WEATHER = State of the atmosphere, such as temperature, moisture, pressure etc. NOW in the present.
- Impact of natural variability; questions of rates of change.
Science of past changes in ocean conditions. Let's look at some EVIDENCE for global warming:
- Arctic Sea ice has changed dramatically in YOUR lifetime
- North pole may one day be ice-free in the summer
- Glaciers are melting everywhere too
- Global mean temperature and average sea level have risen about 1.5deg. F in YOUR PROFESSORS' lifetime!
WHY has this occurred?
- CO2 in atmosphere has steadily increased - the "Mauna Loa curve" shows the ups and downs of the global vegetation "breathing" on the planet surface, but the average trend shows a strong increase from 1950s until present (from 310 ppm before the 1950s to 390 ppm today)
- CO2 is a "greenhouse" gas that traps heat on the planet
We can BO BACK IN HISTORY to look at climate changes. How fast has climate change been? Is it natural or normal?
- there is 60 times more CO2 in the oceans than on land
- therefore, the oceans control the chemistry of the atmosphere
- therefore, we must understand the oceans in order to understand long-term climate
- Antarctic ice is ~2 miles thick
- snowfall adds to that - snowflakes are very porous - the snow falls, compacts (into ferns), air bubbles are trapped. Hence air bubbles trapped in snow and ice and retrievable through ice cores provide us with a sample of the air at the time when the snow fell --> sample of ancient air
- measure of CO2 from these air bubbles extends the Mauna Loa curve BACK through time
- not much change in 19th century CO2 and even further back to 10,000 years ago
- Look again at Dr. Schmittner's slide on proxy records
Ocean sediments give us the oldest record of all
Ocean/Atmospheric Chemistry (1000 yr)
Sea Ice Variations (years to 1000 yr)
- what would happen if the sea ice disappeared?
- ice is white, ocean is blue
- white reflects sunlight, blue absorbs it
- oceans would heat up unbearably without the ice
Continental Ice Sheets (Glaciers - 10,000 yr)
Landmass changes (continental drift, mountain building; 1,000,000 yr)
Melt all modern glaciers, raise sea level by over 30 m.
How fast can all this happen?
- made of biogenic (or biogenous) sediments
- light/dark sequences = sediments responded to changes in climate through
Differ by number of neutrons
Chemically identical, but molecular weight is a little HEAVIER (because of the extra neutrons)
Only processes that are mass dependent fractionate
Normal Oxygen has a molecular weight of 16 - we will concentrate on this molecule, plus the Oxygen 18 isotope (molecular weight of 18)
During the ice age, the oxygen atoms in ocean water and in the shells of organisms became "heavier" due to a change in the content of the oxygen isotopes.
Planktonic foraminifers - calcium carbonate secreting animals that live
near the ocean surface at different latitudes:
Coccoliths - calcium carbonate secreting algae that live near the ocean surface:
Radiolarians - silica-bearing animals that live near the ocean surface at different latitudes
Radiolarian occurrence can be tied to sea surface temperature
Orbit of Earth (eccentricity) is usually an ellipse but can change to a circle and then back to an ellipse, very 100,000 years or so: Milankovitch cycle
This can greatly impact our climate.
- Earth is farther away from sun in winter (their winters are cooler)
- Earth is closer to sun in summer (their summers are warmer)
Occasional wobble of Earth will make these relationships be the exact opposite, but the total amount of energy is always the same, just distributed differently.