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Chapter 1 Overview of the Greenhouse Effect
1
Chapter 1
OVERVIEW OF THE GREENHOUSE EFFECT Global change syndrome; general outlook H.W. Schapenseel and P . Becker-Heidmann
Institute of Soil Science, University of Hamburg Allende-Platzz, D-2000 Hamburg 13. Federal Republic of Germany
ABSTRACT Accumulation of cosmic dust and planetesimals was most likely the mechanism that created our planet. Due to dominance of hydrogen, the extruded gases produced a primordial reducing atmosphere. enriched with methane and ammonia. Then, after a slow start, continued oxidation with oxygen, released from photolysis of water, and the later development of life from photosynthesis caused the atmosphere to become dominated by COz, water vapor and N. The two former components were able to trap IR radiation and to produce a warming greenhouse effect of 33"C, shifting the surface temperature to +15"C. Oxygen from photosynthesis (at present yearly c a 330 bil t from terrestrial photosynthesis) was used over at least 2 billion years, for sustaining respiration of the various facets of life and for iron oxidation in marine and terrestrial sediments. During the last billion years oxygen began to enrich in the atmosphere, parallel to reducing CO2 concentration, due to its consumption by photosynthesis, chemical weathering and the carbonate precipitating pumping effect of the oceans. C02 replenishment occurs via volcanism and release from subduction zones. The faster biochemical cycle of smaller pool size (organic matter production, respiration, humification, kerogene formation, and biotic-abiotic-photochemical organic matter turnover) and over longer geological periods especially the slow but very large geochemical cycle (exchange of carbon between atmosphere, ocean, biosphere, and sediments), are decisive for CO2 concentration and its contribution to temperature. Some features of the biochemical cycle against the background of climate changes, including those due to Pangaea/Gondwana shifting, are discussed. Life is on a carbon trip. Wasteful consumption of fossil C based fuel, due to rising living standard and population explosion in conjunction with increasing release of greenhouse active (radiatively active) gases - which are fingerprinted - threatens to exert climate changes detrimental to our life conditions and civilization. Arguments to characterize the situation are assessed, also those expressing potential advantages of increasing C02 concentration for crop yields and expansion of the farmland area, doomed to shrinking at the present level of population explosion. The need for a change from the carbon trip to a mixed carbon - hydrogen trip is evident.
INTRODUCTION Environmental consciousness, especially watchfulness with focus on all anthropogenic activities causing pollution, tend to deviate our attention from tf-e dominant natural processes, underlying the whole web of contributing factors,
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H.W. Schorpenseeiand P.Beckr-Heidmann
actions and feed-back systems in our unique earthly environment. A predictive analysis of the possible effects of a global climate change on soil processes and land degradation should be preceded by a short review of the scene as it existed, before a steadily growing human population created the syndrome of changing climate, basic to our worries. Its background is population explosion in conjunction with carbon-based energy sources and technologies, accompanied by steadily increasing release of nitrogen oxides (N20,NO), that absorb IRradiation or consume ozone in the stratosphere and produce ozone in the troposphere, as well as by increased infrared radiation trapping and stratospheric ozone destroying CFCs (chloro-flouro carbon compounds). These compounds, C02, CH4, N 2 0 , 0 3 , CFCs are expected by the majority of atmospheric chemists to lead to a further indirect temperature increase at the earth surface and decrease in the stratosphere. The estimated temperature rise of 3 to 5°C in the next 50 to 100 years may cause an eustatic sea level rise of 0.7 to 3 m due to water expansion and melting of polar ice masses. How did it all dcvelop and finally become a problem ?
