Download The Earth System

The Earth System
 Life is possible on Earth due to interaction between the…
 Lithosphere.
 Atmosphere.
 Hydrosphere.
 The “Earth System” is comprised of these physical
components interacting with the biosphere.
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Global Change
 the Earth constantly changes.
 Why?
 Plate tectonics (plate rearrangements, mountains, etc).
 Changes in orbit, changes in sun activity.
 Surface temperatures right for liquid water.
Weathering and erosion continuously reshape the surface.
Biotic evolution has transformed the planet.
Complex, lots of feedbacks, both positive and negative
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Greenhouse Gases
 Sun provides radiant energy to Earth (black body radiator)
 Of incoming solar radiation, 50% is absorbed by surface,
30% reflected (clouds), 20% absorbed by atmos (UV).
 Of 50%, re-emmitted IR-all but 18% is re-adsorbed by GHG
 CO2 is a major player in absorbing outgoing radiation--it is
a greenhouse gas. So are CH4, H2O (feedback!) and CFCs
 Greenhouse gases exert a strong control on climate.
 More GHG – Warmer atmosphere.
 Less GHG – Cooler atmosphere.
 Processes that add or remove GHGs regulate climate.
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
The Goldilocks Effect
 Venus --too much CO2 (+466°C of GH warming)
 No liquid water, so CO2 is not removed from the
atmosphere (more about why in a bit).
 (>1000x CO2 than Earth’s atmosphere)
 Runaway greenhouse conditions – too hot for life.
 Mars too little (only +3°C of GH warming)
 Mars lost much of its atmosphere--no liquid water
 small atmospheric CO2 to trap heat
 As in the story of Goldilocks, Earth is “just right.”
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Global Change
 The Earth System – The global interconnectedness of
physical and biological phenomenon.
 Global changes transform or modify both realms.
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Biogeochemical Cycles
 Chemical fluxes between the living and the non-living.
 Cycles involve storage and transfer between reservoirs.
 Non-living reservoirs.
Atmosphere.
Lithosphere.
Hydrosphere.
 Living reservoirs.
All living organisms
Rates of transfer between reservoirs
vary widely-”residence times”
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
The Carbon Cycle
 The Carbon cycle -key to life, climate.
 Subduction and volcanism keep C (mostly as CO2 in steady
state between mantle and crust-atmosphere
 In crust-atmosphere, carbon is largely found in:
1. Rocks--limestone (1019 kg) and shales (1018 kg)
2. Oceans--dissolved as bicarbonate (1016 kg)
3. Atmosphere- CO2 (currently ~350 ppm or 1014 kg)
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Carbon Cycle
Ocean and atmosphere relationship:
H2O + CO2 <--> H+ + HCO3- (ocean buffers atmosphere)
Ocean and rock relationship:
Ca+2 + CO3-2 <--> CaCO3 (rocks buffer ocean)
Weathering consumes CO2 as CaO + CO2 <--> CaCO3
Photosynthesis removes CO2 to form organic matter.
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
The Carbon Cycle
 Longest residence times in largest reservoirs
 Limestones.
 Fossil fuels (coal and oil).
 Organic shales.
 Methane hydrates.
 Carbon is returned to the atmosphere.
 Biotic respiration creates CO2 from organic matter.
 Oxidation (combustion) of organic matter creates CO2.
 Metamorphism of carbonate rocks liberates CO2.
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Recent record
 Global warming – Human GHG additions alter climate.
 CO2 in the atmosphere has steadily climbed since 1958.
In 1958. CO2 was ~ 315 ppm; in 2000, CO2 was ~ 370 ppm.
 CO2 varies seasonally by ~5 ppm due to plant activity.
Northern hemisphere summer – Global CO2 decreases.
Northern hemisphere winter – Global CO2 increase.
 Why?
Intergovernmental
Intergovernmental Panel
Panel on
on Climate
Climate Change
Change (IPCC)
(IPCC)
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Is it us or a natural cycle?
 Preindustrial CO2 levels have been between 270 and 290
ppm over last 1000 yrs. Over last 220,000 yrs, never
higher than 300 ppm (ice cores)
 Although rise in CO2 strongly correlates with the
expected inputs from fossil fuel burning,it is less than
expected--means there is a sink (oceans? plants?)
 southern hemisphere CO2 lags behind northern--thus,
reflects industrial northern input
 BUT, anthropogenic flux of CO2 is much smaller (>10x)
than other fluxes (plants, ocean)--strange
 Answer must be that timescale of addition is important
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Anthropogenic Changes
 Global warming.
 Human additions of
CO2 and CH4 outstrip
natural removals.
Fossil fuel
combustion (CO2).
Organic decay in rice
paddies (CH4).
Cow flatulence (CH4).
 Gas increases began
with the industrial
revolution.
 Increases continue.
 How high will it go?
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Anthropogenic Changes
 Most scientists accept that Earth is warming.
(urban island effect does not account for increase)
 Fewer dispute warming as data accumulates.
 Surface air temperatures have warmed by 0.9oC since 1880.
 1900s warming has reversed a 1000-year cooling trend.
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Global Climate Change
 Earth’s climate changes over geologic time scales.
 Long-term climate change.
Millions to 10s of millions of years in scale.
 Short-term climate change.
10s to 100s of thousands of years in scale.
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Global Climate Change
 Climate studies reveal Earth’s past; suggest it’s future.
 Kinds of climate changes.
 Rates at which these changes occur.
 Effects of climate changes on Earth and its inhabitants.
 Methods of Study.
 Paleoclimates – Investigations of past climatic variation.
 Computer simulations – Modeling past and future changes.
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Global Climate Change
 Paleoclimate – Past climates are revealed by…
 Datable Earth materials that are also…
 Climate sensitive.
 Paleoclimatic indicators.
 Stratigraphic records – Sequences of rock strata.
Depositional environments are often climate sensitive.
Coral reefs – Tropical marine.
Glacial tills – Cold and continental.
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Global Climate Change
 Paleoclimates:
 Pollen evidence
Species assemblages are often climate sensitive.
Assemblage changes record climatic shifts.
Pollen in pond sediments.
Spruce – colder; Hemlock – warmer.
Tree vs. grass; colder, drier vs. warmer, wetter.
Deglaciation caused spruces to move north.
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System
Global Climate Change
 Paleoclimate:
 Oxygen isotope ratios – 2 Major O isotopes.
16O water evaporates faster than 18O water.
During ice ages…
16O water evaporates from the ocean faster.
Falling on land, this water is trapped as ice.
Seas become 16O depleted; 18O enriched.
18O/16O increases.
During interglacials…
Melting glacial ice returns water to oceans.
16O returns to oceans.
18O/16O decreases.
 Ice core 18O/16O data track climate over 400 Ka.
Earth: Portrait of a Planet, 2nd edition, by Stephen Marshak
Chapter 23: Global Change in the Earth System