Global Climate Change

Climate Review

Global Circulation

• The solar radiation hitting the Earth is unequal…WHY?– Earth is oblate (slightly flattened)

Global Circulation• Although the loss and gain of radiation is balanced

over the entire climate system, no one part of the planet’s surface is in equilibrium at a given time.

Winter (Northern Hemisphere tilts away from sun)

Spring (sun aims directly at equator)

Summer (Northern Hemisphere tilts toward sun)

Fall (sun aims directly at equator)

23½°To Polaris

The tilt (23½° inclination) causes the seasons

The Earth is tilted and rotating and revolving

Solar Heating of Earth Varies with Latitude

• The atmosphere reflects, scatters and absorbs solar radiation.

• At high latitudes solar radiation travels a longer path through atmosphere.

• Equal amounts of sunlight are spread over a greater surface area near the poles than in the tropics.

• Ice near the poles reflects much of the energy that reaches the surface there.

• Heat gained at Equatorial latitudes• Heat lost at higher latitudes• Winds and ocean currents redistribute heat

around the Earth• Oceans do not boil away near the equator or

freeze solid near the poles because heat is transferred by winds and ocean currents from equatorial to polar regions.

Heat Redistributed

Physical Properties of the Atmosphere: Density• Warm, low density air

rises• Cool, high density air

sinks• Creates circular- moving

loop of air (convection cell)

Physical Properties of the Atmosphere: Water Vapor• Cool air cannot hold

much water vapor, so is typically dry

• Warm air can hold more water vapor, so is typically moist

• Water vapor decreases the density of air

• A column of cool, dense air causes high pressure at the surface, which will lead to sinking air

• A column of warm, less dense air causes low pressure at the surface, which will lead to rising air

Physical Properties of the Atmosphere: Pressure

Physical Properties of the Atmosphere: Movement

• Air always moves from high-pressure regions toward low-pressure regions

• Moving air is called wind

Atmospheric Circulation (convection)

• Heated air rises at equator

• Cooler air descends at poles

Maximum Sun warming

The Coriolis Effect

• As Earth rotates, different latitudes travel at different speeds

• The change in speed with latitude causes the Coriolis effect

The Coriolis Effect• The rotation of the Earth deflects

the path of moving objects.

• As observed from space, cannonball 1 (shot northward) and cannonball 2 (shot southward) move as we might expect; that is, they travel straight away from the cannons and fall to Earth.

• Observed from the ground, however, cannonball 1 veers slightly east and cannonball 2 veers slightly west of their intended targets.

• The effect depends on the observer’s frame of reference.

The Coriolis effect• The Coriolis effect

– Is a result of Earth’s rotation– Causes moving objects to follow

curved paths:• In Northern Hemisphere, curvature is to right• In Southern Hemisphere, curvature is to left

– Changes with latitude:• No Coriolis effect at Equator• Maximum Coriolis effect at poles

Add rotation Add land massUnequal heating and cooling of the Earth

Wind Belts of the World

The Total Atmosphere Effect

Global air circulation as described in the six-cell circulation model. Air rises at the equator and falls at the poles, but instead of one great circuit in each hemisphere from equator to pole, there are three in each hemisphere.

Ocean Currents

• Surface Currents– The upper 400 meters of the

ocean (10%).

– Wind-driven currents occur in the uppermost 100 m or less

• Deep Water Currents– Thermal Currents (90%)– Density differences causes by

salinity and temperature produce very slow flows in deeper waters.

Upwelling and Downwelling

Vertical movement of water – Upwelling = movement of deep water to surface

• Hoists cold, nutrient-rich water to surface• Produces high productivities and abundant marine

life– Downwelling = movement of surface water

down• Moves warm, nutrient-depleted surface water down• Not associated with high productivities or abundant

marine life

El Niño-Southern Oscillation (ENSO)

• El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around Christmastime

• Southern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El Niño

• ENSO describes a combined oceanic-atmospheric disturbance

Thermalhaline circulation of the Earth’s oceans transfers heat from the equator to the higher latitudes

How does water vapor affect climate?

• Warmer conditions increase the amount of evaporation, which then leads to the vast amount of clouds forming

• Some clouds trap heat (positive feedback) or they may reflect the sunlight and cool the air (negative feedback)