Transcript Lecture 07 Climate Change A perspective • Change is normal – Seasonal – Yearly: El Nino/La nina – Mid-term: • Medieval warming  little ice age –

Lecture 07
Climate Change
A perspective
• Change is normal
– Seasonal
– Yearly: El Nino/La nina
– Mid-term:
• Medieval warming  little ice age
– Long term: Milankovitch Cycles
• Induced by major events/disturbances
El Niño Southern Oscillations “The Christ Child”
• Prevailing condition: east-to-west trade winds
push warm surface water westward  upwelling
off coast of Peru
• El Nino conditions: winds drop/cease  Fishers
in Peru, Ecuador and Chile get some time off!
• An El Niño winter - unusual weather
patterns all over the world
http://www.osdpd.noaa.gov/ml/ocean/index.html
http://www.noaanews.noaa.gov/stories2009/20090709_elnino.html
• La Niña
– Not as well known as El Niño
– Causes extreme effects that are nearly opposite
to those of El Niño
• In the US, effects are more apparent in winter
–Northwest is wetter and cooler than normal
–Southeast is dryer and warmer than normal
Global temperatures
have fluctuated in the
past
• Ice age temps 4 – 5
C cooler
• Past 1000 years:
– Warm periods: + 0.5C
– Cool periods: -0.5C
• Medieval Warming: roughly AD 950-1250
– Global nature debated
– Warmer in Europe, drier middle east, western
NA
– Probably impacted China
• Probably not associated with changes in
atmospheric CO2 levels
– Mechanism associated with changes in sea
surface temperatures and wind patterns
Long-term Climate Trends – Milankovitch
Cycles
• Summer-winter flux due to inclination of
axis of earth
• Orbit of earth more elliptical that circular
• Periodic coupling of inclination with
eccentric orbit means ~ 100,000 to
400,000 year variation in intensity of solar
radiation at 65N latitude 
warming/cooling at polar latitides
• Catastrophic events and Climate Change:
• Volcanic eruptions, meteor strikes
• Alterations in atmospheric gas
composition
• atmospheric concentration of CO2: 25 percent
increase over the past 100 years
– Continuous observations of atmospheric CO2 started in
1958
– Earlier evidence from air bubbles trapped in the glaciers
of Greenland and Antarctica
• Exponential rise since mid-19th century
• Evidence For
Climate Change
• Temperature
records
• Phrenological
indicators
• Melting of ice
fields and glaciers
• Reduction in size
of ice caps
• Sea/land surface
temperature
anomaly:
difference
between 29 year
average (195180) and annual
temperatures (fig
b shows 2010 in
text)
Atmospheric CO2 and
Global Warming
• Minor component
– 180 ppm during
cooler periods
– 270 ppm during
warmer periods
• Historical association
with changes in
global temperatures
• Current levels ~
375ppm
Long-term Climate Trends
• Human observational records: 200-500 yrs
• Other sources:
•
•
•
•
•
Tree ring/growth
Isotopic analysis
Pollen analysis of sediments
ice core analysis
Fossil evidence
Uptake of carbon dioxide by marine ecosystems:
• The rate of diffusion of CO2 is a function of the diffusion gradient
• Although the oceans have the potential to absorb most
atmospheric carbon derived from fossil fuel combustion and
deforestation, this does not happen
– Thin layer of warm water floating on a much deeper layer of cold water
– Mixing of CO2 does not extend into the deep waters because of the
thermocline
• Greenhouse gases
– Water vapor ~ 60% of effect
– CO2 ~ 20% of effect
– Others ~ 20% of effect
• Methane
• N2O
• Various man made gasses
• Greenhouse effect
– The average surface air temperature of the earth
is 30°C higher than it would be without the
absorption and reradiation of thermal energy
• Since the industrial period began, the
concentrations of greenhouse gases in
Earth’s atmosphere have increased
dramatically
Contributers to Greenhouse Effect
Positive Feedback : Occurrence of an effect
further strengthens effect
Positive Feedback : Occurrence of an effect further
strengthens effect
• Positive Feed Back Effects
– Atmospheric water vapor
– Albedo
• Decreased reflectance
– Release of methane from permafrost and methane
hydrate in deep sea waters
• http://www.youtube.com/watch?v=Wofv9o0j1Ew
– Increase in detrital food chain processes  more CO2
– forest growth decline due to environmental factors
– Decrease in effectiveness of marine food chains in
absorbing atmospheric CO2
–  adds uncertainty to General Circulation Models
Projections for temperature rise
General Circulation Models – or - Global
Climate Models
• Sophisticated numerical mathematical
models used to predict future changes in
climate
• 3 dimensional aspect – consider potential
positive and negative feedback factors
• Make various assumptions
• Provide basis for most climate models
• Unknown or problamatic factors:
– Positive and negative feedbacks
– Changes in ocean circulation patterns
– Tipping points
Ecosystem Effects
• Major focus: Alpine and arctic ecosystems
– Expectations for the future:
• Shifts in vegetation communities up-slope
• Decreased winter snow pack and consequent
drier/longer summer period
• Decreased ‘island’ effect
– GLORIA: Global Observation Research
Initiative in Alpine Environments
Shifts in precipitation
• Sea level rise
– an ice free
planet
Indicators of Climate Change in California
• Rising sea levels, temperatures and
dropping pH
• Rise in lake temperatures
• Decline in spring runoff, glacier melt and
decrease in salmon runs
• Changes in vegetation patterns in the
Sierra
• Massive wild fires