L6- other anthropogenic impacts on climate Flashcards
(16 cards)
Describe the main components of the Earth’s energy budget
Incoming shortwave radiation from the sun (mostly visible and UV light)
Reflected shortwave radiation from clouds, aerosols, and Earth’s surface (albedo effect)
Absorbed shortwave radiation by the atmosphere and surface
Outgoing longwave radiation (infrared) emitted by Earth’s surface and atmosphere
Absorbed longwave radiation by greenhouse gases
Re-emitted longwave radiation back toward the surface, contributing to the greenhouse effect
What are the internal forcings influencing the main components of Earth’s energy budget?
Internal forcings are within the Earth system and include:
Cloud cover (affects both albedo and greenhouse effect)
Atmospheric water vapor and aerosols
Surface albedo (e.g., snow, ice, forests, deserts)
Carbon cycle feedbacks, including vegetation response and oceanic absorption
What are the external forcings influencing the main components of Earth’s energy budget?
External forcings come from outside the climate system:
Solar variability (solar output)
Orbital changes (Milankovitch cycles)
Volcanic eruptions (inject aerosols into the stratosphere, increasing albedo)
Anthropogenic emissions (GHGs, aerosols, land-use change)
What factors would you consider when assessing how these forcings influence the main components of Earth’s energy budget?
Radiative properties (reflectivity, absorptivity)
Geographical distribution (latitude, surface type)
Atmospheric lifetime (how long they persist)
Magnitude of radiative forcing (W/m²)
Feedback mechanisms (e.g., water vapor, ice-albedo)
Rapid adjustments (e.g., cloud formation or evaporation)
How does aerosol influence the energy budget?
Directly (Aerosol–Radiation Interaction):
Non-absorbing aerosols (sulfate, nitrate) scatter sunlight → cooling effect
Absorbing aerosols (black/brown carbon) absorb sunlight → warming, especially over clouds
Indirectly (Aerosol–Cloud Interaction):
Act as cloud condensation nuclei (CCN) → more, smaller cloud droplets
Increase cloud albedo (more reflection = cooling)
May prolong cloud lifetime
Semi-direct effects: absorption can warm air and evaporate clouds, reducing cooling
Net ERF from aerosols: ~–1.3 W/m² (cooling)
How does ozone influence the energy budget?
Tropospheric ozone: absorbs infrared radiation, contributes to warming (positive radiative forcing)
Stratospheric ozone: absorbs UV radiation, protects life and has a smaller warming effect
Radiative forcing:
Tropospheric ozone = major anthropogenic influence
ERF is positive, about half the size of aerosols, and double that of land-use change
How does land-use change influence the energy budget?
Alters surface albedo
Forest → farmland in snow-covered areas = higher albedo → cooling
In tropical zones = less evapotranspiration → warming
Impacts vertical distribution of energy
Less water = more sensible heat (warming effect)
More water = more latent heat (cooling via evapotranspiration)
Mixed effect on cloud formation
Irrigation may increase clouds; deforestation may decrease clouds
Rapid adjustments ≈ zero, ERF ≈ half of ozone and ¼ of aerosols
what is effective radiative forcing
- Quantifies change in Earth’s energy balance from a climate driver
INCLUDES:
- Instantaneous forcing - direct radiation effects
- Rapid adjustments - uncouples from surface temperature
ERF accounts for effects like aerosol cloud interaction, stratospheric temperature changes etc
what is the role of aerosol colour in the energy budget
- Dark, e.g. black carbon = absorbs sunlight = warming
- light, e.g. sulphate = scatter sunlight = cooling
dark aerosols above clouds have larger warming effect than over clear skies
what is the average atmospheric lifetime of aerosols
minutes to weeks, average = days
affects how far they travel and their climate impact
which aerosols are more hygroscopic and afficient CCN
inorganic aerosols e.g. sulphate and nitrate, are more hygroscopic than carbonaceous
define hygroscopic and carbonaceous
H = readily taking up water
C= the attribute of any substance rich in carbon, unsaturated
how does ozone form and persist in the troposphere
- formed via reactions involving NOx, CO, CH4 and VOCs in sunlight
- lifetime = 3 weeks
- not well-mixed, varies spatially
- anthropogenic emissions of precursors -> increased O3 -> positive ERF
why is land-use change considered a local climate driver with global relevance
alters evapotranspiration, surface heat fluxes -> local temperature and cloud impacts
Can cause feedbacks e.g. Amazon forest dieback hat influence global climate
how do natural and anthropogenic forcings compare in the industrial era
- anthropogenic changes (GHGs, aerosols, land use) now exceed natural variations
- natural drivers - solar variation, volcanoes, GHG sinks
- same physical processes, but differenbt orgins
Relative magnitudes of ERF (Anthropogenic):
Aerosol (total): ~ -1.3 W/m²
Ozone: ~ half of aerosol
Land-use change: ~ quarter of aerosol
Ozone > land-use change, but all smaller than GHG (CO₂, CH₄)
