The Greenhouse Effect and Global Warming

Diffuse RadiationDiffuse Radiation

- Clear skies: 80% of insolation reaches the surface

- Cloudy skies: 10-45% of insolation may reach the surface

The Greenhouse Effect Popular name for process whereby greenhouse gases in

atmosphere absorb longwave radiation from Earth and then emit or counterradiate it back to the surface providing additional heating

The Greenhouse Effect (cont’d)

Process acts to warm lower atmosphere by keeping longwave radiation from escaping to space (like insulation holding in heat in a house)

With no atmospheric greenhouse effect, Earth would be much colder: current mean global temp is 15°C (59°F); w/o greenhouse effect, temps would be about -18°C (0°F), which is a difference of 33°C (59°F)...

Greenhouse Gases Gases involved in this

process are called greenhouse gases

All are considered trace gases, meaning they only constitute a small percentage of atmospheric content, but they play a very important role

Include CO2, H2O, CH4, and Water vapor

How Do Greenhouse Gases Get into the

Atmosphere? CO2: burning of fossil fuels (coal, oil, natural gas) and

vegetation, during plant decomposition, during volcanic eruptions

H20: evaporation, evapotranspiration, airplane exhaust, volcanic eruptions

CH4: decay of organic matter, human activity (rice cultivation, farm animal wastes, bacterial decay in sewage and landfills, fossil fuel extraction and transportation, and biomass burning)

Quick Focus on Carbon Dioxide

Charles Keeling started taking CO2 observations at Mauna Loa, HI, in 1958

Now 45+ years of observations – what do we see?

A Bit More about CO2

Industrial Revolution 1750-Europe, early-mid 1800s in US

A Few More Facts CO2 and H2O vapor considered most important

greenhouse gases CFC-12 absorbs 10,000 times more longwave radiation

than CO2 (adding one CFC-12 molecule is equivalent to adding 10,000 CO2 molecules)

CFC’s: widely used in refrigeration process, formerly major component in aerosol spray cans (banned in 1976 by U.S. EPA)

Liquid water droplet and ice particles in clouds also very important in atmospheric greenhouse effect

NOAA’s Viewpoint

Global Warming Debate Its happening…and that

is not the debate.Although scientists agree that Earth is getting warmer, there is debate about the impact of human activities

Many think human activity is a major cause, while others claim it’s part of a natural cycle

Data sources and beliefs

What Natural Processes Lead to Climate Change?

Changes in solar radiation: solar constant variations, 11-year sunspot cycle

Astronomical changes: 23,000-year precession cycle (wobbling of axis), 41,000-year cycle in axial tilt, 100,000-year cycle in orbital eccentricity (revolution path not always elliptical)

Volcanic activity (Mt. Pinatubo, Philippine Islands, April 1994 – Fig. 3.25, p. 112)

Cloudiness

Warming vs. Cooling Natural cycles can lead to warming or cooling, depending on phase of cycle (solar

radiation changes and astronomical changes) or location/time of day in atmosphere (dust from volcanic activity and cloudiness)

All greenhouse gases tend to cause warming (exception is when CFC’s destroy O3)

Greenhouse Gases and Global Warming

What Do the Records Show?

Problem with observations: organized, continuous recording of weather only goes back ~140 years

Have other sources to determine temperature and atmospheric composition

1. Tree rings: 1 ring = 1 yr; wider rings = more tree growth = warmer temperatures, more precipitation

2. Ice cores: drill ice and sample gases in bubbles 3. Oceanic sediment cores: drill ocean floor and look at

what’s there (including plankton) 4. Reef cores: similar to #3 5. Pollen: in soil and packrat middens

Temperature Records

Temperature Records

How could global warming affect us?

Rising sea levels – flooding of coastal/low-lying areas, harm water supply, shift in crop patterns

Change in growing seasons Warmer temps = more evaporation drier soils Animal/plant habitat expands or contracts More cloud cover Stronger hurricanes farther north/south due to

warmer ocean temps