L5 - radiative forcing and feedback Flashcards
What is radiative forcing?
Radiative forcing is the change in the Earth’s radiation balance at the tropopause between incoming solar radiation and outgoing Earth’s radiation (net irradiance)
What is the significance of radiative forcing?
Increased greenhouse gases reduce the amount of longwave radiation leaving the troposphere, leading to climate warming (positive radiative forcing)
What does positive radiative forcing do to the climate?
A positive radiative forcing warms the climate system
What does negative radiative forcing do to the climate?
A negative radiative forcing cools the climate system
Why must the outward flux balance the incoming flux?
If the outgoing and incoming radiation are not balanced, the Earth’s temperature will change, leading to climate shifts.
What would happen if CO₂ levels doubled from pre-industrial levels (280 ppmv to 560 ppmv)?
The world would experience a warming of approximately 1.37K due to radiative processes alone.
How has estimated radiative forcing changed since pre-industrial times?
It has increased significantly, but large uncertainties remain due to measurement limitations.
Why is future warming difficult to predict?
Climate systems involve complex interactions and feedbacks, making precise calculations challenging.
What is a feedback mechanism?
A process that can amplify (positive feedback) or counteract (negative feedback) climate changes.
What is positive feedback?
A process that reinforces an initial change, leading to further climate change.
What is negative feedback?
A process that counteracts an initial change, stabilizing the climate
How does ice-albedo feedback contribute to cooling?
Earth cools → ice coverage increases → albedo increases → sunlight absorption decreases → further cooling (positive feedback).
How does water vapor feedback contribute to cooling?
Earth cools → evaporation decreases → atmospheric water vapor decreases → greenhouse effect weakens → further cooling (positive feedback)
How does water vapor feedback contribute to warming?
Earth warms → evaporation increases → atmospheric water vapor increases → greenhouse effect strengthens → further warming (positive feedback).
How do clouds influence the climate?
Clouds can either warm or cool the atmosphere by reflecting sunlight or trapping heat.
How do low clouds affect climate?
Low clouds reflect solar radiation, cooling the surface (negative feedback).
If low clouds decrease, less sunlight is reflected, leading to warming (positive feedback).
How do high clouds affect climate?
High-altitude cirrus clouds trap outgoing longwave radiation, enhancing greenhouse warming (positive feedback).
How does cloud optical thickness impact radiative forcing?
Thicker clouds block more sunlight (cooling).
Thinner clouds allow more radiation through (warming).
How does cloud lifetime and precipitation affect radiative forcing?
More persistent clouds = more cooling (negative radiative forcing).
Shorter-lived clouds = more warming (positive radiative forcing).
What are the two main geoengineering approaches?
Carbon capture from the atmosphere.
Solar radiation management techniques.
How does cloud seeding work for geoengineering?
Adding aerosols to clouds increases their reflectivity, cooling the planet.
What effect would cloud seeding have on climate?
CO₂ doubling could be compensated by:
120% increase in droplet concentration.
40% decrease in cloud droplet size.
12% increase in oceanic cloud cover.
What is the role of aerosols in geoengineering?
Aerosols increase cloud condensation nuclei (CCN), making clouds more reflective and reducing surface warming.
How does stratospheric aerosol injection work?
Aerosols (like sulfates) mimic volcanic eruptions, scattering solar radiation and cooling the planet.
Why is stratospheric aerosol injection risky?
It alters weather patterns.
Difficult to stop once implemented.
Can disrupt rainfall and temperature patterns.
What are some alternative geoengineering approaches?
Space mirrors to reflect sunlight.
Painting deserts white to increase reflectivity.
Carbon sequestration (removing CO₂ from the atmosphere).
What are the risks of carbon sequestration (CCS)?
Potential CO₂ leakage from storage sites.
Risk of contaminating groundwater and soil.
Possible induced earthquakes near injection sites
What is the solar constant?
The amount of solar energy received at Earth, currently 1367 W/m²
How do Milankovitch cycles affect climate?
They alter Earth’s orbit and tilt, changing solar radiation patterns over thousands of years.
Why can recent warming not be explained by solar changes?
Recent warming is too rapid to be caused by orbital changes.
Solar activity trends are opposite to recent temperature increases.
What happens if we fail to control anthropogenic warming?
Rising temperatures could threaten ecosystems and societies.
Space colonization may become necessary to sustain human civilization.
Why do anthropogenic aerosols impact climate?
They modify clouds by increasing CCN, leading to more but smaller droplets, enhancing cloud albedo (cooling effect).
What is the first Twomey aerosol indirect effect?
More aerosols → more cloud droplets → smaller droplets → increased cloud albedo → cooling.
What is the second indirect aerosol effect?
Aerosols can extend cloud lifetimes, amplifying or reducing their cooling impact.
How do anthropogenic aerosols differ from climate-induced feedbacks?
They are an external forcing rather than a response to climate change.
What is the overall net effect of cloud feedbacks on climate?
Cloud feedbacks are likely positive (warming), mainly due to reduced low cloud cover in a warmer world.
