Earth Sciences 240A - Lecture 34 - Climate III

The Younger Dryas Event: 13,000-11,700 ya

Most pronounced around N. Atlantic; Records from pollen [of ‘dryas octapetala’]

Dramatic cooling because of ‘Lid’ of cold, fresh melt water over sea; Density effect; After mixing, recovery rapid

The Little Ice Age (1400-1900 A.D.)

Followed ‘The Medieval Climatic Optimum’:  (1000-1300)

Likely the ‘top’ of the interglacial event

Dramatic worsening in Europe/N.A. by 1400; Global T drop of 1 to 1.5oC

1810-19 coldest in Europe; much emigration (to N.A.)

Gradual warming began mid-1800s; Initial rise of CO2 above long-term base: ~1800

Possible Factors

Milankovitch factors: Too simple alone (doesn’t account for variations)

Millennial oscillations (Example: Younger Dryas Event)

The sum of effects from:

Volcanic dust and/or CO2; changes in sedimentation rates; temporary ocean current changes; solar radiation variations; El Niňo; etc.

Observed short-term (as short as 1000 years) climate changes for which causes are not necessarily defined

Volcanic?

Laki: 1783; Mayon: 1814; Tamboro: 1815

Certainly didn’t start it! [1-2 year effects?]

Solar radiation variation?

Too short for Milankovitch cycle

Sun spot cycle: 11 years; too short

El Niňo?

Cycles roughly 2-7 years, but vary

9 v. severe event between 1525-1980; also 1983 and 1998

Zero correlation with Little Ice Age

Humans and the Greenhouse

First human-induced changes: mid-1800s

Atmospheric CO2: land-clearing added little

Industrial Revolution: added hugely

Warmed air means faster decomposition

Increased CO2 and methane CH4

Is it this factor which ended the Little Ice Age?

Climate in the Next 100-1000 Years

Natural Climate Variation

Short-term

Little Ice Age marked beginning of natural down-trend (…probably…)

Human intervention gives us the ‘superinterglacial’

End: final fossil fuel use + lag time

Long-term:

Glacial period will continue

Next interglacial peak:~100,000 years

It will be (much) smaller than present one (?)

Projected Changes (short-term)

Models

2xCO2 of preindustrial

Previously: at least 7 mya

4xCO2 of preindustrial

Previously: at least 100 mya

Forcing will be too short to reach eq’m.

Only fast-response systems will adjust quickly

Continental ice sheets are ‘slow-response’

Sea ice and vegetation are ‘fast-response’

Likely Impact

Peak T should last 100 years

Preindustrial levels should last 1000 years

Bulk of Greenland/Antarctic ice will survive (but margins go)

Climate of 2100 will be ~ to 5-10 mya

Catastrophic effects on Canada’s north

Although seas will warm and evaporation increase, interiors of continents will get less precipitation

Coastal areas flooded (seas up 50 cm)

Gone:

Most of Bangladesh and Netherlands

Large sections of Florida, Louisiana, Texas,….

 

Seasons will change, Especially at high latitudes

Fresh water: Most continental interior users must be more inventive in recycling

With warming tropical seas hurricanes/typhoons will increase in strength and possibly in number

Coastal erosion will be dramatic

High latitude winters will be less harsh

Time for adaptation for sea life and land life will be too short

Expect a huge extinction rate unless we attempt to save species in artificial preserves

 

Please read the Appendix: The Mackenzie Basin Impact Study

See you in the final exam