Week 6 Flashcards
(19 cards)
What are the main “other” anthropogenic drivers of radiative forcing?
aerosols, ozone, and land-use change
Where does anthropogenic aerosol come from?
Anthropogenic aerosols primarily come from several human sources:
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Agriculture
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Industrial processes
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Fossil fuel production
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Transportation
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Residential heating and cooling Specifically, combustion processes from residential biofuel use and commercial fossil fuel use release primary aerosols like black carbon and organics, as well as aerosol precursors such as sulfur dioxide (SO2), nitrogen oxides (NOx), and volatile organic compounds (VOCs). These precursors can then form secondary aerosols through atmospheric reactions
What is aerosol?
defined as a mixture of gas and suspended particles
- specifically, it refers to suspended solid or liquid particles in the atmosphere, originating from both natural and human sources
What are the three mechanisms of aerosol radiative forcing?
Aerosol-radiation interaction (Direct effect):
-Non-absorbing aerosols (like sulfur, nitrate, and most organics) scatter sunlight back into space, which increases the Earth’s albedo and has a cooling effect
-absorbing aerosols (like black carbon and some organics called brown carbon) absorb solar radiation, which warms the surrounding air and contributes to a warming climate effect
Aerosol-cloud interaction (Indirect effect):
-can act as cloud condensation nuclei (CCN), providing surfaces for water vapor to condense and form cloud droplets
-More aerosols acting as CCN typically lead to more cloud droplets with smaller droplet sizes, making clouds more reflective and enhancing their cooling effect
Semi-direct effect:
-involves rapid adjustments to atmospheric thermodynamics due to aerosols (DONT NEED FOR EXAM)
Which of the “other” anthropogenic impacts on climate has the greatest radiative forcings?
aerosols have the greatest radiative forcing magnitude
-two times greater than the ozone effect (which is positive) and four times greater than the land-use change effect (which is negative) in terms of absolute magnitude
How does ozone affect the global energy budget?
it is a greenhouse gas. It is special in that it can absorb both incoming ultraviolet radiation (short-wave) and outgoing infrared radiation (long-wave)
-absorption bands mean that an increase in tropospheric ozone has a positive effective radiative forcing, resulting in warming
considered the third most important greenhouse gas
For anthropogenic impact on the global energy budget, is tropospheric or stratospheric ozone more important?
tropospheric ozone is significantly more important than stratospheric ozone
-positive radiative forcing effect from the troposphere is around 20 times greater than the positive radiative forcing effect from the stratosphere
How do the atmospheric lifetimes of aerosol and ozone compare against carbon dioxide?
aerosols= short lived with an average lifetime of 3 days
ozone= also short lasting about 3 weeks
carbon dioxide= much longer
What is the effective radiative forcing of anthropogenic land-use change?
generally a cooling effect
Describe how anthropogenic land-use change affects albedo in mid-latitudes and semi-arid regions?
mid-latitudes, changing tall vegetation, such as trees, to farmland increases albedo
semi-arid regions, changing dark bush-cover to relatively light soil also increases albedo
What process is key to the local effect of land-use change on the vertical distribution of energy?
Evapotranspiration transfers heat as moisture from vegetation moves into the atmosphere.
Trees and plants enable evapotranspiration, converting solar energy into latent heat.
Removing vegetation reduces evapotranspiration, especially in dry areas.
Less latent heat means more solar energy becomes sensible heat, directly warming the air.
This shift alters the vertical distribution of energy, increasing surface and near-surface temperatures.
Mathematical model for aerosol, ozone and land use effect on Earth’ surface temperatures?
Incoming energy: 𝐸𝑖𝑛 = 𝑆0(1 − 𝛼)𝜋𝑟𝑒^2
Outgoing energy emitted by a black body: 𝐸𝑜𝑢𝑡 = 𝜎𝑇𝑒^4 4𝜋𝑟𝑒^2
the equation for the equilibrium temperature of Earth, incorporating albedo (affected by aerosols and land use) and ozone absorption, is: 𝑇𝑒 = ([𝑆0(1 − 𝛼)] / [4𝜎(1 − 𝐹𝑂3,𝐼𝑅)]) ^ (1/4)
Describe the main components of the Earth’s energy budget
Incoming: shortwave solar radiation
Outgoing: longwave terrestrial radiation
At equilibrium: incoming = outgoing
What are the internal forcings influencing the main components of Earth’s energy budget?
Originate within Earth or atmosphere
Affect albedo (e.g., land use, clouds, aerosols)
Influence greenhouse gas absorption (e.g., CO₂, CH₄, O₃)
What are the external forcings influencing the main components of Earth’s energy budget?
Originate outside the Earth system
Affect solar radiation input
Examples: solar output changes, Milankovitch Cycles
What factors would you consider when assessing how these forcings influence the main components of Earth’s energy budget?
Lifetime: Duration a forcing remains in the system (e.g., aerosols = days)
Efficiency: Effectiveness at reflecting or absorbing radiation (e.g., CH₄ > CO₂ per molecule)
How does aerosol influence energy budget?
Direct: Reflect sunlight (cooling) or absorb it (warming)
Indirect: Alter cloud reflectivity and lifetime (increase cooling)
Net effect since industrial era: ~−1.3 W/m² (cooling)
How does ozone influence energy budget?
Absorbs UV (incoming) and IR (outgoing) radiation
Acts as a greenhouse gas
Increased tropospheric ozone causes warming (positive forcing)
3rd most important greenhouse gas
How does land-use change influence energy budget?
Increases surface albedo (e.g., forest → farmland = more reflection = cooling)
Reduces evapotranspiration → more sensible heat near surface (warming effect)
Alters vertical energy distribution locally
