Milankovitch Theory of Climate Change
The Earth changes its:
a) orbit (eccentricity), from ellipse to
circle at 100,000 year cycles,
b) wobble (precession), affects timing
of seasons with respect to
perihelion, at 23,000 year cycles
c) tilt (obliquity), from 22° to 24.5° at
41,000 year cycles.
THESE FACTORS AFFECT GLOBAL CLIMATE BECAUSE OF
GREATER LAND AREA IN THE NORTHERN HEMISPHERE
Climate Change is Nothing New
TODAY
The rate of climate warming projected by the IPCC is
believed to be very rapid compared to past climate changes
*NB: The temporal scale used to examine climate change
is very important, as different patterns are revealed, depending
on the timescale used.
*
The Jurassic
A much warmer Earth with more CO2
The last glacial maximum
Temperature variation during
the past two millenia
[insert fig 16-6]
Climate and CO2 Concentrations: 2 to 590 million years BP
Current Global
Mean Temperature &
[CO2]vap
Berner RA and Kothavala Z. 2001. GEOCARB III: A revised model of atmospheric CO2 over Phanerozoic time. American Journal of
Science. 301: 182-204
Climate Change
•Carbon dioxide
absorbs outgoing
longwave radiation
emitted by the Earth
•This causes
temperature to rise
on a global scale
•CO2-induced global
warming first predicted
by Arrhenius (1896)
•Concentrations have
increased from 280ppm
(preindustrial) to
390 ppm (2011)
http://www.glumbert.com/media/globalwarming1958
K TO SPACE=31
L
L TO SPACE=69
100-31-69=0
100
GREENHOUSE
EFFECT HERE
ABSORPTION
46+19+4=69
Heat transfer
7+24=31
Compensates
for radiation
imbalance at
surface
L<K !!
46-15=31
Source: NOAA
Source: IPCC
Climate Change
The Observed Record (IPCC)
The 20th century was unusually wet in much of North America.
Global
Circulation
Models
Future Scenarios
THE YEAR 2050 IN SOUTHERN ALBERTA
Temperature Increase
+2.5 to + 5.7C
above 1971-2000
climate normals
(McGinn and
Shepherd, 2003)
Growing Degree Days
Barrow and Yu (2005) In: Sauchyn (2007), with permission
Future Scenarios
THE YEAR 2050 IN SOUTHERN ALBERTA
Precipitation Increase
+3 to +36 %
above 1971-2000
climate normals
(McGinn and
Shepherd, 2003)
More rain and
less snow from
autumn to spring
(Lapp et al., 2005)
Annual Moisture Index: ET > P
Barrow and Yu (2005) In: Sauchyn (2007), with permission
OLDMAN RIVER FLOW
PROJECTIONS
Annual flow projected to
vary from -13 to +8%
(mean -4%).
•
Increased winter rain:snow
ratio and above-freezing
temperatures will increase
winter runoff
•
Earlier spring melt and
increased
evapotranspiration will
decrease summer runoff
SEASONAL FLOWS (2039-2070)
m3 s-1
•
CURRENT
ECH
HAD
NCAR
Pietroniro et al. (2006) In: Sauchyn (2007)
Carbon ‘Enrichment’
MORE EFFICIENT PLANTS?
Faster growth rates
Increased water-use efficiency
•lower stomatal conductance required
to maintain ci
Increased nitrogen-use efficiency?
Impact of global change on WUE
depends on net result of opposing
effects of increased Ta and VPD
vs. elevated [CO2]vap
Will the same species
be dominant in a 2xCO2
environment?
Future Scenarios
NET PRIMARY PRODUCTIVITY OF ALBERTA GRASSLANDS
Ecosys Model accounts for both climate change and
CO2 enrichment (Li, Grant and Flanagan, 2004)
Input
Canadian Regional Climate Model II climate change projections
(IS92a emissions scenario).
Results
•Lengthened growing season
•Transpiration increases from higher temperatures were offset by
increasing plant water-use efficiency caused by rising CO2
•Increased net primary productivity offset by increasing respiration, so that
carbon sequestration only increased very slightly (2 g C m2 y1) under climate
change
N.B.: Climate change may alter interspecies competition/dynamics and cause
migration. Rapid change may also reduce biodiversity.
Enhanced photosynthesis
Source: IPCC
Meanwhile, we are detecting
stratospheric cooling !
Why ?
Ozone depletion
Tropospheric [CO2] increases