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 Plus extremes in weather – Temperature, precipitation, air pressure – Wind speed, cloudiness (may use entire station record)

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 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 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Earth’s Climate Record Based on Historical documents Fossil plants and animals Pollen profiles Tree growth rings Glacial ice cores Deep sea sediment cores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 Earliest fossil record of life

Plate Tectonics Fig. 15.8, p. 462

Geologic Record Fig , p. 463 A.Glacial ice volume from deep-sea sediment oxygen isotope analysis B.Temperature variation from ice core oxygen isotope analysis

The Last Glacial Maximum Fig. 15.9, p. 463 Occurred thousand years ago

Glacial/Interglacial Climatic Episodes Fig , p. 464 Younger Dryas

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 non- uniform 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 glacial- interglacial shifts Climate change impacts society