10-22 Greenhouse Effect

APES 2024

Greenhouse Effect

Greenhouse Effect

Absorption of infrared radiation by atmospheric gases and reradiation of the energy back toward Earth

• Necessary for life on Earth

When radiation from the Sun hits the atmosphere,

1/3 is reflected back

Some of the UV radiation is absorbed by the

ozone layer

Remaining UV passes through the atmosphere and strikes the Earth where it is converted into

low energy infared radiation

The infrared radiation then goes back toward the atmosphere where it is absorbed by

reenhouse gasses that radiate most of it back to the Earth

Major greenhouse gases

• Water vapor (H 2O)

• Carbon dioxide (CO2)

• Methane (CH 4)

• Nitrous oxide (N 2O)

• Tropospheric Ozone (O3)

• The most abundant natural greenhouse gas

• Has a short residence time in the atmosphere

• Does not contribute significantly to global climate change due to short residence time

water vapor

The contribution of each gas to global warming depends in part on

its greenhouse warming potential

Greenhouse warming potential

An estimate of how much a molecule of any compound can contribute to global warming over a period of 100 years relative to a molecule of CO2

Some greenhouse gases are produced from natural sources:

• Volcanic eruptions: ash, carbon dioxide
• Decomposition and digestion: methane
• Denitrification: nitrous oxide
• Evaporation and evapotranspiration: water vapor

Some greenhouse gases are produced by human activity:

• Burning of fossil fuels
• Agricultural practices
• Deforestation
• Landfills
• Industrial production

Increases in Greenhouse gases

• Melting of polar ice caps, Greenland, and Antarctica
• Melting of many glaciers around the world
• Melting of permafrost
• Rising of sea levels due to the melting of glaciers and ice sheets and as water warms it expands
• Heat waves and cold spells
• Change in precipitation patterns
• Increase in storm intensity
• Shift in ocean currents

Measurements of ice mass from 2002 to 2017 have detected decline in both

Antarctica and Greenland

Kyoto Protocol (1997)

An international agreement that sets a goal for global emissions of greenhouse gases from all industrialized countries to be reduced by 5.2 percent below their 1990 levels by 2012

Although the United States signed the original Kyoto Protocol,

the U.S. Congress never ratified the agreement and the protocol has never been legally binding on the United States

In 2005 mayors from 141 U.S. cities and both major political parties gathered in San Francisco to

organize their own efforts to reduce the causes
and consequences of global warming.

Paris Climate Agreement (2015)

A pledge by 195 countries to keep global warming less than 2°C above pre-industrial levels

Aim of Paris Climate Agreement

to limit the increase to 1.5°C, since this would significantly reduce risks and the impacts of climate change

Paris Climate Agreement amendments(?)

• On the need for global emissions to peak as soon as possible, recognizing that this will take longer for developing countries;

• To undertake rapid reductions thereafter in accordance with the best available science