Earth Systems ScienceChapter 1

I. CHANGES• it is the nature of dynamic systems to change, often even in the

absence of external “forcings”. Some important environmental problems today require discriminating between “natural” and “anthropogenic” changes.

• Human impact on local environments have been known for years: e.g. deforestation in New England and Europe

• Today, regional impacts (acid rain, air pollution) and global impacts (“global warming”, stratospheric ozone, deforestation) are also realized to be important.

II. 3 MAJOR THEMES OF THE TEXT:

1. Global environmental issues (“global warming”, stratospheric ozone, deforestation)

2. Paleo-environmental changes

3. Systems

Our goal in this class is to cover #1 and #2 as we go, but to really focus on #3.

The Earth System: atmosphere, hydrosphere, lithosphere, biosphere. In this course we focus on the first three, the continuation of this course will focus more on the biosphere.

III. GLOBAL CHANGE ON SHORT TIME SCALES

1. Global Warming

2. Stratospheric Ozone Depletion

3. Deforestation and Loss of Biodiversity

How are these problems related?

How are they examples of dynamic systems / dynamic equilibrium

1. GLOBAL WARMING

• define: global warming, greenhouse effect

• EVIDENCE OF GREENHOUSE GAS CHANGES:

CO2 fluctuations Keeling curve, and ice core data

Other greenhouse gases: methane (CH4), nitrous oxide(N20), and CFCs.

• EVIDENCE OF TEMPERATURE CHANGES

Surface temperature observations

The Keeling Curve

http://scrippsco2.ucsd.edu/graphics_gallery/mauna_loa_record/mauna_loa_fossil_fuel_trend.html

Black Curve: Monthly average atmospheric carbon dioxide concentration versus time at Mauna Loa Observatory, Hawaii (20°N, 156°W) where CO2 concentration is in parts per million in the mole fraction (p.p.m.).

Red Curve: Fossil fuel trend of a fixed fraction (57%) of the cumulative industrial emissions of CO2 from fossil fuel combustion and cement production.

Data from Scripps CO2 Program.

Ice Core Data and The Keeling Curve

Surface Temperature Observations

http://data.giss.nasa.gov/gistemp/graphs/

2. STRATOSPHERIC OZONE DEPLETION

• stratospheric vs tropospheric ozone

• The ozone hole: How was it discovered, how was it “solved” (not in text)

• Ozone depletions in other regions

The Antarctic Ozone Hole

The Antarctic Ozone Hole

3. DEFORESTATION AND LOSS OF BIODIVERSITY

• e.g. Europe, New England, and now tropical forests

• Always changes the landscape, often reduces the complexity (e.g. forest to crops) in terms of flora and fauna

• Global tropical forest coverage less than half the area estimated for prehistoric times.

1. Global Warming

2. Stratospheric Ozone Depletion

3. Deforestation and Loss of Biodiversity

HOW ARE THESE DIFFERENT PROBLEMS RELATED?

HOW ARE EACH OF THESE AN EXAMPLE OF “DYNAMIC EQUILIBRIUM” ?

IV. GLOBAL CHANGE ON LONG TIME SCALES

Long = thousands of years or more

Geologic Time Scale: eon, era, period, epoch

Three examples of long term changes:

1. GLACIAL CYCLES: The Vostok Ice core data

2. MASS EXTINCTIONS: Iridium at the K-T boundary

3. CHANGES IN SOLAR LUMINOSITY: the “faint young sun paradox”

1. GEOLOGIC TIME SCALE

Eon: 108-1010 yrs

Era : 107-108 yrs

Period : 106-107 yrs

Epoch : 104-106 yrs

GEOLOGIC TIME SCALE

K-T Boundary

Glacial Cycles

1. GLACIAL CYCLES: THE VOSTOK ICE-CORE DATA

C02, CH4, and temperature time series for the last 400,000 years

How are they derived: isotope analysis (O and H)

These co-varying changes are interpreted as evidence of system-like behavior

http://www.realclimate.org/epica.jpg

2. MASS EXTINCTIONS: IRIDIUM AT THE K-T BOUNDARY

• Extinction of dinosaurs, many other marine and terrestrial species (both animal and plant)

• Iridium: deposited at a very slow, but known, rate from extraterrestrial sources. The iridium concentrations in the layer at the K-T boundary were so high that it could not have been deposited by normal deposition. So, it must have been a very massive, sudden extraterrestrial source.

• Example of a “shock” to the earth system. The climate, biosphere, recovered, but at different rates. Biosphere “recovery” was very different from prior biosphere.

• Relevance to anthropogenic changes in biodiversity today

IRIDIUM AT THE K-T BOUNDARY

3. CHANGES IN SOLAR LUMINOSITY

• Solar physicists tell us that the amount of energy emitted by the sun was ~30% less 4.6 billion years ago when the sun formed

• The “faint young sun paradox”: why wasn’t the earth frozen over when the solar luminosity was so low?

3. CHANGES IN SOLAR LUMINOSITY (cont’d)

• The Gaia Hypothesis: Lovelock and Margulis. Believe that the biosphere, responding to climatic changes, have affected the earth system in such a way as to help maintain a relatively stable climate. Not a conscience action; not resilient to all possible changes

• Also possible that abiotic factors in the earth system played a role, not necessarily the biosphere.