Chapter 2: The Physical Environment
Case study: Salmon
Salmon are born in fresh water streams, then swim out to the ocean, then complete their life
cycle as adults by coming back to the fresh water stream and laying eggs again
A lot of then salmon we catch are in the ocean
Potential causes of salmon declines in the North Pacific Ocean:
- dam construction (blocking the salmon from coming back to the steams)
- sediment from logging operations: affecting the breeding habitat
- water pollution
- overharvesting of the salmon
they tried to fix all these problems, and the salmon still were not rebounding….
the conditions of oceans, where salmon spend most time as adults, have also been implicated.
Study found: fish harvest records and showed
alternating periods of high and low production
associated with climatic variation in the North Pacific.
Maybe its just a natural climate variation occurring,
and this is not a real problem.
Study found: Periods of high salmon production in
Alaska corresponded with periods of low production in
Oregon and Washington.
They also found a correlation between these salmon
production shifts and sea surface temperatures.
North Pacific Warm phase = cold phase Alaska
*Cool water has a lot of upbringings of deep ocean
nutrients, so theres a higher production of things the
salmon eats –therefore more salmon
warm water = low nutrition = less food supply
The physical environment ultimately determines where organisms can live (in terms of their physiological tolerance – hot, cold, dry), and the
resources that are available. (minerals available for plants – prey/soil)
Thus, understanding the physical environment is key to understanding all ecological
Weather: Current conditions—temperature, precipitation, humidity, cloud cover.
- Short term changes on a daily/weekly basis
Climate: Long-term description of weather, based on averages and variation measured over
- states in general what the weather is like in a certain area over a 30 yrs timespan
Climatic variation includes daily and seasonal cycles, as well as yearly and decadal cycles.
Long-term climate change results from changes in the intensity and distribution of solar
Current climate change is due to increased CO an2 other gases in the atmosphere due to
Climate determines the geographic distribution of organisms.
- Ex. Mean temperature is important to know where some organisms can live
Climate is characterized by average conditions – which effects which organisms can live there
based on the averages
BUT extreme conditions are more important to the distribution of organisms (where they can
live in persist), as extremes can contribute to mortality.
- IE extremes determine what organism will be there in the long-term – not means
Ex. Pinon pine tree in the S/W US that are physiologically well adapted to tolerate
the average dry & warm conditions in that area – BUT there are limits
3 years of very high temperatures and extreme drought (most died)
o now it may take 4-5 decades for this forest to return if there are no
more extreme drought conditions
Thus, the physical environment must also be characterized by its variability (extremes)
over time, not just by average conditions
Why do we have different climate patterns globally?
The sun is the ultimate source of energy that drives the global climate system.
- Differential gains of solar radiation across the world determine why we have different
Global energy BALANCE drives the climate system
- Energy gains from solar radiation must be offset by energy losses if Earth’s temperature
is to remain the same. INPUT OF ENERGY SUN RADITION
Climate – Earth’s energy balance 1. MOST (½) is absorbed by the earth heat up earth
2. 1/3 reflected back: by clouds; some off earth surface
3. 1/5 is absorbed by gas / atmosphere
*This is balanced by energy lost to maintain stable
OUTPUT OF ENERGY (#’d increasing
1. MOST is lost with long wave radiation from clouds,
atmosphere & earth
2. Latent heat: evapotranspiration – state change of water
from a liquid to a gas, it gives off heat (ex b/c plants
3. Sensible heat: when warm earth/water is in contact
with cold atmosphere, it’ll loose some of its energy to it
a. Conduction & convection
* Earth actually emits more energy than it receives, BUT most is reabsorbed
The atmosphere contains greenhouse gases that absorb and reradiate the infrared (long
wave) radiation emitted by Earth.
- They are only bad b/c we’re increasing them very rapidly, which is causing earth to
absorb more of the radiation which is causing global warming
- BUT THEY ARE NEEDED – w/o them our climate would be ~33°C cooler.
Thus, they are required to maintain our temperatures and life on earth
These greenhouse gases - radiatively active gases – include:
Water vapor (H O2
Carbon dioxide (CO )2– highest concentration
Methane (CH ) 4
Nitrous oxide (N O)
- these are produced through biological activity, thus linking the biosphere to the
2 Main Latitudinal Differences in Solar Radiation at Earth’s Surface
Equator: hit’s perpendicular: straightes: hit’s obliquely: on an angle
1) radiation does NOT need to 1) radiation TRAVELS LONGER through the
TRAVEL FAR through the atmosphere, *thus more energy
atmosphere absorbed/reflected by atmosphere before it
reaches the surface
2) (small circle) radiation is
distributed over a small area 2) same amount of incoming energy is
distributed over a larger area
IE: the amount of energy PER SQUARE METER coming in at the equator > at the poles
- This is the driving force for climate dynamics (warm/cold fronts, storms,pressure
systems) Why does this matter?
