The unnatural carbon dioxide cycle and oceanic processes over the last few hundred years. OCN 623 Chemical Oceanography

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1 The unnatural carbon dioxide cycle and oceanic processes over the last few hundred years OCN 623 Chemical Oceanography In the 19th century, scientists realized that gases in the atmosphere cause a "greenhouse effect" which affects the planet's temperature. These scientists were interested chiefly in the possibility that a lower level of carbon dioxide gas might explain the ice ages of the distant past. At the turn of the century, Svante Arrhenius calculated that emissions from human industry might someday bring a global warming. Other scientists dismissed his idea as faulty. In 1938, G.S. Callendar argued that the level of carbon dioxide was climbing and raising global temperature, but most scientists found his arguments implausible. In the early 1960s, C.D. Keeling measured the level of carbon dioxide in the atmosphere: it was rising fast. Researchers began to take an interest, struggling to understand how the level of carbon dioxide had changed in the past, and how the level was influenced by chemical and biological forces... 1

2 Absorption of incident and emitted radiation 2

3 Ocean Carbon Chemistry Review CO 2(gas) CO 2 + H 2 O H 2 CO 3 Carbonic acid H 3 CO 2 H + + HCO 3 - Bicarbonate HCO 3 - H + + CO 3 2- Carbonate TCO 2 CO 2 + CO HCO 3 - Ocean Carbon Chemistry Review CO 2(gas) 280 µatm 560 µatm CO 2 + H 2 O H 2 CO 3 Carbonic acid H 3 CO 2 H + + HCO 3 - Bicarbonate HCO 3 - H + + CO 3 2- Carbonate TCO 2 8 µmol kg µmol kg µmol kg µmol kg µmol kg µmol kg µmol kg µmol kg -1 CO 2 + CO HCO 3 - Taken from Feely et al. (2001) 100% ΔpCO 2 8% ΔTCO 2 3

4 Factors influencing CO 2 flux estimates Wind Wind Waves Biology Surface Film Bubbles k ΔpCO 2 SST Near Surface Turbulence Bock et al. (1999) Air-Sea CO 2 Flux Transport Annual cycle of plant growth and death moves CO 2 between atmosphere and biosphere and back again 4

5 Carbon dioxide MRT 5 yrs, seasonal variation, greatest in N. hemisphere Recent atmospheric carbon dioxide levels Atmospheric CO 2 levels have risen from ~315 ppmv in 1958 to 392 ppmv in 2011 (~25%) 5

6 Air bubbles trapped in ice indicate pre-industrial CO 2 levels Put together, the anthropogenic effect is unmistakable 278 ppmv to 392 ppmv (2011), a 41% increase 6

7 Rate of increase of atmospheric CO 2 is not constant Varies with: Economic activity Natural variations: El Nino Droughts, fires Volcanic activity Carbon reservoirs Largest reservoirs are carbonate sediments and organic carbon in soils Are not believed to have changed significantly over last 300 years Oceans have 70 times as much CO 2 in them as atmosphere Fossil fuels and sedimentary organic carbon contain 13 times as much CO 2 as current atmosphere Planetary biomass constant over last years? 7

8 Natural and anthropogenic carbon dioxide cycle Global fossil fuel combustion adds 7 billion tons C/yr Only 50 % remains in atmosphere Other emissions Cl + O 3 ---> ClO + O 2 ClO + O 3 ---> 2O 2 + Cl 8

9 Emissions from Fossil Fuel + Cement 2007 Fossil Fuel: 8.5 Pg C : 0.9% y : 3.5% y -1 Data Source: G. Marland, T.A. Boden, R.J. Andres, and J. Gregg at CDIAC Fossil Fuel Emission: Actual vs. IPCC Scenarios Raupach et al 2007, PNAS (updated) 9

10 Regional Shift in Emissions Share Percentage of Global Annual Emissions 62% 38% FCCC Kyoto Reference Year 57% 43% Kyoto Protocol Adopted 49.7% 50.3% 53% 47% Kyoto Current Protocol Enter into Force J. Gregg and G. Marland, 2008, personal communication Regional Share of Fossil Fuel Emissions 100% 80% D3-Least Developed Countries D2-Developing Countries 60% India 40% 20% 0% Cumulative Emissions [ ] Flux in 2004 Flux Growth in 2004 Population in 2004 China FSU Japan EU USA D1-Developed Countries Raupach et al. 2007, PNAS 10

11 Carbon Intensity of the Global Economy Photo: CSIRO Carbon intensity (KgC/US$) Kg Carbon Emitted to Produce 1 $ of Wealth Raupach et al. 2007, PNAS; Canadell et al. 2007, PNAS Drivers of Anthropogenic Emissions Factor (relative to 1990) World F Emissions (emissions) P Population (population) g Wealth = G/P = per capita GDP 0.6 h Carbon = F/G intensity of GDP Raupach et al 2007, PNAS 11

