nats 101 lecture natural climate variability artist’s rendition of snowball earth, 650 mya

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NATS 101

LectureNatural Climate Variability

Artist’s rendition of snowball earth, 650 Mya

Perspective: Time Scales

13.7 Gya

4.6 Gya 2.1 Gya

3.5 Gya

65 Mya

Avg. human life span=0.15 s

21 s

http://ocw.mit.edu/OcwWeb/Earth--Atmospheric--and-Planetary-Sciences/12-301Fall-2006/LectureNotes/index.htm

1 ly = 1016 mly=light year

13.7 Ga (+/- 1%)

http://ocw.mit.edu/OcwWeb/Earth--Atmospheric--and-Planetary-Sciences/12-301Fall-2006/LectureNotes/index.htm

Perspective: Astronomic Space Scales

http://en.wikipedia.org/wiki/Earth

What is Climate Change?

• Climate change - A significant shift in the mean state and event frequency of the atmosphere.

• Climate change is a normal component of the Earth’s natural variability.

• Climate change occurs on all time and space scales.• We know that “a plethora of evidence exists that

indicates the climate of the Earth has changed.” What is that evidence? What is that evidence? How do we know what we know?How do we know what we know?

Causes of Climate Change

AstronomicalAstronomical

SurfaceSurface

CompositionComposition

Detecting Change With Proxies

Scientifically, the best way to detect change is to directly measure it. Data available last 100-200 yrs.

Unfortunately for the timescales of interest in climate science, we were not always able (interested in?) to measure quantities such as temperature, precipitation, wind speed, direction, greenhouse gas levels, etc.

But, obviously we want to know what these properties were and how they changed in the past to test our understanding of how climate changes.

The study of past climate is known as paleoclimate science. Courtesy J. Thornton, U Wash

Detecting Change With Proxies

Another property/qty that is a function of property of interest.

The measured property is a PROXY for the one of interest.

Think approximate

Courtesy J. Thornton, U Wash

Record: 1000 ~ Present day“Length” of growing seasonGood versus stressed yearsMajor fires

Unlocking “Stored” Climate Change

• Modern Instrument Record

• Tree Rings

• Ice Cores

• Sediment cores

• Rock formations/typesCourtesy J. Thornton, U Wash

Record: ~ 1Mya to 20th centInert gases (CO2, CH4, N2O,…)Particulates (soot, ash, etc)Temperature??

Unlocking “Stored” Climate Change

• Modern Instrument Record

• Tree Rings

• Ice Cores

• Sediment cores

• Rock formations/typesCourtesy J. Thornton, U Wash

Record: ~ 200 MyaMicrofossils (ocean T),Volcanic glassOrganic detritusMagnetic pole location

Unlocking “Stored” Climate Change

• Modern Instrument Record

• Tree Rings

• Ice Cores

• Sediment cores

• Rock formations/types

Courtesy J. Thornton, U Wash

Unlocking “Stored” Climate Change

• Modern Instrument Record

• Tree Rings

• Ice Cores

• Sediment Cores

• Rock formations/types

Record: ~ 4.5 GyaGeologic formation Geochemical analysisMagnetic poleContinental LocationFossil record

Banded Iron Formations BIFs tied up oceanic O2 Prevented atmospheric O2 Date no later than ~2 GYA

18O/16O low

18O/16O high

18O/16O lower18O/16O lower still

Water Cycle – Water Isotope T Proxy

Courtesy J. Thornton, U Wash

T based on water isotope proxy

Last Ice Age

During last ice age (18,000 years ago)Temps 6oC colder CO2 levels 30% lower

CH4 levels 50% lower

(Sea level was higher)than pre-industrial

interglacial values

Courtesy J. Thornton, U Wash

Vostok Ice Core Record

T and GHG correlatedCausality?

O18 analysis of ocean sediments can be used to construct past

temperatures

http://en.wikipedia.org/wiki/%CE%9418O

Warm

Cold

600 Million Years of Climate

http://www.scotese.com/climate.htm

The past climate of the Earth can be deduced “by mapping the distribution of ancient coals, desert deposits, tropical soils, salt deposits, glacial material, as well as the distribution of plants and animals that are sensitive to climate, such as alligators, palm trees & mangrove swamps.”

542 Mya

65 Mya

490 Mya

200 Mya

145 Mya

251 Mya

299 Mya

417 Mya

359 Mya

444 Mya

1.8 Mya

540 Mya of Climate Change from O18

http://en.wikipedia.org/wiki/Oxygen_isotope_ratio_cycle

http://www.snowballearth.org/images/geologic_column.gif

Snowball Earth!

http://nai.nasa.gov/newsletter/03182005/snowball.jpg

Snowball Earth: Some Evidence

dropstones

http://www-eps.harvard.edu/people/faculty/hoffman/Snowball-fig11.jpg

Basic physics are understood: Runaway ice-albedo feedback

How does earth thaw? CO2?

cap carbonates

http://si.wikipedia.org/wiki/%E0%B6%BB%E0%B7%96%E0%B6%B4%E0%B6%BA:Oxygen_atmosphere.png

Life is responsible for the “recent” rise of oxygen

Use of sunlight for metabolism. Oxygen is a byproduct.