Solar radiation heats Earth’s surface, which emits infrared radiation to the atmosphere,
warming the air above it.
- because not every location on earth receives the same amount of energy from the sun –
solar radiation effects the wind patterns & precipitation patterns
What happens when you heat one area more than another?
Overtime this is what’s happening at the equator
Warm air is less dense than cool air, and it rises—this is called uplift.
Air pressure decreases with altitude, so the rising air expands and cools.
- cool air retains less moisture, so condensation/CLOUDS form until the moisture can not
longer be held in the air and it starts to rain
This is a low pressure system: less pressure
from the atmosphere because the (warm)
air is constantly rising…(& cooling &
moisture comes out and it rains.)
Differential Solar heating of Earth’s surface
Tropical regions receive the most solar radiation and therefore most precipitation.
Uplift of air in the tropics results in a low atmospheric pressure zone.
Uplift evidentially has to stop because of the different layers of the atmosphere:
- When air masses reach the troposphere–stratosphere boundary, air flows (sideways)
towards the poles.
As air moves towards the poles, it cools more b/c of heat exchange with the
surrounding colder air – once it’s the same temp as surroundings, it drops
Tropical Heating and Atmospheric Circulation Cells
Hadley cell: circulation of air flow from equator moving 30°C
N & S of equator from low to high to low pressures
@ equator: LowPressure: heating = uplift = ^ precipitation
@ 30°C N/S: High pressure: subsidence (air cools more &
drops back down)
Very dry - b/c subsidence inhibits cloud formation
The worlds major desserts are found at these latitudes Global Atmospheric Circulation Cells and Climatic Zones
Hadley cell: formed by tropical uplift of warm air at the
equator – LOW PRESSURE
Polar cell: formed by subsidence of cold air at poles; moves
towards the equator when it hits the earths surface – HIGH
PRESSURE (so low precipitation) – ―polar desserts)
Ferrell cell: intermediate cell – ―parasitic‖ b/c driven by the
movement of Hadley and polar cells in the same direction,
which pushes this cell in the opposite direction
- & driven by exchange of energy between tropical
and polar air masses at the polar front
These three cells result in the three major climatic
zones in each hemisphere—tropical, temperate, and
These cells divide up how we view the earths climate AND EFFECT WIND PATTERNS:
Areas of high and low pressure created by the circulation cells result in consistent patterns of
air movements called prevailing winds (in the direction of the arrows) – west/east
The winds appear to be deflected due to the rotation of the Earth —the Coriolis effect. – b/c
the observer is moving with the earth rotation
- Northern hem = winds appear deflected to the right
- Southern hem = winds appear deflected to the left
- An observer from a standpoint in space does not see the deflection of wind
The Coriolis Effect on Global Wind Equator/tropics: – Hadley cells
Patterns - NE/SE Trade winds: blow towards the west
o b/c Sailships during 15 century
Poles: - Polar cells
- Easterlies - in the same direction of the trade winds
- – b/c from the east to the west.
Temperate: - Ferrell cells -- (US!)
- Westerlies - only ones that move in the opposite
o b/c from west to east (why east is ghetto here)
- this is b/c the Ferrell cells move in the opposite
direction of the polar and Hadley cells Prevailing wind patterns are actually more complicated b/c of continents & oceans
Water has a higher heat capacity than land—it can absorb and store more energy without
changing temperature. --- takes a lot longer to heat up or cool down than land
Summer: Air over oceans is cooler and denser (than land air), so air subsides and high
pressures develop over the oceans.
Winter: Air over continents is cooler and denser (than ocean air); so high pressure develops
- *These are known as semipermanent high and low pressure cells *
semipermanent b/c they occur there for one season at a time
remember: AIR FLOWS FROM HIGH TO LOW PRESSURES
follow same general prevailing patterns…but all messed up
have more effects in the northern hem b/c more land mass here
Prevailing Wind Patterns (JULY) Prevailing Wind Patterns (JANUARY)
SUMMER: -like the equator WINTER: Opposite – reversal of semiperm cells
Over land (warmer) = low pressure systems Over land (cooler) = high pressure systems
Over Oceans (cooler) = high pressure systems Over Oceans (warmer) = low pressure systems
Major ocean surface currents are driven by surface winds, so patterns are similar.
Speed of ocean currents is about 2%–3% of the wind speed.
Ocean currents affect clima