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Climate Drivers:
Internal
Global Change Ecology
PBIO 275
External and Internal
Drivers of Climate
External Drivers
-Sunspot Cycles
-Orbital Variations
Internal Drivers
-Plate Tectonics
-Volcanic Activity
-Albedo
-Greenhouse Effect
Climate Drivers
Distribution of heat
Incoming radiation
Outgoing IR radiation
Latitudinal differences in net energy balance cause
atmosphere and ocean circulation
Denser waters in high latitude oceans
create a thermohaline circulation system
that has a major impact on regional climates
Questions:
How can warming climate shut
down thermohaline circulation?
How would this influence climate?
A general picture of climate change over the last 18,000 years
Pleistocene
Wisconsin glaciation
of North America
Holocene
Figure SPM.6
Climate Drivers
Plate Tectonics
Plate Tectonics
Pangaea 300
million years ago
Today
Plate Tectonics over the last
700 million years
Impacts: Ocean Circulation
25-35 million years ago
Impacts: CO2 Cycle
Plate Tectonics
1. Influences latitudinal transfer of
heat by ocean and atmosphere.
2. Allows accumulation of ice sheets
near the poles.
3. Exerts long term control on CO2
levels through volcanic activity,
weathering, and burial of organic
carbon.
Questions:
How do you think the rate of
movement of continental plates
influences climate?
What would the effect of an
increased rate of movement be on
climate?
Is this relevant to current climate
change?
Climate Drivers
Albedo or Reflectance
Albedo
The amount of solar radiation reflected or
scattered back into space without any change in
wavelength.
The mean global albedo is about 30%. The albedo of
different land surfaces varies greatly from 90% to less
than 5%.
Surface
Albedo
Tropical Forest
0.10-0.15
Woodland (deciduous)
0.15-0.20
Woodland (coniferous)
0.05-0.15
Grassland
0.16-0.26
Sandy desert
0.30-0.45
Tundra
0.18-0.25
Sea water
0.10
Water (0-60º)
<0.08
Water (60-90º)
0.10-1.0
Fresh Snow
0.80-0.95
Sea ice
0.25-0.60
Clouds (low)
0.60-0.70
Clouds (high)
0.18-0.24
Questions:
What is the effect of melting sea ice
on albedo and climate change?
What is the effect of deforestation on
albedo? Is is it a negative feedback?
What is the effect of desertification
on albedo? Will it slow warming at
least regionally?
Albedo effects if earth were completely
forested, desert, water, or ice.
Land use and albedo effect on radiative forcing
Past Change
Fig. 1. Representation of present-day land cover and land-cover change for each of the scenarios
J. J. Feddema et al., Science 310, 1674 -1678 (2005)
Fig. 2. JJA and DJF temperature differences due to land-cover change in each of the scenarios
J. J. Feddema et al., Science 310, 1674 -1678 (2005)
Climate Drivers
Aerosols
Aerosols are small airborne particles and droplets.
Direct effect: Affects incoming and outgoing radiation
Indirect effect: Affects cloud formation (condensation
nuclei)
Some sources: sulfates, organic carbon, black carbon
(fossil fuels)
Short-lived in the atmosphere (< 1 year)
Overall effects are not well understood, dependent on
particle size, and direct and indirect effects.
Figure 2.10
Figure 7.20
Volcanic Activity
Mt. St. Helens, May 1980
Volcanic Ash Downwind
of Mt. St. Helens
Eruption of Mt. Pinatubo, Philippine Islands, April 1991
Timeline of Troposphere temperature
Timeline of lower stratosphere temperature
Tambora (Indonesia), eruption 1815: 150 km3 of ejecta
90,000 dead (26 of 12,000 on island survived)
For comparison:
Krakatoa (Indonesia), eruption 1883: 20 km3 of ejecta
Mt. St. Helens, eruption 1980: <1 km3 of ejecta
Other eruptions in
same period:
1812: Soufriére
(St. Vincent)
1814: Mayon
(Phillippines)
1816: The year without a summer
Danville (VT) North Star (15 June 1816)
Melancholy Weather
"Some account was given in last week's issue of the
unparalleled severity of the weather. It continued without any
essential amelioration, from the 6th to the 10th instant--freezing
as hard five nights in succession as it usually does in December.
On the night of the 6th, water froze an inch thick -- and on the
night of the 7th and morning of the 8th, a kind of sleet or
exceeding cold snow fell, attended with high wind, which
measured in places where it was drifted, 18 to 20 inches in
depth. Saturday morning the weather was more severe than it
generally is during the storms of winter. It was indeed a gloomy
and tedious period."
“Eighteen Hundred and Froze to Death” (1816)
At least one frost each month of the summer:
May 12: Frosts penetrate to Pennsylvania and Virginia
May 30: Frosts penetrate to Rhode Island
Erie Pennsylvania had 1/4 inch ice
Emerging corn killed in Maine
June 5-9: Winter storm in VT and upstate NY. Frosts reach central MA
July 6: Frost in northern New England. Kills crops in NH. 40° in MA
August 13: Frost in northern New England
August 20: Severe cold front with frost following, kills corn in southern NH
Mid September: Frosts in Northern New England
September 27: Major frost ends dismal growing season.
Source: http://www.islandnet.com/~see/weather/history/1816.htm
Indicators of the Human Influence
on Sulphate aerosols during the Industrial Era
Source: IPCC TAR 2001
Figure 7.24
Solar and volcanic forces have affected
the climate system
1
Radiative forcing (W/m2)
0
-1
-2
-3
-4
1900
1950
2000
Figure SPM.2
Putting this all together…
Tectonics, albedo, and
volcanoes.
Volcanoes and CO2
Earth Homeostasis
Questions:
1. How is the earth’s climate system maintained
in a long-term equilibrium?
2. How do we expect the earth’s ‘thermostat’ to
respond to current anthropogenic greenhouse
gas forcing?
3. Can you imagine a scenario where we push
the system outside of its ability to respond?
4. How might we use our understanding of this
homoestasis mechanism to help with current
anthropogenic forcing?
Snowball
Earth
The trigger: ice forming at
latitudes as low as of 30°
The escape: CO2 levels 350x
higher than today
-635 million years ago
-Lasting ~12 million years
-Oceans froze to depth of 1km
Climate forcing mechanisms
Mechanism
1. Solar Forcing
Solar intensity (sunspots)
Orbital Variations
2. Plate Tectonics
Time period
(10’s to 100’s of years)
(Thousands of years)
(Millions of years)
Mountain building, continent locations
3. Albedo
4. Aerosols
(all time scales)
(1-10 years)
Volcanoes, pollution
5. Greenhouse Effect
(all time scales)
CO2, Methane, Water vapor
6. Land use
(1 to 100’s of years)
Radiative Forcing of Climate Change
Radiative forcing is the global average impact on surface or
troposphere temperature due to natural or humancaused (anthropogenic) causes.
Forcing agents (or mechanisms) that cause climate change
•
•
•
•
•
Greenhouse gases
CO2 (Carbon dioxide)
CH4 (Methane)
N2O (Nitrous oxide)
Halocarbons
Aerosols
Ozone
Land-use effect on albedo
Solar
How much do we know about how these agents change the
climate?
How have these agents changed over time?
Drivers of Climate Change
(forcing mechanisms)
Sunspot Cycles (Decades)
Orbital Variations (Thousands of years)
Plate Tectonics (Millions of years)
Volcanic Activity (1-3 years)
Albedo (All time scales)
Greenhouse Effect (All time scales)