OVERVIEW Basic facts, relating to this question in a nutshell expose the following tableau: Within the sun 700 mil t of hydrogen are fused per second into helium, i.e., ca 4.3 mil t of solar mass are converted into radiation energy, equal to 1.2 x 1015t per year (Wunderlich 1968). From the total solar mass of 2.2 x t , ca 1/40,000 has so far been consumed. The share of the solar radiation hitting the earth, the solar constant, amounts to 2.0 k 0.04 cm-2min-1.This solar radiation with wave lengths of less than 3,000 is absorbed in the ozone layer. Besides, light waves of 3,000 - 20,000A, till near-IR and radiowaves of 1 - lo3 cm wave length enter the atmosphere. The energy invested in the sun radiation is the origin and source of all important features of climate and environment, such as temperature, wind, clouds, precipitation and autotrophic organic matter production. The fact that the earth possesses an atmosphere, is taken as indication, that the origin of the earth is unlikely the result of a cosmic catastrophe, e.g. a collision of the sun with another cosmic body. I may have been formed however, by contracting dust and planetesimals with gaseous inclusions, giving rise after its compaction to extrusion of gases. Provided the gravitational forces are strong enough, those gases will be retained by the planet to form its atmosphere. The very light elements, such as H, He and Ne dissipated into space. This is revealed by comparison of the remaining atmospheric concentration with the share of these elements of the matter in the universe. Estimates are, that about 1 of 50 bil original Ne atoms in the primordial gas cloud is still left; He of the atmosphere is held 10 be almosr entirely radiogenic. The very wasteful atmospheric H, the major
Ilistorical overview of the greenhouse effect
3
cosmic element, may be representing 1 out of 5 mil H atoms in the original dust cloud; the even more reactive 0 about 1 of former 6 atoms; the less reactivc N about 1 of 800,000 N atoms (Asimov 1981). The high cosmic excess of the element H, also early earth, led to an initially reducing atmosphere of chiefly methane (CH4, carbon plus hydrogen) and Ammonia (NH3, nitrogen plus hydrogen). Depending on the amount of oxygen available, water (H20, oxygen plus hydrogen) was formed, which howcvcr was progressively precipitated and collected in depressions and marine basins together with the water vapor emitted by volcanic exhalations, thus leavingCH4, N H 3 , and water vapor as dominating atmospheric gases (Urey's work). Photodissociation of water (H2O + h.v = H+ + OH- ) led to slow oxidation of methane and ammonia into C02 and N2, producing an N2 and C02 atmosphere. With progressing integration of N2 into nitrates, C02 gained dominance till its rising conccntration increasingly blocked the photodissociation of water. Furthcrmorc, ozone formation from free 0 2 in the higher atmosphere absorbcd the UV-radiation and prevcntcd its penetration into the lower atmosphere and action of photolysis. As a rcsult, a stable C02 dominated atmosphere came into existcncc (scc also Habcr 1965). The high C02 concentration could have strongly promoted the greenhouse effect. Due to a rising temperature, water evaporation would have bcen further enhanced, with its additional promotion of the GHE and atmosphcric tcmpcrature rise until a hot earth would have emerged, envclopcd by a water vapor cloud and C02 dominated atmosphere. (For comparison, planct Venus built up a hot and stable COz atmosphere of ca 450" C). But planct earth took a completely different turn in the development of life, probably already slowly bcginning under the reduced CH4/NH3 atmosphere, whcre NH3 was decomposed, releasing N2 into thc aunosphcre, whilc excessive C 0 2 precipitated with Ca, Mg or Fc, which were dissolved by weathering procedures (without oxygen participation) in thc marine basins (not the least enclosed in phytoplancton). Thus, only a moderate GHE occurred due to water vapor and C02 built up, increasing carth's mean temperature by 33" C from - 1 8" C to +15" C (Arrhcnius 1896). This is a temperature level suitable for the liquid state of water and thc colloidal state within living organisms. Other conditions supported the sustainability of life as well, such as: 1 ) the Van Allen belt (the magnetosphere); 2) the shield against cosmic radiation; 3) similarly, the ozone shield for absorption of UV light; 4) the earth magnctic field, although changing its polarity rcpcatcdly in the course of earth history, giving furlher radiation protcction and orientation; 5 ) the high altitude cirrus clouds, heating the atmosphere; 6) the lower altitudc vapor saturated clouds exerting a cooling effect; 7) the inclined earth axis (23.5"), producing annual seasons of climate; 8) the earth rotation, causative for day and night change for regeneration of the metabolisms; and 9) the atmospheric currents for transportation of moisture, heat and dissipation of products of pollution.
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H.W. Scharpenseel and P . Becker-Heidmann
Soil and humus formation, CO, and 0, trends
&M
0 Quaternary Ter t iar y
.
70
. 140
.
180
-
225
. 275
345
'
. 400
.