12 Regional Emission Pathways C emissions Wealth per capita Population C Intensity Developed Countries (-) Developing Countries Least Developed Countries Raupach et al 2007, PNAS Carbon Emissions from Land Use Change Borneo, Courtesy: Viktor Boehm Tropical deforestation 13 Million hectares each year Tropical Americas 0.6 Pg C y -1 Tropical Asia 0.6 Pg C y -1 Tropical Africa 0.3 Pg C y -1 [2007-Total Anthropogenic Emissions: = 10 Pg] 1.5 Pg C y -1 Canadell et al. 2007, PNAS; FAO-Global Resources Assessment

13 Historical Emissions from Land Use Change Carbon Emissions from Tropical Deforestation Pg C yr Africa Latin America S. & SE Asia SUM Pg C y -1 (16% total emissions) R.A. Houghton, unpublished Regional Share of Emissions from Land Use Change Canadell, Raupach, Houghton, 2008, Biogeosciences, submitted 13

14 13 C is affected by fossil fuel combustion Missing CO 2 Oceans Dissolution into surface water Limited by slow mixing of surface and deep waters Land Regrowth of temperate forests (logged out in the past) Fertilisation of forests by CO 2 and N, P 14

15 Fate of Anthropogenic CO 2 Emissions ( ) 1.5 Pg C y Pg y Atmosphere -1 46% 7.5 Pg C y Pg y -1 Land 29% 2.3 Pg y -1 Oceans 26% Canadell et al. 2007, PNAS (updated) Climate Change at 55% Discount Natural CO 2 sinks absorb 55% of all anthropogenic carbon emissions slowing down climate change significantly. They are in effect a huge subsidy to the global economy worth half a trillion US$ annually if an equivalent sink had to be created using other climate mitigation options (based on the cost of carbon in the EU-ETS). 15

16 Factors that Influence the Airborne Fraction 1. The rate of CO 2 emissions. 2. The rate of CO 2 uptake and ultimately the total amount of C that can be stored by land and oceans: Land: CO 2 fertilization effect, soil respiration, N deposition fertilization, forest regrowth, woody encroachment, Oceans: CO 2 solubility (temperature, salinity),, ocean currents, stratification, winds, biological activity, acidification, Springer; Gruber et al. 2004, Island Press Decline in the Efficiency of CO 2 Natural Sinks Fraction of all anthropogenic emissions that stay in the atmosphere % CO 2 Emissions in Atmosphere Emissions 1 tco 2 400Kg stay Emissions 1 tco 2 450Kg stay Canadell et al. 2007, PNAS 16

17 Efficiency of Natural Sinks Land Fraction Ocean Fraction Canadell et al. 2007, PNAS Causes of the Decline in the Efficiency of the Ocean Sink Part of the decline is attributed to up to a 30% decrease in the efficiency of the Southern Ocean sink over the last 20 years. This sink removes annually 0.7 Pg of anthropogenic carbon. Credit: N.Metzl, August 2000, oceanographic cruise OISO-5 The decline is attributed to the strengthening of the winds around Antarctica which enhances ventilation of natural carbon-rich deep waters. The strengthening of the winds is attributed to global warming and the ozone hole. Le Quéré et al. 2007, Science 17

18 Human Perturbation of the Global Carbon Budget 18

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21 Human Perturbation of the Global Carbon Budget Fossil fuel intensity CO 2 budget ( ) sources fate of emissions Canadell et al. 2007, PNAS (updated to 2007) Drivers of Accelerating Atmospheric CO : 1.3 ppm y : 1.6 ppm y : 1.5 ppm y : 2.0 ppm y -1 To: Economic growth Carbon intensity Efficiency of natural sinks 65% - Increased activity of the global economy 17% - Deterioration of the carbon intensity of the global economy 18% - Decreased efficiency of natural sinks (calculations based on the period ) Canadell et al. 2007, PNAS 21

22 Conclusions (i) Anthropogenic CO 2 emissions are growing x4 faster since 2000 than during the previous decade, and above the worst case emission scenario of the Intergovernmental Panel on Climate Change (IPCC). Less Developed Countries are now emitting more carbon than Developed Countries. The carbon intensity of the world s economy is improving slower than previous decades. Conclusions (ii) The efficiency of natural sinks has decreased by 5% over the last 50 years (and will continue to do so in the future), implying that the longer it takes to begin reducing emissions significantly, the larger the cuts needed to stabilize atmospheric CO 2. All these changes have led to an acceleration of atmospheric CO 2 growth 33% faster since 2000 than in the previous two decades, implying a stronger climate forcing and sooner than expected. 22

23 Consequences of the enhanced Greenhouse effect Temperature and precipitation changes Response of the atmosphere-ocean system: deep water circulation, sea level, calcification rates Response of the atmosphere-land system: Photosynthesis and respiration/decay rates: shifts in biomes/habitats Knowledge stems from models, historical and proxy records, observations of modern climate system 23