Global Warming • The name given to the increase in the average temperature of the Earth’s near surface temperature and oceans that has occurred since the middle of the 20 th century. • In the graph to the right, panel a gives the Earth's surface temperature is shown year by year (red bars) and approximately decade by decade (black line, panel b gives the year by year (blue curve) and 50 year average (black curve) variations of the average surface temperature of the Northern Hemisphere for the past 1000 years have been reconstructed from "proxy" data calibrated against thermometer data.
Global Warming. The name given to the increase in the average temperature of the Earth ’ s near surface temperature and oceans that has occurred since the middle of the 20 th century. - PowerPoint PPT Presentation
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Global Warming• The name given to the increase in the
average temperature of the Earth’s near surface temperature and oceans that has occurred since the middle of the 20th century.
• In the graph to the right, panel a gives the Earth's surface temperature is shown year by year (red bars) and approximately decade by decade (black line, panel b gives the year by year (blue curve) and 50 year average (black curve) variations of the average surface temperature of the Northern Hemisphere for the past 1000 years have been reconstructed from "proxy" data calibrated against thermometer data.
Greenhouse effect• Main culprit behind global
warming• Sunlight enters the atmosphere
and warms the Earth (UV, visible, IR)
• At night, Earth radiates heat energy it gained during the day(mostly at IR wavelengths)
• Not all of this energy escapes the atmosphere-some of it is absorbed and re-emitted back into the atmosphere, warming the atmosphere and the Earth.
• Not necessarily a bad thing-without it the Earth would be cold and life (a least as we know it) would not be possible
Venus• Hottest planet in the solar
system• But not the closest to the sun• Atmosphere is 96.5% carbon
dioxide• Venus once had immense
amounts of water, but no ozone layer-the UV radiation broke up the water molecules
• Unfortunate, water absorbs carbon dioxide wand mitigates the greenhouse effect
• Resulted in an extreme greenhouse effect
Greenhouse effect-What could happen
• Global temperatures rise until boiling point of water is reached
• As water boils away, it becomes water vapor in the atmosphere, accelerating the heat rise (called positive feedback).
• At a few hundred degrees celsius, carbon dioxide would be released from the rocks (sublimation), accelerating the heating again
• Eventually the Earth would stabilize at surface temperatures similar to Venus (T=860F)
• Worst case, not realistic scenario
Greenhouse Gasses –in order of importance
• water vapor• carbon dioxide• methane• nitrous oxide• ozone• CFCs
Changes in greenhouse gas concentrations
• Historical variations can be tracked via analysis of ice cores– Ice core - a core sample (a cylindrical section of a naturally occurring
medium consistent enough to hold a layered structure) from the accumulation of snow and ice over many years that have re-crystallized and have trapped air bubbles from previous time periods.
– The composition of these ice cores provides a picture of the climate at the time.
• Natural variations occur in the greenhouse gas concentrations
Post industrial revolution
Man made sources of greenhouse gasses
• Also called Anthropogenic, which designates an effect or object resulting from human activity
• burning of fossil fuels and deforestation leading to higher carbon dioxide concentrations. – Account for one third of total anthropogenic CO2 emissions.
• livestock enteric fermentation and manure management, paddy rice farming, land use and wetland changes, pipeline losses, and covered vented landfill emissions leading to higher methane atmospheric concentrations. Many of the newer style fully vented septic systems that enhance and target the fermentation process also are sources of atmospheric methane.
• use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs and halons in fire suppression systems and manufacturing processes.
• agricultural activities, including the use of fertilizers, that lead to higher nitrous oxide (N2O) concentrations.
What are we seeing?• Since 1860-1900, global
surface temperatures have increased by 1.35 F
• Urban heat island effect only accounts for 0.02 C rise
• Since 1979 land T have increased twice as fast as ocean temperatures
• Temperatures on the lower troposphere have have increased by 0.62 between 1979 and 2000.
Hold on, could it be the sun?
• No overall increase in solar brightness in over 1000 years
• Solar cycles do cause small variations in brightness, but not enough to account for what has been seen
• No its not the sun
Feedback-making the problem worse (or better)
• Positive feedback-when the warming induces further warming
• Negative feedback – when the warming induces a cooling
• Lapse Rate• Increased heating means increased IR
emission• Global warming reduces the rate of
temperature decrease with height, which means more long wavelength radiation will be emitted by the upper atmosphere
• This will weaken the greenhouse effect
Positive feedback• Water vapor
– Warming increases the amount of water vapor in the atmosphere, which increases the warming since water vapor is also a greenhouse gas
• Clouds– Act as a blanket, reflect IR radiation downward toward the surface
• Ice albedo– Melting ice reveals land and water, both reflect less light than ice-
more warmth is absorbed increasing warming• Arctic methane release
– Warming releases sources of carbon dioxide• Reduce carbon dioxide absorption in oceans
– Warm waters favor the growth of plankton rather than diatoms-diatoms are more efficient carbon dioxide absorbers
Global dimming
• An effect that has been counteracting some of global warming from about 1960 forward
• Aerosols produced by volcanoes and pollutants such as sulfur dioxide reflect incoming sunlight
• Soot –suspended in the atmosphere, it can absorb solar radiation and heat the atmosphere, but cool the surface
What are we seeing:• Besides the increases in Temperature:
– World’s glaciers are melting– Arctic sea ice is reducing in both extent ( 9% reduction in area per
decade) and thickness (15-40% in thickness in the last 30 years)– Ocean levels are rising-both due to melting of Antarctic ice and
thermal expansion of sea water– Longer growing seasons– Thawing of permafrost in Alaska– Coral reef bleaching-whitening of reefs due to increased temperature– Earlier plant flowering– Earlier bird arrivals– Shifting of animal ranges poleward– More frequent EL Nino-warming of the Pacific ocean surface
temperatures-causes changes in local weather patterns