Climate System Change - Outline

Climate Sensitivity and Feedback

Tectonic-Scale Climate Changes

Orbital-Scale Climate Changes

Deglacial and Millennial Climate Changes

Historical Climate Change

Anthropogenic Climate Changes

Tectonic Scale

Tectonic Scale: the longest time scale of climate change on Earth, which encompasses most of Earth’s 4.55-billion years of history.

Tectonic processes driven by Earth’s internal heat alter Earth’s geography and affect climate over intervals of millions of years.

On this time scale, Earth’s climate has oscillated between times when ice sheets were presented somewhere on Earth (such as today) and times when no ice sheets were presented.

Orbital Scale

Orbital-scale climate changes are caused by subtle shifts in Earth’s orbit.

Three features of Earth’s orbit around the Sun have changed over time:

     (1) the tilt of Earth’s axis,

     (2) the shape of its yearly path of revolution around the Sun

     (3) the changing positions of the seasons along the path.

Orbital-scale climate changes have typical cycles from 20,000 to 400,000 years.

Deglacial and Millenial Scales

Climate changes of these scales in the past several tens of thousands of years occurred within the time span of recorded human civilization.

These change can be resolved by ¹⁴C-dated records.

The major boundary conditions that have driven climate changes during the last 21,000 years have been the changes in:

      (1) size of ice sheet

      (2) seasonal insolation

      (3) level of greenhouse gases in the atmosphere.

Climate Sensitivity and Feedback

Definition and Mathematic Form

Climate Sensitivity: the relationship between the measure of forcing and the magnitude of the climate change response.

Direct Impact and Feedback Process

Major Climate Feedback Processes

Water Vapor Feedback - Positive

Snow/Ice Albedo Feedback - Positive

Longwave Radiation Feedback - Negative

Vegetation-Climate Feedback - Positive

Cloud Feedback - Uncertain

Water Vapor Feedback

Mixing Ratio = the dimensionless ratio of the mass of water vapor to the mass of dry air.

Saturated Mixing Ratio tells you the maximum amount of water vapor an air parcel can carry.

The saturated mixing ratio is a function of air temperature: the warmer the temperature the larger the saturated mixing ration.

     è a warmer atmosphere can carry more water vapor

     è stronger greenhouse effect

     è amplify the initial warming

     è one of the most powerful positive feedback

Snow/Ice Albedo Feedback

The snow/ice albedo feedback is associated with the higher albedo of ice and snow than all other surface covering.

This positive feedback has often been offered as one possible explanation for how the very different conditions of the ice ages could have been maintained.

Longwave Radiation Feedback

The outgoing longwave radiation emitted by the Earth depends on surface temperature, due to the Stefan-Boltzmann Law: F = s(T_s)⁴.

      è warmer the global temperature

      è larger outgoing longwave radiation been emitted by the Earth

      è reduces net energy heating to the Earth system

      è cools down the global temperature

      è a negative feedback

Vegetation-Climate Feedbacks

Cloud Feedback

Clouds affect both solar radiation and terrestrial (longwave) radiation.

Typically, clouds increase albedo è a cooling effect (negative feedback)

clouds reduce outgoing longwave radiation è a heating effect (positive feedback)

The net effect of clouds on climate depends cloud types and their optical properties, the insolation, and the characteristics of the underlying surface.

In general, high clouds tend to produce a heating (positive) feedback. Low clouds tend to produce a cooling (negative) feedback.


	Climate Sensitivity and Feedback
	Tectonic-Scale Climate Changes
	Orbital-Scale Climate Changes
	Deglacial and Millennial Climate Changes
	Historical Climate Change
	Anthropogenic Climate Changes


	Tectonic Scale: the longest time scale of climate change on Earth, which encompasses most of Earth’s 4.55-billion years of history.
	Tectonic processes driven by Earth’s internal heat alter Earth’s geography and affect climate over intervals of millions of years.
	On this time scale, Earth’s climate has oscillated between times when ice sheets were presented somewhere on Earth (such as today) and times when no ice sheets were presented.


	Orbital-scale climate changes are caused by subtle shifts in Earth’s orbit.
	Three features of Earth’s orbit around the Sun have changed over time:
	(1) the tilt of Earth’s axis,
	(2) the shape of its yearly path of revolution around the Sun
	(3) the changing positions of the seasons along the path.
	Orbital-scale climate changes have typical cycles from 20,000 to 400,000 years.


	Climate changes of these scales in the past several tens of thousands of years occurred within the time span of recorded human civilization.
	These change can be resolved by ¹⁴C-dated records.
	The major boundary conditions that have driven climate changes during the last 21,000 years have been the changes in:
	(1) size of ice sheet
	(2) seasonal insolation
	(3) level of greenhouse gases in the atmosphere.


	Climate Sensitivity: the relationship between the measure of forcing and the magnitude of the climate change response.


	Water Vapor Feedback - Positive
	Snow/Ice Albedo Feedback - Positive
	Longwave Radiation Feedback - Negative
	Vegetation-Climate Feedback - Positive
	Cloud Feedback - Uncertain


	Mixing Ratio = the dimensionless ratio of the mass of water vapor to the mass of dry air.
	Saturated Mixing Ratio tells you the maximum amount of water vapor an air parcel can carry.
	The saturated mixing ratio is a function of air temperature: the warmer the temperature the larger the saturated mixing ration.
	è a warmer atmosphere can carry more water vapor
	è stronger greenhouse effect
	è amplify the initial warming
	è one of the most powerful positive feedback


	The snow/ice albedo feedback is associated with the higher albedo of ice and snow than all other surface covering.
	This positive feedback has often been offered as one possible explanation for how the very different conditions of the ice ages could have been maintained.


	The outgoing longwave radiation emitted by the Earth depends on surface temperature, due to the Stefan-Boltzmann Law: F = s(T_s)⁴.
	è warmer the global temperature
	è larger outgoing longwave radiation been emitted by the Earth
	è reduces net energy heating to the Earth system
	è cools down the global temperature
	è a negative feedback


	Clouds affect both solar radiation and terrestrial (longwave) radiation.
	Typically, clouds increase albedo è a cooling effect (negative feedback)
	clouds reduce outgoing longwave radiation è a heating effect (positive feedback)
	The net effect of clouds on climate depends cloud types and their optical properties, the insolation, and the characteristics of the underlying surface.
	In general, high clouds tend to produce a heating (positive) feedback. Low clouds tend to produce a cooling (negative) feedback.