Transcript Chapter 20

Global Warming
Climate
• Climate: the average weather conditions over a
period of years in a particular place
• Climate is influenced by a variety of processes,
including geologic processes
– Volcanism
– Sea-floor spreading
– Configuration of landmasses due to plate tectonics
• Climate changes impact geologic processes
– Rates of erosion and deposition
– Types of sediments deposited and sedimentary
rocks formed
– Geomorphology (surface features)
– Fossil record
The Climate System
• Multidimensional System, many
interacting parts
• Atmosphere, hydrosphere, geosphere,
biosphere, and cryosphere
• Exchange of energy and moisture
The Climate System
Paleoclimatology – the study of past
climates.
• Earth’s climate varies in cyclical fashion over a
number of time-scales
• The study of natural climate processes is
important to understand the role of humans in
climate change.
• Scientists measure climate change in the past
in many different ways, depending on the timescale.
Paleoclimatology – Study of past
climates
What can paleoclimatology
tell us about climate change
that is relevant to society in
the future?
• Is the last century of climate change
unprecedented relative to the last
500, 2000, and 20,000 years?
• Do recent global temperatures
represent new highs, or are they just
part of a longer cycle of natural
variability?
• Is the recent rate of climate change
unique to the present or was it
commonplace in the past?
• Can we find evidence in the
paleoclimate record for mechanisms
or climate forcings that could be
causing recent climate change?
Proxy Climate Indicators
• Instrumental records (from thermometers,
rain gauges, etc.) only exist for the last 150
years.
• Proxy climate indicators provide indirect
indications of climate change. These
include:
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Seafloor Sediments
Oxygen Isotopes
Glacial Ice Cores
Corals
Pollen
Historical Data
Proxy climate indicators and their useful time
range
Climate Data from Historical Records
Wine is a serious
business in Europe!
Careful records of the
first day of the grape
harvest in Europe
have been kept since
the 14th century.
Trends in these
records show changes
in climate, as the
harvest started earlier
or later in the year.
Tree rings
•Trees can live for
thousands of
years.
•The width of tree
rings provides
information about
growing
conditions,
including
temperature
conditions and
CO2
concentrations.
Oxygen Isotope Analysis
One of the most
important ways
that proxy data
indicators reveal
climate
information is
through the use
of oxygen
isotope analysis.
Oxygen Isotope Analysis
• Isotope – varieties of an element with different numbers of
neutrons, resulting in different atomic masses.
• The most common isotope of oxygen has an atomic mass
of 16 and is called 16O. A heavier, less common variant is
18O. Both occur naturally, and neither is radioactive. You
breathe both kinds. Both isotopes bond with 2 hydrogen
atoms to make water, H2O.
• Water made of 16O evaporates more easily. Water made of
18O condenses more easily.
18O
has two extra neutrons
Oxygen Isotope Analysis
• During colder weather, more light 16O evaporates, leaving
ocean water with more heavy 18O.
• This oxygen is incorporated into coral, plankton shells and
sediments at the ocean bottom.
• In colder climates, these proxy indicators will be enriched in
18O.
• The ratio of 18O to 16O, (δ 18O) can be correlated to
temperature. For benthic (deep-water sediments), colder
temperatures are related to higher values of δ 18O.
Reading the Graph
• Horizontal (x) axis: Note older data as you move right.
• Left vertical (y) axis - δ 18O ratios. A value of zero indicates
the “standard” value for ocean water. The higher the value,
the more 18O, and the colder the ocean waters. Note colder
is down on this graph.
• Right vertical (y) axis - ∆T (temperature difference from
“normal” annual average ocean temperature) Zero (dashed
line) indicates “normal”.
Oxygen Isotope Analysis
•Conversely, glacial ice
cores are made of
evaporated water that
precipated.
• Precipitation water
always has a negative
value of of δ 18O.
• Colder temperatures
are related to lower
(negative values) of δ
18O.
•The arrow points to a
sudden cooling event
that occurred over
10, 000 years ago,
known as the Younger
Dryas Event.
Great website explaining oxygen
isotope analysis
http://earthobservatory.nasa.gov/Features/P
aleoclimatology_OxygenBalance/
Left: The type of fossil can
indicate the temperature range
in ocean waters.
Their shells can be analyzed
chemically to measure CO2
concentrations and oxygen
isotope ratios
Oxygen isotope analysis
(below): the ratio of O-18
(heavier, less common) to O-16
(lighter, more common) is a
proxy measurement of
temperature.
Ice Cores – a very valuable proxy data indicator
•Ice cores have annual
rings, like trees, so age of
core can be determined
•Air bubbles trapped in the
ice can be analyzed for
oxygen-isotope data,
carbon dioxide
concentration, presence of
aerosols etc.
