DARGAN M. W. FRIERSONDEPARTMENT OF ATMOSPHERIC SCIENCES

DAY 8 : 04 /22 /2010

ATM S 111, Global Warming: Understanding the Forecast

The Oceans (RG p. 106-127) From sticks to satellites: measuring sea levelMonitoring the ocean below the surfaceBalancing the sea level budgetHow high the sea?Climate change and El NiñoWill the Atlantic turn cold on BritainLiving in a changing seaCoral reefs at risk ocean acidification

20th Century Sea Level Rise

20th century sea level rise was 12-22 mm/decade on average

red = “reconstructed” from tide gauges and other sources

blue = tide gaugesblack = satellite altimetry

Mean Sea Level - The average height of the ocean at a given location

What controls it?

Thermal expansion of the oceanThe exchange of seawater/ice with lake/soil water or land iceTidesOcean currentsAtmospheric windsTsunamis

The first two vary with global warming

From sticks to satellites: measuring sea level

Tide gauges are measuring sticks or sometimes floats in wells

Always coastal

Few long records

Instruments emits a short radar flash and measures the time-of-flight of its reflection from earth. 1,000 times per second.

TOPEX-Poseidon Radar Altimetry

Measures sea level and icesheet height

From sticks to satellites: measuring sea level

Updated version of IPCC 2007 Fig 5.14http://sealevel.colorado.edu andLeuliette, et al (2004) Marine Geodesy, 27(1-2), 79-94

Each 10 day measurement has an accuracy of 3-4 mm

Sea level rise from TOPEX-Poseidon Radar Altimetry

IPCC 2007 Figure 5.21.

Balancing the Sea Level Rise Budget

1961 to 2003 (blue) 1993 to 2003 (brown)

No more enigma

~60%

~25%

~15%

Monitoring the ocean

Many instruments are usedto measure ocean heatcontent

Argo floats

Stephen Riser, UW Oceanography

Monitoring the ocean heat content

Argo floats, since ~2000 measure to 2000m depth

Expendable Bathyermographs (XBT)

About 70 Voluntary ships toss them overboard

14,000 each year (they are cheap, even these figures are ugly)

measure down to 1500 m, in use since 1962

Monitoring the ocean heat content

1950 1960 1970 1980 1990 2000

Domingues et al 2008

Observations in black with uncertainty shaded greyModels are colored lines - span the observations

Ocean Heat Content

What will sea level be by the end of the 21st century?

FAQ 5.1, Figure 1

200-500 mmfor 3 intermediatescenarios

But had noincrease indynamical thinning from Greenland and Antarctica!

Criticized byJames Hansen

More recent estimates:

0.5 to 1.4 m by considering past SLR to past warming dependence and used IPCC estimate of future warming, Rahmstorf 2007http://www.sciencemag.org/cgi/content/abstract/315/5810/368

Accelerated but plausible dynamic thinning could give 0.8-2 mPfeffer et al 2008http://www.sciencemag.org/cgi/content/abstract/321/5894/1340

The very latest on Greenlandfrom the GRACE superstar

GRACE - Gravity Recovery and Climate Experiments

Greenland contributed 0.5 mm/yr to SLR between 2000-2008

or 237 Gt/yr loss

more than 2X the IPCC 2007 estimate for 1993-2003

van den Broeke et al 2009

D=dynamic loss (+ = loss), SMB = accumulation - ablation

2002-2009 Antarctica losing ice - despite increased snowfall

cause - dynamic thinning

http://grace.jpl.nasa.gov/news/index.cfm?FuseAction=ShowNews&NewsID=33

The very latest on Antarctica from the GRACE superstar

192 +/- 92 Gt/yr from 1996-2006 according to Rignot et al 2008

Frequency of storm surge passing a given threshold is likely to be as serious as mean sea level rise

“The Day After Tomorrow” had it wrong: a disintegrating floating ice shelfis sea level neutral. The cooling that ensued should have caused sea level to drop!

Gulf Stream

North America

Colors showTemperature

AVHRR satellite

Gulf Streamtransports heat

it is mostly wind driven(not subject tostopping)

Thermohaline circulation driven by buoyancydifferences also moves heat

Atlantic circulationRed branches carry heat northward

When water loses enoughheat it tends to sink

Weaken this circulationwould cool England and Norway

Global warming is expected to weaken theportion that is buoyancydriven as the water would not lose as muchheat.

Coral reefs at risk

Coral reefs at risk

Coral reefs at riskCoral bleaching

Coral reefs at riskCoral bleaching

Another risk to coral: ocean acidification

Coral reefs at riskCoral bleachingChemistry of ocean acidification

What happens when you open a can of sparkling water?

CO2 comes out of the water.

The opposite is happening on Earth today. So CO2 is goinginto the ocean. And this acidifies the ocean…

When CO2 dissolves in water, carbonic acid is produced via the reaction:

This carbonic acid is like sparkling water.

CO2 (aq) + H2O <-> H2CO3

Coral reefs at riskCoral bleachingWhen CO2 dissolves in water, carbonic acid is produced via the reaction:

Acid dissociate into ions, including hydrogen ion

Chemistry of ocean acidification

CO2 (aq) + H2O <-> H2CO3

H2CO3 <-> H+ + HCO3-

The increase in the hydrogen ion concentration causes an increase in acidity, since acidity is defined by the pH scale, where pH = -log [H+] (so as hydrogen increases, the pH decreases).  This log scale means that for every unit decrease on the pH scale, the hydrogen ion concentration has increased 10-fold.

so far the hydrogen ion concentration has increased by 30%

Coral reefs at riskCoral bleachingWhen CO2 dissolves in water, carbonic acid is produced via the reaction:

Acid dissociate into ions, including hydrogen ion

Chemistry of ocean acidification

CO2 (aq) + H2O <-> H2CO3

H2CO3 <-> H+ + HCO3-

H+ reacts with carbonate ion as in

H+ + CO32- <-> HCO3

-

Coral reefs at riskCoral bleaching

The source of the carbonate ions CO3

2- is calcium carbonate CaCO3

In your stomach or in the ocean, the chemistry is the same

Just as the Tums dissolve, creatures with shells dissolve… such as phytoplankton, which are responsible for1/3 of all photosynthesis on the planet and feed the marine food web.

Coral reefs at riskCoral bleachingPre-industrial (1700s) 8.18Recent past (1990s) 8.102050 (2×CO2 = 560 ppm) 7.952100 (IS92a) 7.82

Ocean AcidificationpH

Harmful algal blooms (HABs)