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