Part IV: Historical Climate Changes

Lecture 18: The Little Ice Age

(Chapter 15)

Frequency of sea ice intrusion along the coast of Iceland

MW: 1000-1300 LIA: 1400-1900

Vikings invaded southwestern Greenland

Vikings abandoned Greenland

Canada arctic lichen

Dead lichen due to snow expansion indicates the time of LIA

Mountain glacier:

Annual layer,

δ18O,

Dust content,

Ice core in Peruvian Andes

MW LIA

Ice cores in

four regions

MWLIA

Warming?

Global?

Temperature change, not uniform!

MW and LIA seems to be present in tropical mountain glaciers, but not obvious in Greenland and Antarctic ice sheets

Tasmanian tree rings

MW? LIA? Not obvious in SH

Unprecedented warming?

Reconstructed NH temperature (hockey stick pattern)

MW? LIA?

Global warming?

Longest Instrument record

LIA? Global warming?

Temperature stations,

Urban heat island effect

Global surface temperature

Source: D. Fagre, USGS, 2004

Recession of the Grinnell Glacier

“Glacier National Park”

1910

1997

Ice on Kilimanjaro

0

5

10

15

1900 1920 1940 1960 1980 2000 2020

Year

Kilimanjaro ice extent (km2)

?

Little Penck Glacier, Kilimanjaro

Sea level rise

5cm upper ocean warming, 3 cm land ice melting, 2 cm Greenland ice melting

Increased cloud cover

Unclear warming or cooling effect because

unknown high or low clouds

Arctic sea ice Arctic clouds

(warming or cooling?)

The growing season lengthens in Alaska

Tree Ring WidthTree Ring Width

Obs. Trend

Tree ring

Tair

Model

Obs.

P ~ R

Global Greening TrendGlobal Greening Trend

Total CO2

Physiology

Carbon fertilization

Radiation

Obs. >1980

Obs. – crops

(FPAR: Fraction of Photosynthetically Active Radiation)(FPAR: Fraction of Photosynthetically Active Radiation)

Decrease in snow cover

Reduced Arctic sea ice cover

and thickness !

Global Lake Open/Close Date

Lake

Mendota

2) Is it cause by orbital forcing of reduced summer insolation or millennial variability?

Fundamental Questions on MW/LIA

1) Are these change regional or global?

3) What caused the rapid warming since 1900 that terminates the LIA?

Forcing mechanism for centennial and decadal variability

• Solar forcing

• Natural variability: PDO, NAO

11 year cycle: solar radiation and sunspots

More Sunspots More solar radiation from faculae

Sunspot history from telescopes

Forcing mechanism for interannual variability

• Volcanic forcing

• Natural variability: ESNO

Relation between ENSO and volcanic activity?

Eruption of Mount Pinatobo in 1991 and global cooling

(Tropical) Volcanic cooling

End of Lecture 19

Lecture 20: El Nino, La Nina and Southern Oscillation

(Chapter 16)

Change of Climate Variability Change of Climate Variability Tropical Pacific SST

El Nino and Southern Oscillation: ENSO

http://iri.columbia.edu/climate/ENSO/currentinfo/SST_table.html#figure

Historical record of El Nino

Corals and tropical ocean

Annual layers made of CaCO3, take ocean water δ18O (a proxy of temperature, but also with salinity effect)

LIA?

El Nino

Evolution of the last 21,000 yrs

Deglaciation, but not smooth

Change of Climate Variability Change of Climate Variability Tropical Pacific SST

1935 Texas (Dustbowl)1935 Texas (Dustbowl)

1997 Kansas1997 Kansas

Global surface temperature

SAHEL RAINFALL

North Africa Climate ChangeNorth Africa Climate Change

S. NicholsonCharney Charney

?

SST decadal variability!

Global US

Wisconsin Madison

Climate Change: Global to Regional PerspectiveClimate Change: Global to Regional Perspective

End of Lecture 20

Tibet ice core

Tree-ring

(dendroclimatology)

Arctic tree ring

Asian tree ring

Strong centennial /decadal variability

Natural Climate Variability Natural Climate Variability