Honors 1360 Planet Earth Last time: Measuring Earth’s Hydrosphere Obs : Gravity changes (allow us to see “hidden” groundwater; can also separate steric from mass sea level change) The Cryosphere: Obs : Surface landforms including moraines, cirques, U-shaped valleys, ancient lakeshores, shallow sediments … Hyp : All tell us about past glacial cycles Obs : 40,000 to 100,000 year natural cycles similar to periodicity of Earth-sun orbital changes… Hyp : Milankovitch Cycles: Summer insolation at high northern latitudes controls glacial/interglacial cycles! Today: The Cryosphere Cryosphere Now 15 October 2008 Read for Thur:

Glacial-Interglacial Cycles Through Pliocene-Pleistocene

These are Natural cycles of climatic variation! 40,000–100,000 year cycles → Changes in Earth Insolation? Milankovitch cycles: Variations in (1) Eccentricity (“ellipticity”) of Earth orbit around the sun (T = 100,000 years) (2) Obliquity (tilt of Earth’s spin axis relative to plane of orbit) (T = 41,000 years) (3) Precession (changes in orientation of the spin axis) (T = 26,000 years) The important factor: How much insolation does high latitude (particularly northern!) receive in summer?

Planetary orbits are ellipses with Sun at one focus: Current Earth distance to Sun changes by ~3.4% Recall S = S 0 (R/R 0 ) = (i.e. ~7% total change over a year!) Min-Max distance varies between 0% to 12%

N S Jan 3 Jul 4 Tilt of the Earth gives us seasons: Precession determines what season in the year we are closest (Now, northern hemisphere has less insolation in summer, more in winter, and a shorter winter than southern hemisphere)

Glaciers form on continents At latitudes 40-80º, very sensitive to seasonality Right now, a very large fraction of continental area is in that range of northern hemisphere!

--Major deglaciations occur when insolation is increasing, but clearly more going on here! Prediction : If high-latitude insolation controls glaciation, expect a one-to-one correlation between the two…

Ice Cores, Palaeotemperature Proxies, and “Natural” Climate Variations: Drill into an undisturbed part of a glacier & retrieve core Chronology from patterns of accumulation, ablation, melt Measure water chemistry, gas chemistry in trapped bubbles with mass-spectrometer (e.g.,  18 O); dust & particulates Use statistics to estimate pre-instrumental climate & temperature

How can you use statistics to infer temperature from proxy? Year  18 O Temperature  18 O Example: Take slope and intercept of a line that best fits T versus  18 O and use that relationship to calculate earlier T from  18 O!

Hansen et al. PNAS 2006 concludes “Global mean temperature in 2005 was the warmest in 120,000 years”… Mann et al.,Eos 2003 concludes four different palaeo- temperature proxies are in general agreement (but with large uncertainties)

Ice volume and orbital forcing “wiggles” don’t match one-for-one, BUT Orbits are the metronome for glaciation as evidenced by similar spectral power! Temperature and CO 2 DO match closely! Hence, orbits are the metronome but CO 2 calls the tune!

Ice core data suggest CO 2 increase lags behind temperature What does this imply about the process taking place?

Feedbacks: Ice increases albedo → cooling Observe CO 2 in step with glaciations: Hypothesize * Improved uptake of CO 2 by ocean organisms? Observe increased sulfuric acid in glacial times (in S) * Marine algae produce more sulfide when water is salty? Satellite Measurements of Ocean Chlorophyll

Earth Climate System Solar Energy Ice Albedo (+) Bio-CO 2 (+) Bio-SO 2 (+) Because of feedbacks, small changes in input (solar) lead to large changes in the system state: In chaos/system theory, like Lorenz’ butterfly effect… Earth climate history for the past 2 Myrs suggests two stable points (glacial, interglacial) with unstable transitions