Use of oxygen for metabolism. Water and CO2 are byproducts.

Multicell organisms

Cambrian explosion

Atmospheric constituents have changed radically through the ages

http://www.ozh2o.com/atmos.jpg

Dimmer Sun Brighter Sun

Long-Term Climate Change

250 million years ago, the world’s landmasses were joined together and formed a super continent termed Pangea.

As continents drifted apart to their present configuration, they moved into different latitude bands.

This altered prevailing winds and ocean currents.

NAE-A

AfSAIndia

NAIndiaAf

SA

E-A

AntAus

Ant

Aus

180 M BP Today Ahrens, Fig 13.6

Long-Term Climate Change• Circumpolar ocean

current formed around Antarctica 40-55 MY ago as Antarctica and Australia separated.

• Kept warm air from low latitudes from reaching into Antarctica.

• Absence of warm air accelerated growth of the Antarctic ice sheet.

http://www.ace.mmu.ac.uk/eae/Climate_Change/Older/Continental_Drift.html

Most Recent Ice Age

Extend of continental glaciers 18,000 years BP.

Sea level was 100-125 m lower than present.

Bering land bridge between Siberia and Alaska.

Aguado and Burt, Fig 16-4

http://en.wikipedia.org/wiki/Image:Recent_Sea_Level_Rise.png

SST 18,000 years BP

Much cooler over the North Atlantic Ocean.

Ocean currents were undoubtedly different.

North Atlantic Drift was probably much weaker.

18,000 BP TodayAhrens, Fig 13.2

Milankovitch Theory of Ice Ages• Attempts to explain ice

ages by variations in orbital parameters

• Three cycles:

Eccentricity (100,000 yrs)

Tilt (41,000 yrs)

Precession (23,000 yrs)• Changes the latitudinal

and seasonal distributions of solar radiation.

MilankovitchTheory

Change in daily solar radiation at top of atmosphere at June solstice

Changes as large as ~15% occur

Milankovitch Theory of Ice Ages• Ice ages occur

if summers are cool and less snow melts.

• Partially agrees with observations, but many questions unanswered.What caused the onset of the first Ice Age?

http://en.wikipedia.org/wiki/Milankovitch_cycles

Temperatures since the last Ice Age… the time that humans have

flourished

Younger-DryasRapid cooling at the start occurred over a period of 1,000 yrs. The abrupt warming at the end occurred in only a few yrs!

Glacial retreat Rapid melt

Glacial advance

Apline advance

Ahrens, Fig 13.3

FRESH WATER FRESH WATER

TO NORTH TO NORTH ATLANTICATLANTIC

As the ice sheets were retreating, a giant prehistoric lake formed called Lake Agassiz.The lake eventually broke through the ice sheet and drained into the North Atlantic.The freshening of the sea water shut down the Gulf Stream and the heat transport toward Europe, what happened then??

What caused the Younger Dryas?

Climate affects human societies

Temperatures for Europe during the last 1200 years.

Viking settlements lost in GreenlandViking colonization

in Greenland

Ahrens, Fig 13.4

Evidence of Climate Change

Surface temperatures based on meteorological observations.Is the warming of the past century due to human activities?

0.6oC warming past century

Ahrens, Fig 13.5

Anthropogenic warming?

Complexity of Climate System

The climate system involves numerous, interrelated components

Feedback Mechanisms

Examples of feedbacks in the Examples of feedbacks in the climate system with global climate system with global

warmingwarmingPositive feedback = Enhances the warming

Negative feedback = Mitigates the warming

IF YOU HAVE THE FOLLOWING:

MORE WATER VAPOR: Positive feedback because it’s a greenhouse gas.

LESS SEA ICE: Positive feedback because more solar radiation is absorbed instead of reflected.

MORE CLOUDS: Feedback can be positive or negative depending on the type of clouds. THIS IS STILL A BIG UNKNOWN…

HiGH CLOUDS: Positive feedbackLOW CLOUDS: Negative feedback

MORE AEROSOLS: Negative feedback because more solar radiation is reflected.

Key Points: Climate Change

• Proxy data are used to infer the past climate.

• Data show that the Earth’s Climate

Has changed in the past

Is changing now

And will continue to change

• There has been 1F warming during the past century, half of which has occurred during the past 30 years.

Key Points: Climate Change

• The climate system is very complex.

Contains hundreds of feedback mechanisms.

Feedbacks are not completely understood.

Biosphere-Atmosphere interactions.

Key Points: Climate Change

• Three general climate change mechanisms:1) Astronomical2) Atmospheric composition3) Earth’s surface

• Humans modifying 2 and 3 on global scale.• Are recent climate and weather changes

due to natural causes or human activities?Next Time

Assignment for Next Lecture Anthropogenic Climate Change

• Reading- Ahrens

4th: 373-399

5th: 383-409

• Homework11- D2L

4th-Pg. 399: 14.12, 15, 16, 19

5th-Pg. 412: 14.12, 15, 16, 19

Do Not Submit D2L