Weather, Climate & Society ATMO 336 Impact of Extreme Weather
Weather, Climate & Society ATMO 336 Natural Climate Variability.
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Transcript of Weather, Climate & Society ATMO 336 Natural Climate Variability.
Weather, Climate & SocietyATMO 336
Natural Climate Variability
Perspective: Time Scales
13.7 b.y.
4.6 b.y. 2.1 b.y.
3.5 b.y.
65 m.y.
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 lt.y.=1016 m
13.7 Ga (+/- 1%)
http://ocw.mit.edu/OcwWeb/Earth--Atmospheric--and-Planetary-Sciences/12-301Fall-2006/LectureNotes/index.htm
Perspective: Astronomic Distance 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.• It was stated that “a plethora of evidence exists that
indicates the climate of the Earth has changed.” What is that evidence? How do we know what we know?
Determining the Past Climate
Paleoclimatology - the study of past climates.• Past 100-200 years (weather observations)• Must use indirect climate measures, proxies, to
examine further into the past. Some proxies:
- Tree rings (1,000+ years before present BP)
- Trapped pollen (10,000+ years BP)
- Glacial ice cores (100,000+ years BP)
- Ocean sediment cores (1 Million+ years BP)
- Geology (1 Billion+ years BP)
Detecting Change With Proxies
Scientifically, the best way to detect change is to directly measure it.
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
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
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
18O/16O low
18O/16O high
18O/16O lower18O/16O lower still
Water Cycle – Water Isotope T Proxy
Courtesy J. Thornton, U Wash
Vostok Ice Core Record
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
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?
Simple climate models exhibit hysteresis between ice-no ice states
http://www.snowballearth.org/slides/Ch7-6.gif
Delayed response between CO2 forcing and rapid jumps between ice free and snowball earth.
Snowball cycles show freeze-thaw-hothouse
http://www.snowballearth.org/images/snwbltvst.gif
Is snowball earth a mechanism for jump starting evolutionary leaps?
http://www.snowballearth.org/slides/Ch7-6.gif
Metazoa and plants appear after last episode
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
Long-Term Climate Change
250 million years ago, the world’s landmasses were joined together and formed a super continent termed Pangea.
As today’s continents drifted apart, 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 seaway
leads to large latitudinal temperature gradient.
Current S.H. Situation
• Circumequatorial seaway leads to small latitudinal temperature gradient.
Situation 50 MYahttp://www.ace.mmu.ac.uk/eae/Climate_Change/Older/Continental_Drift.html
Long-Term Climate Change• Circumpolar ocean
current formed around Antarctica 40-55 MY ago once Antarctica and Australia separated.
• This prevented warm air from warmer latitudes to penetrate 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
http://earthobservatory.nasa.gov/Study/BorealMigration/Images/pleistocene_modern.jpg
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
Temperatures since the last Ice Age… the time that humans have
flourished
Rapid warming occurred at end of Younger-Dryas period.
Ice cores indicate that Ice Age conditions ended in 3 years!
Glacial retreat Rapid melt
Glacial advance
Apline advance
Ahrens, Fig 13.3
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
Controversial “Hockey Stick”
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
• Key question is determining whether recent changes are due to natural causes or man.
Key Points: Climate Change
• The climate system is very complex.
Contains hundreds of feedback mechanisms
Feedbacks are not completely understood.
• Three general climate change mechanisms:
Astronomical
Atmospheric composition
Earth’s surface