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Shamitha Pula

on 17 December 2014

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The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions.
Absorption Mechanism
H20 and CO2 have strong absorption at the wavelengths given off by thermal radiation.
The absorption of infrared radiation is due to vibrations of molecules. When a vibration causes change in charge distribution (dipole moment) the radiation is absorbed.

Carbon Dioxide (CO2): Chemical sources
Greenhouse gases decrease the planetary albedo; increase radiative forcing.
More radiative forcing means more heat transfer to the atmosphere from solar radiation.
Increased atmospheric heat disrupts the thermohaline cycle and reduces air-ocean heat transfer.
MINOR component of atmosphere
LONG-TERM "forcing" of climate change
Natural: Respiration, Volcano Eruptions
Human Activities: Deforestation, Fossil Fuels
Increased by a third from the time of the Industrial Revolution
Thus, a positive feedback loop,
lasting a thousand years.
Increased temperatures
keeps temperatures increased, keeps oceanic heat absorption low,
keeps temperatures increased, keeps oceanic heat absorption low,
reduce oceanic heat absorption,
keeps temperatures increased, keeps oceanic heat absorption low,
keeps temperatures increased, keeps oceanic heat absorption low...
And so on, allowing ice to melt, and this to happen:
Higher temperatures are more conducive to the spread of insect-vector diseases, as well as heat-related health problems (heat stroke, heart attacks, etc.)
Also affected are large-scale weather patterns, such as tropical storms and droughts (as previously mentioned)
What are the "Greenhouse Gases"?
Major Gases:
Water Vapor (H2O)
Carbon Dioxide (CO2)
Methane (CH4)
Nitrous Oxide (N2O)
Three Main Factors affecting the Greenhouse Effect:
1. Total energy influx from Sun
- depends on distance from Earth and solar activity
2. The ability of the earth's surface to reflect light back into space, which is referred to as Albedo.
The only factor that has changed significantly in the last 100 years is the chemical composition of the atmosphere—and that is because of
human activity.
Natural Greenhouse Effect:
The greenhouse gases (N20, CO2, CH4, H2O), naturally trap the incoming solar radiation and convert it to heat.
These gases act as "thermal blankets" which warm the Earth's surface to a life sustaining 59 F.
The equilibrium of the incoming and outgoing radiation is what makes life sustainable on Earth.
Human Enhanced Greenhouse Effect:
incoming solar radiation 100%
Because of human activities (deforestation etc.), the level of these greenhouse gases in the atmosphere

So more re-radiated heat to the Earth, and less heat escapes into space.
This causes the warming of the earth, leading to the Global Warming issue.
1% absorbed in stratosphere
23% reflected by clouds
3% absorbed by clouds
24% absorbed in troposphere
4% reflected by Earths' surface
Earth's surface

45% reaches Earth's surface overall
Methane (CH4) sources
-Released by natural sources such as wetlands, termites, and bacteria in the oceans
-Humans contribute the majority of methane released to the atmosphere through fossil fuel production, livestock and manure management, waste water treatment and landfills, accounting for 70% of methane released
-New ways of herding/ wetlands for growing rice
Nitrous Oxide (N2O) Sources
Future changes will depend on many factors:
The rate at which levels of greenhouse gas concentrations in our atmosphere continue to increase. This is due to greenhouse gases staying in our atmosphere for long periods of time.
How strongly features of the climate (e.g., temperature, precipitation, and sea level) respond to the expected increase in greenhouse gas concentrations
Natural influences on climate (e.g., from volcanic activity and changes in the sun's intensity) and natural processes within the climate system (e.g., changes in ocean circulation patterns)
-6% of all U.S. greenhouse gas emissions from human activities.
-human activities such as agriculture, fossil fuel combustion, waste water management, and industrial processes are increasing the amount of N2O in the atmosphere.
Increasing greenhouse gas concentrations will have many effects:
Earths average temperature
Sea level
Acidity of oceans
Influence patterns and amounts of precipitation
Ice and snow cover
CFC'S: chlorofluorocarbons
Man-made; used in foaming agents, pesticides, aerosols, fire extinguishers and coolants in refrigerators and air conditioners
Stable molecular structures and resistance to chemical reactions in the atmosphere has resulted in these compounds being potent greenhouse gases.
Although they account for only 2% of the total greenhouse gas emissions, their GWP (global warming potential) make them a larger threat.
These fluoridated gases are 140 to 23,900 times more potent than carbon dioxide in trapping re-radiated heat.
ex: fire extinguishers
Water Vapor (H2O)
Naturally occurring gas that is not significantly impacted by human activities.
Of the three phases in which water exists, water vapor has the highest heat energy and the lowest density.
As temp. , surface water evaporates leading to an increase in relative humidity.
This is because warmer air can hold more water than colder air due to its lower density.
The more water vapor the air holds, the more heat that is held within the atmosphere.

