GEO-113: ENVIRONMENTAL GEOLOGY
GLOBAL CLIMATE CHANGE
I. Glaciers and Ice Ages
1) Glaciers themselves are generally not a great hazard. Generally occur in areas with cold climates with low populations and they move slowly. However, some may dam streams or melt suddenly and cause flooding. Also generate icebergs if they flow to the sea.
2) Important because of the huge amount of fresh water stored in glaciers. Exert a short-term (geologically) control on sea level. 97% of earth's surface water in oceans, 2.25% of earth's surface water in glaciers. Represents 75% of earth’s available freshwater.
3) 15,000 years ago glaciers covered all of Canada and much of the northern United States and Europe – as far south as NYC. Sea level was 300 feet lower and shoreline was 75-100 miles east of present day New Jersey coast. Similar scenarios have happened repeatedly throughout earth's history.
4) What causes Ice Ages? Many possibilities. More than one controlling factor may be required.
a) Changes in solar energy: Sun's energy output varies slightly over time.
b) Wobble of earth’s rotation axis: Varies from 21.2 degrees to 24.5 degrees
c) Orbital eccentricity and precession of the equinoxes: Changes the amount of solar energy earth absorbs.
These first three are referred to as extraterrestrial controls
d) Distribution of the continents due to plate tectonics: Large continental masses near poles tend to have more extreme climates than isolated island continents
e) Volcanic activity: Ash can block sunlight lowering temperatures or gases can absorb energy increasing temperature.
f) Subduction of carbonates: Increased subduction of carbonates increases CO2 in the atmosphere due to subsequent volcanic activity. Amount of CO2 in the atmosphere may control global temperatures through the "Green House Effect." Rates of weathering of carbonates also may play a role. Other gasses, such as methane, also may be involved.
II. Global warming
1) Carbon dioxide (CO2) is produced by the burning of fossil fuels (oil, coal, and natural gas) in order to produce energy. Atmospheric CO2 has increased 35+ % since the early 1800s (15% in last 50 years). The more CO2 in the atmosphere, the more heat absorbed. CO2 blocks IR radiation from escaping back into space, much like a pane of glass traps heat in a green house. Other gases do the same thing. However, CO2 is the most abundant and the one we worry about the most.
2) The green house effect may be offset by air pollution. Dust particles and aerosols reflect sun's energy back into space. Clouds do the same thing. Leads to many uncertainties as to what will happen. Try to use complex computer models of the earth's atmosphere and oceans to make predictions about the future. These models are getting better, but still only give gross generalizations.
3) Best estimates are that we may see an average worldwide temperature increase of 2-6 degrees C (4-11 degrees F) by 2100. Already have seen an increase of one degree C in the last 100 years (most of this has occurred in the last 50). Largest increase may be near poles, least near the equator. How the climate may change for any particular spot on the globe is very hard to predict. Some places may even cool down due to changes in ocean currents.
4) Possible Consequences of Global Warming:
a) Shift in climate and agricultural regions – Midwestern U.S. becomes drier and hotter, Canada and Russia become the world’s breadbaskets.
b) Rise in sea level – due to expansion of warmer water plus increased glacial melting
c) Most probable scenario is a 1-5 foot rise in sea level by 2100. Would cause increasing and potentially catastrophic coastal flooding in many coastal areas, cities (Houston, New Orleans, New York, Philadelphia, Trenton, London) and countries. Beach erosion (migration) would become even more pronounced.
d) Spread of tropical diseases such as malaria and West Nile virus.
e) Species either have to migrate quickly or face loss of habitat and extinction.
f) More numerous and severe storm events, such as hurricanes, thunderstorms, and winter blizzards. Due to increased heat (energy source for storms) and evaporation.
It is as warm now, globally, as it has been in the past 400,000 years. By 2100 it may be warmer than in the past 50 m.y. We are running an experiment on our planet that we do not know the outcome of. Are we willing to take the risk?
1) Driven by solar energy. Warmer air rises, causing areas of low pressure, and colder air sinks, causing areas of high pressure. Air flows (wind) between areas of high pressure to areas of low pressure.
2) Globally, air rises at the equator and sinks at poles. Earth’s rotation (deflected to the right in the northern hemisphere and to the left in the southern hemisphere due to Coriolis Effect) and topography deflect air currents from being mostly north-south to being predominantly east-west, depending on latitude. In the United States, winds are mostly west to east (except Florida). In the Caribbean they are predominantly east to west.
3) If the velocity is high enough, the wind can cause erosion, particularly for unconsolidated sediments. Particles get lifted into the air and blown hundreds and hundreds of miles.
4) Dust particles in the wind may cause serious property damage due to abrasion. Ground deflation occurs as smaller grains removed, leaving larger pieces behind. Produces a rock-strewn surface known as desert pavement.
5) Fine silt particles that are blown away are later deposited downwind from the deserts. Form loess deposits. These are very nutrient rich and porous materials. They have good moisture retention and make for excellent agricultural soils. Found in the center of the United States and the steppes of the Ukraine. Deposited there over the last 25,000 years.
6) If enough of the topsoil is removed by the wind a dust bowl situation may result, such as occurred in the U.S. in the 1930s. If this process is severe enough, desertification can occur. This is largely a human-caused phenomenon and is due to a combination of extreme vegetation and soil loss, caused by deforestation, overgrazing, and poor agriculture practices, with drought. Causes an expansion of the desert into formally productive lands. This is a major cause of famine today in Africa.
7) Natural deserts are defined as any area that receives less than 10 inches of rain a year. Many different types and reasons why and where they occur.
a) Polar - Found in Antarctica and northern Canada. Too cold for the air to hold any moisture.
b) Sub Tropical – Areas of perpetual high pressure and sinking air. Found in the Sahara, Australia, and Saudi Arabia. Typically found at 30 degrees north and south latitude.
c) Mid Latitude – Located far from any ocean and therefore little moisture available.
d) Rain Shadow – Caused by large mountain ranges. As air rises over the mountains it cools and precipitation occurs. On the leeward side of the mountains, air sinks, warms, and dries out. Therefore, very little precipitation falls downwind of the mountain range. Known as the orographic effect. Western deserts of the U.S.
e) Coastal – located near cold coastal currents. Causes a constant sinking of warming and drying air. Namib Desert of Southwest Africa.