Transcript Climate Variability, Climate Change

NATS 101
Lecture
QuickTime™ and a
decompressor Variability
Natural
Climate
are needed to see this picture.
Artist’s rendition of snowball earth, 650 Mya
Perspective: Time Scales
4.6 Gya
2.1 Gya
13.7 Gya
3.5 Gya
65 Mya
21 s
Avg. human life span=0.15 s
http://ocw.mit.edu/OcwWeb/Earth--Atmospheric--and-Planetary-Sciences/12-301Fall-2006/LectureNotes/index.htm
Perspective: Astronomic Space Scales
13.7 Ga (+/- 1%)
1 ly = 1016 m
ly=light year
http://ocw.mit.edu/OcwWeb/Earth--Atmospheric--and-Planetary-Sciences/12-301Fall-2006/LectureNotes/index.htm
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?
How do we know what we know?
Causes of Climate Change
Astronomical
Composition
Surface
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.
Think approximate
The measured property is a PROXY for the one of interest.
Courtesy J. Thornton, U Wash
Unlocking “Stored” Climate Change
• Modern Instrument
Record
• Tree Rings
• Ice Cores
• Sediment cores
• Rock formations/types
Record: 1000 ~ Present day
“Length” of growing season
Good versus stressed years
Major fires
Courtesy J. Thornton, U Wash
Unlocking “Stored” Climate Change
• Modern Instrument
Record
• Tree Rings
• Ice Cores
• Sediment cores
• Rock formations/types
Record: ~ 1Mya to 20th cent
Inert gases (CO2, CH4, N2O,…)
Particulates (soot, ash, etc)
Temperature??
Courtesy J. Thornton, U Wash
Unlocking “Stored” Climate Change
• Modern Instrument Record
• Tree Rings
• Ice Cores
• Sediment cores
• Rock formations/types
Courtesy J. Thornton, U Wash
Record: ~ 200 Mya
Microfossils (ocean T),
Volcanic glass
Organic detritus
Magnetic pole location
Unlocking “Stored” Climate Change
• Modern
Instrument Record
• Tree Rings
• Ice Cores
• Sediment Cores
• Rock formations/types
Banded Iron Formations
BIFs tied up oceanic O2
Prevented atmospheric O2
Date no later than ~2 GYA
Record: ~ 4.5 Gya
Geologic formation
Geochemical analysis
Magnetic pole
Continental Location
Fossil record
Water Cycle – Water Isotope T Proxy
18O/16O
18O/16O
18O/16O
lower
18O/16O
lower still
low
high
Courtesy J. Thornton, U Wash
Vostok Ice Core Record
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
T and GHG correlated
Causality?
T based on water
isotope proxy
Courtesy J. Thornton, U Wash
O18 analysis of ocean sediments can be
used to construct past temperatures
Cold
Warm
http://en.wikipedia.org/wiki/%CE%9418O
600 Million Years of Climate
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.”
1.8 Mya
65 Mya
145 Mya
200 Mya
251 Mya
299 Mya
359 Mya
417 Mya
444 Mya
490 Mya
542 Mya
http://www.scotese.com/climate.htm
540 Mya of Climate Change from O18
http://en.wikipedia.org/wiki/Oxygen_isotope_ratio_cycle
Snowball Earth!
http://www.snowballearth.org/images/geologic_column.gif
Snowball Earth: Some Evidence
cap carbonates
dropstones
http://www-eps.harvard.edu/people/faculty/hoffman/Snowball-fig11.jpg
Basic physics are understood:
Runaway ice-albedo feedback
http://nai.nasa.gov/newsletter/03182005/snowball.jpg
How does earth thaw? CO2?
Life is responsible for the “recent” rise of oxygen
Cambrian explosion
Multicell organisms
Use of oxygen for metabolism.
Water and CO2 are byproducts.
Use of sunlight for metabolism.
Oxygen is a byproduct.
http://si.wikipedia.org/wiki/%E0%B6%BB%E0%B7%96%E0%B6%B4%E0%B6%BA:Oxygen_atmosphere.png
Atmospheric constituents have changed
radically through the ages
Dimmer Sun
Brighter Sun
http://www.ozh2o.com/atmos.jpg
Long-Term Climate Change
NA
E-A
SA Af
180 M BP
India
Aus
Ant
NA
E-A
Af India
SA
Today
Aus
Ant
Ahrens, Fig 13.6
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.
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
Aguado and Burt, Fig 16-4
Extend of continental glaciers 18,000 years BP.
Sea level was 100-125 m lower than present.
Bering land bridge between Siberia and Alaska.
http://en.wikipedia.org/wiki/Image:Recent_Sea_Level_Rise.png
SST 18,000 years BP
18,000 BP
Ahrens, Fig 13.2
Much cooler over the North Atlantic Ocean.
Ocean currents were undoubtedly different.
North Atlantic Drift was probably much weaker.
Today
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.
Milankovitch
Theory
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
Glacial
advance
Glacial retreat
Apline
advance
Rapid melt
Ahrens, Fig 13.3
Younger-Dryas
Rapid cooling at the start occurred over a period of 1,000 yrs.
The abrupt warming at the end occurred in only a few yrs!
What caused the Younger Dryas?
FRESH WATER
TO NORTH
ATLANTIC
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??
Climate affects human societies
Viking colonization
in Greenland
Viking settlements
lost in Greenland
Ahrens, Fig 13.4
Temperatures for Europe during the last 1200 years.
Evidence of Climate Change
0.6oC warming
past century
Anthropogenic
warming?
Ahrens, Fig 13.5
Surface temperatures based on meteorological observations.
Is the warming of the past century due to human activities?
Complexity of Climate System
The climate system involves numerous, interrelated components
Feedback Mechanisms
Examples of feedbacks in the climate
system with global warming
Positive 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 feedback
LOW 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 1F 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) Astronomical
2) Atmospheric composition
3) 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