ESS 111 – Climate & Global Change

Lecture 3

Greenhouse Effect

El Nino – Southern Oscillation

What is the Greenhouse Effect?

Review of Energy

– What is energy? – 3 methods of energy transfer?

– Conduction– Convection– Radiation– http://www.hk-phy.org/energy/domestic/heat_phy/

flash/heat_transfer_e.html

– Insolation (Incoming Solar Radiation) = shortwave radiation

– Heat energy emitted by the Earth (ground) = longwave radiation

Earth’s energy budgetYellow: shortwave

Red: longwave

Satellite Measurements of the Earth’s Radiation Budget

NASA’s Earth Radiation Budget Satellite (ERBS) 1985-1989

Earth’s energy budget (averaged over the whole globe & a long time

At the top of the atmosphere: Incoming shortwave = Reflected Shortwave + Emitted longwave

At the surface: Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) + Latent heat flux + sensible heat flux

Sensible heat 7%

Latent heat 23%

Net Longwave 21%

Yellow: shortwave

Red: longwave

Atmospheric influences on radiation

ReflectionReflection ScatteringScattering Absorption Absorption (absorber (absorber warms)warms)

Atmospheric Absorption - The Greenhouse EffectAtmospheric Absorption - The Greenhouse Effect

Transparent Transparent to solar to solar (shortwave) (shortwave) radiationradiation

Opaque to Opaque to earthearth’’s s (longwave) (longwave) radiationradiation

Major GH gases: CO2, H20(v), CH4

Impact of the Greenhouse Effect

The Goldilocks Principle can be summed up neatly as "Venus is too hot, Mars is too cold, and Earth is just right." The fact that Earth has an average surface temperature comfortably between the boiling point and freezing point of water, and thus is suitable for our sort of life, cannot be explained by simply suggesting that our planet orbits at just the right distance from the sun to absorb just the right amount of solar radiation. Our moderate temperatures are also the result of having just the right kind of atmosphere. A Venus-type atmosphere would produce hellish, Venus-like conditions on our planet; a Mars atmosphere would leave us shivering in a Martian-type deep freeze.

Greenhouse GasesWater Vapor is by far the most abundant GHG.Methane (CH4) 23 times more powerful as a greenhouse gas than CO2

The livestock sector is a major player, which accounts for 35-40% global anthropogenic emissions of methane (their burps!)

3 Types of Scattering: 1. Raleigh2. Mie3. Non-Selective

Atmospheric Scattering

A discussion of each type follows…A discussion of each type follows…

• involves gases smaller than insolation wavelength• scatters light in all directions • most effective at short wavelengths (violet, blue)

… hence, blue sky

Rayleigh Scattering

The Earth has an atmosphere. So it has Rayleigh scattering and its sky appears blue

The Moon has no atmosphere. So it has no Rayleigh scattering and its sky appears dark

• Rayleigh scattering also explains reddish-orange sunsets when light travels through thick slice of atmosphere

Monet: Impressions, Sunrise

2) Mie scatteringinvolves aerosols (e.g. dust, smoke) larger than gas moleculesforward scatterequally effective across visible spectrumexplains hazy, gray days

3) Non-selective scatteringHappens when atmospheric particles are much larger than the wavelength of incoming radiation (e.g. water droplets in clouds)Act like lenses; scatter all wavelengths equally to create a white appearanceThat’s why clouds appear white

Summary: Earth’s energy budget

At the top of the atmosphere: Incoming shortwave = Reflected Shortwave + Emitted longwave

At the surface: Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) + Latent heat flux + sensible heat flux

Sensible heat 7%

Latent heat 23%

Net Longwave 21%

Yellow: shortwave

Red: longwave

What Are the El Nino and La Nina?

The Walker Circulation• Mean ascent (rising air), and low surface pressure, over warmest SST associated with deep convection (T-storms)

• Subsidence (sinking air), and high surface pressure, in non-convection regions (clear skies)

• Equatorial trades blow from high to low pressure, thus the easterly trade winds blow from east to west

Low slp

High slp

El Nino

During El Nino trade winds slacken

E-W tilt of thermocline & upwelling of cold water are reduced.

SST rises in central/eastern equatorial Pacific

Changes Walker Circulation

Tropical mean state: Sea surface temperature (SST)

Indo-Pacific warm pool

Eastern Pacific cold tongue

2 basic regions

Ocean Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water.

Ocean upwelling & the Thermocline

The thermocline is the transition layer between the mixed layer at the surface and the deep water layer. The definitions of these layers are based on temperature.The mixed layer is near the surface where the temperature is roughly that of surface water. In the thermocline, the temperature decreases rapidly from the mixed layer temperature to the much colder deep water temperature.

The mixed layer and the deep water layer are relatively uniform in temperature, while the thermocline represents the transition zone between the two.

Thermocline and wind patterns during the normal Walker Circulation. Cooler, nutrient rich water moves upward from below along the South American coast.

Thermocline, Upwelling, & El Nino

Thermocline and wind patterns during the normal El Nino – Southern Oscillation conditionsCooler, nutrient rich water does not “upwell” to the ocean surface.Warm surface water piles up along the South American Coast.

Mean climate El Niño ’82/83

El Nino

SST anomalies during El Nino

Dec 1982

Sept 1987

ENSO Comparison Animations

https://www.youtube.com/watch?v=9rPqIuXlWuA

https://www.youtube.com/watch?v=whsQbIwWjBo

The 1997/98 El NinoJan 1997

Trade Winds

The 1997/98 El NinoNov 1997Jun 1997

Trade Winds

The 1997/98 El NinoNov 1997

Trade Winds

The 1997/98 El NinoMar 1998

Trade Winds

The 1997/98 El NinoMar 1998Jan 1997

The 1997/98 El NinoJun 1997

The 1997/98 El NinoNov 1997

The 1997/98 El NinoMar 1998

What about La Nina?

Dec 1982

Nov 1988

La Nina conditions sometimes occur in the year following an El Nino event (e.g. 1988 followed 1987 El Nino)

In La Nina conditions SST in the central and eastern equatorial Pacific is unusually cold & easterly trade winds are unusually strong

Typical ENSO period is 3-7 years, but with significant irregularity

The dramatic impacts of ENSO around the globe

Flood in Lakeport, California as a result of the 1998 El Nino event

Bushfire in Australia as a result of the 1998 El Nino event

The dramatic impacts of ENSO around the globe

Flood in Lakeport, California as a result of the 1998 El Nino event

Bushfire in Australia as a result of the 1998 El Nino event

Disastrous effects of 1982-1983 El Nino:1.Australia-Drought and devastating brush fires 2.Indonesia, Philippines-Crops fail, starvation follows3.India, Sri Lanka-Drought,fresh water shortages4.Tahiti-6 tropical cyclones5.South America-Fish industry devastated - decrease in nutrients off Peru- fewer fish (anchovy)6.Across the Pacific-Coral reefs die7.Colorado River basin-Flooding, mud slides8.Gulf states-Downpours cause death, property damage9.Peru, Ecuador-Floods, landslides10.Southern Africa-Drought, disease, malnutrition

• A seasonal reversal of wind due to seasonal thermal differences between landmasses and large water bodies

• Orographic lifting often enhances precipitation totals

The Seasonal “Monsoon”