440
. 490
Cretaceous Jurassic
plus humus of Angiosperms
Triassic Permian Carbonian Devonian
first complete soil cover plus humus of Gymnosperms
Silurian Ordovician Cambrian
'
580
C02 trend decreasing 0 trend increasing
Fig. 1.1
Soil and humusformation in earth is history
Life on earth was slowly turning the N/C02 atmosphere into a N/O atmosphere. The 0 2 concentration increased by almost one order of magnitude (Fig. 1.1) during the last ca 600 million years, that is since the beginning of terrestrial plant growth (the Phanerozoic; flowering plants, the angiosperms since just ca 150 million years) . This is mainly the effect of oxygen release during the photosynthesis process of organic matter production from CO2, and 0 and H from H20, previously dissociated by sunlight energy (light reaction of photosynthesis). The slow development of our oxygen rich atmosphere after exhaustion of the enormous demand for marine and terrestrial Fe-oxidation is shown in Fig. 1.2. Meanwhile the total free oxygen pool in the atmosphere and dissolved in the oceans is estimated to amount to 1.3 x 1021 g. Most of the biologically produced oxygen, at present ca 3.3 x 1017g of 0 2 per year (corresponding with ca 1.2 x lOI7 g of C per year by terrestrial photosynthesis) plus ca 1.3 x 1017 g of 0 2 per year (corresponding with ca 5 x 10l6 g of C consumed by marine photosynthesis), is bound in the earth crust as metal oxide, sulfate, silicate, and carbonate and represents about 6 x g of oxygen (Chem. Ind. 1987). Considering the high reactivity of oxygen, its existence as free 02-gas in the atmosphere is possibly only the result of constant new 0 2 production and
5
Historical overview of the greenhouse effect
addition. Without replenishment by photosynthesis, our atmospheric oxygen may
be consumed in about 3000 years due to oxidation processes in the earth crust
(Haber 1965, 1971). But also atmospheric C02 needs replacement outside the biochemical cycle of photosynthesis and respiration due to consumption of C02 by silicate weathering, where from 2 molecules of C02 involved in the bicarbonate reaction always only one is returned to the atmosphere, whereas the second one is precipitated as carbonate, which would use up the present atmospheric CO2-pool in about 10.000 years (2 COz + H 2 0 + CaSi03 t Ca2' + 2 HCO3- + Si02) (Berner and Lasaga 1990). Similarly the gas exchange pump of the oceans induce C02 intake to replace C02 of precipitated carbonate. After longtime involvement of the geochemical cycle, these carbonates may under high pressure and temperature be subjected to metamorphic processes and eventually release the C02 through volcanism or expulsion by subduction zones.
4 B I L L I O N Y E A R S AGO
3 TO
Primordial m l m o ~ p h e r e
Formallon 01
co2
S o l u l l o n O d 0, I " w a t e r
S O l U l l O " I " "11*,
4
B I L L I O N Y E A R S AGO
0, I n
water
CA
2 B I L L I O N Y E A R S AGO
Formillon 01
0, I n w a t e r
T B ~ l d S l I 1 ~l 1l x a l l o n 01
0,
......~
CA
0 5 B I L L I O N Y E A R S AGO
T e r r e $ t r i a l o r m ~ t i a n0 1
0, R I S E
0,
I N ATMOSPHERE
IIIIII
0 2
0 A C T E A IA
W E AT H E R I N G
CaCO, A
I
Fig. I .2
Fe*O 3
-
MUD
,
History of oxygen formation and dynamics
This gas exchange process would exhaust atmospheric C02 in about 300,000 years (Bemer and Lasaga 1990). Planet earth, its atmosphere and biosphere become vitally predetermined by the consequences of the vast but slow geochemical and faster biochemical cycle, which however represents a much smaller carbon compartment.
6
H.W. Scharpenseel and P . Becker-Heidmann
FEATURES OF THE BIOCHEMICAL CYCLE Only carbonaceous materials, produced by abiotic processes till ca 3 billion years ago are exclusively geochemical (Rankama 1948). All others also have a biochemical component. The organic matter residues of living organisms are preserved almost exclusively in aquatic sediments as carbonates or in contact with shales and clay minerals. The latter as clay domains provide also the matrix for organo-mineralcomplexation of younger or even today's terrestrial organic matter (Aylmore and Quirk 1960; Theng and Scharpenseel 1975; Theng 1979) (Fig. 1.3). 70-
60-
50I
P
E" 40-
1
H m i c acid concentration (mg/rnl)
Fig. 1.3
Isotherms at 20°C f o r the adsorption of 14 C-humid acid by montmorillonite saturated with diflerent cations (Theng and Scharpenseel 1975)
Most of recent as well as ancient sediment's organic matter stcms from phytoplancton and bacteria (Bordowsky 1965; Murphy et al. 1966); this forms the major sink of organic C and of CO2. Sediments, produced by precipitation, such as evaporites and carbonates, rarely contain large amounts of allochthonous organic matter. Detrital rocks like sandstone or shales engulf, usually diagenetically formed, relatively stable, secondary polymerized compounds, such as humic acids as oxidative or kerogene as reductive products (Tappan and Loeblich, ref. Welte 1963). Both together represent the major organic carbon sink
Historical overview of the greenhouse effect
7
