Climate Change

Monday, November 5th

Anthropogenic Climate Change

• Thomas Jefferson, 1781 Notes on the State of Virginia– Springs are warmer– Less winter snowfall– Climate moderating

• Causes?

Thompson Article

• Meier (1984) – sea-level rise a result of thermal expansion of water and melting of warm glaciers– No need to postulate any contribution from

the Greenland and Antarctic ice sheets

• Uhlig (1996) – East Antarctic ice sheet stable for 16 million years, through the Pliocene period– Polar ice sheets immune from global warming

Disintegration of Ice Shelves

• In 2002, Larsen-B ice shelve collapsed in 35 days after existing for 11,000 years

• Warmer ocean and air temperatures are melting shelves on both sides

• Clear evidence of changes in Earth’s energy balance

• Worst case scenario:– If all ice on planet melted, sea level would rise

213ft

Antarctic Ice Disintegration

Figure 10.32

Pleistocene Epoch

• 2.5 mya to 10,000 ya

• Not a period of continuous glaciation

• 10,000-yr period of interglacial

• Younger-Dryas (11,000 ya) – influx of freshwater into North Atlantic disrupted Thermohaline Circulation and ended interglacial period– Lasted 1000 years– Shift took 3 years

20th Century Temperatures

Low point: 1884 = -0.7

High point: 1998 = +0.7

1.4°C = 2.5°F

Current Trends in Global Warming

• The greatest warming over the midlatitudes in winter and spring

• Most of the warming at night

• Lengthening of growing season

• Levels of CO2 at highest levels ever

– 450ppm by 2036

• US is warming at slower rate than rest of world– Why?

Feedback Mechanisms

• The Earth-Atmosphere system’s checks and balances that counteract climate change

• Positive feedback – response in a system is encouraged

• Negative feedback – response in a system is discouraged

• Examples?

• Impacts on Meteorology?

Causes of Climate Change

• External causes:– Changes in incoming solar radiation (natural)– Changes in the composition of the

atmosphere (natural and anthropogenic)– Changes in the Earth’s surface (natural and

anthropogenic)

Milankovitch Cycle

• Produces variations in solar radiation received at Earth’s surface– Changes in shape (eccentricity) of the Earth’s

orbit around the sun– Precession of the Earth’s axis of rotation, or

wobbling– Changes in the tilt (obliquity) of the Earth’s

axis– When taken into account, the present trend

should be towards cooler summers over the higher latitudes of the Northern Hemisphere

Arctic Climates

• Arctic region warmed 9°F since 1987

• This has led to a freshening of northern oceans

• Greenland ice melting at 1m/year

• Permafrost is melting

• Increased precipitation in Arctic/Antarctic areas

• What does this mean for ice sheets?

Three States of Water