Download Chapter 16 - Global Climate

Climate Change
• Most solar energy is in the form of shortwave radiation (e.g. light, uv
rays)
• Earth absorbs this energy and re-emits as longwave radiation (infrared, “heat”)
• Greenhouse gases (CO2, CH4 H2O) in the atmosphere absorb
infrared radiation
• This natural process allows the Earth to maintain an average yearly
temperature of about 150 C (600 F).
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 represent an interglacial
warming episode and the ice will
return
– Recent records show mean
temperature increase from the
late 1800s
“Recent” Climate change data from
the Summit Ice Core.
Fig. 21-4, p.503
Fig. 21-5, p.504
Measuring recent climate change
• Historical records – accounts recorded as
records, or in stories
– Vikings’ tales of the Little Ice Age (1450-1850)
– 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
• Plant pollen – the pollen record records
what was able to grow, which is linked to
temperature and precipitation
– i.e; 10,500 years ago pines replaced spruce in
what is now northern Michigan, indicating
warmer temperatures.
Measuring climate change
• Oxygen isotopes in glacial ice
– 18O & 16O (common isotope) both occur
– 16O evaporates more readily (lighter)
– Ice from Greenland and Antarctica show a
record back >100,000 yrs
• Glacial evidence – till, tillites, striations all
give information on climate at that time
– 14C dating of organic material preserved in till
Comparing oxygen isotope analysis
with temperature in coral
•
•
This figure shows a δ O18
ratios from a coral core. This
record is plotted against
variations from average annual
sea surface temperature (SST)
rainfall, and coral growth in
order to observe how well
these corals have recorded
recent climate variability.
Red shows higher than
average SST/ rainfall/negative
δ O18 (expected for warmer
temperatures)/more coral
growth.
Figure courtesy of Dr. Julie Cole,
University of Colorado.
Fig. 21-6, p.505
“Recent” Climate change data from
the Summit Ice Core.
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
Causes of Climate Change
• Astronomical
• Natural Variations in the Carbon Cycle
• Tectonic
– Position of the Continents
– Volcanic Eruptions
• Human Activity
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
Astronomical Causes –
Milankovitch Cycles
Orbital Eccentricity
• Earth’s orbit
becomes more/less
elongated, changing
distance from the
Sun.
• This is a cycle on the
order of 100,000
years.
Astronomical Causes – Milankovitch Cycles
Axis Shift
• Earth’s equator is
presently tilted at a 23.5 °
angle from the orbital plane
• This changes from a
minimum (22.5°) to a
maximum (24.5°) over a
period of approximately
40,000 years
• This change influences
length and severity of the
seasons
Astronomical Causes – Milankovitch Cycles
Precession (Wobble)
• Earth’s axis wobbles in a circle every 26,000
years.
Natural Variations in the Carbon Cycle
• Carbon is primary material of biosphere.
• 5 times as much carbon in the crust and upper mantle as in the
atmosphere from carbonate rocks.
• Fossil fuels primarily carbon.
• These materials cycle through atmosphere, changing the carbon
concentration.
Carbon Reservoirs
Fig. 21-9, p.508
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.
Fig. 16-12, p.384
Volcanoes and climate change
• Volcanic eruptions
can cause either
warming and cooling
of the atmosphere
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.
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
How CO2 in atmosphere relates to
temperature
Changes in CO2 Concentration
from 1958
Possible Consequences of Global
Warming
– Increased temperatures tend to decrease
plant productivity.
– Extreme weather events increase (hurricanes,
heat waves).
– Changes in biodiversity: increase in extinction
rates.
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
– Stopping of Thermohaline currents in North
Atlantic caused the Younger Dryas Event, 1011,000 years ago.
Fig. 21-19a, p.519
Fig. 21-19b, p.519
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
Possible Consequences of Global
Warming
• Sea-level changes – sealevel 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
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
Oxygen Isotope Analysis
•
Oxygen isotope changes during
production of glaciers via
seawater extraction. The ratio of
to O18 to O16 in a sample is
expressed by scientists as the
deviation (designated by the
Greek letter δ) from the ratio of
isotopes in a standard, where δ
O18 = (sample ratio/standard
ratio) -1. Note how during low sea
level (cold weather conditions,
when glaciers are expanding) the
ocean becomes enriched in O18,
leading to a positive δ O18 value
(+1‰), while the glacier becomes
depleted in O18, giving it a
negative value (-30‰).