Transcript clouds
CE 401 Climate Change Science and Engineering modeling of climate change predictions from models 10 February 2011 team selection and project topic proposal (paragraph): due electronically 2.22.2011 exam on first half of class: 2.24.2011 new on website: IPCC chapter on models HW 7 due next Thursday now on the website where are we in the syllabus: latest version always on website we have finished our discussion of the observations of climate – any questions? POLICY MAKERS ARE INTERESTED IN THE FUTURE What will happen and what is the cause? Models are used to predict future climate How well do these models predict the past? Can we trust models to predict the future? Decisions are based on the models! “this is a difficult subject; by long tradition the happy hunting ground for robust speculation, it suffers much because so few can separate fact from fancy” G.S. Callendar, 1961, climate modeler take a look at this climate model that you can run source: IPCC 2007 The Climate System - very complicated NASA Global Temperature Record 1880 - 2008 source: GISS, 2010 satellite based temperature anomaly, lower atmosphere temp anomaly relative to 1981 – 2010 average what analysis did this cartoon come from ? factors that influence the radiative equilibrium of the Earth system average solar input: 342 w/m2 Model Testing and Evaluation • atmosphere • temperature • radiation balance • moisture and precipitation • GHG and trace gases that drive chemistry • ocean • mean temp and salinity • circulation features • sea ice • land surface • snow cover • land hydrology • surface fluxes • carbon • variability – various meteorological and oceanic variables • pacific decadal variability • atlantic multidecadal variability’ • El Nino Southern oscillation • Madden-Julian Oscillation • Quasi biennial oscillation • monsoon variability Figure 10.1 19th century development of climate thoughts • 1820 – Joseph Fourier – atmosphere retains heat radiation – got 255K, not 288K – GH effect • Tyndall 1862 – H2O and CO2 are opaque to heat rays (IR radiation) – shined light of different wavelengths through a glass cylinder and measured the transmission • Arrhenius – 1896 – studied how changes in CO2 affect climate • energy budget • added up solar energy received, absorbed, and reflected • idea of feedbacks – could not calculate • crude physics x2 [CO2] 5 - 6°C temp change What Goes into Atmospheric Climate Models • mathematical equations to describe air motion and processes physical process and parameters in an atmospheric model What Goes into Atmospheric Climate Models • mathematical equations to describe air motion and processes • solar flux and its changes in time - Earth energy balance • clouds - largest source of uncertainty in the models • 61% of the globe on average is covered with clouds • clouds both reflect energy (cooling) - feedbacks • and serve as thermal blankets (warming) - feedbacks clouds schematic of physical processes associated with clouds Cloud radiation feedback clouds • reflect radiation back to space (albedo effect) - SW component • trap IR radiation emitted by surface and lower trop (GHG effect) - LW component • balance between these two components of cloud RF depends on • macrophysical and microphysical cloud properties • cloud feedbacks are the largest source of uncertainty in climate sensitivity • in current models, clouds exert a net cooling effect (global RF < 0) • > ~ half predict this, but not very convincing • understanding physical processes in cloud feedbacks • many types - lower boundary layer to deep convective clouds • climate changes affect cloud types and radiative properties and radiative budgets Model Estimates of Cloud Radiative Forcing with CO2 Doubling Global average change in T °C Greenhouse Gases Clouds Change in T None As Now As Now As Now X2 CO2 X2 CO2 As Now None +3% high +3% low As Now + feedbacks -32 4 0.3 -1 1.2 2.5 Houghton, 2001 What Goes into Atmospheric Climate Models • mathematical equations to describe air motion and processes • solar flux and its changes in time - Earth energy balance • clouds - largest source of uncertainty in the models • 61% of the globe on average is covered with clouds • clouds both reflect energy (cooling) - feedbacks • and serve as thermal blankets (warming) - feedbacks • Earth reflectivity (land, sea/water, ice, snow, vegetation, etc.) • thermodynamics of water and radiation • chemistry and carbon cycle (atmosphere, oceans, biosphere) • anthropogenic contributions (e.g. CO2 increases with time, biomass burning, land use changes, etc.) • aerosols which cool the atmosphere (natural and anthropogenic) The atmospheric models must be coupled to: • cryosphere • biosphere • oceans • hydrosphere Figure 4.1 components of the cryosphere and their time scales cryosphere • in terms of heat capacity, cryosphere is 2nd largest component of climate system • physical properties affecting climate • albedo (snow ~ 80-95%) • latent heat associated with phase changes • 75% of fresh water on Earth • 10% of earth surface permanently covered with ice • 7% of oceans on average covered with ice • ice sheets of Greenland and Antarctica are main reservoirs capable of affecting sea level (Greenland 7.3 m, Antarctica 56.6 m) • observations hampered before 1970 due to lack of satellite coverage • glacier records go back to the 1600’s • general retreat started around 1800 • most important feedback is an increase in absorbed solar radiation as ice decreases • first speculation (Brooks, 1925) for a polar melt feedback through albedo was dismissed a “preposterous” The atmospheric models must be coupled to: • cryosphere • biosphere • oceans • hydrosphere Coupled atmosphere / ocean climate model Radiation Atmosphere: Exchange of: Density Motion Water Heat Momentum Water Ocean: Density (inc. Salinity) Motion example for ocean coupling Sea Ice Land The atmospheric models must be coupled to: • • • • cryosphere biosphere oceans hydrosphere • all on a high resolution global spatial grid of latitude and longitude and altitude as a function of time and incorporating the many feedback mechanisms that control atmospheric processes This is a huge job that requires experts from many fields and a large computer! There are a number of groups around the world working on this problem. geographical grid for a model 19 levels in atmosphere Hadley Center model in England 1.25 1.25 grid sizes 20 levels in ocean -5km 30km 2.5 lat 3.75 long far = first assessment report IPCC, …, AR4 = assessment report 4 IPCC