Notes

Outline

Earth System Climatology (ESS200A)

Syllabus

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Circulation of the Solid Earth

Tectonic Control of CO2 Input – The Seafloor Spreading Rate Hypothesis During active plate tectonic processes, carbon cycles constantly between Earth’s interior and its surface. The carbon moves from deep rock reservoirs to the surface mainly as CO2 gas associated with volcanic activity along the margins of Earth’s tectonic plates. The centerpiece of the seafloor spreading hypothesis is the concept that changes in the rate of seafloor spreading over millions of years control the rate of delivery of CO2 to the atmosphere from the large rock reservoir of carbon, with the resulting changes in atmospheric CO2 concentrations controlling Earth’s climate.

Chemical Weathering The precipitation process in the atmosphere dissolve and remove CO2 from the atmosphere. Rocks exposed at Earth’s surface undergo chemical attack from this rain of dilute acid. This whole process is known as chemical weathering. The rate of chemical weathering tend to increase as temperature increases. Weathering requires water as a medium both for the dissolution of minerals and for the transport of the dissolved materials to the ocean       è The rate of chemical weathering increases as precipitation increases.

Tectonic-Scale Climate Change The faint young Sun paradox and its possible explanation. Why was Earth ice-free even at the poles 100 Myr ago (the Mesozoic Era)? What caused Earth’s climate to cool over the last 55 Myr (the Cenozoic Era)?

Climate Roles of Land Surface  greenhouse gas emissions       è affects global energy and biogeochemical cycles  creation of aerosols       è affects global energy and water cycles  surface reflectivity (albedo)       è affects global energy cycle  impacts on surface hydrology        è affect global water cycle

Surface Albedo

Feedback Mechanism: Albedo è Energy Cycle

Feedback Mechanism: Transpiration è Water Cycle

Lecture 1: Atmosphere Composition

Thickness of the Atmosphere The thickness of the atmosphere is only about 2% of Earth’s thickness (Earth’s radius = ~6400km). Most of the atmospheric mass is confined in the lowest 100 km above the sea level.

Vertical Structure of the Atmosphere

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Origins of the Atmosphere When the Earth was formed 4.6 billion years ago, Earth’s atmosphere was probably mostly hydrogen (H) and helium (He) plus hydrogen compounds, such as methane (CH4)  and ammonia (NH3). Those gases eventually escaped to the space. The release of gases from rock through volcanic eruption (so-called outgassing) was the principal source of atmospheric gases. The primeval atmosphere produced by the outgassing was mostly carbon dioxide (CO2) with some Nitrogen (N2) and water vapor (H2O), and trace amounts of other gases.

What Happened to H2O? The atmosphere can only small fraction of the mass of water vapor that has been injected into it during volcanic eruption, most of the water vapor was condensed into clouds and rains and gave rise to oceans. è The concentration of  water vapor in the atmosphere was substantially reduced.

What happened to CO2? Chemical weather is the primary process to remove CO2 from the atmosphere. In this process, CO2 dissolves in rainwater producing weak carbonic acid that reacts chemically with bedrock and produces carbonate compounds. This biogeochemical process reduced CO2 in the atmosphere and locked carbon in rocks and mineral.

What Happened to N2? Nitrogen (N2):    (1) is inert chemically,    (2) has molecular speeds too slow to escape to space,    (3) is not very soluble in water. The amount of nitrogen being cycled out of the atmosphere was limited. Nitrogen became the most abundant gas in the atmosphere.

Where Did O2 Come from?  Photosynthesis was the primary process to increase the amount of oxygen in the atmosphere. Primitive forms of life in oceans began to produce oxygen through photosynthesis probably 2.5 billion years ago. With the concurrent decline of CO2, oxygen became the second most abundant atmospheric as after nitrogen.

Formation of Ozone (O3) With oxygen emerging as a major component of the atmosphere, the concentration of ozone increased in the atmosphere through a photodissociation process.

Ozone (O3)

Where Did Argon Come from?   Radioactive decay in the planet’s bedrock added argon (Ar) to the evolving atmosphere. è Argon became the third abundant gas in the atmosphere.

Other Atmospheric Constituents  Aerosols: small solid particles and liquid droplets in the air. They serve as condensation nuclei for cloud formation. Air Pollutant: a gas or aerosol produce by human activity whose concentration threatens living organisms or the environment.

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Variations in Tropopause Height

Stratosphere

Ozone (O3)

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