at a level of ca 3.6 x loi5t, compared with petrol or coal with stocks of the order of 10l2- l O I 3 t only (Degens 1967). Finally, climatic and tectonic events have a great influence on the organic compound production and preservation, e.g. bituminous sequences often seem to be related to orogenic phases or epimgenic oscillations with corresponding eustatic lifts, trans- and regressions (Bitterli 1963). The C02 and 0 2 balance in ocean water and in the atmosphere changed with the organic matter production in the course of earth history, with its carbonate precipitation as well as the emergence of higher plants and animals (Tappan and Loeblich, ref. Welte 1969). During sediment diagenesis organic matter supports the microbial metabolism and it exerts influence on chemical reactions through pH and Eh changes, especially those involving C02 - SO2 CH4. After microbial activity terminates, chemical interactions with the inorganic matrix occur, leading to complexation and chelation, and reactive chemical groups like carboxyl, hydroxyl, and amino groups are released. The origin of life is believed to have occurred in an aquatic milieu, which provides more continuity due to less zoographic isolation than terrestrial life which developed later. According to Schilder (1956), 63 among 68 animal classes live in a marine environment, but, due to geographic/ecologic isolation in terrestrial environments, the differentiation in species is more pronounced, comprising ca 83 % of all known animal species. The transition from marine to land based life, that contributed most to an oxygenation of the atmosphere and that became a major sink for C02 excess in the biochemical cycle, must have begun preferably in marginal shelf fringes of the epipelagial, the euphotic zone, mostly under tidal influence, such as in marshy or mangrove environments and in shallow littorals. Since organisms sustaining the biochemical cycle by photosynthesis (C02 consumption) and respiration (C02 release) survive in evolutionary processes, due to their capability to adopt flexibly to environmental changes and to find ecological niches or refuges, the eco/geographical boundaries governing the distribution of species are constantly shifting due to climate changes as well as to tectonic effects. This applies particularly to stenothermic animal species requiring a narrow temperature regime. In biomes, animal life usually is more flexible and stretches further into critical environments than growth of vegetation (Wurmbach 1971). The spread of terrestrial life has also been largely influenced by plate tectonics in conjunction with the dissolution of Pangaea, the Gondwana and Europe-Angara drifting with the corresponding climate changes. In this context, the most striking process of soil degradation, a land fossilization and lateritic cuirass formation, occurred due to changed erosion and drainage patterns. These cuirasscs represent an extreme form of humid tropical weathering under the changing climate of the floating Gondwana subcontinents (mainly Jurassic to Oligocene) (Valeton 1984). A sporadic soil blanket (pers. comm. Dudal 1990)
8
H . W . Scharpenseel and P . Becker-Heidmann
existed probably since the end of thc Silurian, a soil continuum came into being some time after the cold spell during the Permian.
IMPACTS OF GEOCHEMICAL AND BIOCHEMICAL CARBON CYCLE A comparison of the magnitudes of the compartments of carbon in the (bio)geochcmical (exchange of C between sediments, atmosphere, biosphere and ocean) and biochemical (organic matter production, respiration, turnover) cycle shows the dominance in pool size of the former, which over geological time pcriods is all decisive with its enormous buffer capacity (Table 1.1). Shortcuts in the biochemical cycle and short-term excessive inputs may produce a flicker, strong enough though for consequences on the GHE, the earth temperature, the prccipitation and the circulation, which may damage or even exterminate species causativc of the disturbance. Thus, in our short historical span we can not rely on the buffcr capacity of the large but slow gcochcmical cycle to neutralize the consequcnces of our mistakes. Table 1.1
Comparison of carbon pool sizes in biochemical and geochemical cycle*
Componcnts CaC03 in sediments CaMg (CO& in sediments Organic sediments (kerogcne) HCOf and C032- dissolved in sea Fossil fuel (coal, gas, oil) Dead soil biomass (humus) C02 in atmosphere Living biomass (plant, animals) * Data slightly modified from Berner and
C-amount in 10'2 t of c 35,000 25,000 15,000
42 5
2 0.72 0.56 Lasaga 1990.
LIFE ON EARTH, A CARBON TRIP Lifc on earth is on a carbon trip. We must get aware of the need for changing course in time to avoid an erratic trip back into chaos, from which evolution made us ascend. Looking at the biochemical carbon cycle (Fig.1.4). about 115 to 120 x l O I 5 g of C are turned over annually in the terrestrial ecosystems by photosynthesis and inversely by respiration through the bio- and pedosphere. Worrysome is the surplus due to respiration of ca 1.5 x lOI5 g of C from annual land clearing (slash and bum) as well as the 5.5 x l O I 5 g of C from
9
Historical overview of the greenhouse effecr
combustion of fossil fuel, which are adding up at a ca 50% rate to the 720 x 10'5 g of C in the atmospheric carbon pool. However, recent results of Esser (1990) suggest that the C-sink due to C02 fertilization is already overcompenzating the C02 source from forest clearing (ca. 1.5 Gt C y - l from 10 to 15 mil. ha of clearing a year). Principally, carbon oxidation products, C02 and CH4, although being greenhouse active trace gases, are minor in importance compared with water vapor (1:5) in generating the temperature rising greenhouse effect of 33"C, lifting the surface temperature from -18°C to +15"C. According to Ramanathan (1989) as well as Raval and Ramanathan (1989), the total natural 33°C greenhouse effect generated by water vapor plus C02 equals 155 Wm-2 (ca 145 W at clear sky, 180 W at cloudy sky). Doubling of the C 0 2 concentration would add ca 4 Wm-2 only; human activities so far have enhanced the GHE of the atmosphere by ca 1.5 % only.
