Lecture 7/8

atmospheric conditions over short time periods (e.g. hours, days) within small geographic areas

atmospheric conditions (e.g. precipitation, temperature) across large geographic regions over long periods of time (e.g. decades, centuries)

• sun • atmosphere • oceans

without it, Earth would be dark and frozen

without it, Earth’s temperature would be colder

shape climate by storing/transporting heat/moisture

• average annual precipitation • average annual temperature

trends and variations in the earth’s climate

An increase in Earth’s average temperature - average temperature naturally increases but rapid change is due to human activity

• orbital cycles of Earth • solar output variations • ocean absorption of atmospheric gases • ocean circulation patterns • changes in absorption of solar radiation by Earth’s surfaces • changes in atmospheric gases (especially ‘greenhouse gases’)

periodic long-term changes in Earth’s rotation and orbit around Sun - (referred to as Milankovitch Cycles)

drives temperature change on Earth’s surface because of variation in solar flare activity and solar storms

the ocean holds 50 times more carbon than the atmosphere and by absorbing CO2 from the atmosphere, the ocean acts as a carbon sink that maintains stable levels of atmospheric gases

worldwide currents changing - warmer, fresher water moves along surface; and colder, saltier water moves deep beneath the surface - impacted by melting of glaciers and polar ice caps

changes in atmospheric gases can alter the amount of solar radiation absorbed by the Earth’s surface (= albedo) - with more absorption, Earth’s surface increases in temperature and emits more infrared radiation that warms lower atmosphere

changes in atmospheric gases that absorb infrared radiation (e.g. water vapor, CO2, CH4, N2O, chlorofluorocarbons) can alter amount of solar radiation absorbed by the Earth’s surface

• not most potent • most abundant / long lived • major contributor to climate change

• very potent (25 times greater than CO2) • less abundant / short-lived • due to human activities

• very potent (300 times greater than CO2) • less abundant • due to human activities

• With more solar absorption, Earth’s surface warms and emits more heat that warms the lower atmosphere • Warming of lower atmosphere further warms Earth’s surface

Permafrost Carbon Feedback Loop

an amplification of surface warming due to the thaw of organic material currently frozen in permafrost - Leads to decay and release of CO2and CH4into atmosphere - It is irreversible

increased: - temperature over land - temperature over oceans - sea surface temperature

• There are more positive forcers of climate change (e.g. greenhouse gasses, solar irradiance, etc.) • There are fewer negative forces to offset positive forcers and cause cooling