External Causes Change in incoming radiation Change in composition of the atmosphere Change in...
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External CausesChange in incoming radiationChange in composition of the atmosphereChange in Earth’s surface
Feedback MechanismsWater vapor-greenhouse gas feedback (+)Snow-albedo feedback (+)Infrared radiation (-)
Big Picture
65 55 34 24 5.4 1.8
Glo
bal
Tem
p
Time (Mybp)
Eocene Oligocene Miocene
Pleis
toce
ne
Plio
cene
KT
60-7
0% lo
ss o
f
spec
ies
COOLING
Pleistocene climate: highly variable
http://uregina.ca/~radenbat/envgeol/glaciers/Iceages_climatechange.html
~23 ice ages
~40Kyr
~100kyr
41Kyr cycle
100kyr cycle
Causes of Climate Change
Plate Tectonics and Mountain BuildingTheory of plate tectonicsRidge and subductionMountain interaction with airflow and ocean
currents Variation on the Earth’s Orbit
Milankovitch Theory○ Eccentricity○ Precession○ Obliquity
Pleistocene climate: highly variable
http://uregina.ca/~radenbat/envgeol/glaciers/Iceages_climatechange.html
~23 ice ages
~40Kyr
~100kyr
Past 700,000 years: Ice cores
http://www.ngdc.noaa.gov/paleo/slides/slideset/20/20_406_slide.html
Ice core being extracted
Annual dust layers in GISP2
At Vostok 3.4km ice
Antarctic Ice core showing last 4 ice ages
(CO2 – Temp Feedback)
http://www.ipcc.ch/pub/tar/wg1/fig2-22.htm
Wis
con
sin
Gre
at G
laci
atio
nCovered all but the highest summits of the Rockies
T
emp
erat
ure
CO
2
Greenland Ice Coreshowing last ice age
Ramstorf, Nature, 419, 207-213,2002.
D/O warm events
Heinrich ice/cool events
•Dansgaard/Oeschger events : warm
•Heinrich events: ice-rafting
Time (kyr)
stage 3
Laurentide ice sheet and the Great Lakes
http://www.uwgb.edu/dutchs/glkhist/glkhist0.htm
Younger DryasCamp Century (Greenland) d18O record
Boyle & Keigwin, 1987 see http://www.doc.mmu.ac.uk/aric/gccsg/5-3-2-1.html, http://www.clivar.org/publications/exchanges/ex15/pc_nl_2000_1.html
YD
Te
mp
era
ture
Time
Alley et al., 1993http://www.pbs.org/wgbh/nova/warnings/stories/
-25of in 5 years!!
Black Sea flooding Straits of Bosphorus began to leak around 5550 BCMany middle eastern creation stories refer to a massive flood
Babylonian mythology (Ghilgamesh, a 12-tablet long saga discovered in a palace in Nineva. Flood is described on the 11th tablet. Copied from the 1,800BC Akkadian Atra-Hasis epic)
Egyptian mythology (out of Nu {Nun: watery chaos} Atum created a hill …) Greek mythology (following the opening of Pandora’s box …) Judao-Christian (Genesis 7:20: “…Fifteen cubits [7m] upward did the waters
prevail; and the mountains were covered.” King James)
http://www.robotwisdom.com/science/blacksea.htmlhttp://abcnews.go.com/sections/Science/DailyNews/flood000914.html
Straits as shallow as 36m!
African paleoclimatelast 15,000 years
15ky: Arid conditions. Sahara desert zone expanded: Rainforest changes to savanna (Thorp 1994)
10ky: likely in response to the shift of perihelion from July to Dec, Sahara shrank. Monsoon strengthened and expanded north and east. Lakes (e.g. Lake Chad) in the Sahara. Increasing Nile discharge deposited oxygen-rich
black muds (sapropels). 6.7ky: drier conditions began. (Nicholson and
Flohn, 1980) 4-3.6ky: brutal drought causes massive population
movement (Claussen et al., 1999). Akkadian empire collapses.
0ky: poor agricultural practices lead to further drop in water table and increasing salinity of ground water
Massive Lake Chad
Effect of expanded monsoon on northern Sahara (10ky)
Paleo-lake sediments contain organic material and mollusc shells. These paleo lakebeds are the source of much of the Saharan dust
African dust outbreak
http://science.nasa.gov/headlines/images/dust-quicky/dustmovie_big.gif
Greenland climate history
700-1100s: little sea ice was present to hinder navigation. 980s: Norse move from Iceland to Greenland led by Eirik Thorvaldsson
(known as Erik the Red), who was the father of Leif Eiriksson. Erik was escaping a death sentence for killing 2 guys in a fight.
1350: western settlement was abandoned 1408: eastern settlement was largely abandoned. A few persisted until
~1500. 1430s had particularly severe winters. 1492: “due to the severe freezing of the seas, no ship is believed to have
put in to land there for eighty years." (Letter from Pope Alexander VI ). But other factors included: Poor soil management Rise of the Hunseatic League shutting down Danish trading Greater opportunities further east, partly due to the plagues of the 14 th C Collapse of the ivory market due to African trade
1721: Danes reestablish an outpost.
http://www.archaeology.org/online/features/greenland/
A Frost Fair on the Thames at Temple Stairs by Abraham Hondius in 1684
http://www.museumoflondon.org.uk
Detail
Global Warming
Recent Global Warming: PerspectiveSince the beginning of the 20th century
average global surface temperature has increase 0.8ºC
Radiative Forcing AgentsCarbon dioxide and other greenhouse gases
disrupt radiative equilibrium, forming an increase in temperature
http://lwf.ncdc.noaa.gov/img/climate/research/trends/1901-annual-pg.gif
Changing SSTLinear trend 1900 - 1991
What the models show
Global Warming
Future Global Warming: ProjectionsDouble carbon dioxide levels will cause a
surface warming of 2-4.5ºCUncertainties:
○ The effect of water and land on rising levels of carbon dioxide
○ Amount or greenhouse gasesQuestion of Clouds
○ Clouds reflect radiation and emit infrared radiation, positive and negative feedbacks.