water unit introduction outline: unique chemistry distribution on planet - changes with time...
Post on 20-Dec-2015
216 views
TRANSCRIPT
Water Unit Introduction
Outline:• Unique chemistry• Distribution on planet - changes with time • Hydrologic cycle - redistribution, climate effects• Ocean circulation - basic wind & thermohaline
Chemically unique because it:• exists in all three phases at atmospheric temp & pressure (high melting
and boiling points for size & bond type- ammonia-NH3-mass 17, MP -78, BP 33)
and is the only substance that does this!• has covalent bonds for molecule, hydrogen bonds for liquid/solid
phase (10x stronger than usual inter-molecular bonds, but weaker than metal or ionic bond)
Chemically and physically unique because it has:• high heat capacity - 4.2 J/g/K- i.e., takes more
energy to raise temp, therefore stores more, important for spreading planet’s heat
• high heat of fusion (solid <> liquid ~ 335 J/g/ºK) and vaporization (liquid <>gas ~ 2400 J/g/ºK) so more effectively transfers heat when changing phase in atmosphere/ocean
• conducts heat more readily as a liquid
Water is chemically and biologically unique because it: • has high surface tension so forms drops & helps make good cell
membranes• can dissolve other compounds very easily (most common solute),
so can transport many things, e.g. NaCl, nutrients• mediates or facilitates most chemical reactions in living systems
(e.g., takes water to photosynthesize) - neutral pH
Water is physically unique because it is less dense as a solid (ice) than as a liquid.
Distribution on Earth“Water, water everywhere, nor
any drop to drink.” – Coleridge, Rime of the Ancient
Mariner
Hydrologic Cycle (in 103 km3)
Global warmingGlobal warming(temperature increase)(temperature increase)
Effects of global warming on water cycleEffects of global warming on water cycle
Speeds up globalSpeeds up globalwater cyclewater cycle
More extreme weather eventsMore extreme weather events• DroughtsDroughts• StormsStorms• FloodsFloods
Projected Changes in Annual Precipitation for the 2050sProjected Changes in Annual Precipitation for the 2050s
Source: The Met Office. Hadley Center for Climate Prediction and Research
The projected change is compared to the present day with a ~1% increase per year in equivalent COThe projected change is compared to the present day with a ~1% increase per year in equivalent CO 22
GreenGreen •• = increasing, Brown= increasing, Brown •• = decreasing= decreasing
Global Precipitation Trends Global Precipitation Trends (% per decade) (% per decade) 1900 - 19941900 - 1994
Source: Watson 2001
U.S. Precipitation Trends: 1901 to 1998U.S. Precipitation Trends: 1901 to 1998
Source: National Climatic Data Center/NESDIS/NOAA
GreenGreen •• = increasing, Brown= increasing, Brown •• = decreasing= decreasingAll stations/trends displayed regardless of statistical significanceAll stations/trends displayed regardless of statistical significance
Extreme Precipitation Events in the U.S.Extreme Precipitation Events in the U.S.
Source: Karl, et.al. 1996.