Earth’s Climate System

Dr. R. M. MacKay

Natural and Anthropogenic Climate Forcing

Carbon Dioxide in Prehistoric times

Plate tectonics canremove CO2 from the atmosphere

Milankovitch Theory of Ice Age CyclesPast 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 TiltNo 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 changeI'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