21, March 2012
Chapter 12: Climate and Climate Change
Learning objectives
o Know the difference btw weather and climate and how their variability is related
to NH
o Know how climate has changed in the last 1-2 million years through glacial and
interglacial conditions and how human activity is altering climate
o Know ways that may mitigate climate change and its assoc. hazards
Weather vs. Climate
o Weather is day to day. It constantly changes.
o Climate is long-term averages. Climate change is rare.
How can changes in weather and climate lead to natural hazards?
o El Nino: disrupts normal weather patterns, making it difficult for economies to
adapt
El Nino years have a reverse of ocean and wind currents making typically
dry places to become wet, and wet places to become dry
o Sea level increases can threaten coastal communities
o Warmer climates may produce more hurricanes
o Some areas may experience more rain others may experience drought
Can climate change? Globally or regionally
Medieval Warm Period
o Between 900 and 1,250 AD: warmer than normal temperatures in the North
Atlantic region (1C warmer than today) that mostly affected western Europe
o Grapes grown as far north as southern England
o Radiocarbon dates of 880-1140 on trees that grew in Canada far north of modern
treeline
o Iceland (874) and Greenland (985) colonized
1020-1200: minimal sea-ice around Iceland
1126: Norse population of 2,000 to 4,000 in two well-developed
settlements in Southern Greenland
The Little Ice Age
o Occurred from approx. 1300-1850 AD
o Sea surface temperatures in the North Atlantic 1C colder than today
o 1408-10: last reliable account of Norsemen still living in Greenland
1460: increased sea ice in coastal waters of Iceland
1510: German merchants visited Greenland and found Inuits living among
the ruins of Norse settlements
o 1588: Grindelwald glacier in the Alps breaks through its terminal moraine
Global Warming Perspectives:
o There are two primary (and polarized) perspectives
Preservationist perspective (democrats)
perspective Skeptical (republicans)
Preservationist Perspective
o Greenhouse gases absorb and radiate energy
o Greenhouse emissions are increasing
o Glaciers are receding
o The tree-line is advancing northward
o Preservationists encourage the use of renewable energy
Skeptical Perspective
o Too many uncertainties to make drastic changes
o Negative feedback systems may curtail warming
o Additional carbon dioxide is good for crops
o Climate fluctuations are normal
Insolation travels as wave energy
o Shortwave radiation energy is that which is directly from the sun
o Long-wave energy is radiated from earths surface
Long-wave radiation has a harder time penetrating through clouds and
pollution so it bounces back off the atmosphere and the heat doesnt
escape
o The greenhouse effect arises when shortwave energy reaches the lower
atmosphere but longer waves cannot radiate out into space due to pollution
Could Global Warming introduce a new Ice Age?
March 23, 2012
Evidence for Global Warming
o Shrinking of alpine glaciers
o Antarcticas ice sheets breaking up
o Rising sea level
o Rising ocean temperatures
o Arctic pack ice is retreating
o Tree line advancing northward/upslope
o Tropical diseases spreading poleward
Is Global Warming causing glaciers to diminish?
o Many glaciers appear to be retreating due to warmer temperatures
o Others are shrinking as a result of less precipitation (which may also be human
caused Mt. Kilimanjaro)
o Other glaciers appear stable
o A few glaciers are actually advancing
Global temperature data
o 2005 was the warmest year of record
o 8 of the 10 warmest years on record occurred since 1990
o The 10 warmest years on record occurred since 1983
o The 1990s were the warmest decade on record
o The 20th century was the warmest century of the millennium
Muir Glacier: 1941 2004
Sea level changes
o Sea level rose about 7 inches during the 20th century
o Sea level is expected to rise about 3 feet this century
o Much of the rise in sea-level is due to thermal expansion
o