People, Oceans and Climate Change

Transcription

1 People, Oceans and Climate Change or the unnatural carbon dioxide cycle and oceanic processes over the last few hundred years OCN 623 Chemical Oceanography Reading: Libes, Chapter 25 (a good summary)

2 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 20th 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. In 1975, Wally Broecker introduced the phrase global warming when he published a paper titled: Climate Change: Are We on the Brink of a Pronounced Global Warming?

3 Absorption of Incident and Emitted Solar Radiation

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5 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 -

6 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 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

7 Recent atmospheric carbon dioxide levels Atmospheric CO 2 levels have risen from ~315 ppmv in 1958 to 392 ppmv in 2011 (~25%)

8 Rate of increase of atmospheric CO 2 is not constant Varies with: Economic activity Natural variations: El Nino Droughts, fires Volcanic activity

9 Global Carbon Reservoirs Reservoir Amount* Carbonate sediments Soils (organic carbon) Oceans and freshwater (dissolved CO2) 140 Biomass (living matter) 30 Fossil fuels (plus organic carbon in the sediments) 27 Atmosphere (CO2) 2 * The amounts are in units of tonnes of CO2 equivalent. 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

10 Natural and Anthropogenic Carbon Dioxide Cycle Global fossil fuel combustion and land use changes add ~8 billion tons C/yr; only about half remains in atmosphere????

11 Other Atm. Greenhouse Gas Concentrations

12 Emissions from Fossil Fuel and Cement 2007 Fossil Fuel: 8.5 Pg C Fossil Fuel Emission (GtC/y Emissions Rates of increase: : 0.9% y : 3.5% y -1 Data Source: G. Marland, T.A. Boden, R.J. Andres, and J. Gregg at CDIAC

13 Regional Shares 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

14 Drivers of fossil fuel emissions

15 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

16 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/Gintensity of GDP Raupach et al 2007, PNAS

17 Regional Emissions C emissions Wealth per capita Population C Intensity Developed Countries (-) Developing Countries Least Developed Countries Raupach et al 2007, PNAS

18 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 Pg C y -1 Canadell et al. 2007, PNAS; FAO-Global Resources Assessment 2005

19 Historical Emissions from Land Use Change Carbon Emissions from Tropical Deforestation Africa Pg C y -1 (16% total emissions) 1.40 Latin America Pg C yr S. & SE Asia SUM R.A. Houghton, unpublished

20 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) Fertilization of forests by CO 2 and N, P

21 Fate of Anthropogenic CO 2 Emissions ( ) 2007) 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)

22 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.

23 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

24 Decline in the Efficiency of CO 2 Natural Sinks Fraction of all anthropogenic emissions that stay in the atmosphere % CO 2 Emissions in Atmosphere T CO 2 emissions, 400 kg stays Canadell et al. 2007, PNAS 1 T CO 2 emissions, 450 kg stays

25 Efficiency of Natural Sinks Land Fraction Ocean Fraction Canadell et al. 2007, PNAS

26 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

27 Summary of the Global Carbon Budget

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29 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)

30 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

31 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.

32 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.

33 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

34 Clear effects of global temperature change appear in available records

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36 Global temperature change predictions Warmer N hemisphere warmer continents

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38 Global thermohaline circulation

39 Predictions of change in thermohaline circulation Bryden (2005), Nature Estimate a 30% (9 Sv) decrease in lower NADW production,

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41 Saturation State Varies with Depth

42 Ω > 1 Ω = 1 Ω < 1 Animation of the saturation state of surface water with respect to aragonite.

43 Ω > 1 Ω = 1 Ω < 1 The magenta line, which first becomes visible in 2025 (in the Weddell Sea), separates saturated waters (orange colors) from undersaturated waters (blue colors). By the end of this century, undersaturation spreads throughout the entire Southern Ocean (all ocean south of 60 S) and into a portion of the subarctic Pacific. (Orr et al Nature)

44 Another Model of the Surface Ocean... Ω aragonite Feely et al. 2009, Oceanography 22:36-47

45 Calcification rates of organisms are decreased even when saturation level >1 Aragonite and agnesian calcite are much more soluble

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47 Politics of CO 2 science Well known non peer-reviewed science journal

48 Petition to Earth scientists from oil industry-backed group

49 CO 2 fertilization of plants not a simple phenomena: Most plants are water- or nutrient-limited,not CO 2 -limited

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51 The enhanced greenhouse effect and global warming are we headed for a Super Interglacial?

52 Where do we stand with respect to the enhanced greenhouse effect and global warming? Without doubt greenhouse effect exists and has influenced climate change in the past Without doubt human activities are increasing levels of greenhouse gases General consensus is that global warming due to human activities is already occurring.the problems lie in the rate and magnitude of the warming and effects on ecosystems