Past, present, & future changes in ocean chemistry

OA_iRUG 1st annual meeting, Monaco, 2 Decembre 2013

James Orr Institut Pierre Simon Laplace (IPSL) Laboratoire des Sciences du Climat et de l’Environnement (LSCE), CEA-CNRS-UVSQ Gif-sur-Yvette, France

Atmospheric CO2 increase well documented

C. David Keeling (1928-2005)

Direct atmospheric CO2 measurements (increase since 1958)

Data: Bates (2007) Dore et al. (2009) Santana-Casiano et al. (2007) Gonzàles-Dàvila et al. (2010)

As atmospheric CO2 increases, ocean pH declines

IPCC  AR5  WG1  Report,  Chap.  3  (2013)  

Station ESTOC

overwhelms natural variations (last 800 000 years)

may be 10 times faster than natural event (55 million years ago)

rate may be unprecedented (last 300 million of years)

30% increase in acidity (H+) during industrial era

100% increase (or more) projected by 2100

Barker and Ridgwell, 2012

Today’s rate of ocean acidfication, fastest in millions of years

Current change:

average glacial pH

future geological past

1900 2000 2100 100 200 300 400 600 700 800 7.7

7.8

7.9

8.0

8.1

8.2

8.3 su

rfac

e pH

(tot

al s

cale

)

200

300

400

500

600

700

900

Atm

osph

eric

CO

2 (p

pm)

Year Age (thousands of years)

average interglacial pH

500

More atmospheric CO2 means increased ocean acidity

CO2 is an acid gas (it produces acid when combined with water)

Each of us adds 4 kg CO2 per day to the ocean (increasing acidity, reducing pH)

Ocean acidity up by 30% since start of industrial age

Most of that only in last 40 years

deforestation Land uptake océan combustion fossile

Ocean absorbs 1/4 of man-made CO2 emissions

Half of emitted CO2 remains in atmosphere (causing global warming)

Half absorbed by ocean & land (trees, plants, and soils)

Ocean absorbs 24 million tons of CO2 every day

Increase in atmospheric carbon 8.6 + 0.8 – 2.6 – 2.6 = 4.2 Pg C / yr

Global Carbon Project (2013)

2.6 ± 0.5 Pg C/yr 2.6 ± 0.8 Pg C/yr 0.8 ± 0.5 Pg C/yr

deforestation land uptake ocean

8.6 ± 0.4 Pg C/yr

Fossil fuels

2002-2013 Carbon budget

• Le Quéré et al 2013; CDIAC Data; Global Carbon Project 2013

• Peters et al. 2012a; CDIAC Data

l Emissions from fossil fuels and cement

Current emissions tracking high emission scenarios

IPCC: 4 generations of emission scenarios

936 ppm

670 ppm

538 ppm

450 ppm

Atmospheric CO2 (ppm)

Year

The intensity of ocean acidification depends on us

Intensity  of  ocean  acidificaAon  (change  in  pH)  varies  by  factor  of  3  

Future  atmospheric  CO2  (latest  IPCC  scenarios)  

pH (total scale)

IPCC  AR5  WG1,  Technical  Summary  (2013)  Year

RCP4.5

RCP6.0

RCP8.5

RCP2.6

historical

RCP8.5

RCP4.5

RCP6.0

RCP2.6

Models  project  that  cold  waters  soon  become  corrosive  to  aragonite,  a  (CaCO3)  mineral  in  some  marine  shells  &  skeletons    

Corrosivity  of  waters  to  aragonite  (when  <  1,  aragonite  dissolves)  

Polar oceans corrosive to shell material within decades

Confirms original warnings: Orr et al. 2005 (Nature), Calderia & Wickett (2005), Steinacher et al. (2009)

Latest model projections (IPCC AR5 WG1, 2013)

Better projections by correcting for present-day bias

Bias correction critical in deep ocean

Saturation state (Ωa) in Pacific in 2050 (zonal mean)

Future surface pH change similar most everywhere

• A2

• B1

*Equil. calcs w/ characteristic T, S, Alk & atm pCO2 No model required:

pH

[CO32-]

Summer Winter

Orr et al. (2011, OA book)

Some coastal regions particularly vulnerable

Gruber et al. (2012, Science)

Conclusions

•  Atmospheric CO2 rising; ocean pH declining

•  Rate of OA unprecedented for millions of years

•  Coastal regions particularly vulnerable

•  Largest uncertainty is our behavior (scenario)

•  Monitoring needed to refine predictive capacity in –  High latitudes & Deep ocean –  Coastal areas & Marginal Seas