Download proxy climate indicators

Global Warming
Global Warming
• 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.
Global Warming
• It is also widely agreed
upon that the cause of
this warming trend is the
increase in greenhouse
gases in the Earth’s
atmosphere.
• Is this increase part of a
natural cyclical process,
such as has occurred in
the geologic past?
• Or, is human activity
responsible for the rise in
greenhouse gases?
• Most solar energy is in the form of shortwave radiation
(e.g. visible light, UV rays). Our atmosphere allows most
of these energy waves to pass through it.
• Earth absorbs this energy and re-emits as longwave
radiation (infrared or “heat”).
• This heat radiates away from the planet at night. If all of
it escaped, the average temperature of Earth would be
about -200 C (00 F).
Greenhouse Gases
• Greenhouse gases in the atmosphere do not
allow infrared radiation to pass through them like
shortwave radiation. Instead they absorb this
energy, keeping it close to the Earth.
• This natural process allows the Earth to maintain
an average yearly temperature of about 150 C
(600 F). This is necessary for life on the planet.
• The most important greenhouse gases are water
vapor (H2O), and carbon dioxide (CO2).
• Other include: methane (CH4) ozone (O3) and
chlorofluorocarbons (CFCs).
• Until the 19th century, ice core data show
atmospheric CO2 levels at less than 300 parts
per million (ppm)
• By the middle of the 19th century, levels were at
about 300 ppm (0.03%).
• In 1958, Roger
Revelle and
Charles David
Keeling started
direct monitoring
of atmospheric
CO2 from the
Mauna Loa
Observatory.
• Levels have
increased to as
high as 380 ppm.
Can scientists correlate temperature change
with atmospheric concentrations of CO2?
Red line is atmospheric CO2: ice core data
Blue is temperature: isotope analysis
A more recent comparison, using
thermometers for temperature data and
direct sampling of atmospheric CO2
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.
Paleoclimatology – Study of
ancient 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 just part of a longer cycle of
natural variability?
• Is the recent rate of climate change unique
or commonplace in the past?
• What does it mean if the last century is
unprecedented in terms of warming?
• Can we find evidence in the paleoclimate
record for mechanisms or climate forcings
that could be causing recent climate
change?
Climate change in the geologic
past
• How can scientists create a
graph like this when
thermometers, rain gauges and
other instrumentation did not
come into use until the late 19th
century?
• By using proxy climate data!
• What are proxy climate data?
• What are some examples of
proxy climate data indicators?
Proxy Climate Data
• Proxy climate data are
obtained from natural
recorders or indicators of
climate variability
• These proxy climate indicators
cannot directly measure
temperature, rainfall, etc. as
do modern instruments.
Scientists must analyze and
interpret the results.
• What are some examples of
proxy climate data indicators?
Proxy Climate Data
The chart shows
sources of climate
information and the
time frame over which
they are useful. All
except the instrument
records are examples
of proxy climate
indicators.
Measuring recent climate change
• Instrument records - measure only about
the last hundred years
• Historical records – accounts recorded as
records, or in stories
– Vikings’ tales of the Little Ice Age (1450-1850)
and the retreat from Vineland
– Wine harvest records
– Landscape paintings, other historical &
archeological accountings chronicle changes
over the span of human history
Climate Data from Historical
Records
Measuring climate change
• Tree rings – growth rings of trees hold
climate information (thinner rings mean
less growth due to lower temperatures or
less rainfall
• Plant pollen – the pollen record records
what was able to grow, which is linked to
temperature and precipitation
– e.g.10,500 years ago pines replaced spruce
in some areas of northern U.S., indicating
warmer temperatures
Oxygen Isotope Analysis
• How does oxygen isotope analysis enable us to
study climate changes in the past?
Oxygen Isotope Analysis
• Oxygen isotopes in glacial ice
–
–
–
–
–
18O
& 16O (common isotope) both occur, although 16O
is more common.
18O is heavier, needs warmer air/water temperatures
to evaporate.
Glacial ice is made up of precipitation from ocean
evaporation.
Therefore glacial ice with a higher 18/16 ratio was
deposited when the earth’s average temperature was
greater.
Ice from Greenland and Antarctica show a record
back >100,000 yrs.
Fig. 21-6, p.505
Measuring climate change
• Oxygen isotopes in marine fossils
– When earth’s average temperatures are
lower, more 18O remains in the water.
– Coral take in seawater to make their
exoskeleton.
– Therefore in coral and plankton a higher
18/16 ratio indicates lower average
temperatures.
Using δ O18 ratios in coral to
measure ocean temperatures
• Oxygen isotopes in coral
– When earth’s average
temperatures are lower,
more 18O remains in the
water
– Coral take in seawater to
make their exoskeleton
– Therefore in coral and
plankton a higher 18/16
ratio indicates lower
average temperatures
Measuring climate change
• Plankton and isotopes in ocean sediment
– Shells and other “hard parts” preserved in
marine rocks / muds give two lines of
information
• What was alive at the time gives climate
information
• 16/18O ratios in biogenic carbonate
• Rock and fossil record
– fossils give much information, what lived
when
– Rock records formative environment
Fig. 21-7a, p.506
Fig. 21-7b, p.506
Tectonics and climate change
• Position of the continents
– 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
Fig. 21-12, p.511
Does Data from the Vostok ice core support those
who claim that humans are responsible for global
warming? Why or Why not
Human contribution to the
Greenhouse Effect
• Humans release, fossil fuels,CFCs and
other greenhouse gases into the
environment.
– Concentrations of these gases has increased
in the recent past
– The atmosphere has warmed 0.8oC during the
last century
Thermohaline circulation – how
global warming could cause global
cooling
– 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
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
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.
Fig. 21-20, p.520
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. 21-15, p.514
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
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.
Fig. 21-20, p.520
Fig. 21-21, p.521
Fig. 21-16, p.515
Fig. 21-18ab, p.518
Fig. 21-18c, p.518
Climate change in the geologic
past
• Early Precambrian Time (4-2.7
bya)
– Sun was 20-30% fainter,
delivered less energy
– Effect offset by large
greenhouse effect of Earth’s
early atmosphere, largely
composed of CO2, and H2O.
• Late Precambrian to Permian
(2.7 bya to 250 mya)
– Severe ice ages occurred at
least five times in this period
Climate change in the geologic
past
• Mesozoic to Present
– Climate mostly warmer than
today.
– Most recent ice ages occurred
over the last 2 million years.
– Some scientists think the last
10,000 years represent an
interglacial warming episode
and the ice will return.
– Recent records show mean
temperature increase from the
late 1800s.