G & R CC: January 17Oceans, Atmosphere,

Land Surface, Cryosphere • Follow up on questions from 12 Jan

• Lecture: Oceans, Atmosphere, Land Surface, Cryosphere

• Break

• Discussion: Kolbert, Ganopolski et al 1998, Ganopolski and Rahmstorf 2001

• Other sources for discussion of next week’s readings

• Assigment: Out of class writing #1

Bush set for climate change U-turn

Gaby Hinsliff, Juliette Jowit and Paul HarrisSunday January 14, 2007The Observer

Downing Street says that belated US recognition of global warming could lead to a post-Kyoto agreement on curbing emissions. George Bush is preparing to make a historic shift in his position on global warming when he makes his State of the Union speech later this month, say senior Downing Street officials.

Tony Blair hopes that the new stance by the United States will lead to a breakthrough in international talks on climate change and that the outlines of a successor treaty to the Kyoto agreement, the deal to curb emissions of greenhouse gases which expires in 2012, could now be thrashed out at the G8 summit in June.The timetable may explain why Blair is so keen to remain in office until after the summit, with a deal on protecting the planet offering an appealing legacy with which to bow out of Number 10.

Electromagnetic Spectrum

Visible light: 400-700 nm

Transmittance and reflectance spectra for the atmosphere

Solar irradiance

Groupe InfraRouge de Physique Atmosphérique et Solaire

• The spectrum of the radiation emitted by the sun is close to that of a black body at a temperature of 5,900K.

• 8% of the energy is in the ultra-violet

• 44% is in the visible region

• 48% is in the infra-red region

O3 CO2CO2CH4

CH4 +

N2O• Different GHGs

absorb energy in different parts of the spectrum

• H2O, CO2, CH4, N2O, and O3 are efficient GHGs because of the portions of the spectrum they absorb energy

Mostly IR

Mostly near IR/H2OMostly near IR/H2O

Dec-Feb

Jun-Aug

Oceans• The oceans influence climate over long and short time-

scales (seasons to centuries)

• The oceans and the atmosphere are tightly linked and together form the most dynamic component of the climate system

• The oceans play a critical role in storing heat and carbon

• The oceans’ waters are constantly being moved about by powerful currents

• These currents influence the climate by transporting heat

• Currents involved in "deep-water formation" are particularly important for climate

• An apparently small change in just one aspect of the oceans’ behavior can produce major climate variations over large areas of the earth.

The oceans influence climate over

long and short time-scales

• Patterns of ocean circulation and up-welling change over seasons to centuries.

• These changes result in climate variations and fluctuations.

• Paleo and instrumental records of global and regional climate show periods (years to centuries) during which the climate was systematically different from earlier and later periods.

• This behavior is related to changes in the way the oceans store and transport heat.

PDO

El Niño

The oceans play a critical role in storing heat (and carbon)

• When the earth's surface cools or is heated by the sun, the temperature change is greater - and faster - over the land than over the oceans.

• The ocean is fluid, so it diffuses the effects of a temperature change for great distances via vertical mixing and convective movements.

• One consequence of the ocean's ability to absorb more heat is that when an area of ocean becomes warmer or cooler than usual, it takes much longer for that area to revert to "normal" than it would for a land area.

• This also explains why "maritime" climates tend to be less extreme than "continental" ones, with smaller day-night and winter-summer differences.

Currents

Ocean currents 1943,

Currents

• Surface currents are largely wind-driven, but rotation of the earth, the continents, and the oceans' internal dynamics also have a strong influence

• Deep-ocean flow (and, to a lesser extent, surface flow) is driven by density differences produced by heating and cooling and by precipitation and evaporation (cool saline water is denser than warm fresh-water).

• The behaviour of the atmosphere strongly affects these density differences. For example, clouds can cool the sea by blocking solar radiation or precipitation can reduce surface salinity. Winds influence evaporation rates.

Currents influence climate by transporting heat

• Gulf stream and Kuroshio current transport petawatts of energy from equatorial waters to the poles

• San Francisco (37 N, but has the cool, upwelling California Current) is about as warm as Dublin (53 N, but is at the business end of the Gulf Stream)

Currents, "deep-water formation" and climate. • In winter, surface cooling causes water to become more dense. (Cooled fresh water starts

to expand below 4 C, salt-water compresses down to its freezing point of -2 C.)

• In areas where evaporation exceeds precipitation, the resulting rise in salinity also increases density. When the surface water becomes denser than the underlying water, "convective overturning" occurs and the dense surface water mixes downwards.

• In certain places this downward mixing can extend all the way to the bottom, even in deep oceans. The dense, deep water thus formed spreads out over ocean floor.

• As a result, when downward mixing takes place at high latitudes it creates a circulation pattern in which warm water from tropical and subtropical regions moves poleward, surrenders heat to the atmosphere, cools and sinks, and flows back towards the equator.

• The net result is a transport of heat poleward.

How to shut down the NADW• Recent observations, ocean core

records, and some modeling results indicate that North Atlantic deep-water formation and its associated ocean heat flow fluctuate substantially over time-scales ranging from years to millennia.

• The system is vulnerable because even a relatively small decrease in surface salinity prevents water - no matter how cold it is - from sinking. This could occur if there is a flood of fresh-water run-off from the Arctic due to global warming.

Surface melt on Greenland ice sheet descending into moulin, a vertical shaft carrying the water to base of ice sheet. Photo credit: Roger Braithwaite

Atmosphere• Solar radiation on a sphere

results in unequal distribution; more at the equator (where angle of incidence is about perpendicular), less at the poles

• This results in convective currents because of the “heat flow” from warm to cool.

• If the earth didn’t rotate, this would be simple: warm air rises at the equator, heads to the poles, sinks as it cools, and returns.

• Coriolis force breaks this up, and the dynamical nature of the atmosphere is complex, not simple

Atmosphere and Climate• The ocean/atmosphere system, coupled with the

hydrological cycle, basically completes the circulation system.

• The main influence of the atmosphere is heat transport (mostly via water vapor) and to couple the oceans, land surface, and cryosphere.

• The greenhouse effect and aerosols

Clouds• Cirrus clouds are composedentirely of ice crystals. They usually

form at 6,000 + meters. Cirrusclouds trap more heat in the atmosphere than they reflect fromthe sun, so a change in the percentage of this cloud typecould affect global change scenarios.

• Cumulus, stratocumulus and other low elevation, thicker clouds are better at reflecting more radiation than they absorb, thus cooling the surface.

Aerosols• Direct forcing (reflectance or absorbance) and indirect (through influences

on cloud formation)

• Natural and human sources; SO2 sources are coal burning and volcanoes

• 20th century warming due to GHGs: +2.5 W m-2

• 20th century cooling due to SO2: -1.3 W m-2

• Other particulates/aerosols are implicated in changes in circulation

• Geo-engineering: using SO2 to cool the surface while warming the middle atmosphere

Land Surface• Vegetation, configuration of

continents, geomorphology

• Surface topography

• Albedo: ice, vegetation

• Gas exchange (water, CO2,

etc)

• Land use change is very important

MODIS Northern Mexico, southwest US.Composite of data from April 14 - 22, 2000.

Landsat image of PAD Peixoto 1990 Landsat image of PAD Peixoto 1999, R. Lorena UCL

• http://www.uoguelph.ca/~rmckitri/research/trc.html• http://www.realclimate.org/• http://www.climateaudit.org/