CARBON CYCLE
l
120
I
A
n 2'
B'OSPHERE + PEDOSPHERE
i...ca.?3P..!!.!v!na.! .......
$.
C6 2000 (dead)
ca 100
ca 60
01
,
5"
DEPOSITS 5000 i ......COAL, . ...........OIL, .........GAS ............................................ SEDIMENTS/LITHOSPHERE 66 000 000 o,2 from l o r e s t a n d sol1 d e g r a d a t i o n
ca 100
OCEAN SURFACE WATER c a 700 ................................................................... DEEPER OCEAN WATER c a 37000
l r o m c o a l , 011.
gas combusllon
a m o u n t s ~n G I ( I O " ~ ) , f l u x e s i n G I I ~
Fig. 1.4
Carbon compartments in biochemical and geochemical cycle
But the increments of C02, CH4, as well as the other radiatively active trace gases, such as the CFCs, N20 and tropospheric ozone, are wholly or to greatest extent the product of anthropogenic activities. Human civilization was in its earlier phases sustained by the direct products of photosynthetic C reduction and
10
H.W. Schorpenseel and P.Becker-Heidmann
photolysis of water (Calvin 1962). Since beginning craftsmanship and industrialization it progressively built up a dependency on minable and consumable forms of organic matter, produced mainly throughout the last 350 million years, such as coal, kerogene/petrol and methane. While the first scientists, expressing the vision of an expanding greenhouse effect with temperature and in consequence an eustatic sea level rise (Arrhenius 1896; Callendar 1938; Flohn 1941, cited in Lausch 1989) found little attention or enthusiastic response, at present an almost overheated scientific climate and preferably apocalyptic predictions thtcaten to misinterpret the real facts, needs and situative, curative potentials. We also should not ignore the main trend of decreasing C02 concentration over most of the geochemical and biochemical evolutionary phases of the past, with at least five times the present level still during Tertiary times and about 200 ppm after fluctuations during glacial and interglacial periods at the end of last Wisconsin-, Wurmian-, Weichselian glacial. Since even the present 350 ppm are at the lower end of the plant physiologically suitable C02 range, could there have been an acute C02 deficiency developing, and the C02 rise since begin of industrialization in reality being beneficial in our endeavour to increase food production for the growing world population ? The temperature rise of 0.7"C since 1860 and a sea level rise of about 17 cm are acknowledged by most climate research units, but a highly rated group of scientists from the G.C. Marshall Institute in Washington, D.C. draws attention to a better correlation between the observed trend in temperature and the solar activity/sun spot activity than the more commonly considered increasing C02 concentration (ref. Economist Vol. 313, No. 7633, 1989). R.S. Lindzen from M.I.T. Boston a.0. reported to be expecting nominal temperature increases only. Other critical observations focus in many different ways on the overestimation of the C02 concentration change and neglect of the importance of changes in atmospheric moisture level, which, as mentioned before, is undisputed the major promoter of the basic greenhouse effect. While the determination to reduce the release of the other greenhouse active trace gases, such as CH4, N 2 0 , CFCs, tropospheric ozone (see overview in Table 1.2) is apparently worldwide accepted, a production oriented pedologist/plant nutritionist can argue, whether the rise of C02, which is expected to enhance especially C3 photosynthetic efficiency and to improve the water economy of plants due to closing of stornatal aperture with increasing C02 concentration, which even under rising temperature and water evaporation may also conserve precious water (Schleser and Kirstein 1990), would be really all that bad. Fig. 1.5 shows the wide range of C02 concentration versus light intensity capable of increasing photosynthetic efficiency. The relative effect of increasing C02 on the major cultivated plants as well as the most obnoxious weeds requires thorough attention.
