Ice ages and climate change

 

 Ice Ages

  • Quaternary Ice Ages
    • begin around 3 Ma (Pliocene) and continues today
  • Permian 250-220 M.y.
  • Ordovician 450 M.y.
  • Precambrian
  • 900-650 M.y. Snowball Earth
  • 2300 M.y.

 

What is climate?

  • the long-term average (30 year) of the weather conditions in a region or globally (the average of weather over time and space).
  • plays an important role in
    • determining which ecosystems flourish and in which areas,
    • controlling weathering patterns and rates,
    • influences the behavior of the oceans
  • influences/is influenced by atmosphere, hydrosphere, biosphere, pedosphere, etc.

 

What is weather?

  • specific condition of the atmosphere at a particular place and time.
  • measured in terms of such things as wind, temperature, humidity, atmospheric pressure, cloudiness, and precipitation.
  • can change from hour-to-hour, day-to-day, and season-to-season.

A simple way of remembering the difference is that 'climate' is what you expect (e.g., cold winters) and 'weather' is what you get (e.g., a blizzard).

 

Greenhouse effect

greenhouse gases allow incoming visible light radiation to pass through the Earth's atmosphere, but prevent most of the outgoing infra-red radiation from the surface and lower atmosphere from escaping into outer space.

  • This process occurs naturally and has kept the Earth's temperature about 59 degrees F warmer than it would otherwise be.
  • If there were no greenhouse effect Earth would be too cold for life
    • Venus is too hot - too much GHG vs. Mars is too cold - not enough GHG
  • Sunlight hits Earth è Earth radiates heat
  • Atmosphere holds some heat

Main gases: CO2

H2O

CH4

CFCs

N2O

CO2 increases in atmosphere as measured in Hawaii

 

Earth's climate varies naturally over time

  • Long times: solar changes, Earth orbit changes
  • Medium: ocean circulation
  • Short: El Niño, volcanoes

 

Can't measure past climate directly before mid-1800s - no accurate instruments

  • Use various proxies:
    • Tree rings: growth rings' width related to climate
    • Pollen samples
    • Cultural: wheat prices, transport modes vs. time
    • Records show 0.3--0.6 °C warming since 1860
    • Land and sea cores - pollen, algae, plankton
    • Ice cores: oxygen isotope ratios, direct gas samples ice core - clip
      • Oxygen isotopes - 16O to 18O ratios - indicator of temperature
      • Evaporation preferentially removes 16O in H2O
      • during times of glaciation 16O falls on land and becomes ice sheets
      • Ocean becomes enriched in 18O as ice sheet grow
      • Ice sheets melt and 16O is released back into the ocean

What Causes Ice Ages?

Within Earth (Endogenic)

  • Changes in the atmosphere
    • affect its ability to filter solar radiation because much of the solar energy reaching our planet is either reflected back out to space or absorbed by the atmosphere.
    • Volcanic Eruptions - cools global climate
    • Air bubbles in ancient glacial ice suggests that CO2 and CH4 are much higher in the atmosphere during interglacial periods than during glacial periods.

  • Mountain Building - raises elevation, local alpine glaciers
    • Buries more carbon, CO2 levels decrease
    • Example – continued erosion of Himalayas:
  • Changing of the positions of the continents
    • Continental land masses on poles are favorable for glaciation.
    • During the Permian a large continental land mass was located at the south pole and may have contributed to glaciation.
    • Land masses may prevent warm ocean water from circulating in polar regions .
  • Changes in circulation of sea water
    • Today’s condition of warm Atlantic Ocean water freely circulates into the Arctic Ocean.
      • A warm Arctic Ocean allows moisture to evaporate and then precipitate as snow on continents.
    • How did this happen?  Closure of the Isthmus of Panama 3 million years ago (more)
      • Started Oceanic Conveyer Belt (global thermohaline circulation)
      • Cools northern waters, causing build up of polar and northern continental glaciers

Outside Earth (Exogenic)

  • Changes in Sun
  • Variations in Earth Orbit - Milankovitch and revolution (eccentric) cycles

Milankovich Cycles

Milankovitch, a Serbian astronomer, observed that variations in the earth's orbit, wobble of its axis, and inclination to the sun affects the amount of heat from solar radiation received by any particular portion of the earth.

  • Cool Summers More Important Than Cold Winters
  • Obliquity of Earth (relative to Sun) varies for 21.2o to 24.5o in an 23,000 year cycle

Obliquity or Axis Tilt - graph

  • Tilt of the earth's axis ranges from 21.5° to 24° on a cycle of every 41,000 years. The earth wobbles on its axis like a spinning top, making one revolution every 26,000 years.
  • Small Axis Tilt: Mild winters but cool summers. Favors Ice Age
  • Large Axis Tilt: Cold winters but hot summers. Favors Interglacial

Eccentricity or shape of orbit

  • Eccentricity Earth's orbit around the sun is not a circle, but rather it is an ellipse. The Shape varies from between one and five percent through time
  • Eccentricity of the earth's orbit changes from a more circular to a more elliptical orbit on 100,000 year and 400,000 year cycles.
  • Today, summer in Northern Hemisphere at Aphelion or farther away from Sun
    • Mild winters but cool summers. Favors Ice Age
    • Summer at Perihelion (Eccentric Orbit)
    • Cold winters but hot summers. Favors Interglacial

Precession or wobble of Earth's axis

  • Precession Twice a year, the equinoxes, the sun is positioned directly over the equator. Currently the equinoxes occur on approximately March 21 and September 21. However, because the Earth's axis of rotation "wobbles" (like a spinning top), the timing of the equinoxes changes
  • The cycle has two periods of approximately 19,000 and 23,000 years. Together these combine to produce a generalized periodicity of about 22,000 years.

