Transcript Climate Change PPT - Dr. Robert MacKay

Earth’s Climate System
Dr. R. M. MacKay
Natural and Anthropogenic
Climate Forcing
Carbon Dioxide in Prehistoric times
Plate tectonics can
remove CO2 from the atmosphere
Milankovitch Theory of Ice Age Cycles
Past 1,000,000 years
Changes in Earth’s orbit about the sun
results in changes in High latitude NH
summer sunlight. When summer sunlight is
low ice sheets can slowly grow from year to
year.
Orbital factors include:
•Changes in Earth axial tilt (now 23.5
degrees)
•Changes in the eccentricity of Earths orbit.
•And the precession of perihelion.
Earth’s Axial Tilt
No Tilt no seasons
Extreme tilt extreme seasons
Orbital Eccentricity
What does Precession of
perihelion mean?
Today we are actually closer to the
sun during winter and farthest
during summer. Earth is at its
perihelion position (position of
closest approach) on January 4.
This make for cooler summers and
warmer winters. These conditions
would promote glacial growth from
year to year.
~20,000 Years ago
18,000 years
Climate of the last 1000 yr
http://www.nasa.gov/centers/goddard/news/topstory/2003/0313irradiance.html
Greenhouse Gases
http://data.giss.nasa.gov/gistemp/graphs/
Climate of the last 1000 yr
1000 years
Volcanoes
Volcanic aerosol loading
Pinatubo
Aerosol lifetime
Last 50 years
Troposphere and Stratospheric Response
Tropospheric Sulfate Aerosols
Cooling to offset warming
Estimated Sulfur Emissions
Ozone and Climate Change
Ozone and Climate Change
• Increased greenhouse gases result in warmer
surface temperatures and Cooler cooler
stratospheric temperature. This results in
increased abundances of Polar stratospheric
clouds which enhance Ozone destruction.
Thus despite the phase out of CFC production
the healing of the ozone hole will likely be
delayed by increases in CO2.
Ozone and Climate Change
• Less ozone in the stratosphere can cause a
decrease in the global greenhouse effect. This
likely offset global warming from 1980 to 2000
masking the true effect of increased
atmospheric CO2.
Greenland Ice Sheets
Latest satellite data on
Greenland mass change
I've just updated the Greenland is
losing ice page as a new paper
analysing satellite data on
Greenland mass change has been
released (Wouters 2008). The
Gravity Recovery and Climate
Experiment (GRACE) measures
changes in the Earth's gravity field
and found that from February 2003
to January 2008, Greenland lost
mass at a rate of 179 Gigatonnes
per year. This is equivalent to a
global sea level rise of 0.5mm per
year. The rate is also increasing
over time, suggesting an
acceleration of mass loss.
Artic Sea Ice
Artic Sea Ice
Climate Models
1-D Radiative
convective
models
2-D Models
3-D Atmosphere Ocean General Circulation Model