Part 6. Current, Past, and Future Climates

Chapter 15

Earth’s Climates

IntroductionClimate is the long-term statistical properties of the atmosphere for an area

Climate classifications are based on properties such as temperature, precipitation, air mass types, and water budget characteristics

The Koeppen climate classification system• Most widely used classification scheme• Based on natural vegetation types as

indicators of average weather

Koeppen Classifications

Tropical Climates• Warm annual temperatures and minimal

seasonal temperature variation• Differentiated on precipitation variations

Tropical Wet (Af)– Even precipitation through year– High humidity – Temperatures

– Highs = low 30°s C (80°s F) – Lows = low 20°s C (70°s F)

Af climographs

Monsoonal effects seen in the precipitation trends throughout the year

Monsoonal (Am)• Near tropical coastal areas • Monthly precipitation variations are

significant, with very high annual totals• Small annual temperature variations

Am climographs(strong monsoonal precipitation)

Tropical Wet and Dry (Aw)• Poleward tropical margins• Distinct temperature and precipitation

seasonality • Low sun dry period• Unreliable precipitation

– Sahel region• Savanna vegetation

Aw climographs

Dry Climates30% of Earth’s land surface

Defined by water balance• Potential evapotranspiration > precipitation

Subtropical Deserts (BWh)– Largest deserts

– Western sides of continents– Areas with atmospheric subsidence– High diurnal temperature ranges (low

dew points/humidity)

BWh climographs

High precipitation variability of BWh regions

Southern California site; 1983 and 1992 were El Nino years

Subtropical Steppe (BSh)– High aridity – High precipitation and temperature

variability – Large temperature ranges– Extreme summer temperatures– Summer precipitation

BSh climographs

Mid-Latitude Deserts (BWk)– Extreme continentality and/or rain

shadows– Asia and the Western U.S.

– Very high temperature ranges – Summer temperatures – very hot– Nighttime and winter temperatures - very

cool– Higher humidity and precipitation

BWk climographs

Mid-Latitude Steppe (BSk)– A transition zone– Higher annual average precipitation than

true desert

BSk climographs

Mild Mid-Latitude Climates• Eastern continental areas • Varying precipitation regimes• Mild winter temperatures • Summer temperatures may be high

Mediterranean (Csa, Csb)• Distinct summer dry period

– Subtropical high interactions• Winter precipitation is variable • Mild winter temperatures • Mild to hot summers

Csa, Csb climographs

Humid Subtropical (Cfa, Cwa)• Eastern continental areas of the lower mid-

latitudes• High heat and moisture

– Abundant and even monthly precipitation – Weather influenced by subtropical highs

• Mild winters• Hot summers

Cfa, Cwa climographs

Marine West Coast (Cfb, Cfc)• Poleward of Csb• Cold ocean current influence

– Often has fog and/or low cloud cover • Mild and even annual temperatures• High frequency of rain days

Cfb, Cfc climographs

Severe Mid-latitude Climate• Very cold winters• Large continental areas• Evenly distributed annual precipitation

Humid Continental (Dfa, Dfb, Dwa, Dwb)– Eastern continents - 40o-55o N – Warm to hot summers– Cold winters– Even and abundant annual precipitation

Dfa, Dfb, Dwa, Dwb climographs

Subarctic (Dfc, Dfd, Dwc, Dwd)– Poleward of humid continental climates – Coniferous boreal forest (taiga)– Warm, short summers – Low annual precipitation (summer

maximum)

Dfc, Dfd, Dwc, Dwd climographs

Polar Climates• Very high latitudes • Very cold

Tundra (ET)– Tundra vegetation – Harsh winters– Mild summers of long days– Permafrost region

ET climographs

Ice Cap (EF)• Constant ice cover

– Greenland and Antarctica• Warmest monthly temperatures < 0oC• Katabatic winds• Low precipitation

EF climographs

Highland Climates (H)• Governed solely by topography• Vertical zonation

– Highly variable local climates

End of Chapter 15

Understanding Weather and Climate

4th Edition

Edward Aguado and James E. Burt