•The ice itself can be
melted and analyzed for
these proxy data indicators.
Vostok Ice Core Data
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This is partial data from an ice core from Antarctica.
Temperature data from oxygen/hydrogen isotopes.
Interglacial” is a warm period between ice ages.
Peak of last ice age about 20,000 years ago.
The modern atmosphere
• Two most abundant gases:
– 78% N2
– 21% O2
• Less abundant gases (< 1%)
– Argon
– Water vapor
– CO2 (only about .035%) It’s up to almost .040% now!
• Non-gaseous components
– water droplets
– dust, pollen, soot and other particulates
Fig. 17.6, p.437
Thermal Structure of Atmosphere: Upper Layers
• Troposphere - Extends to
about 12 km (40,000 ft)
elevation. Where we live.
• Stratosphere – heated
primarily by solar radiation
– Ozone (O3) layer
absorbs UV energy,
causing temperatures
to rise
– Above 55km
(stratopause) temps fall
again
• Mesosphere – thin air
(can’t absorb energy), very
cold up to 80km
• Thermosphere – above
80km, temps rise rapidly
(to just below freezing!)
Solar Energy (Insolation)
– Also called solar radiation, although NOT
radioactive!
– Composed of electromagnetic waves with
different properties depending on wavelength,
frequency
• Longwave (low frequency): includes heat
(infrared), radio waves
• Shortwave (high frequency): includes visible
light as well as ultraviolet, x rays, gamma rays
• Electromagnetic spectrum – shows EM
wavelengths by frequency and wavelength.
Electromagnetic Spectrum
Solar Radiation in the atmosphere
• Reflection/scattering – bounces off with no effect
• Absorption – eventual re-emission in a different form
Reflection and Albedo
• Reflection–electromagnetic radiation bouncing of
from a surface without absorption or emission, no
change in material or energy wavelength
• Albedo – proportional reflectance of a surface
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a perfect mirror has an albedo of 100%
Glaciers & snowfields approach 80-90%
Clouds – 50-55%
Pavement and some buildings – only 10-15%
Ocean only 5%! Water absorbs energy.
Typical Albedos of Materials on the Earth
Absorption and Emission
• Absorption of radiation – electrons of absorbing
material are “excited” by increase in energy
– Increase in temperature; physical/chemical change
– Examples: sunburn, cancer
• Emission of radiation – excited electrons return
to original state; radiation emitted as light or heat
• Earth absorbs short wave radiation from sun (i.e.
visible light) and emits longwave (infrared or
heat) into the atmosphere.
“Greenhouse gases” (water vapor, carbon dioxide, methane,
etc.) let shortwave energy pass, but absorb longwave
energy radiated upward by the Earth. The longwave
energy is then re-radiated by the gases in all directions,
some of it returning to the Earth’s surface.
The greenhouse effect keeps our atmosphere at a livable
temperature of about 15 degrees C (59 degrees F). If all
heat escaped, the average temperature of Earth would be
about -200 C (00 F).
How CO2 in atmosphere relates to temperature
How CO2 in atmosphere relates to temperature
Human Impact on Climate
• Our planet has been
through many cycles of
climate change in the
past.
• At the present time, we
are undergoing a period
of global warming.
• There is almost no
disagreement on this
point in the scientific
community.
Human Impact on Climate
• Most also agree
upon that there
has been an
increase in
greenhouse gases,
notably CO2 in the
Earth’s
atmosphere, and
that human activity
is responsible for
at least a part of it.
• It has been shown
that CO2 and
temperature are
related.
The Controversial Questions
• Is this
increase part
of a natural
cyclical
process, such
as has
occurred in
the geologic
past?
• Or, is human
activity
primarily
responsible?
• Until the 19th century, ice core data show atmospheric
CO2 levels at less than 300 parts per million (ppm)
• Rapid increase in CO2 concentrations since the
Industrial Revolution (mid 19th century) is apparent
• Present-day levels exceed 390 ppm. This represents a
30% increase.
In 1958, Roger
Revelle and
Charles
David
Keeling
started direct
monitoring of
atmospheric
CO2 from
the Mauna
Loa
Observatory.
Addition of Keeling Curve to the Vostok Ice
Core Data
Comparison, using thermometers for
temperature data and direct sampling of
atmospheric CO2
Temperature Deviation Map for 2009. Note Arctic
Does this mean that human activity
is responsible for global warming?
Those who say Yes would argue the
following:
• The Earth’s yearly average temperature has
increased in the last century.
