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EESA09H3 (185)
Lecture

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Department
Environmental Science
Course
EESA09H3
Professor
Tanzina Mohsin
Semester
Fall

Description
Wind Lecture #11: Changing Winds: Global Climatic Change Climate vs. Weather – Weather: what is it like outside? – Climate: what is it usually like outside? ○ A description of typical weather conditions for a location and time of year (long-term weather data) ○ Based on statistics accumulated over a long period of time (at least 30 years)  Toronto’s Climate for July: 30 years of data from Environment Canada • Tmean = 22.2deg C • Tmax = 26.4deg C • Tmin = 17.9deg C • Rain: 67.5 mm • Extreme Tmax = 40.6deg C • Extreme Tmin = 3.9deg C • Extreme daily rain: 98.6 mm Factors that influence local climate:  Latitude – incident radiation from the sun • How much sun radiation you receive • Tropics – most amount of sun exposure (climate in the tropics is way different from the Midlatitude regions)  Global circulation – prevailing winds (easterlies, westerlies), jet streams, ocean current • SSTS can affect formation of hurricanes • We have subtropical jet, polar jets, that we are known to create the Midlatitude cyclones  Air masses – transport of warm or cold, moist or dry air • CP air masses, CA air masses  Geography – e.g., rain-shadows from mountains, land/sea breezes • Most important factor • Toronto’s climate is hugely impacted by convective storms because of the land/sea breeze • Toronto is shielded by the Niagara escarpment so that we don’t get much ice or snow storms comparing to the regions (New York, Buffalo) around us  Land cover – Albedo, evapotranspiration, heat capacity • Urban heat island effect • Urban area, there are a lot of concrete not much vegetation or farm lands • Therefore, there is much more warming condition What is feedback? – Two types: positive, negative ○ A change in “A” will cause a change in “B”, which in turn will cause a change in “A” in the same direction is called a positive feedback ○ However, if a change in “A” cause a change in “B: and that will cause in “A” in the opposite direction then it is a negative feedback Albedo: – Reflectivity – Changes in albedo will change the local climate – Large-scale albedo changes can affect the global climate – Feedback: climatic change can cause changes in cloud and snow cover, which in turn causes further climatic change ○ Different clouds have diff. characteristics ○ Some clouds absorb, some clouds reflect the sun ○ Therefore, clouds can create positive or negative feedback ○ *clouds are major areas of uncertainty of climate modelling – they keep changing* – Snow/Ice Feedback: ○ Fresh snow has a high percentage of albedo  When fresh snow on the ground is clear, it loses reflectivity and cause warming  Warming will cause more fresh snow to melt and therefore losing more reflectivity  Therefore, POSITIVE FEEDBACK!  Therefore, Arctic regions will be more warmer, therefore, more melting of sea ice, which causes more warming Historical Climate Change: – Volcanic eruptions ○ Dust and sulfuric acid particles launched into the stratosphere ○ These aerosols remain in the air for several years  Aerosols have cooling effect on climate – opposite of greenhouse gases  Therefore, NEGATIVE FEEDBACK on climate system (they are causing cooling effect) ○ E.g., 1816 – “Year without a Summer”  Massive eruptions in 1812 (St. Vincent), 1814 (Philippines) and 1815 (Indonesia)  Major June snowstorms in North America  Crop failure and starvation across the Northern Hemisphere  Therefore, global cooling is not always a good idea – Solar variation ○ Long term cycles in solar characteristics have been observed  The “Maunder Minimum” in 17 century  Coincided with the “Little Ice Age”  It still can’t be proved whether the low temp. were caused by a decrease in solar strength – Milankovic theory and ice ages ○ Slight changes in the shape of the orbit and axial tilt of the Earth would cause huge change in local climate and weather ○ Colder winters lead to increased ice and snow cover ○ Timescale are 21 000, 41 000 and 100 000 years, roughly coinciding with glacial periods ○ Last glacial period ended 10 000 years ago – Interannual variability – Short-term atmosphere-ocean cycles such as ENSO and NAO – Long-term climate cycles are poorly understood because of the lack of data ○ Limited long-term, global observation Thermodynamics and the Greenhouse Effect: – First law of thermodynamics ○ Energy cannot be created or destroyed ○ Ein = Eout + deltaEstored ○ At equilibrium, deltaEstored = 0 and Ein = Eout ○ When there is extra energy in the atmosphere (fossil fuels), it is stored in the atmosphere of the Earth and causes global warming – Stefan-Boltzmann Law ○ All matter emits radiation proportional to the fourth power of its temp. ○ If there is extra sun radiation, there is extra temperature change (effect the temp.) ○ Eout is proportional to T^4 Thermodynamics: – For the Earth: ○ Ein is radiation coming from the sun ○ Eout is radiation emitted by the Earth ○ Estored determines the Earth’s temperature – So: ○ If Eout is less than Ein, the temp. will increase until the two are equal again – Wien’s Law: ○ The sun radiated most of its radiation near the visible range  Short-wave radiation  Emitting radiation only in the day time ○ The Earth radiated most of its radiation in the infrared range  Long-wave radiation  Emitting radiation day and night, all the time – ****KNOW SLIDE 21 AND 22 BY HEART!!!**** ○ If there is a surplus on the right side, the greenhouse gases constantly absorb the Earth’s radiation, and therefore contributing to global warming ○ Same amount of suns ray coming to the earth in rural and city areas  Eout is huge for cities – because of the concrete • Not so much in rural areas • Warmer in urban areas than rural areas – Selective absorbers: ○ Most substances absorb only certain wavelengths of radiation  E.g., glass absorbs ultraviolet and infrared radiation, but not visible radiation ○ Greenhouse gases are transparent to visible radiation, but absorb infrared radiation  Therefore, they have no effect on Ein but reduce Eout – The Greenhouse Effect ○ The action of greenhouse gases is to trap heat ○ The natural greenhouse effect keeps the global avg. temp. 33degC warmer than it would be otherwise (15deg C instead of -18degC) The enhanced greenhouse effect: increase in the past 50 years! – Carbon Dioxide (CO2) ○ Prior to 1800;s, varied between 180-300 ppm ○ Current concentration is about 390 ppm ○ Emissions: fossil fuels (6 GtC/yr), Deforestation (2 GtC/yr)  Gt (Giga-ton) ○ Roughly half of this remains in the atmosphere  Irreversible, once you emit greenhouse gases in the atmosphere, it will warm the Earth and y
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