11
Historical overview of the greenhouse effect
Table 1.2
Greenhouse active and other (polluting)trace gases, basic pool sizes
Trace gases
% share of antrogenic
GHE
co2
50 19 17 8 6 Residence time Concentration 100 y 350 ppm
co
1 - 6 months
CH4 CFCs (ClOx -radicals)
10 Y 50 - 150 y
100-150ppb N 40-80 ppb S (N, S. hemisphere) 1.7 ppm 0.2 - 0.3 ppb
170 y few days only
0.31 ppm 0 - 100 ppb
co2 CH4 CFCs 0 3 (tropospheric) N20
Components
N20
NOx (NO, NO21 0 3 (stratospheric) 0 3 (tropospheric)
OH (atmospheric)
so2
Atmospheric C-pool Photosynthesis (terrestr.) Soil organic matter pool Ocean C-cycle flux
Fossil fuel C
few seconds only
10 ppm (35 km) 0.02 ppm (0.1 ppm max.) < O.oooO1 ppb
GHE-rising potential of trace gases rel. to c02 1 32 14 - 17,000 2000 150 Increase per year (1800->280, 1950>310); ca. 0.5% variable 1.1 % (18 ppb) 5% 4% 0.3 % (ca 1 ppb) 0.2 - 0.3 % (stratospheric)
0.5 %
50 ppb (max.) 740 bil t 115 bil t (ca 1/2 respired, ca. 1/2 Wmpo@ 1.8 x 10l2 t
38.5 x 10l2 t (3x 109tpery precipitated as carbonate) 5 - 10 x 1012 t
The vegetation belt, which may be particularly affected by increasing heat and drought, the inigation-dependent and responsive sub-tropics, may hopehlly
12
H.W. Scharpemeel and P . Becker-Heidmann
replenish water deficits by stepped up sea water distillation, which may become technically feasible in nearer future. Besides, the leading Russian climatologist from Leningrad, M.I. Budyko (ref. Spiegel 1990) expects even for the (semi)arid tropics more rainfall and a vegetation cover similar to that of the Pliocene. Increase of temperature and precipitation in the boreal belt could bear grave consequences due to enhancement of organic matter decomposition and consequent COs release, but may also hold unforeseeable opportunities to increase agricultural production in vast areas of so far low productive boreal lands, which may even become important carbon sinks (see for more details Chapters 16 and 17). The catalogue of pros and contras of effects of climate change is certain to expand. Net photosynthetic rate for different light intensities and C 0 2 concentrations Rp (mg C O P / q m
I Fig. 1.5
I
s)
I light Intens.. Rp net photosynth. r a t e
Influence of light intensity and CO;, on photosynthesis. (modified from Mengel and Kirkby 1979,acc. to Warren-Wilson 1969)
We should be critically alert towards the climate change syndrome, but as critically open to the more constructive and may be even optimistic arguments before destroying productive structures without having replacements in panic, through poorly conceived legal actions as well as preventive or curative measures, . The most important reaction, though, should be to prepare t k follow-up phase of a mixed hydrogen plus carbon trip. In geological times the geochemical cycle is absolutely dominating and decisive for CO2 concentration and its influence on temperature. However, the anthropogenic shortcut of the
H k l o r i c a l overview of the greenhouse effect
13
biochemical cycle that we practice with wasteful consumption of fossil fuel reserves, with rising population and living standards, may suffer under t k unsentimental regime of natural processes, such as temperature and sea-level rise, to destroy our species and civilization (only a fast forgotten flicker in earth history), We must therefore concentrate all our efforts on the development of the photovoltaic hydrogen technology for replacement of C-based fossil fuels, as well as on the methodology for use of sun energy in desalination of sea and brackish ground water to stabilize life and productivity in the (semi)arid lands.
