Overview of the Past and Present

Earth System

Observations of the Earth

OSHR 1609

Climate 101

September 20, 2013

Scott Denning, CSU

The Earth System

The Earth SystemThe Earth’s climate results from the interaction of many

properties and processes– Solar radiation and orbital geometry– The size, gravitational force, and rotation rate of the planet– The composition, structure, and internal dynamics of the

planet– The geography of continents, glaciers, mountain ranges, and

oceans– Ocean properties and circulation– Atmospheric constituents, their chemical interactions,

circulation, and the hydrologic cycle– The living ecosystems that inhabit the planet, and the

biogeochemical transformations they conduct

Origins

• Earth formed by gravitational accretion ~ 4.7 billion years ago

• Solar “constant” was ~ 30% less than today

• Impact heating kept surface hot and sterile

• Giant collision separated the Moon and helped differentiate chemical layers

Evolution of the Atmosphere

1) Volcanic emissions– Water vapor 85%– Carbon dioxide 10%– Nitrogen 1 - 5 %– Sulfur 1 - 5 %– Particles and surface materials

2) When collisions became less frequent, planet cooled3) Water vapor condensed, forming oceans

4) Strong acids (HCl, HNO3, H2SO4) dissolved readily into the oceans, taken out of atmosphere, combined with dissolved materials from continental weathering to make sea salt

5) Condensation of oceans, aqueous chemistry, and sedimentation have steadily depleted CO2

6) Role of life in creating oxygen & O3 and in depleting CO2

Plate Tectonics• Continental plates are lighter (buoyant) and rise in

collisions, whereas oceanic plates subduct• Continents can “bunch up” due to collisions,

forming supercontinents (“Pangea,” “Gondwana”)• Continental drift can radically alter the geometry

of ocean basins, with corresponding dramatic changes in ocean circulation and poleward heat transport

Image Courtesy USGS

Land and Ocean

• What controls these variations?• What are the consequences in the atmosphere?• What are the consequences in the oceans?

Water on Earth

• Should be called “Planet Water”• Atmosphere is a bit player in storage of

water• Very dynamic cycling

Energy Reservoirs• The oceans are

about 4000 m deep

• The top 10 m equal the mass of the atmosphere

• The top 3 m equal the heat capacity of the atmosphere!

The state of the oceans determines the climateon time scales of thousands to millions of years!

Ocean Atmosphere

Deep, Dark, and Cold

• Warm buoyant “raft” floats at surface• Cold deep water is only “formed” at high

latitudes• Very stable, hard to mix, takes ~ 1000 years!• Icy cold, inky black, most of the ocean

doesn’t know we’re here yet!

sfc

4 km

Ice and

Snow

• Greenland is covered with ice to depths of several kilometers

• Permanent ice cover further north overlies an isolated ocean basin

Land and Sea Ice

Continental Ice

Sea Ice

Cause and Effect

• Climate is a result of physical, chemical, & biological processes

• Forcing causes a response

• Strength of response to unit forcing is called “sensitivity”

Response Times• Response to

climate forcing can be fast, slow or in between

• Persistent forcing produces a range of responses on different time scales

• Eventual equilibration to forcing

Responses to forcing can be fast, slow, or both!

Response Times

Cycles of Forcing

and Response

• Strength of response depends on matching time scales of forcing and response!

• Mismatched time scales may produce a weak response to strong forcing or vice versa

Feedback• Forcing can be

either amplified or reduced by the climate system itself

• Amplifying effects are called “positive feedback”

• Damping effects are called “negative feedback”

Cause and Effect

• External forcing affects internal processes• Internal feedback can amplify or damp

forcing• System responds in many ways over time

Changing Earth System

Climate Changes