Environmental Geology Spring 2010

Greenhouse Effect:

Trapping effect of the atmosphere – atmosphere is relatively transparent to shortwave radiation – about 51% reaches the Earth’s surface.

Earth radiates longwave radiation upwards

Gases and water vapor trap terrestrial longwave radiation. This heats the atmosphere.

This is a totally natural process. If it did not exist life on Earth would not exist as we know it.

Humans have disrupted the balance by burning fossil fuels and deforestation, among other.

Burning of fossil fuels releases carbon dioxide, carbon monoxide, nitrogen gases, and sulfur dioxide into the atmosphere.

Deforestation results in less uptake of CO2 by plants.

Water vapor is the most important heat trapping substance in the atmosphere.

CO2 is next most important, then methane, then CFC’s, then NOx

Atmospheric composition:

• 78% nitrogen
• 21% oxygen
• 1% trace gases not including the water vapor

This 1 % is made up of about 0.93% argon and 0.03% CO2; everything else including O3 account for only 0.00006%.

Positive and Negative Feedback Mechanisms

Positive Feedback:

• Initial change is reinforced by other processes

• More CO2 in atmosphere >>>greater trapping of longwave radiation>>>greater global temperatures

• Greater global temperatures>>>greater evaporation and more water vapor in the atmosphere

• Greater water vapor in the atmosphere>>>more longwave radiation trapping>>>greater global temperatures.

Negative Feeback:

Initial change tends to weaken interaction among the variables.

• Greater water vapor in atmosphere>>>more clouds>>>greater planetary albedo>>>less shortwave radiation reaching the Earth>>>less longwave radiation>>>less atmospheric heating

Record of Atmospheric CO2

Collected at Mona Loa Observatory, Hawaii

1958-present

Site is removed from industrial impacts and is believed to be very representative of global atmospheric CO2.

Atmospheric CO2 at this site has risen from 315 ppm to about 385 ppm in the last 50 years

Data from this site show a saw tooth pattern which is related to seasonal fluctuations resulting from less uptake of CO2 in the northern hemisphere winter when the plants go dormant. This affect is not as pronounced in the southern hemisphere because there is less land mass and fewer seasonally active plants.

Vostoc Ice Core: presents geologic evidence of atmospheric CO2 concentration over about the last 400,000 years.

Data from the ice core were obtained from isotopic analysis of air trapped in the ice when the ice formed. The data indicate that when atmospheric temperatures were high, CO2 and CH4 were also high.

One alarming thing is that over this 200,000 year period the CO2 concentration never exceeded 295 ppm, but it has jumped to about 385 ppm in just over 100 years.

Can’t tell from the ice core data which occurred first; global temperature increase or increase in greenhouse gas concentrations.

Global temperatures have increased about 0.6 degrees C over the last 80 to 100 years and are projected to increase about another 0.5 degrees over the next 20 years and about 1.5 degrees C over the next 60 years.

Is this really so dramatic?

Is it just part of a natural trend?

Is it the end of the world?

Projected rise in sea level resulting from this temperature increase is on the order of 6 to 12 inches.

Some shifts in regional climate patterns may occur.

Grain production in the U.S. heartland and other areas “may” be impacted.

There are a lot of unanswered questions about the impacts of global warming. If you live in North Dakota, it might be a blessing. If you live in western Kansas it might be the end of agriculture as we know it. We just don’t have the answers at this point.

Age of Earth is about 4.6 billion years

Earth’s climate has fluctuated since the planets creation

Factors governing climate change:
1.    composition of gases and aerosols in the atmosphere
2.    amount of solar radiation reaching the Earth
3.    Effect of orbital parameters on radiation budget
4.    shape and location of the continents and oceans
5.    atmospheric/ocean circulation patterns
6.    interaction with global biogeochemical cycles
7.    changes in Earth’s albedo
8.    catastrophic events such as meteor impacts

Proxies for estimating temperature records:
•    Air trapped in ice collected by coring glacial masses (Greenland and Antarctica)
•    Deep sea sediments (fossils of creatures that were temperature sensitive or sensitive to the ratio of oxygen and carbon in their shells)
•    Tree ring analysis
•    Pack rat dens (seeds, and other plant materials stored in these dens)
•    Ancient soils
•    Lake sediments (preserve pollen from plants growing at time sediments were deposited)

Four well documented Ice Houses over geologic time which typically lasted for several 10’s of millions of years.
2.5 billion years bp
700 million years bp
300 million years bp
35 million years bp

Mesozoic Era and Early-Cenozoic Era- Hot House period with average global temperatures 8 to 10 degrees C warmer than today (200 million years bp to 35 million years bp)

Cyclic cooling and warming during later-Cenozoic Era with a downward cooling trend until the Earth entered below average temperatures for an extended period starting at about 2 million years bp.

During last 1 million years there have been 10 major and about 40 minor glacial episodes.  Only twice during this period did average global temperatures exceed the 15 degree normal level.

The last major glaciation began about 110,000 years ago and ended about 18,000 years ago.  This is typical of the cycle, we see glacial periods of about 100,000 years and interglacial periods of about 20,000 years.  If the cycle holds than we should be about to plung into the next glacial period!!!????

During the last 18,000 years steady temperature increase has been observed with a few downturns such as the Little Ice Age in the period from about 1370 to 1880 AD (Ice skating on the Thames – not a chance today!!).