The Changing Climate
Chapter 14

• The Climate System
• Variability
• Radiative Forcing (definition)
• Radiative Forcing Components
• Is Our Climate Changing?
  • past climates have changed at all time scales from decades to millions of years.
    • History of Climate Change
    • Recent Climate Change
  • research on human activities shows that humans are changing the earth's climate.
  • there is evidence that world climate has become more variable.

   

• Detecting Climate Change
  • Evidence From Seafloor Sediments (JOIDES Resolution). The numbers and types of organisms living near the surface change with the climate.
  • Evidence From Oxygen Isotope Analysis. Ratio between ¹⁶O and ¹⁸O in glacial ice and shell fragments in sediments.
    • Recently, cores have been removed from the ice at Vostok Station in Antarctica. The longest cores are about 2000 meters, sampling layers of ice deposited as early as 160,000 years ago. The ice trapped bubbles of air when it froze. The ratio of oxygen isotopes in this air indicates the average air temperature at the time the bubble was trapped in ice. The bubbles also trap atmospheric greenhouse gases that can be measured.
    • National Ice Core Lab
    • Temperature Variation
  • Evidence Form Other Sources
    • Plate Tectonics
    • Tree Ring Analysis
• Natural Causes of Climate Change
  • Plate Tectonics and Climate Change
  • Volcanic Activity and Climate Change
    • Mt. Tambora, Indonesia in April 1815 largest eruption of modern times expelled more than 24 cubic miles of volcanic debris. The summer of 1816 saw snow storms in June in the NE US as well as frost in July and August.
    • Mt. Etna
      • Sulfur Dioxide Plume
      • Space Shuttle Photo
    • Mt. St. Helens - no measurable climate change.
    • El Chichon - 1982, increased global temps about 0.5 - 0.9^oF
    • Mt. Pinatubo - 1991, ejected 25-30 million tons of sulfur dioxide. Lowered global temps by 0.9^oF during the next year.
  • Orbital Variations
    • Orbital Eccentricity
    • Change of Axial Tilt
    • Precession
    • Milankovitch Cycles - analyzed the three variables, above, and found that they can increase the degree of contrast between seasons.
  • Solar Variability and Climate
    • Sunspots (close up) and Temperature - lack of sunspots correlated with colder temps in N. America and Europe and plentiful sunspots correlated with warmer times in these regions.
    • Mean Annual Sun Spot Numbers
• Human Impact on Global Climate
  • Carbon Dioxide, Trace Gasses and Climate Change
    • US Energy Consumption - 1999
    • CO2
      • The Iron Hypothesis: Fertilizing the Ocean to Reduce Global Warming - experiment
      • Changes in CO² concentrations - 1000AD - 2000AD
      • Annual average global temperature variations for the period 1860–2002
      • Variations in average surface temperatures
      • Projected Changes and Effects of Global Warming in the 21st Century ( 1, 2 )
    • Trace Gasses
• Climate Feedback Mechanisms
• How Aerosols Influence Climate
  • Human-Generated Aerosols
• Some Possible Consequences of Global Warming
  • Water Resources and Agriculture
  • Sea-Level Rise - Coastal Structures

Global Warming

• Feedback Mechanisms - natural systems have mechanisms enhance or resist change
  • negative feedback mechanisms - work to maintain the system. For example, when we get too hot, we perspire to cool down.
  • positive feedback mechanisms enhance change.
• tipping point - a point where small changes suddenly give way to a sudden and self-perpetuating changes. For example, pump enough CO₂ into the atmosphere, and that last part per million of greenhouse gas behaves like the 212th degree Fahrenheit that turns a pot of water into a plume of billowing steam.

Examples of possible global warming tipping points:

• Recent measurements indicate several Greenland ice sheets have doubled their rate of slide.
• Greenland ice is not just melting but doing so more than twice as fast, with 53 cu. mi. draining away into the sea last year alone, compared with 22 cu. mi. in 1996. A cubic mile of water is about five times the amount Los Angeles uses in a year.* (see copy)
• An April 2006 article in Science suggests that by the end of this century, the world could see as much as a 20 foot rise in sea level.

"Things are happening a lot faster than anyone predicted," says Bill Chameides, chief scientist for the advocacy group Environmental Defense and a former professor of atmospheric chemistry.

 

• Last ice age CO₂ concentrations were just 180 p.p.m. putting the earth into a deep freeze.
• After the glaciers retreated and just before the dawn of the modern era, the concentrations had risen to a comfortable 280 p.p.m.
• In just the past 150 years we have pushed the level to 381 p.p.m. and feeling the effects.
• Of the 20 hottest years on record, 19 occurred in the 1980s or later.
• According to NASA scientists, 2005 was one of the hottest years in more than a century.

Feedback Mechanisms

• Polar ice cap melting. Ice reflects 90% of the energy that strikes it. Ocean water does the opposite, absorbing most of the energy that reaches it. The more energy the water retains the warmer it gets, with the result that each mile of ice that melts vanishes faster than the mile that preceded it.
  
  Remove the North Polar ice cap and the comparatively warm water beneath begins to release its heat to the atmosphere  accelerating global warming.

• Permafrost melting. Permafrost contains a lot of partially decayed organic matter, rich in carbon. In high-altitude regions of Alaska, Canada and Siberia, the soil is warming and decomposing, releasing methane and CO₂. That, in turn, will lead to more global warming.
  
  How much carbon is stored in the permafrost soils? 200-800 gigatons. The total human carbon output is only 7 gigatons per year.

• Warmer oceans, colder continents. The Gulf Stream keeps Europe relatively mild. At the end of the last ice age, the warm current was temporarily blocked and temperatures in Europe fell 10^oF. locking the continent in glaciers.
  
  Warm Gulf Stream water floats over colder water until it gives up heat to the atmosphere near Europe where it sinks and returns to the tropics.  Freshwater melt from the Arctic and Greenland ice dilutes the saltwater and keeps it at the surface, turning off the return flow. Europe gets colder.

• Drought. In the North America west people, animals and plants make it through the summer thanks to snow pack that melts slowly during the summer. Lately, the early arrival of spring and blistering summers have caused the snow pack to melt too early.
  
  Areas around deserts such as the Sahel, experience warmer temperatures that bake the soil causing desertification.

• Flora & Fauna. Wildfires in Indonesia, the western US and even inland Alaska have been increasing as timberlands and forest floors become parched. The blazes create a feedback loop of their own, pouring more carbon into the atmosphere and reducing the number of trees, which inhale CO² and release oxygen.

• What about us? We're suffering destruction of habitat too. Ocean temperatures have warmed by a full degree F since 1970, and warmer water is rocket fuel for hurricanes. The south Atlantic ocean saw it's first recorded hurricane in 2004 (click here for information)
  
  Two studies in 2005 found that in the past 35 years the number of Category 4 and 5 hurricanes worldwide has doubled while the wind speed and duration of all hurricanes has jumped 50%.

• What can we do?
  • The US has 5% of the world's population and produces 25% of the world's CO² emissions.
  • Sign the Kyoto Protocol that pledges countries to reduce CO² emissions.
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