Milankovitch Theory of Climate Change
The Earth changes its:
a) orbit (eccentricity), from ellipse
to circle at 100,000 year cycles,
b) wobble (precession), from the
north pole pointing toward or
away from the sun in June at
23,000 year cycles, and
c) tilt (obliquity), from 22° to 24.5°
at 41,000 year cycles.
Climate Since the
Most Recent Ice Age
Does a large, composite volcano
affect climate on a global scale?
Effect of Mount Pinatubo Eruption
Note:
Volcanoes also
release CO2, and
warming occurs
in the long term
during tectonically
active periods
(eg. Triassic/Jurassic
boundary)
TEMPORARY
COOLING
Ice core data
Temperature,
CO2 and CH4
are all in
phase
Are the gas
concentrations
an effect or a
cause of
warming or
both?
The Jurassic
A much warmer Earth with more CO2
Source: IPCC
The Global Carbon Cycle - 1990s
Units Gt C and Gt C y-1
Atmosphere
…are leading to a
build up of CO2
in the atmosphere.
500
3.2
750
63
Plants
60
Soil
2000
6.3
About
16,000
1.6
Fossil emissions
91.7
90
…and land clearing
in the tropics...
The KP seeks to reduce net
carbon emissions by about
0.3 Gt C below 1990 levels
from industrial countries
Fossil Deposits
Oceans
39,000
2xCO2 ENVIRONMENT
Enhanced photosynthesis
Source: IPCC
1950
Climate
Modelling
2006
Temporary,
regional
cooling
effect
Source: IPCC
1. Reduced Biodiversity
Rapid change may exceed capacity of
plants and animals to adapt to changing
climate and new interspecies dynamics
2. Sea level rise and coastal flooding
Thermal expansion + melting ice
3. Expansion of tropical disease range
4. Soil Moisture Decreases and
Desertification
Evapotranspiration increases may
exceed increases in precipitation
5. Increased frequency of heat illness
6. Increased frequency of severe events?
More energy for tropical cyclones
(supports this hypothesis), but reduced
latitudinal temperature gradients could
reduce middle-latitude storm intensity
7.
Engineering problem of thermokarst
(transportation and housing)
8.
Affect on outdoor winter recreation
and winter tourism
Alberta’s Fragile Fresh Water Supply
•Partially supported by glacial meltwater
•Glaciers are retreating
•Future ET >> P?
1. Increasing ecosystem productivity
Higher photosynthesis rates due to
carbon fertilization
2. Increased food production
Higher photosynthesis rates, wider
range where soils adequate, longer
growing season (depends on soil
moisture/depth/nutrients)
3. Increased water-use efficiency
• Plants can reduce stomatal aperture,
yet maintain sufficient internal CO2
• May mitigate desertification and soil
moisture deficit somewhat
4. Increased nutrient-use efficiency?
Is less Rubisco required at higher
temperatures? (Contains N)
5. High latitude warming
Both a negative effect (loss of key Arctic
species, ways of life) and positive effect
(crop growth & NPP, soil permitting)
Free Air Carbon Dioxide Enrichment (FACE)
FACE Results:
NPP increases
(eg. 40% in cotton; 25%
for Sweetgum for 550
ppm vs. 370 ppm)
Carbon sink increase limited for forests: Increase in
wood production is short-lived; C goes mainly to fine
roots and leaves; affected by soil fertility
No effect on LAI
Stomatal conductance decreases (increased wateruse efficiency)
Lower leaf nitrogen concentration:
Do they need less? Have less? Due to C:N ratio?
Source: IPCC
Meanwhile, we are detecting
stratospheric cooling !
Why ?
Ozone depletion
Tropospheric [CO2] increases
Further Reading:
Fundamentals of Physical Geography Online
7h. The Greenhouse Effect
http://www.physicalgeography.net/fundamentals/7h.html
Climate Change 2001: The Scientific Basis
International Panel on Climate Change
http://www.grida.no/climate/ipcc_tar/wg1/index.htm