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  1. 1. Climate
  2. 2. Overview Climate Components and Controls Climate Classification and Global Patterns Climate Regions Tropical Mesothermal Microthermal Polar Climates Dry and Semi-Arid Highland Climate Change
  3. 3. Climate and Climate Components Climatology: Studying long term weather patterns in order to identify areas of similar characteristics More recently, it has become focused on climate change Climate Regions: areas of the Earth that exhibit similar climatic characteristics Characteristic biomes: forests, savanna, grasslands, desert, and tundra Components of Climate Insolation: Varies with latitude, daylength Temperature: Varies with latitude, altitude, continental- maritime effects, pressure systems, air masses Air masses: Varies with maritime/continental surfaces, latitude Moisture: varies with temperature, pressure systems, continental/maritime surfaces
  4. 4. Classification Classification systems Empirical classification uses statistical data to classify Genetic classification uses causal factors to classify Boundaries between climate regions Are transition zones, not abrupt changes Shift over time With climate change, climate regions are expected to shift poleward between 150-550 km
  5. 5. Example: Tropical Monsoon climates Empirical classification Genetic classification high temperatures with The ITCZ influences the little annual variation onshore flow of warm, moist air, producing Over 6 cm of rainfall heavy rainfall during for 9 – 11 months of the summer months the year Subtropical Highs Less than 6 cm of forming over rainfall for 1 -3 months continental masses of the year create a dry offshore flow during the winter months
  6. 6. Köppen-Geiger Climate Classification System (Empirical) Uses Average monthly temperatures, average monthly rainfall, and total annual rainfall for classification to distinguish arid areas
  7. 7. An Empirical Classification System
  8. 8. Some Genetic Generalizations Monthly average temperatures decrease with increasing latitude annual range increases with increasing latitude Where a single pressure system dominates, rainfall patterns are convectional (highest monthly rainfall averages correspond to highest monthly average temperatures – i.e. summer) ITCZ Polar High Pressure
  9. 9. Where the subtropical highs are present, effects on weather are variable, depending on whether they are motivating maritime or continental air masses Continental air masses create arid conditions Maritime air masses create moist condition In mid latitudes where cyclonic systems are present, rainfall patterns follow the shift of the storm tracks Continental and Maritime influences Greatest between Northern (more continental) and Southern Hemispheres (more maritime) Greater between Asia (continental winter influences) than North America (maritime and continental influences during the winter)
  10. 10. Tropical Climates General Characteristics (A) Lie between Tropics of Capricorn and Cancer Largest climate region on Earth Genetic factors High Insolation: even day length and near vertical sun rays year- round ITCZ exerts a great influence for part or all of the year, bringing high rainfall Unstable maritime air masses Empirical factors Average temperature of each month above 18oC Little range in annual temperatures High total annual rainfall, although monthly averages can vary Subcategories Tropical Rainforest (Af) Tropical Monsoon (Am) Tropical Savanna (Aw)
  11. 11. Tropical Rainforest (Af) ITCZ is present throughout the entire year High monthly average rainfall throughout the year – Monthly average > 6 cm Average monthly temperatures are fairly high, with a small annual range Ecosystem Broadleaf rainforest Nutrient poor soils nutrients stored in the vegetation itself basis of swidden (“slash and burn”) agriculture
  12. 12. Tropical Monsoon (Am) Feature a distinct wet season and dry season Significant rainfall for 9-12 months of the year ( > 6cm) ITCZ brings rain from the moist onshore flow of winds wet summers Continental subtropical highs create dry seasons through the dry offshore flow of winds dry winters Monthly average rainfall < 6 cm for 1 -3 months per year Very high amount of rainfall during wet season Fairly high average monthly temperatures with a small annual range Ecosystem Broadleaf rainforest grading to thorn scrub on margins with tropical savanna Soils are nutrient poor, similar to those of the Tropical Rainforest climate
  13. 13. Tropical Savanna (Aw) Lie poleward of Tropical Rainforest and Monsoon climates Features a distinct wet and dry season ITCZ affects these areas for less than six months of the year wet summers Average Monthly precipitation > 6 cm for 6 – 9 months Subtropical highs create dry conditions during the rest of the year dry winters Average monthly rainfall < 6 cm for 3 – 6 months moisture budget deficit during this time Ecosystem: Savanna (grasslands)
  14. 14. Mesothermal Climates General Characteristics (C) Mild Mid-latitude climates Low mid-latitudes Variable weather patterns continental and maritime air masses brought into conflict from shifting pressure systems (e.g., midlatitude wave cyclones during the winter) Ocean currents exert strong influence on air masses East coast currents are warm and strengthen airmasses West coast currents are cold and weaken air masses Summers cool with higher latitude (warm – cool) Summers are humid except under subtropical highs Monthly average temperatures are above freezing Monthly average temperature for coldest month between 18 oC and - 3 oC Monthly average temperature for warmest month above 10 oC Annual temperature range from 5 – 20 oC
  15. 15. Subcategories Humid Subtropical Climates Cfa Cwa Cwb Marine West Coast Climates Cfb Cfc Mediterranean Climates Csa Csb
  16. 16. Humid Subtropical Occur on the East coast of continents, just poleward of the tropics Humid subtropical – hot summer pattern (Cfa) Winter weather patterns dominated by midlatitude cyclonic storm tracks which bring precipitation winter storm tracks follow routes at lower latitudes Summer patterns dominated by subtropical highs which bring mT air masses over the continents Heating by warm ocean currents create instability and precipitation Rainfall occurs year-round Humid subtropical - winter dry pattern (Cwa, Cwb) Mainly in Asia – “temperate monsoons”: wet-dry seasons ITCZ brings rainfall during the summer Less rainfall during the winter (subtropical highs) Wettest summer month has 10 times the precipitation of driest winter month
  17. 17. Marine West Coast (Cfb, Cfc) Occur on West coast of continents Mild winters, cool summers mP air masses dominate Cyclonic storm systems occur throughout the year rainfall occurs year-round In Western Hemisphere, mountains along the West Coast restrict the extent of this climate region (rain shadow effect) Exception: Appalachians Elevation moderates summer temperatures Cyclonic storms bring rainfall during the winter and rainfall is enhanced in the summer due to convectional heating and cooling and orographic effects as well.
