Earth’s Energy Balance Complexity, climate change and human systems HCOL 185

Incoming Solar Energy Outgoing Heat Energy Earth’s Energy Balance

Estimating Earth’s Expected Temperature using Stefan-Boltzmann law Net Incoming Solar Energy Outgoing Heat Energy = (S 0 (1-A)  R 2 )(4  R 2 kT e 4 ) S 0 is the solar constant A is average albedo, or reflectivity R is the radius of the earth k is Boltzmann’s constant T e is earth’s apparent temperature (seen from space ) Demonstrate calculations where

Estimating Earth’s Expected Temperature using Stefan-Boltzmann law Net Incoming Solar Energy Outgoing Heat Energy = (S 0 (1-A)  R 2 )(4  R 2 kT e 4 ) S 0 is the solar constant A is average albedo, or reflectivity R is the radius of the earth k is Boltzmann’s constant T e is earth’s apparent temperature (seen from space )  TeTe equals -19  C However, average global surface T is + 14  C Natural greenhouse effect warms the surface by 33  C  where

Present-day Atmospheric Composition of Planets

Evolution of Earth’s atmosphere Tied to changes in development of organisms and their influence on gases. James Lovelock has suggested that Earth’s temperature has remained relatively constant over billions of years, through the development of organisms which have changed atmospheric concentrations, while the Sun has increased radiation loading. The earth as a superorganism?

The Gaia Hypothesis “The theory that views the evolution of biota and their material environment as a single, tightly-coupled process, with the self-regulation of climate and chemistry as an emergent property” --The geophysiology of the earth. Margulis and Lovelock 1976

Albedo The amount of solar radiation reflected or scattered back into space without any change in wavelength. The mean global albedo is about 30%. The albedo of different land surfaces varies greatly from 90% to less than 5%.

SurfaceAlbedo Tropical Forest Woodland (deciduous) Woodland (coniferous) Grassland Sandy desert Tundra Sea water0.10 Water (0-60º)<0.08 Water (60-90º) Fresh Snow Sea ice Clouds (low) Clouds (high)

Albedo effects if earth were completely forested, desert, water, or ice.

Snowball earth

Snowball Earth The trigger: ice forming at latitudes as low as of 30° The escape: CO 2 levels 350x higher than today -635 million years ago -Lasting ~12 million years -Oceans froze to depth of 1km

Volcanoes and CO 2

Earth’s homeostasis

Earth Homeostasis

Carbon cycle

Carbon Cycle IPCC 2007

Atmosphere Estimated Fossil Deposits Plants Soil Oceans ,000 About 16, This is the “greenhouse” problem Driven by fossil fuel emissions …and land clearing The oceans and land vegetation are currently taking up 4.6 Gt C per year Balanced carbon cycle Units Gt C for stores & Gt C y -1 for fluxes

Thermohaline circulation

Denser waters in high latitude oceans create a thermohaline circulation system that has a major impact on regional climates

Anthropogenic forcing

Figure SPM.2