What happens during Glacials and Interglacials?

  • Glacials

1. Global temperature declines 5-10C

2. Sea level drops up to 425 ft.

3. Base level drops --> erosion increases

4. Climatic belts migrate toward equator

 

  • Interglacials

1. Presently Earth is in an interglacial period retreat of last glacier - clip

Sea level higher -- if caps melt --> 210 ft rise in sea level (Most major cities ex. New Orleans, New York, London, Tokyo are flooded)

3. Glacial lakes ex. Lake Bonneville (Great Salt Lake)

4. Coastal areas drown

5. Estuaries dominate

 

Global warming

Are We Headed For Another Ice Age or is the Earth warming up?

We don't really know, but…

Global climate patterns stretching back 740,000 years have been confirmed by a three-kilometre-long ice core drilled from the Antarctic, (Nature 2004).

·        8 glacial periods during that period, punctuated by rather brief warm spells - one of which we enjoy today.

·        Tests on gas trapped in the ice core show that current carbon dioxide (CO2) levels are higher than they have been in 440,000 years.

·        If past patterns are followed in the future, we can expect our "mild snap" to last another 15,000 years

 

The rate of global warming may be increasing due to fossil fuels burning. Although this may not have much affect the longer-term cycles, it will effect our society.

Climate Change on the Canadian Prairies? PowerPoint presentation from PFRA and PARC

Dryer and warmer

 Env. Canda

 

PARC Interactive Maps

Environment Canada - Climate Change in Prairie Province

Government of Alberta - impacts of climate change

Global consequences and near future scenarios

If greenhouse gas emissions continue on a "business as usual" basis, models predict that:

  • carbon dioxide levels will double from pre-industrial levels by 2050.
  • When the effect of other factors such as increased water vapor is added, the estimated average global temperature rise will be between 1.5 and 4.5 ° C, the most likely value being 2.5 ° C.
  • Global sea levels are likely to rise by about 50 cm over the next century, and will continue to rise further in the future.
  • Low-lying coasts will flood and some habitats such as saltmarshes will be lost unless they can be protected from flooding.
  • expect more extreme weather events
  • heatwaves, floods, droughts, hurricanes.
  • The world's vegetation zones will undergo major changes, in particular boundary shifts between grasslands, forests and shrublands.
  • Deserts will become hotter, desertification will extend and is more likely to become irreversible.

  • Half the world's glaciers could melt and Arctic ice would be reduced in extent.
  • More solar radiation will be absorbed by the exposed land, warming will be amplified.
  • Freshwater systems will experience changes in temperature, flows and levels, affecting biodiversity, water supplies and probably quality

 Env. Canda

  • Human conflict over access to water resources may increase.
  • Agricultural productivity is likely to vary across regions. Although global productivity may stay about the same, there may be increased risk of famine in arid and semi-arid regions.
  • Mass movements of people away from flooded or arid regions would cause conflicts and health problems.
  • Human and animal diseases may spread to new areas

Global warming: what we know…

  • Certainties:
  • Atmospheric CO2 and CH4 will continue to increase.
  • CO2 is continually being removed. However, not as fast as it is being added. A new balance will be achieved. Atmospheric CO2 will not rise indefinitely.
  • Global temperatures will increase.
  • Effect will be largest at high latitude (net radiation deficit), smallest at low latitude (net radiation excess).
  • Sea-level will continue to rise.
  • Uncertainties:
  • How high will atmospheric CO2 rise? (500-700 ppm??)
  • How much warming will that produce? (<1 -5 °C ??)
  • How high will sea-level rise? (0.5 >5.0 meters?- it was 5-7 m higher during the last interglacial)
  • What other changes will occur? (e.g., pole-ward shift in the N limb of the Hadley cells, and a decrease in mid-latitude precipitation).

 

Some solutions for the problem

  • Mitigation - Reduce emissions directly
  • Adaptation - Deal with changes - Geoengineering
  • Attack problem with large-scale scientific and technical solutions - society is always looking to science for solutions, many time is provides them, but may create other problems…
  • Carbon Sequestration - The uptake and storage of carbon. Trees and plants, for example, absorb carbon dioxide, release the oxygen and store the carbon. Fossil fuels were once live biomass and will continue to store the carbon until burned.
  • Increase Carbon Sinks. Carbon reservoirs and conditions that take in and store more carbon (carbon sequestration) than they release. Carbon sinks can serve to partially offset greenhouse gas emissions. Forests and oceans are common carbon sinks.

Other info:

Global climate change articles - from American Geophysical Union, Nature: Ice ages and instabilities

Prairie Adaptation Research Collaborative