  18. 18. Mediterranean (Csa, Csb) Characterized by a distinct wet-dry seasonal pattern winter-wet, summer-dry Wettest winter month has at least 3 times the precipitation as the warmest summer month Dominated by Subtropical Highs Continental (dry) air masses in the summer Cyclonic storm tracks in the winter (wet) Moisture deficits in the summer vegetation adapted to these conditions hard, waxy leaves retain moisture chaparral, maquis, mattoral, mallee scrub
  19. 19. Microthermal Climates General characteristics (D) High mid-latitude climates with severe winters Increasing seasonality: greater variability in day length and temperature range Polar high pressure and subtropical lows are the main motivators of air masses (cP, mP) Rainfall follows convectional patterns At lowest latitudes of this region, cyclonic storm tracks influence rainfall patterns Continental effects create dry winter conditions in Asia Average monthly temperatures decrease with increasing latitude 1 – 7 months with average below freezing Warmest month above 10 oC, coldest month below -3 oC Annual range of temperatures increases dramatically with increasing latitude 20 – 65 oC differences possible
  20. 20. Subcategories Humid continental hot-summer climates Dfa Dwa Humid continental mild-summer climates Dfb Dwb Subarctic climates Dfc Dfd Dwc Dwd
  21. 21. Humid Continental Hot-Summer (Dfa) Few months with monthly average temperatures below freezing North America Cyclonic storm tracks from interaction of mT and cP air masses provide precipitation year- round, sustained in the summer by convectional rainfall as well Asia (Dwa) Winters dominated by strong dry cP air mass, producing monsoonal rain patterns Vegetation Forests (where precipitation is high) Grasslands (where precipitation is low)
  22. 22. Humid Continental Mild-Summer Climates Dfb) Roughly half the year experiences average monthly temperatures below freezing Weather patterns dominated by cP air mass Rainfall follows a convectional pattern Summers wetter than winters Dry winters more pronounced in Asia (Dwb) Spring melt of winter snows provides additional moisture input Thin soils with moderate fertility
  23. 23. Subarctic Climates (Dfc, Dfd, Dwc, Dwd) Over half the year experiences average monthly temperatures below freezing Summers are cool and winters harsh Extremely high range of temperatures Weather patterns are dominated by cP air mass Rainfall follows a convectional pattern (highest in the summer) Low total annual precipitation Ecosystem features Boreal forests (taiga forest) permafrost (soils frozen beneath the surface year round)
  24. 24. Polar Climates General characteristics (E) Above 66.5o N/S Latitude Low levels of insolation Low sun angle all year High albedo of snow and ice Extreme variation in day length Dominated by Polar High Pressure systems Low humidity, little precipitation No true summer Subcategories Tundra (ET) Ice Caps/Sheets (EF) Polar Marine
  25. 25. Tundra Climate (ET) Average monthly temperatures below freezing with continuous snow cover for 8 – 10 months each year Maximum summer temperature no more than 10oC Short burst of vegetation when snow melts lichen, moss, sedges, some flowering plants, no trees Permafrost
  26. 26. Ice Cap/Ice Sheet Climate (EF) All monthly average temperatures below freezing -78oC has been recorded in Antarctica Polar high pressure system Cold, dry air, little precipitation Ice has accumulated for hundreds of thousands of years 900,000 years maximum age recorded in an ice core dissolved gases in the ice give a profile of changes to Earth’s atmospheric composition. Ice sheets can be several kilometers thick
  27. 27. Polar Marine Climate Oceans moderate temperatures -7oC is maximum low Colder than Tundra Climates on average Small annual temperature range (no more than 15oC) More precipitation than other Polar climates sleet Predominant in coastal areas at the southern extreme of the Polar range
  28. 28. Arid and Semiarid Climates General Characteristics (B) Climate Region defined by permanent moisture deficits The potential demand for water exceeds its availability throughout the entire year Deserts: Available moisture is less than half of demand Steppe: Available moisture is greater than half, but less than the total demand Genetic factors Subtropical highs dominate Continental effect dominates Asia Rain shadows Vegetation Xerophytes: plants adapted to retain moisture, such as cacti Phreatophytes: plants with roots that penetrate deep down to where the water is
  29. 29. Subgroups Low Latitude Hot Desert Climates BWh Midlatitude Cold Desert Climates Bwk Low Latitude Hot Steppe Climates BSh Midlatitude Cold Steppe Climates BSk
  30. 30. Low Latitude Hot Desert Climates (BWh) Tropical and Subtropical High temperatures (Average annual temperature above 18oC) 0 – 38 cm rainfall annually Dominated by Subtropical Highs, Continental Effect Typically occur on western edges of continents, but desert conditions extend across North Africa into Saudi Arabia When the subtropical highs depart, instead of moist wind being brought in from the east, dry wind off the Asian steppes and deserts is brought in instead Rainfall follows a convectional pattern
  31. 31. ITCZ?