• Atmospheric concentration of CO2, a principal
greenhouse gas, has increased since the mid19th century (the Industrial Revolution). Rise has
been especially rapid since the 1950s.
• It is a known fact that humans emit carbon
dioxide into the atmosphere due to
transportation and industrial processes.
• Loss of forested land exacerbates this process,
since photosynthesis is a process that removes
CO2 from the atmosphere.
And those who would say No?
• Is it possible that Global Warming is
occurring naturally?
• It is only through the reconstruction of past
climates that we can truly evaluate the
magnitude of this present warming trend.
Ocean temperatures from 60 million years ago
•Climate change is the
norm, not the exception.
• Overall trend in the
Cenozoic Era (Age of
Mammals) has been a
temperature decrease.
•For the last 800,000 years,
the planet has alternated
between cold ice ages and
warmer interglacial periods.
•Compare last interglacial
period at about 120,000
years ago to present.
Evidence of past temperature comes from
multiple sources
Which came first, the increase in CO2 or the
increase in temperature?
American Impact
on Climate
Adds up to over
16 metric tons
annually
CO2 emissions by
country (1995)
A. Emissions by
country. In the
last year, China
has overtaken
us.
Present Populations
China: 1300 million
US: 310.5 million
CO2 emissions by
country (1995)
B. Per capita
emissions by
country
US number closer to
40 metric
tonsHaves vs.
have-nots
The Kyoto treaty on greenhouse
warming
• Dec. 1997, 160 nations met to discuss
global warming
– By Feb. 2005 a treaty was ratified by many of
them
– Creates a global trading market for CO2
emissions
– Sets limits and goals
– Caps and goals tied to nations’ economies
– Developing nations, eg China, India excluded
from CO2 caps
Fig. 21-21, p.521
21.9 The Kyoto treaty on
greenhouse warming
– The U.S. has never ratified the treaty
– Treaty supporters argue:
• Wealth not necessarily tied to fuel consumption
• Curbing consumption and emissions could help the
economy
• Models show the longer we wait, the worse it will get
• Consider the alternatives: runaway temperature
changes, famine, global unrest.
• The treaty expires in 2012 – the sequel is looking
less than inspired.
Natural Causes of Climate
Change
• Astronomical
• Tectonic
– Position of the Continents
– Volcanic Eruptions
Astronomical Causes – Sunspot cycles
• The sun’s output varies
over time - Local
activity such as
sunspots and solar
storms has effect on
solar output
• Some studies show
relationship between
changes in global
temperature and
sunspot cycles, which
change solar intensity
by a minute amount.
• This change in solar
radiation may be
responsible for a very
small part of world
temperature change.
Astronomical Causes – Milankovitch Cycles
These large-scale cycles (100,000, 41,000 and
26,000 respectively) are visible in the climate record
and do not correspond to the rate of temperature
change we see today.
Changes in seawater chemistry attributed to
– Milankovitch Cycles
• Changes in seawater
chemistry which
resulted in alternating
layers of limestone and
carbon-rich marl.
• Many researchers say
that these cycles have
a small effect on world
temperatures and are
not responsible for
recent changes
Tectonics and climate change
• The position of
the continents
influences winds
and ocean
currents.
– North and South
America joined,
separating
Atlantic from
Pacific in the
tropics.
– Current
configuration of
continents keeps
Arctic Ocean
landlocked.
Tectonics and climate change
• 200 mya, the single continent Pangea was near the south pole
– Continental interiors tend to have more severe winters. For
a single large landmass, even more so.
– Influences winds and ocean currents
Volcanoes and climate change
• Volcanoes emit ash,
particulates and sulfur
compounds, which
block sunlight and so
cool the atmosphere.
• Volcanoes emit large
quantities of CO2,
which leads to
warming of the
atmosphere.
Possible Consequences of Global
Warming
• Sea-level changes – sea-level has risen
markedly from 1900 to 2000
– water expands when warm
– Glacial (ice on land) melting is increasing
• Effects on people
– Tropical diseases flaring up in new areas
– Population stress on food and water supplies as
well as other global systems
Fig. 21-16, p.515
Thermohaline circulation – how global
warming could cause global cooling or
“the day after tomorrow”
– Warmer sea surface temperature could slow
or stop vertical currents
– This would stop, or re-route the Gulf Stream,
which would cool the Earth
– Thermohaline currents have decreased 30%
from 1988 - 2000
If the Labrador
Current (Cold) is
too fresh to sink, it
may block passage
of the N. Atlantic
Drift (warm) which
moderates the
climate of Great
Britain and
Scandinavia
Fig. 21-19a, p.519
Fig. 21-19b, p.519
Fig. 21-18ab, p.518
Fig. 21-18c, p.518