3 Theoretical constructs and models in science Science uses idealized constructs unlikely to ever occur as a way to make comparisons and infer mechanismsModels are similar: they are simplifications that are used to convey the essence of a concept or process
6 BlackbodiesAny object that is a perfect absorber of all radiation that strikes it and a perfect emitter of this radiation at its given temperatureNo substances in nature are true blackbodies, but only approximations of themTerrestrial surface of Earth approximates a blackbody in that it absorbs sunlight and reemits it as infrared radition
7 BlackbodiesRadiative equilibrium: when rate of absorption = rate of emissionTheoretical temperature at radiative equilibrium for Earth is 0 degrees F.Observed temp: 59 degrees FReason: atmosphere is much less a blackbody than Earth’s surface. The atmosphere is not a black body. It is a selective absorber
8 Selective absorbersGases that selectively absorb radiation also emit radiation at that same wavelength (Kirchoff’s Law).Natural and anthropogenic greenhouse gasesWater vapor (0-4%)Carbon dioxide (0.04%)Insert atmospheric windowsWater vapor accounts for about 50% of the natural greenhouse effect.Y axis is intensity of absorption
9 Selective absorbers Water vapor and carbon dioxide Strong absorbers of infrared radiation, ie longwave radition (LW)Absorption of LW results in molecular motion and transference of kinetic energy to other atmospheric molecules (conduction)Strong emitters of LWRadiative transfer of LW to groundThus form a “blanket” of warming in the atmosphere
10 Atmospheric windowsWavelengths between 8-11 micrometers are not absorbed by water vapor nor carbon dioxide
11 Atmospheric windowsHowever, clouds (liquid water droplets), are good absorbers in this range of wavelenths, especially low thick clouds like stratus.Cloud bases radiate LW downward and block incoming shortwaveTemperature ranges are smaller with stratus deckHigher nighttime temps and lower daytime temps
12 Radiative forcing at the global scale Sum of atmospheric and surface properties that determine net radiation balance
13 Temp controls at any single point Determined by:Radiative forcingWater availabilitySensible heat contentLatent heat transferAdvective heat transportAlbedo also shapes net balance of radiations….
14 Other controls on tempGeographic factors are more contingent, variable over time and/or spaceNitrogen (78%)Oxygen (21%)
18 Altitude As elevation increases, temperatures are cooler Higher altitude: lower air pressure: fewer molecules to absorb LW radiation (i.e. moreradiative coolingShow YouTube of altitude sickness; Long’s Peak
19 Why are there large annual temperature ranges over interior Canada and Asia?
20 How would the annual temperature for Vancouver and Winnipeg differ? The climate in Winnipeg is very extreme; overall, it is one of the coldest large cities in the world, with temperatures averaging below freezing from mid-November through much of March (and most nights below −24 °C (-11.2 °F) in mid-winter), although from May to September temperatures often reach 30 °C (86 °F) and sometimes exceed 35 °C (95 °F).Vancouver's climate is unusually temperate by Canadian standards; after Victoria, it is the second warmest major city in Canada during the winter, with temperatures rarely dropping below 0°C.
22 Geographic location relative to sea and water Maritime effectApplies to locations near large bodies of waterSmaller temperature rangeContinentalityApplies to locations distant from large bodies of water (i.e., landlocked)Larger temperature range (Siberia: -70 F to 70 F annually)
23 Water buffers temperature extremes because it heats up and cools down more slowly than land.
24 Which hemisphere has the lower average annual temperature?
25 Cloud coverage Cloudy conditions predominate: small temperature range Clear conditions predominate: larger temperature rangeCloud type importantStratus type clouds promote more cooling and smaller temperature rangeCirrus clouds promote warming
30 Fallacies of scaleIndividualistic fallacy: extrapolating to the broad scale based on observations conducted at small, local scalesEcological fallacy: making local-scale characterizations based on broad-scale observations.To an extent, humans have to commit the individualistic fallacy and the ecological fallacy to certain extents in order to navigate the world
31 What is the normal temperature? 30 year average is standardWhat would be a record setting high or low temperature depends upon the length of the record you have available.Temperatures are often referenced to their departure from a climatic normal. Again, the length of the record that provided the average determines the amount of departure.