Unit 5 - Radiative Forcing Flashcards
What is radiative forcing and what is its unit of measurement?
Answer: Radiative forcing is the change in net vertical irradiance at the troposphere’s top due to internal or external climate system changes. It is measured in W/m².
- Positive radiative forcing (e.g., increased greenhouse gases) warms atmosphere
- Negative radiative forcing (e.g., sulfate aerosols that reflect incoming solar radiation) cools atmosphere
measure of how much the Earth’s energy balance is pushed out of equilibrium by a change in the climate system (net radiation coming in and going out of the atmosphere)
What is thermal radiation?
- All objects emit thermal radiation.
- At terrestrial temperatures, this is long wave radiation in the infrared part of the spectrum
Explain the natural greenhouse effect and its importance.
Answer: The natural greenhouse effect makes Earth habitable by:
- Allowing sun’s radiation to reach Earth’s surface (168 W/m²)
- Surface emits infrared radiation
- Greenhouse gases trap heat and re-emit infrared radiation back to Earth
What is the Stefan-Boltzmann law and how is it modified for non-black bodies?
Stefan-Boltzmann law describes maximum radiative flux
- For black bodies: F = σT⁴ (where T is temperature and σ is Stefan-Boltzmann constant)
- For non-black bodies: emission is reduced by emissivity F = εσT⁴ (where ε is emissivity)
Name three primary contributors to radiative forcing.
- Well-mixed greenhouse gases - CO2, methane, N2O, CFCs
- Tropospheric and stratospheric ozone
- Aerosols (direct and indirect effects)
- Sulfate aerosols
- cloud formation influence
- Organic and black carbon from biomass and fossil fuels
- Anthropogenic mineral dust - Contrails → artificial clouds that form behind aircrafts; they affect the Earth’s climate by either reflecting sunlight back to space (cooling effect) or trapping heat below themm (warming effect)
- Land-use changes affecting albedo
- deforestation, urbanization can affect surface albedo (albedo is how a reflective a surface is to incoming solar radiation)
- ice-albedo feedback → melting ice also reduces surface reflectivity
- Solar variability
What is Global Warming Potential (GWP) and why is it important?
GWP measures the relative radiative forcing impact of different gases compared to CO2 (which has a GWP of 1). It’s used to:
- Compare warming effects of different greenhouse gases
- Determine equivalent CO2 emissions
- Help in climate policy decisions
What is the difference between the Montreal Protocol and Kyoto Protocol in terms of regulated substances?
- Montreal Protocol focuses on ozone-depleting substances like CFCs and HCFCs
- Kyoto Protocol regulates greenhouse gases like CO₂, CH₄, N₂O, PFCs, SF₆, and HFCs
Why is stratospheric temperature adjustment important in calculating radiative forcing?
Stratospheric temperature adjustment is considered because the stratosphere responds rapidly (within months) to changes compared to the surface-troposphere system (which takes decades). This provides a more accurate measure of the long-term climate impact.
How do contrails affect Earth’s climate?
Contrails (artificial clouds behind aircraft) affect climate in two ways:
- By reflecting sunlight back to space (cooling effect)
- By trapping heat below them (warming effect)
Explain what equivalent CO₂ concentration means and its significance.
Equivalent CO₂ concentration represents the amount of CO₂ that would cause the same radiative forcing as a mixture of greenhouse gases. It’s significant because:
- It provides a way to compare different greenhouse gas combinations
- It’s calculated using logarithmic relationship with total radiative forcing
- It uses pre-industrial CO₂ concentration (278 ppm) as a reference
