Transcript Climate and Climate Change

Climate and Climate Change
17 January 2011
How and Why Does Climate Change?
• Climate changes over a broad range of time
scales
– Years, decades, centuries, millennia
• Many factors combine to affect climate
– Variability of incoming solar radiation
– Regular changes in Earth’s orbit
– Volcanic eruptions
– Changes in Earth’s surface characteristics
– Human activities
Climate Definition
• Weather of a locality averaged over a time
period
– 30 year periods, beginning with start of a decade
– Current period is 1971-2000
• Plus extremes in weather
– Temperature, precipitation, air pressure
– Wind speed, cloudiness (may use entire station
record)
http://www.ncdc.noaa.gov/oa/ncdc.html
Climatic Anomalies
• Departure from long-term climatic average of
the average for a particular week, month, or
year
• Precipitation anomalies are more complex
than temperature anomalies
– Variability of storm tracks
– Almost random distribution of convective showers
• Mid- and high latitudes affected by westerly
wave patterns
Temperature Anomalies – US, Dec 2007
Precipitation Anomalies – US, Dec 2007
Climate Boundary Conditions
• Climate determine by conservation of energy
and conservation of mass
• Climates of specific localities shaped by
boundary conditions, e.g.,
– Latitude, elevation, topography
– Proximity to large bodies of water
– Earth’s surface characteristics
– Atmospheric and oceanic circulation
• Boundary conditions of first 4 change over
106-108 years
January Mean Sea-level Air
Temperature (C)
Fig. 15.3, p. 455
July Mean Sea-level Air Temperature (C)
Fig. 15.4, p. 456
Mean Annual Precipitation (mm)
Fig. 15.5, p. 458
Köppen
Climate
Classifications
Letters h, k and a,
b, c, d indicate
relative warmth,
coolness
See Appendix III,
p. 509-515
Table, p. 510
Earth’s Climate Record
Based on
• Historical documents
• Fossil plants and animals
• Pollen profiles
• Tree growth rings
• Glacial ice cores
• Deep sea sediment cores
Geologic
Time Scale
Plate tectonics
complicates
climate
reconstruction
Fig. 15.6, p. 460
Geologic Time Scale
8.2
18.4
12.9
34
40 41
48
30
37
3.6
1.69
0.01
Earliest fossil record of life
21.2
64 78
Precambrian
67
Cambrian
65
Ordovician
Silurian
Devonian
Mississippian
Pennsylvanian
Permian
Triassic
Jurassic
Cretacious
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
4030
Holocene
Plate
Tectonics
Fig. 15.8, p. 462
Geologic
Record
A. Glacial ice
volume from
deep-sea
sediment oxygen
isotope analysis
B. Temperature
variation from ice
core oxygen
isotope analysis
Fig. 15.10, p. 463
The Last Glacial Maximum
Occurred
20-18
thousand
years ago
Fig. 15.9, p. 463
Glacial/Interglacial Climatic Episodes
Younger Dryas
Fig. 15.11, p. 464
Lessons of the Climate Past
• Climate is inherently variable over a large
range of time scales (years, decades,
centuries, millennia)
• Variations in climate are geographically nonuniform in both sign (direction) and
magnitude
• Climate change may consist of a long-term
trend in various climate elements and/or a
change in the frequency of extreme weather
events
Lessons of the Climate Past (cont’d)
• Climate change tends to be abrupt rather than
gradual (change is faster than duration)
• Only a few cyclical variations can be discerned
from the long-term climate record
Regular cycles: diurnal and seasonal variations,
incoming solar radiation
Quasi-regular variations: El Niño, Holocene
millennial-scale fluctuations, major glacialinterglacial shifts
• Climate change impacts society