Transcript 03 Natural Causes of Climate Change

Climate change – Natural
Causes
CATASTROPHIC
Volcanic Eruptions
Meteorite Impacts
REGULAR
Orbital Variation,
Solar Cycles & Cosmic rays
Tectonic Shift
Volcanic Explosivity Index
• Volcanoes have the
capability of throwing
cubic kilometers of ash
and debris into the
atmosphere which can
significantly alter the
climate for years at a
time– this is measured
by the Volcanic
Explosivity Index
(VEI)
Source: US Geological Survey: http://volcanoes.usgs.gov/images/pglossary/vei.php
2
Volcanic Eruptions
• Short eruptions can influence climate patterns for years due to
•
•
the outpouring of gases and ash
Droplets containing about 75 percent sulfuric acid can linger as
long as three to four years in the stratosphere.
Major eruptions alter the Earth's radiative balance because
volcanic aerosol clouds absorb terrestrial radiation, and scatter
a significant amount of the incoming solar radiation, an effect
known as "radiative forcing" that can last from two to three
years following a volcanic eruption.
• Source: NASA: http://earthobservatory.nasa.gov/Features/Volcano/
3
The Year Without a Summer
• Mount Tambora, Indonesia erupted in April 1815 with a rating of seven on
the Volcanic Explosivity Index
• The 1815 eruption of Tambora was the largest volcanic eruption in recorded
history. The explosion was heard 2,600 kilometres away, and ash fell at least
1,300 kilometres away
• An aerosol of sulphuric acid circled the globe and blocked a large proportion
of the sun’s energy from reaching the earth. This was called the sulfate
aerosol veil.
• In 1816, global temperatures fell dramatically:
– in June – 30 cm of snow fall was recorded in Quebec City
– Drought conditions were reported in July and August as rainfall patterns changed.
– Widespread crop failure due to lack of direct sunlight in Europe and North America created
famine.
– Early frosts in August and September damaged the few crops which did grow
– Significant livestock deaths were recorded in North America in the winter of 1816-17 due to
lack of food for the animals.
• Source: Wikipedia: http://en.wikipedia.org/wiki/Year_Without_a_Summer4
Volcanic Activity
• Mount Pinatubo, Philippines - 1991
• The powerful eruption of such an enormous volume of lava and ash
•
•
•
injected significant quantities of aerosols and dust into the
stratosphere.
Sulfur dioxide oxidized in the atmosphere to produce a haze of
sulfuric acid droplets, which gradually spread throughout the
stratosphere over the year following the eruption. The total mass of
SO2 of about 17 million tons being ejected.
This very large stratospheric injection resulted in a reduction in the
normal amount of sunlight reaching the Earth's surface by roughly
10%. This led to a decrease in northern hemisphere average
temperatures of 0.5–0.6 °C and a global fall of about 0.4 °C
At the same time, the temperature in the stratosphere rose to several
degrees higher than normal, due to absorption of radiation by the
aerosols. The stratospheric cloud from the eruption persisted in the
atmosphere for three years after the eruption.
• Source: US Geological Survey: http://pubs.usgs.gov/fs/1997/fs113-97/
5
Meteorites
• Large meteorite impacts have been noted in the geological records
• Depending on their size, their impacts on climate can be larger than
volcanoes
– An example of one huge impact is located in the Yucatan peninsuala in
Mexico called the Chicxulub crater – thought to have been formed 65
Million years ago
– The crater is more than 180 kilometers in diameter, the impacting
meteor that formed the crater was at least 10 km in diameter.
– The meteor triggered an extinction level event as debris would have
been thrown into the atmosphere and blocking sunlight from reaching
the surface. Almost all plant and animal life was thought to have been
extinguished by this event.
– A layer of Iridium rich sediment is seen in the geologic record around the
world confirming the impact.
http://www.metacafe.com/watch/2070635/video_of_meteor_crashing_in_canada_meteorit
e_impact_reformulated_earths_crust/
6
Milankovitch Cycles
• Milutin Milankovitch (1920) first proposed that glacialinterglacial cycles were controlled by the amount and
distribution of radiation received from sun.
