Ozone, Air Pollution, and Earth’s Energy Balance Presented by Stephen Schneider Deborah Carlisle June, 2012

Human Energy Consumption  Humans worldwide use ~4 ×10 20 Joules of energy per year. (U.S. 25% of this.)  In just 1 second the Sun generates enough energy to supply humans for: time = 4 × Joules/4 ×10 20 Joules/year time = 4 × Joules/4 ×10 20 Joules/year = 10 6 years = 10 6 years  The amount of sunlight striking the Earth is ~ 5 ×10 24 Joules per year. We use 1/10,000 th as much.

Energy Flow To solve a crime, “follow the money.” To understand the global balance of the Earth, “follow the energy.”  Energy changes form but the total amount is always conserved.  Energy eventually “degrades” into heat.  A place reaches a higher temperature when energy spends more time there—but just as much energy is always emitted as is absorbed. (ex: the Sun’s core generates as much energy as the Sun radiates.)

Energy Balance  To be stable, just as much energy must come in as goes out.  Subsystems (ground, air) also remain balanced A B D E C F

Energy Balance Diagram

The Ozone Problem  What happens when we change the ability of the atmosphere to absorb the Sun’s radiation?

Ozone (parts per million) Altitude (km) Troposphere Mesosphere Thermosphere Ozone In the Atmosphere Altitude (miles) % of ozone is in the stratosphere % of ozone is in the troposphere

UVc - 100% Absorption UVb - 90% Absorption UVa - 50% Absorption & Scattering Ozone (parts per million) Altitude (km) Troposphere Mesosphere Thermosphere Altitude (miles) The Ozone Layer Absorbs Ultraviolet Energy The stratosphere is almost as warm as the surface!

Nuclear Winter  What happens when we add dust to the atmosphere, so it becomes more reflective?

Global Dust Storms Huge dust storms can cover all of Mars, rapidly cooling the planet. This helped to develop the idea of “nuclear winter,” after a nuclear war or asteroid impact

Global Warming  What happens when we make the atmosphere absorb more infrared radiation from the surface?

Global Warming and IR Light Carbon dioxide and water absorb infrared radiation, mostly reradiated from the surface, trapping it and warming the surface.

The Surface of Venus  Several Russian Venera spacecraft landed on the surface of Venus  Surface temperature measured to be ~750K!  Surface pressure about 90 atmospheres— like being 3000 feet underwater!  Earth has a comparable amount of carbon dioxide locked up in rocks and the oceans.

If Earth’s Oceans Got Too Warm  Evaporating oceans add greenhouse gases, causing more heating, so more evaporation… Recent data from the Venus Express mission indicates rocks probably formed in water.

Changes in Insolation  What happens when the amount of light from the Sun changes?

Sunspots  Cooler regions in Sun’s photosphere— still bright, but look dark by contrast!  Huge plasma storms on Sun’s surface.  Regions of intense magnetic fields.  Sun’s overall energy output increases.

Solar Wind When Sun is more active, the outflow of particles is stronger, and we see aurora borealis.

The Solar Cycle  The number of sunspots goes up and down about once every 11 years on average.  After each sunspot maximum, the Sun’s magnetic field reverses.  We are currently in an unusual lull in sunspot activity.

Long Term Changes in the Sun  You might expect that the Sun is darker when it has more sunspots, but when it is more active it generates more power overall.  This appears to affect Earth’s climate.  In the 1600s there was a period with very few sunspots—and a “little ice age” on Earth.

Longer Term Changes in the Sun  Occasional records suggest longer term changes in the Sun’s energy output.  Can also look at trace isotopes carried to Earth by the Solar Wind.  In medieval times the Sun was more luminous and Greenland was green!

The Sun’s Life History

Very Long Term Changes of the Sun The Sun is about mid-way through its main hydrogen fusion phase, and will last another 5-6 billion years. Studies of other stars and computer models indicate stars grow steadily more luminous in this phase The Sun was only ~½ as luminous when it was born, and will be ~2 times more luminous in 5 billion years. In “just” 100 million years, it should be so luminous that Earth will undergo runaway greenhouse (like Venus) Earth is relatively cool now thanks to bacteria that have removed CO 2 from our atmosphere.

Earth Today: The Ice Ages  We live in an “icehouse” period that has been around for the last ~1 million years.  Typified by short warm interglacials and then long declines into glacial episodes.

Earth’s Changing Orbit  Earth’s axis precesses Period = 26,000 yr  Earth’s axis becomes more or less tilted Period = 40,000 yr  Earth’s orbit becomes more or less elliptical Period = 100,000 yr There seems to be a link between these orbital changes and the regular cycle of hot and cool periods

Milankovitch Cycles Sedimentary layers in Welsh coast show variations every ~100,000 yr (from about 300 million years ago)