Clouds and Climate: Cloud Response to Climate Change

of 21
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Information Report



Views: 40 | Pages: 21

Extension: PDF | Download: 0

Clouds and Climate: Cloud Response to Climate Change. SOEEI3410 Ken Carslaw. Lecture 5 of a series of 5 on clouds and climate Properties and distribution of clouds Cloud microphysics and precipitation Clouds and radiation Clouds and climate: forced changes to clouds
Clouds and Climate: Cloud Response to Climate ChangeSOEEI3410Ken CarslawLecture 5 of a series of 5 on clouds and climate
  • Properties and distribution of clouds
  • Cloud microphysics and precipitation
  • Clouds and radiation
  • Clouds and climate: forced changes to clouds
  • Clouds and climate: cloud response to climate change
  • Content of this Lecture
  • The importance of cloud feedbacks: Climate sensitivity
  • Cloud radiative forcing
  • Factors affecting clouds
  • Cloud feedback in climate models
  • Reading
  • Section 7.2.2 Cloud Processes and Feedbacksof IPCC 2001
  • Climate Sensitivity
  • Climate sensitivity determines the global temperature when a radiative forcing is applied
  • Climate Sensitivity
  • DT = change in global mean temperature
  • Q = radiative forcing (W m-2)
  • l = climate sensitivity (W m-2 K-1)
  • Summer 2002GFDL2xCO2 Sensitivity (K)NCARSensitivity of Climate ModelsSensitivity to forcing from doubled CO2 (~4 Wm-2)Cloud Changes and Climate Sensitivity1/l=4.2 K Wm-2% Change in low cloud amount per 1K temperature change1/l=1.8 K Wm-2Change in “Cloud Radiative Forcing”
  • Clouds cause a net cooling effect on climate (net -20 Wm-2 forcing (equivalent to about 8*CO2)
  • All models agree on sign (+/-) of CRF
  • Cloud feedback is about how CRF changes as greenhouse gases increase
  • Models disagree greatly on this
  • Some clouds warm, some cool. DT depends on which clouds change
  • Humidity and TemperatureOverall increase in atmospheric water vapour and temperature
  • Increased T
  • Increased water vapour in atmosphere
  • Increased cloudiness?
  • NO
  • Relative humidity is the relevant quantity
  • Overall increase in atmospheric water vapour100% RHCloud Radiative Forcing (CRF)
  • Factors that determine CRF (or, what does a climate model need to get right?)
  • Cloud location (solar intensity)
  • Depth/thickness
  • Coverage
  • Drop/ice concentrations
  • How would SW and LW impact on climate change for these two cloud field?CRF, dependence on location, thickness and height4040Winter 5o NWinter 65o Nhigh2020cloud heightmedlow00DTs (K)DTs (K)high-20-20medlow-40-400 50 100 150 0 50 100 150 liquid water path (g m-2)liquid water path (g m-2)Equilibrium surface temperature change due to presence of different cloudsReasons for Cloud Changes
  • Large-scale dynamics/circulation
  • Global circulation changes in response to changes in ocean circulation, changes in ocean-atmosphere T contrast, etc
  • Thermodynamic/cloud-scale changes
  • Changes to:
  • vertical T profile,
  • atmospheric stability,
  • turbulence structure of boundary layer,
  • water substance transport
  • aerosol
  • Very difficult to separate in observations
  • Circulation/Dynamical Changes
  • Cloud fields are determined by large-scale circulation
  • Non-local response
  • El Nino
  • Hadley/WalkercirculationTropicalconvectionTradewindcumulusSub-tropical St/ScEquator30oNObserved Clouds With Temperature
  • Observations from the International Satellite Cloud Climatology Project
  • Clouds become optically thinner (less reflective) at higher temperatures
  • +ve or –ve feedback?
  • Ocean low clouds0.10d log(optical depth)/dT0.05-0.1-0.15-60 -40 -20 0 20 40 60latitudeObserved cloud with temperature: Tropical CirrusRichard Lindzen, MIT
  • Japan’s Geostationary Meteorological Satellite
  • 11 and 12 mm wavelength radiometer
  • 130oE-170oW, 30oS-30oN (Pacific)
  • 260 K brightness temperature product is a measure of “high thin cloud” – cirrus
  • Cirrus cover decreases with increasing SST
  • 0.2slope = 10-20% change per 1 K SST0.15observations0.1Cloud Amount0.05025 26 27 28 29 30sea surface temperature (K)The Adaptive Infrared Iris as a Climate Change Regulatormore IR to spaceless cirrusless water vapourless watertransportmore raincold oceanwarm oceanProblems With the Infrared Iris Idea
  • A hotly debated climate feedback
  • See
  • Net Cloud Feedbacks in GCMsDoubled CO2 experiments3WARMING2SW1Change in CRF (W m-2)0LW-1net-2COOLING-3Different modelsDifficulties
  • Different types of clouds have different effects and may change in different ways – many separate problems
  • Some aspects of clouds (thickness, ice content) are difficult to observe
  • Sub-grid scale problems
  • Effects of temperature and circulation can be confused
  • Changes observed on short time scales (e.g., El Niño) may not always be good indicators of climate change-induced changes
  • Questions for this lecture
  • On slide 6, what could explain the wide range of climate model sensitivities to doubling of CO2?
  • Based on slide 6, what would happen to our climate if the coverage of high thin cirrus clouds increased (a) at the equator, (b) 65oN? What explains the difference?
  • On slide 14, explain whether the data indicate a positive or negative climate feedback.
  • For the first model shown on slide 19 explain what cloud changes could account for the changes in global mean SW and LW cloud radiative forcing.
  • Competition
  • Take a photograph of a cloudy scene. Send it to me with a detailed explanation of what the clouds are doing to climate.
  • The winner will be decided based on beauty and complexity of the cloud scene and accuracy of the explanation
  • Closing date: end of term
  • Prize: A large tin of chocolates
  • Recommended
    View more...
    We Need Your Support
    Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

    Thanks to everyone for your continued support.

    No, Thanks

    We need your sign to support Project to invent "SMART AND CONTROLLABLE REFLECTIVE BALLOONS" to cover the Sun and Save Our Earth.

    More details...

    Sign Now!

    We are very appreciated for your Prompt Action!