Lecture 07 Climate Change A perspective Change is

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/stories 2009/20090709_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. 5 C – Cool periods: -0. 5 C

• 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 CO 2 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 65 N latitude warming/cooling at polar latitides

• Catastrophic events and Climate Change: • Volcanic eruptions, meteor strikes • Alterations in atmospheric gas composition

• atmospheric concentration of CO 2: 25 percent increase over the past 100 years – Continuous observations of atmospheric CO 2 started in 1958 – Earlier evidence from air bubbles trapped in the glaciers of Greenland Antarctica • Exponential rise since mid-19 th 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 CO 2 and Global Warming • Minor component – 180 ppm during cooler periods – 270 ppm during warmer periods • Historical association with changes in global temperatures • Current levels ~ 375 ppm

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 CO 2 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 CO 2 does not extend into the deep waters because of thermocline

• Greenhouse gases – Water vapor ~ 60% of effect – CO 2 ~ 20% of effect – Others ~ 20% of effect • Methane • N 2 O • 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=Wofv 9 o 0 j 1 Ew – Increase in detrital food chain processes more CO 2 – forest growth decline due to environmental factors – Decrease in effectiveness of marine food chains in absorbing atmospheric CO 2 – 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 p. H • 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