Overview of Climate Change Throughout Earth History Overview of Climate Change Throughout Earth History During the Phanerozoic (600 Ma), climate fluctuated.

Overview of Climate ChangeThroughout Earth History

Overview of Climate ChangeThroughout Earth History

• During the Phanerozoic (600 Ma), climate fluctuated between• During the Phanerozoic (600 Ma), climate fluctuated between

What were the possible causes of warm-coolmodes during the Phanerozoic?

What were the possible causes of warm-coolmodes during the Phanerozoic?

(think plate tectonics) (think plate tectonics)

— which would have altered ocean and atmosphere circulation

— which would have altered ocean and atmosphere circulation

Proxy data used to study Phanerozoic climates:Proxy data used to study Phanerozoic climates:

e.g., halite, gypsum; indicate that a warm-dry climate prevailed when and where these rocks formed

e.g., halite, gypsum; indicate that a warm-dry climate prevailed when and where these rocks formed

indicate a warm, humid climate

indicate a warm, humid climate

old glacial deposits preserved in ancient rocks

old glacial deposits preserved in ancient rocks

Cretaceous period (100 Ma):Cretaceous period (100 Ma):

• temperatures were• temperatures were

• continents were located• continents were located• existed• existed

Tertiary period—Tertiary period—

• uplift of Rocky Mtns. and Himalayas • uplift of Rocky Mtns. and Himalayas

Quaternary period (~1.8 Ma to present):Quaternary period (~1.8 Ma to present):

• Pleistocene epoch (1.8 Ma to 11.5 Ka) -- climate marked by a• Pleistocene epoch (1.8 Ma to 11.5 Ka) -- climate marked by a

Pleistocene (cont’d):Pleistocene (cont’d):

1. glacials: ~ 90,000 yr interglacials: ~10,000 yr1. glacials: ~ 90,000 yr interglacials: ~10,000 yr

a. continental ice sheets up to 3 km thickcovered N. Am. And N. Eurasiaa. continental ice sheets up to 3 km thickcovered N. Am. And N. Eurasia

(LGM):18 Ka(LGM):18 Ka

b. expanded in the Rocky Mountains and other parts of the worldb. expanded in the Rocky Mountains and other parts of the worldc. in the N. Hemisphere ranged ~10º latitude further south than presentc. in the N. Hemisphere ranged ~10º latitude further south than present

d. oceans were ~2º C cooler than todayd. oceans were ~2º C cooler than today

e. air temperatures 1-12º C cooler, depending on location

f.

e. air temperatures 1-12º C cooler, depending on location

f.

g. melting of ice sheets began ~17 Ka and continued at an uneven paceg. melting of ice sheets began ~17 Ka and continued at an uneven pace

• the YD started• the YD started

• many climate scientists believe that the abrupt cooling and warming at the beginning and end of the YD was cause by a shut- down of the

• many climate scientists believe that the abrupt cooling and warming at the beginning and end of the YD was cause by a shut- down of the

cross-section view of ocean circulationin the Atlantic:cross-section view of ocean circulationin the Atlantic:

--the 3-dimensional circulation of the oceans; it is driven by salinity and temperature differences--the 3-dimensional circulation of the oceans; it is driven by salinity and temperature differences

• the THC and surface ocean currents combine to create a of three-dimensional oceanic circulation

• the THC and surface ocean currents combine to create a of three-dimensional oceanic circulation

Downwelling of cold, salty water in the NorthAtlantic ‘pulls’ surface waters further north thanthey normally would travel; this is termed

Downwelling of cold, salty water in the NorthAtlantic ‘pulls’ surface waters further north thanthey normally would travel; this is termed

• downwelling of water is controlled by water density• downwelling of water is controlled by water density

Is the Atlantic Heat Pump constant?Is the Atlantic Heat Pump constant? NO!NO!

have been blamed for the rapid temp. changes of the YD have been blamed for the rapid temp. changes of the YD

• if less dense freshwater is added to the North Atlantic, it will not sink as rapidly, resulting in a

• if less dense freshwater is added to the North Atlantic, it will not sink as rapidly, resulting in a

What could cause freshwater inputs to the NorthAtlantic to increase? What could cause freshwater inputs to the NorthAtlantic to increase?

during the Hypsithermal than today

during the Hypsithermal than today

temps were warmer than present in some areastemps were warmer than present in some areas

• climate much colder than present (though not a true ‘ice age’)• glaciers advanced in Europe, N. America, Africa, New Zealand• Vikings abandoned Greenland settlements

• climate much colder than present (though not a true ‘ice age’)• glaciers advanced in Europe, N. America, Africa, New Zealand• Vikings abandoned Greenland settlements

[from 13.6º C to 14.4º C (56.8º F to 57.6º F)][from 13.6º C to 14.4º C (56.8º F to 57.6º F)]

Figure 3.1

From 2007 IPCC Report

• Over long time periods,climate is not stable!• Over long time periods,climate is not stable!

• Statements about climate depend on the time scale you are considering.

• Statements about climate depend on the time scale you are considering.

Deep thoughts:Deep thoughts:

• Is the recent warming caused by increased greenhouse gases (CO2) in the atmosphere?• Is the recent warming caused by increased greenhouse gases (CO2) in the atmosphere?

• What should be done, if anything, to address global warming?• What should be done, if anything, to address global warming?

• How much warming will occur in the next 100-200 yr?• How much warming will occur in the next 100-200 yr?