Global Climate Change 1

Common to conflate the stratospheric ozone depletion problem with global climate change. In reality, they are two fundamentally different issues.

Spontaneous Combustion

South Park

Don’t confuse global warming

with ozone depletion, mm-kay.

The Day After Tomorrow

Surface temperature record

Intergovernmental Panel on Climate Change (IPCC) Statements

• “The unequivocal detection of the enhanced greenhouse effect from observations is not likely for a decade or more” (1990)

• “The balance of evidence suggests a discernible human influence on global climate” (1995) 

• “Human activities are modifying the energy balance of the planet” (1999)

• “There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities” (2001)

• “Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” (2007)

Take – Home Message #1

• Global climate change is occurring, human activities are very likely the primary cause of that change, and many ecosystems are already being affected by observed changes in climate.

• The primary debate now centers on HOW and WHEN we should respond to climate change, WHO will pay for that response, and whether we should try to PREVENT rapid climate change or simply ADAPT to the changes.

Solar Radiation

Reflected by atmosphere (34%)

Absorbed by the earth

Radiated by atmosphere as heat (66%)

Greenhouse Effect

Heat radiated by the earth

Energy In = Energy Out

Earth’s Energy Balance

Take – Home Message #2• The Greenhouse Effect is a natural occurrence caused

by the presence of water vapor and trace amounts of greenhouse gases in the atmosphere.

• Greenhouse gases (e.g. carbon dioxide, methane) and water vapor in the atmosphere retain and re-emit enough of the earth’s outgoing long-wave infrared energy to warm the planet to an average surface temperature of 59 degrees Fahrenheit. Without the Greenhouse Effect the earth’s average temperature would be 0 degrees Fahrenheit.

• What’s of concern is an enhanced greenhouse effect caused by anthropogenic (human-caused) additions of greenhouse gases to the atmosphere.

Take – Home Message #3

• Human activities exert positive and negative RADIATIVE FORCING on the planet, altering the earth’s ENERGY BALANCE.

• Human activities that add more greenhouse gases to the atmosphere – thickening the “insulating blanket” – exert positive radiative forcing.

• Human activities that reflect more incoming solar radiation to outer space (e.g. emissions of sulfur particles) exert a negative radiative forcing.

Take – Home Message #4

• The NET effect of these changes in the earth’s energy balance has been a ~1.4 degree F increase in the earth’s average surface temperature in the past 100 years.

• The major greenhouse gases responsible for this increase (in order of importance) are: carbon dioxide (CO2), methane (CH4), halocarbons (e.g. CFCs, CFC substitutes), and nitrous oxide (N2O).

Take – Home Message #5

• Human emissions (sources) of greenhouse gases, while small relative to “natural” emissions, are not balanced by “sinks” for those emissions. Therefore, concentrations of greenhouse gases in the atmosphere are rising steadily.