REFERENCES Asimov, 1. (1984). Asimov’s new guide to science. Basic Books Publ., New York. Aylmore, L.A.G. and J.P. Quirk (1960). Domain or turbostratic structure of clays. Nature 187. 1046- 1048. Berner, R.A. and A.J. Lasaga (1990). Simulation des geochemischen Kreislaufs. Spektrum der Wissenschaft 5, 56. Bitterli, P. (1963). Aspects of the genesis of bituminous rock sequences. Geol. Mijnbouw. 42, 183-201. Bordovskij, O.K. (1965). Accumulation and transformation of organic substances in marine sediments. Marine Geology 3, 3-1 14. Calvin, M. and J.A. Bassham (1962). The photosynthesis of carbon compounds, W.A. Benjamin Inc., New York. Degens, E.T. (1967). Diagenesis of organic matter. In: Diagenesis in sediments, Larsen, G. and G.V. Chilingar, Eds., Elsevier, Amsterdam, chap. 7. Dudal, R. (1990). Global Soil Change, report of an IIASA-ISSS-UNEP Task Force Meet. on the Role of Soil Global Change, Chap. 3 (in print). Esser, G. (1990). Modeling global terrestrial sources and sinks of COz with special reference to soil organic matter. In: Soils and the greenhouse effect, A.F. Bouwman (Ed.) (1990). John Wiley and Sons, Chichester. Fond der Chemischen Industrie, Umweltbereich Luft (1987). Vol 22, p. 15. Haber. H. (1965. 1971). Die Entwicklungsgeschichte der Erde, Deutsche Verlags Anstalt, Stuttgart, p. 79, p. 208. Lausch, E. (1989). Treibhaus Erde. CEO (Gruner u. Jahr, Hamburg) 37,46-49. Mengel, K. and E.A. Kirkby (1979). Principles of Plant Nutrition. Int. Potash Institute, Bern, Switzerland, 233. Murphy, M, B. Nagy, G. Rouser, and G. Kritchevsky (1965). Analysis of sulphur compounds in lipid extracts from the Orguiel meteorite. J. A. Oil Chem. Soc. 43, 189.196. Ramanathan, V. (1989). Spurengase, Treibhauseffekt und weltweite Erwrmung, In: Das Ende des blauen Planeten ? Crutzen and Muller (Eds) Beck, Federal Republic of Germany, 6576. Rankama, K. (1948). New evidence of the origin of pre Cambrian carbon. Bull. Geol. Soc. Am. 59, 389-416. Raval. A. and V. Ramanathan (1989). Observational determination of the greenhouse effect. Nature 342, 758-761. Schilder, F.A. (1956). Lehrbuch der Allgemeinen Zoogeographie, Jena, German Democratic Republic. Schleser, G. and W. Kirstein (1989). Der Treibhauseffekt. Ursachen und Konsequenzen fur
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H.W. Scharpenseel and P . Becker-Heidmonn
Klima und Biosphre. Seminar Technik und Gesellschaft, KFA Jlich, Federal Republic of Germany (preprint). Spiegel (1990). M.I. Budyko - Interview. Der Spiegel, Hamburg, 1, 143. Theng, B.K.G. (1979). Formation and Properties of Clay Polymer Complexes, part 3, Chap. 12, 283-314. Theng. B.K.G. and H.W. Scharpenseel (1975). The adsorption of 14-C labelled humic acid by montmorillonite. Proc. Internatl. Clay Conf., Mexico City, 643-653. Valeton, I. (1983). Klimaperioden, lateritische Verwitterung und ihr Abbild in den synchronen Sedimentationsrumen. Z. Dtsche Geol. Ges. 134, 2. Warren-Wilson, I. (1969) Maximum yield potential. In: Transition from extensive to intensive agriculture with fertilizers, Proc. 7th Coll. Intern. Potash Institute, Bern, Switzerland, 34-56. Welte, D.H. (1969) Organic matter in sediments. In: Organic Chemistry, Springer, Berlin, 262-264. Wunderlich, H.G. (1968). Einfhrung in dic Geologie, Vol. 1, Exogene Dynamik. Bibliographisches Institut, Mannheim. Federal Republic of Germany. Wurmbach, U. (1971). Zoologie. Vol. 2, G. Fischer Verlag, Stuttgart.
Chapter 1
OVERVIEW OF THE GREENHOUSE EFFECT Global change syndrome; general outlook H.W. Schapenseel and P . Becker-Heidmann
Institute of Soil Science, University of Hamburg Allende-Platzz, D-2000 Hamburg 13. Federal Republic of Germany
ABSTRACT Accumulation of cosmic dust and planetesimals was most likely the mechanism that created our planet. Due to dominance of hydrogen, the extruded gases produced a primordial reducing atmosphere. enriched with methane and ammonia. Then, after a slow start, continued oxidation with oxygen, released from photolysis of water, and the later development of life from photosynthesis caused the atmosphere to become dominated by COz, water vapor and N. The two former components were able to trap IR radiation and to produce a warming greenhouse effect of 33"C, shifting the surface temperature to +15"C. Oxygen from photosynthesis (at present yearly c a 330 bil t from terrestrial photosynthesis) was used over at least 2 billion years, for sustaining respiration of the various facets of life and for iron oxidation in marine and terrestrial sediments. During the last billion years oxygen began to enrich in the atmosphere, parallel to reducing CO2 concentration, due to its consumption by photosynthesis, chemical weathering and the carbonate precipitating pumping effect of the oceans. C02 replenishment occurs via volcanism and release from subduction zones. The faster biochemical cycle of smaller pool size (organic matter production, respiration, humification, kerogene formation, and biotic-abiotic-photochemical organic matter turnover) and over longer geological periods especially the slow but very large geochemical cycle (exchange of carbon between atmosphere, ocean, biosphere, and sediments), are decisive for CO2 concentration and its contribution to temperature. Some features of the biochemical cycle against the background of climate changes, including those due to Pangaea/Gondwana shifting, are discussed. Life is on a carbon trip. Wasteful consumption of fossil C based fuel, due to rising living standard and population explosion in conjunction with increasing release of greenhouse active (radiatively active) gases - which are fingerprinted - threatens to exert climate changes detrimental to our life conditions and civilization. Arguments to characterize the situation are assessed, also those expressing potential advantages of increasing C02 concentration for crop yields and expansion of the farmland area, doomed to shrinking at the present level of population explosion. The need for a change from the carbon trip to a mixed carbon - hydrogen trip is evident.
