows up in many faraway regions
Responses of windblown debris in the
Arabian Desert to ice volume
Pollen responses in South
America to ice volume
Pollen responses in New Zealand to ice
volume
Response of Southern Ocean
temperature to ice volume
Northern or southern ice sheet forcing?
Out-of-phase summer insolation between the hemispheres
Phasing of insolation vs. ice volume
Global transfer of signals
from Northern hemisphere
ice sheets, via
sea level: continental vs
marine climate
deep water formation
CO2
CO2 Level and Ice Volume
Which Drives Which ?
Relative timing of ice volume and changes in CO2
Why Have Ice Sheets Grown
Larger since 0.9 Myr Ago ?
Changes in
18O
in the last 4.5 Myr
Ice slipping may affect ice sheet volume
What Causes Abrupt Deglaciations
Strong summer insolation peaks pace rapid deglaciations
?
Strong summer insolation peaks pace rapid deglaciations
Numerical model: insolation control of ice volume
Conceptual (SPECMAP) model of ice-driven climate changes
Summary
Climate scientists are close to a full theory of ice
sheet variations over the last 2.75 Myr. For the first
two-thirds of this interval, growth and melting of
northern hemisphere ice sheets were controlled by
changes in summer insolation at rhythms of 41,000
and 23,000 years, as Milankovitch predicted. By
900,000 years ago, global cooling permitted ice
sheets to begin growing larger. The dominant
100,000-year rhythm of change in these ice sheets
was paced by changes in summer insolation but
ultimately governed by internal feedbacks produced
by the ice sheets, including changes in atmospheric
CO2.