Definitions • Weather: • State of the atmosphere at a particular point in time. • Look outside. • Climate: • The accumulation of “weather” (atmospheric state) over a longer time period. • Look outside for a really long time and do statistics. • A combination of temperature and precipitation. “Climate is what you expect … Weather is what you get.”
Climate VS Weather • Longer-Term (Years and longer) • Broad composite of average condition of a region (e.g., temp, rainfall, etc) snowfall, ice cover, winds) • Mean state of a specific region • An envelope of values • Shorter-term (minutes to days). • State of atmosphere (temp, press, winds, sky cover, rainfall, etc). • Specific location for specific time. • A single number
Climate Classification: A consistent climate classification scheme to understand numerous climate regions. Earliest known scheme was used by the ancient Greeks about 2200 years ago. Morphed into the broad scheme to the right. 3 Major regions: Frigid, Temperate, Torrid.
Köppen climate classification system • Based on a database of annual and monthly average temperature and precipitation • Four of five major groups classified by temperature • Fifth group classified by precipitation • Subdivided the five groups further based on temperature and precipitation relationships • Köppen letter code system • Three letters; first describes group, second describes precipitation, third describes temperature • Used as a springboard for modified Köppen System
Modified Köppen Classification System Designated by a descriptive name and a series of letters First letter = major climate group Second letter = precipitation patterns Third letter (if there) = temperature patterns
Proxy Records • Sources • Tree Rings • Ice cores • Documentary data • Thermometers
Historical Record Instrumental record ( ~150 years) Written accounts Art Pictures
1910 1997 Grinnell Glacier at Glacier National Park Rate of Glacial melt in last 20 years = 4x historical rate
Snow Cover Reduced • Number of days per year with snow cover has reduced since early 1970’s • Water storage in snow pack is reduced • More precipitation is rain
Paleoclimatology Definition: The study of past climates. Why? To help understand current climates and future climates. What about thermometers? They only go back a few hundred years. So we use proxies, or substitutes, to reconstruct past conditions.
Dendrochronology Tree rings! Most trees increase trunk diameter by adding one concentric tree ring for each year of growth. Count the rings to determine how old the tree is. During more favorable years (mild temps. and/or more precip.) tree rings are usually wider. Compare/correlating dead trees to living trees helps determine catastrophic events. Period of record: 10-100s of years. In rare cases 1000s of years.
Southwestern US Water is most precious, least abundant resource…
Drought and the Anasazi Populations expanded dramatically during wet years. Sustainability of population = water Population collapses related to megadroughts Number of habitation sites
Pros and ConsDendrochronology Pros • Well understood. • Direct correlation between growth and moisture. • Indirect correlations between growth and cloud cover, temperature. • Location of tree is usually known. • Local climate Cons • Only record the growing season. • Tropical trees may not have obvious annual growth rings • No clear indication of when tree died, therefor harder to determine when it lived. • Other influences of growth other than climate. • Local Climate
Ocean/lake sediments • Lake and ocean sediment cores. • Sedimentation rate. • Varves: couplets of light (more energy) and dark bands (less energy) produced in some lakes. Thicker = more erosion. • Trapped organic matter (radio carbon dating) • Seeds, leaves, charcoal. • Little critters (Foraminifera or forams and diatoms) that die and sink to the bottom of the ocean and we measure their 18O to 16O ratio. • Period of Record: 10s – 10,000s of years
Oxygen Isotopes • Oxygen Isotopes (atoms of the same element with different atomic weights because they have different numbers of neutrons) Oxygen 16 and Oxygen 18. • Both 16O and 18O are found in common molecules such as water (H2O) and calcium carbonate (CaCO3). • The ratio of 18O to 16O in the water changes based on the climate. • 16O is lighter so it evaporates more easily, leaving the heavier 18O in the ocean.
Oxygen Isotope Cycle More 18O In ice because more heat energy More 16O In ice because less heat energy
Pros and ConsOcean/Lake Sediments Pros • Relatively undisturbed by humans • Fairly consistent rates, especially in the ocean • Long record. • Local climate Cons • Influences other than climate (biology and weather.) • Bioturbation (worms borrowing!) • Can be expensive • Local climate
Ice Cores • Drilling ice cores in glaciers and ice sheets all over the world. • Dating from worldwide events like atom bombs. • The more 18O in the ice the warmer it was because more heat energy was available to evaporate the heavier oxygen isotope. • Wind blown dust can hint towards global air circulation patterns • Trapped air bubbles enable scientists to measure concentrations of CO2and other gasses that were present in the environment. • Historically, the more greenhouse gasses there were the atmosphere the less ice on earth. • Period of record: 10s to almost 1,000,000 years
Ice Cores Age of ice (layers) Isotope ratio (for temps) Air bubbles (atm gas content) Dust content (wind) Salt content (wind) Sulphuric acid content (volcanism)
0˚C : Tipping Point for Climate • Surface energy balance • Feedback processes rest on crossing the 0˚C threshold • Above 0˚C , melt ensues, albedo change positive feedback • Water storage • Below 0˚C , H2O can be stored, not utilized by plants, evaporate away etc. • Above 0˚C , H2O runs off, leads to plant growth, evaporation, etc.
Pros and ConsIce Cores Pros • Actual bubble of past atmosphere • More global than other proxy records. • Chemistry is pretty well understood • Temperature proxy and atmosphere bubble in same location. • Easy to compare across different locations. Cons • Can be hard to date. • Expensive and difficult to obtain and store. • Glaciers are melting all over the world. • Hard to find ideal locations • Cold and hard to get to locations.
Other Coral reefs Relic soils Pollen Cave deposits Shell fish
Sources Dr. Crystal Kolden Dr. John Abatzoglou (http://webpages.uidaho.edu/jabatzoglou/) More information: www.westernclimateinitiative.org/ Icenetmatrix.com http://www.atmos.washington.edu/mm5rt/ http://www.wrcc.dri.edu/research/jtwrcc/idaho-mon/ http://www.wrcc.dri.edu/monitor/WWDT/ http://www.cefa.dri.edu/Westmap/ http://www.cpc.ncep.noaa.gov/products/predictions/90day/