  32. 32. Midlatitude Cold Desert Climate (BWk) Occur at higher latitudes and elevations than hot deserts Average precipitation is below 25cm annually Average annual temperature is below 18 oC Rainfall comes with convectional patterns and midlatitude cyclonic storm systems Locations Southwest US into Nevada Asia (Gobi Desert and Mongolia) Patagonian Desert in Argentina
  33. 33. Low-Latitude Hot Steppe Climates (BSh) Occur on the margins of hot deserts where precipitation is a little higher Average annual precipitation is between 38 – 76 cm Convectional rainfall pattern Average annual temperature is above 18 oC Midlatitude Cold Steppe Climate (BSk) Occur on the poleward margins of cold deserts 25 – 64 cm of precipitation per year Precipitation is both convectional and cyclonic in origin Average annual temperature is below 18 oC
  34. 34. Highland Climates Not one single climate, but a gradual gradation of climate types as one moves up a mountain slope Increases in altitude correspond to increases in longitude Vegetation changes correspondingly Orographic rainfall plays a crucial role in the climate Wet/dry climate conditions with rain shadow effect Mountain-Valley breezes are important regulators of temperature
  35. 35. C A D B E
  36. 36. Global Climate Change Evidence Global average temperatures since 1998 have been the highest on record Rate of increase of temperatures is highest on record Within 1oC of meeting the highest temperatures of the last 125,000 years (which are the highest on record over the last 440,000 years) Concentration of CO2 is the highest over the last 440,000 years Challenge: what warming effects are anthropogenic forcing, and which are natural forcing?
  37. 37. Data sources Contemporary climatology Direct atmospheric monitoring Paleoclimatology Ice cores Tree-ring density Sediments Coral reefs Pollen
  38. 38. Causes Greenhouse gases 90-99% certainty that global warming is from the build-up greenhouse gases Carbon dioxide (CO2) Accounts for 64% of warming 33% increase over pre-industrial levels Attributed to the burning of fossil fuels and net loss of forest Methane (CH4) Accounts for 19% of warming over 100% increase over pre-industrial levels Attributed to anaerobic oxidation of organic compounds 50% from livestock digestion and organic processes in rice fields Nitrous oxide (N2O) Up 17% over pre-industrial period Attributed to fertilizer use – with some uncertainty Halocarbons (CFCs) Absorb a different wavelength of infrared radiation than carbon dioxide reduction in stratospheric ozone creates more surface warming Directly attributable to human activity
  39. 39. Predicted changes Based on General Circulation Models Three scenarios (1990-2100) Low Forecast – 1.4oC Middle Forecast – 3.6oC High Forecast – 5.8oC The Arctic is warming at a rate greater than that predicted by the high forecast
  40. 40. Effects of global warming Droughts that threaten food supply crops very sensitive to climatic conditions Shifting climatic regions species redistribution Polar species especially are at risk Melting of ice sheets/caps and glaciers 11% of Antarctica is composed of ice shelves 8000 km2 have disintegrated since 1993 Changes in sea level Low forecast – 0.09 m Medium forecast – 0.48 m High forecast – 0.88 m 25% in rise attributable to thermal expansion of water
  41. 41. Kyoto Protocol Calls for an overall reduction in carbon dioxide levels of 5.2% (1990 levels) between 2008-2012 Some countries favor a 15% reduction by 2010 Individual country contributions European Union – 8% Australia – 8% Canada – 6% USA – 7%, but never ratified the treaty and withdrew from the process in 2001