Future Temperature:
Even if we stabilized the concentration of our greenhouse gases and the composition of our atmosphere stayed stable, surface air temperatures would continue to increase.
This is because our oceans, which store heat, take decades to fully respond to greenhouse gas concentrations.

By 2100, the average U.S. temperature is projected to increase by about
4°F to 11°F,

depending on emissions scenario and climate model.
Future Precipitation and Storm Events:
Key Global Projections:
Global average annual precipitation through the end of the century is expected to increase, although changes in the amount and intensity of precipitation will vary by region.
The strength of the winds associated with tropical storms is likely to increase. The amount of precipitation falling in tropical storms is also likely to increase.
Future Ice, Snow, and Permafrost:
Reduced snowfall and less snow cover on the ground could diminish the beneficial insulating effects of snow for vegetation and wildlife, while also affecting water supplies, transportation, cultural practices, travel, and recreation for millions of people.
Key Global Projections:
For every 2°F of warming, models project about a 15% decrease in the extent of annually averaged sea ice and a 25% decrease in September Arctic sea ice.
The coastal sections of the Greenland and Antarctic ice sheets are expected to continue to melt or slide into the ocean. If the rate of this ice melting increases in the 21st century, the ice sheets could add significantly to global sea level rise.
Glaciers are expected to continue to decrease in size. The rate of melting is expected to continue to increase, which will contribute to sea level rise.
Future Sea Level Change:
Warming temperatures contribute to sea level rise by: expanding ocean water; melting mountain glaciers and ice caps; and causing portions of the Greenland and Antarctic ice sheets to melt or flow into the ocean.
Ice loss from the Greenland and Antarctic ice sheets could contribute an additional 1 foot of sea level rise, depending on how the ice sheets respond.
Future Ocean Acidification
Oceans become more acidic as carbon dioxide (CO2) emissions in the atmosphere dissolve in the ocean.
The pH level of the oceans has decreased by approximately 0.1 pH units since pre-industrial times, which is equivalent to a
25% increase in acidity.
The pH level of the oceans is projected to decrease even more by the end of the century as CO2 concentrations are expected to increase for the foreseeable future
Ocean acidification adversely affects many marine species, including plankton, mollusks, shellfish, and corals.
As ocean acidification increases, the availability of calcium carbonate will decline.
Calcium carbonate is a key building block for the shells and skeletons of many marine organisms.
If atmospheric CO2 concentrations double, coral calcification rates are projected to decline by more than 30%.
If CO2 concentrations continue to rise at their current rate, corals could become rare on tropical and subtropical reefs by 2050.
Corals require the right combination of temperature, light, and the presence of calcium carbonate (which they use to build their skeletons).
As atmospheric carbon dioxide (CO2) levels rise, some of the excess CO2 dissolves into ocean water, reducing its calcium carbonate saturation.
3. The chemical composition of the atmosphere (what gases are present and in what concentrations)
The atoms in H2O and CO2 are continually rotating and vibrating at certain frequencies. Energy in the form of visible light or infrared heat also oscillates at different frequencies.
When the energy’s frequency matches that of a molecule’s vibration, the molecule can absorb the energy.
H2O and CO2
Nitrogen and oxygen don’t absorb infrared energy in our atmosphere because their molecules don’t vibrate or rotate at infrared frequencies.
Nitrogen and Oxygen
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