class #34: wednesday, november 181 climate types (e, and h) past climates: proxy data and mechanisms...

Class #34: Wednesday, November 18 1

Class #34: Wednesday, November 18

Climate Types (E, and H)

Past Climates: Proxy Data

and Mechanisms of Change


The 6 major climate groups

• A: Tropical moist• B: Dry (can be subtropical or mid latitude)• C: Moist with mild winters (mid latitude)• D: Moist with severe winters (mid latitude)• E: Polar (high latitude)• H: Highland (rapid climate change with

elevation)• 2nd letter: usually latitude (except B)• 3rd letter: differences in temperature


D Climate typeSevere (winter) Midlatitude

• Similar to C but severely cold winter

• Average temperature of coldest month <27ºF

• Snow on ground for extended periods

• Average temperature of warmest month >50ºF

• Overall, large change in temperature with season


D climate subtypes

• 2nd letter – “f” no dry season– “w” winter dry season

• 3rd letter– “a” hot summer– “b” warm summer– “c” cool summer– “d” extremely severe winter


D Climate Subtypes (continued)

• Humid continental– Dfa, Dfb, Dwa, Dwb– Dfa, for example, Chicago

• Subarctic– Dfc, Dfd, Dwc, Dwd– Long winter– Brief cool summer


E climate type

• Polar climate, very dry and cold

• Poleward of Arctic/Antarctic Circle, latitude 66.5º

• E climate subtypes– ET Tundra: mosses, lichens, flowering plants,

woody shrubs, small trees, permafrost– EF Ice caps: no vegetation; Greenland,

Antarctic Plateau


H climate type: Highland

• Large variation of temperature and precipitation over small horizontal distances

• Large diurnal temperature variation

• Can be dry or moist, depending on orientation, humidity, and whether prevailing winds are upslope or downslope


Have today’s climates always been the same?

• This question leads to the study of past climates.

• So do the questions: Can we predict future climates? What is the impact of humans on climate?

• Two kinds of past climate:– Historical, past few thousand years– Paleoclimate, ancient, back billions of years


Historical Climate

• Humans have kept records• Instrumental record

– Since about 1600

• Historical data: proxy data– Humans have kept some sort of record of

climate conditions– Examples: dates of freezes of lakes and rivers,

farmers’ logs, animals in cave paintings, other documents


Another source of data for the historical period is trees

• Tree rings are rings of growth in tree trunks in regions with distinct growing seasons.

• A wider tree ring means more growth.• Growth varies with temperature and precipitation,

depending on the species.• Information from various species is most helpful.• The study of tree rings is dendrochronology, and is

done by dendrochronologists.• Figure shows dry periods in Iowa in 1700, 1740,

1820, 1820, 1890, and 1930 from tree rings.


Proxy measurements of precipitation from tree rings

• Dry periods: 1930s, the “Dust Bowl”

around 1700

1740 1820 1890


Pollen for proxy information

• Pollen degrade slowly, distinctive shapes for each species

• Oldest sediments are deepest

• Spruce need a cool climate• Decline of spruce during

warming• Pine need a warm and moist

climate• Oak need it drier than pine


Dating ancient climates

• Living things all contain carbon• C14 begins to change to C12 in a radioactive

decay process at an exponential rate with a half-life of 5760 years as soon as living matter dies

• Carbon dating good to 50,000 yrs with an uncertainty of about 15%.

• For older samples and rocks need another method


Dating really ancient climates

• Uranium-238 decays into Lead-206 with a half-life of 4.5 billion years

• No other (except possibly human) sources of Lead-206

• How we know how old the Earth and moon are

• If equal amounts of Uranium-238 and Lead-206, then 4.5 billion years old.


Glaciers, Icebergs, Bubbles, and Dust

• Climate clues buried in ice just as in lake sediments

• When snow and ice exceed melting, glaciers form. Ice crystals crush under pressure, trapped air expelled, and bubbles form

• Ice 30-m thick can flow downhill. At the coast, calving produces icebergs when the glacier breaks, with as much as 90% underwater

• Gas bubbles with CO2 and CH4


Dust

• Dust in ice cores can be volcanic activity, or dry and windy conditions

• Acidic dust with sulfuric acid indicates volcanic activity

• Dust storms in Africa can be detected in polar ice cores

class #34: wednesday, november 181 climate types (e, and h) past climates: proxy data and mechanisms...

Documents

e climate typepolar

climate conditionsexamples

climate types e

kinds of past climate

major climate groupsa

h climate type

e climate subtypeset

highland rapid climate