• Milankovitch argued that different periods of major
glaciations were initiated by changes in Earth's orbital
parameters of:
– Eccentricity -100 000 year cycle
– Axial Tilt (obliquity) – 41 000 year cycle
– Precession or Wobble – 21 000 year cycle
7
Eccentricity
• Eccentricity is the change in the shape of the Earth's orbit
•
•
around the sun.
There is only about a 3% difference in distance between the
time when we're closest to the sun (perihelion) and the time
when we're farthest from the sun (aphelion).
– Perihelion occurs on January 3 and at that point, the earth
is 146 million km away from the sun.
– At Aphelion, July 4, the earth is 156 million km from the
sun.
Over a 100,000 year cycle, the earth's orbit around the sun
changes from a thin ellipse (oval) to a circle and back again.
http://oceanworld.tamu.edu/students/iceage/iceage2.htm
8
Obliquity
• The angle of the Earth's axial tilt, or obliquity,
•
•
•
varies with respect to the plane of the Earth's
orbit.
These slow 2.4° obliquity variations take approximately 41,000
years to shift between a tilt of 22.1° and 24.5° and back again.
Less of an angle than our current 23.45° means less seasonal
differences between the Northern and Southern Hemispheres
while a greater angle means greater seasonal differences (i.e. a
warmer summer and cooler winter).
The tilt is in the decreasing phase of its cycle, and will reach its
minimum value around the year 10,000
– This trend would tend to make winters warmer and summers colder
9
Precession
• Precession operates on a 21 000
•
•
•
year cycle; also referred to as
wobble.
12,000 years from now the Northern Hemisphere will
experience summer in December and winter in June
because the axis of the earth will be pointing at the
star Vega instead of it's current alignment with the
North Star or Polaris.
This seasonal reversal won't happen suddenly but the
seasons will gradually shift over thousands of years.
Precession occurs due to the tidal forces generated by
the gravitational attraction of the moon and sun
10
combined on the Earth.
Schwabe Cycle
• Cosmic rays cause high level clouds to
form => cooling
• “active” sun produces more solar wind
that deflects cosmic rays => warming
• cycles see combinations of solar intensity
overlaid with changes in cosmic ray
concentration as we move around the
galaxy
11
Sunspot Observations
The Maunder and Dalton Minimum resulted in a cool period in global temperature
12
Schwabe Cycle
• Sun has direct relationship to temperature on
both long term and short term scales
13
Solar Activity Cycle
14
Tectonic Shift
• The continental land masses have moved throughout
•
•
time. At one time, all of the continents were together
in a single land mass, named Pangea, that fractured,
forming oceans between them.
As continents changed position based on latitude,
their individual climates would obviously change
accordingly. The relative longitudinal positions of the
continents also has an impact on global climate
however. As Africa moved north into Europe, it forced
ocean currents to divert around it, driving these warm
bodies into the cooler polar regions
Youtube video:
http://www.youtube.com/watch#!v=NYbTNFN3NBo&f
eature=related
15
Tectonic Shift
• Continents had been
•
•
arranged so warm
equatorial currents
flow freely.
Equatorial current is
heated more as it
circumnavigates the
Earth more than
once.
North & South
flowing currents
diverging from it are
warmer.
16
Tectonic Shift
• Fossil forests similar to
those found in the
Georgia today have been
found in the Eocene
sediments of Axel Heiberg
Island.
17
Tectonic Shift
• Present Conditions
• Equatorial current
•
•
closed off 3 mya
Gateways at high
latitude allow
circumpolar currents
to pass.
Circumpolar currents
insulate polar
continents from
warmer seas & cause
polar temps to drop.
18
Orogenesis
 Tectonics also cause mountain formation
 Present Monsoons are a geologically NEW
addition to climate there
 Mountains cause rain, plateaus dry conditions
 N.A. forests and
prairies result
19