Honors 1360 Planet EarthLast time:The Cryosphere:Hyp: Milankovitch Cycles: Summer insolation at high northern latitudes controls glacial/interglacial cycles! Pred: Should see strong correlation between hi-N-lat summer insolation and global temperatureObs: Nope. But transitions occur when insolation is changing in the right direction, and power in 18O at orbital periods indicates they are related!Hyp: So there must be something else going on too…Obs: CO2 and palaeotemperature proxy 18O strongly correlateObs: Temperature changes first, then greenhouse gas CO2

changes afterHyp: A Feedback System…

Today: Cryosphere Now

16 October 2008

Read for Mon: 351-363

Hansen et al. PNAS 2006concludes “Global mean temperature in 2005 was the warmest in 120,000years”…

Mann et al.,Eos 2003concludes four different palaeo-temperature proxies are in general agreement (but with large uncertainties)

EarthClimateSystem

Solar Energy

Ice Albedo (+)

Bio-CO2 (+)

Bio-SO2 (+)

Because of feedbacks, small changes in input (solar) lead tolarge 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

Some Perspective:Minimum sea level in Pleistocene~ 100-120 m below present

Maximum sea level in Eocene (50 Mya)~ 100-140 m above present

Temperatures during early Eocene~ 7 degrees above present

CO2 during Eocene ~2000 ppm (currently ~385 ppm)

Cryosphere = ice caps + alpine glaciers + snow + sea ice

The Cryosphere Now…

The modern cryosphere is monitored from satellites!(reflected radar images, reflected laser heights,

gravity measurements)

This plus measurements from ground and airplanesgives pretty good estimates of changes…

Antarctic Sea Ice remains very consistent with the past

… Arctic Sea Ice is finding a “new normal’;Arctic summers may be ice-free in 5-15 years

→ 239 km3 per year since 2002,mostly from the east coastal areas

0.6 mm/yr of sea level change

O N D J F M

A M J J A S

GRACE gravity data over Greenland:

GRACE (gravity) measurements ofice mass change in Antarctica

→ 152 km3 per year from 2002-2006,mostly from West Antarctica

But sped up to ~ Greenland rates after that

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Glacier Bay National Park, Alaska

Alpine Glaciers

6000 cubic km totalreduction in alpineglacier ice in 45 years

= 1.7 cm sea level change (0.4 mm/yr)

Snow extent also dropping ~4% per decade

Global sea ice coverage dropping ~3% per decade: No directeffect on global cryosphere budget, BUT…