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Climate is the state factor that most strongly governs the global pattern
of ecosystem structure and function
Climate is a key mechanism by which ecosystems interact with
the total Earth System
Major goals in this lecture
• Understand how the climate system
works
• Enable you to predict the climate any
place on Earth
Energy in = energy out
Half of solar radiation
reaches Earth
The atmosphere is
transparent to
shortwave but absorbs
longwave radiation
(greenhouse effect)
The atmosphere is
heated from the bottom
by longwave radiation
and convection
The temperature of a body determines
wavelengths of energy emitted
Solar radiation has high energy
(shortwave) that readily penetrates
the atmosphere
Earth emits low-energy (longwave)
radiation that is absorbed by the
atmosphere
The atmosphere is heated from the
bottom
Therefore it is warmest near the
and gets colder with increasing
elevation
Uneven heating of Earth’s surface causes atmospheric circulation
Greater heating at equator than poles
1. sun’s rays hit more directly
2. less atmosphere to penetrate
Therefore
1. Net gain of energy at equator
2. Net loss of energy at poles
Air rises at equator and subsides at poles
(vertical circulation)
Circulation cells explain
global distribution of rainfall
Earth’s rotation determines
wind direction
(horizontal circulation)
(Coriolis force)
tropical easterlies
temperate westerlies
At 30º N & S, air descends more strongly over cold ocean than over land
At 60 º N & S, air descends over cold land (high pressure) and rises over
warm ocean (low pressure)
Pressure gradients create geographic variation in prevailing winds
In summer at 60 º N & S, air descends over cold ocean (high pressure)
and rises over warm land (low pressure)
1. Cool equator-ward flow of air on W coast of continents
2. Warm poleward flow of air on E coasts of continents
Creates planetary waves
Ocean currents are similar to wind patterns:
1. Driven by Coriolis forces
2. Driven by winds
Climate of any region is predictable from topography, wind
and ocean currents
Alaska’s July temperature
Warming leads to thawing of
permafrost in Alaska
Uneven heating of Earth’s surface causes atmospheric circulation
60% of heat transport is carried by atmosphere through storms that
Move along pressure gradients
40% is carried by ocean currents (conveyor belt)
surface (warm) currents move poleward
deep (cold) currents move equatorward
Ocean currents move 40% of “excess heat” from equator to poles
Driven by circulation of deep ocean waters
Deepwater formation occurs near Greenland and in Antarctic
Landform effects on climate
• Land-water interactions
– Monsoons
– Land-sea breezes
• Mountain effects
– Rain shadow
– Effects of aspect
– Air drainage (inversion)
Climate effects on vegetation
Vegetation effects on climate
How can the atmosphere warm?
1. More solar radiation
variation in Earth’s orbit
2. Less reflected shortwave
less sulfate aerosols
darker surface of Earth
(land-cover change)
3. More absorbed longwave
more “greenhouse gases”
Earth’s climate is now warmer than at any time in the last 1000 years
1. increased solar input (small warming effect)
2. Increased sulfate aerosols reflects radiation (small cooling effect)
3. Increased greenhouse gas concentrations (large warming effect)
4. Land-cover change creates a darker surface (large warming effect)
Changes in solar orbit causes long-term variations in solar input to Earth
Most major greenhouse gases are increasing
in atmospheric concentrations
Climate is warming most rapidly at high latitudes
This warming is most pronounced in Siberia and western North America
The Pacific Ocean strongly influences the climate system because
It is the largest ocean basin
Normal ocean current and wind direction in central Pacific is easterly
Interannual climate variation
ENSO events
Teleconnections carry these
climate effects throughout
the globe
(e.g., El Niño creates warm
winters in AK and Calif)
Seasonal variation in climate results from tilt in Earth’s axis
Changes sun angle and day length
Functioning of ecosystems varies predictably with climate
Climate gives rise to predictable types of ecosystems
Ecosystem distribution of ecosystems is predictable from global
patterns of wind and ocean circulation