INTRODUCTION Environmental consciousness, especially watchfulness with focus on all anthropogenic activities causing pollution, tend to deviate our attention from tf-e dominant natural processes, underlying the whole web of contributing factors,
2
H.W. Schorpenseeiand P.Beckr-Heidmann
actions and feed-back systems in our unique earthly environment. A predictive analysis of the possible effects of a global climate change on soil processes and land degradation should be preceded by a short review of the scene as it existed, before a steadily growing human population created the syndrome of changing climate, basic to our worries. Its background is population explosion in conjunction with carbon-based energy sources and technologies, accompanied by steadily increasing release of nitrogen oxides (N20,NO), that absorb IRradiation or consume ozone in the stratosphere and produce ozone in the troposphere, as well as by increased infrared radiation trapping and stratospheric ozone destroying CFCs (chloro-flouro carbon compounds). These compounds, C02, CH4, N 2 0 , 0 3 , CFCs are expected by the majority of atmospheric chemists to lead to a further indirect temperature increase at the earth surface and decrease in the stratosphere. The estimated temperature rise of 3 to 5°C in the next 50 to 100 years may cause an eustatic sea level rise of 0.7 to 3 m due to water expansion and melting of polar ice masses. How did it all dcvelop and finally become a problem ?
OVERVIEW Basic facts, relating to this question in a nutshell expose the following tableau: Within the sun 700 mil t of hydrogen are fused per second into helium, i.e., ca 4.3 mil t of solar mass are converted into radiation energy, equal to 1.2 x 1015t per year (Wunderlich 1968). From the total solar mass of 2.2 x t , ca 1/40,000 has so far been consumed. The share of the solar radiation hitting the earth, the solar constant, amounts to 2.0 k 0.04 cm-2min-1.This solar radiation with wave lengths of less than 3,000 is absorbed in the ozone layer. Besides, light waves of 3,000 - 20,000A, till near-IR and radiowaves of 1 - lo3 cm wave length enter the atmosphere. The energy invested in the sun radiation is the origin and source of all important features of climate and environment, such as temperature, wind, clouds, precipitation and autotrophic organic matter production. The fact that the earth possesses an atmosphere, is taken as indication, that the origin of the earth is unlikely the result of a cosmic catastrophe, e.g. a collision of the sun with another cosmic body. I may have been formed however, by contracting dust and planetesimals with gaseous inclusions, giving rise after its compaction to extrusion of gases. Provided the gravitational forces are strong enough, those gases will be retained by the planet to form its atmosphere. The very light elements, such as H, He and Ne dissipated into space. This is revealed by comparison of the remaining atmospheric concentration with the share of these elements of the matter in the universe. Estimates are, that about 1 of 50 bil original Ne atoms in the primordial gas cloud is still left; He of the atmosphere is held 10 be almosr entirely radiogenic. The very wasteful atmospheric H, the major
Ilistorical overview of the greenhouse effect
3
cosmic element, may be representing 1 out of 5 mil H atoms in the original dust cloud; the even more reactive 0 about 1 of former 6 atoms; the less reactivc N about 1 of 800,000 N atoms (Asimov 1981). The high cosmic excess of the element H, also early earth, led to an initially reducing atmosphere of chiefly methane (CH4, carbon plus hydrogen) and Ammonia (NH3, nitrogen plus hydrogen). Depending on the amount of oxygen available, water (H20, oxygen plus hydrogen) was formed, which howcvcr was progressively precipitated and collected in depressions and marine basins together with the water vapor emitted by volcanic exhalations, thus leavingCH4, N H 3 , and water vapor as dominating atmospheric gases (Urey's work). Photodissociation of water (H2O + h.v = H+ + OH- ) led to slow oxidation of methane and ammonia into C02 and N2, producing an N2 and C02 atmosphere. With progressing integration of N2 into nitrates, C02 gained dominance till its rising conccntration increasingly blocked the photodissociation of water. Furthcrmorc, ozone formation from free 0 2 in the higher atmosphere absorbcd the UV-radiation and prevcntcd its penetration into the lower atmosphere and action of photolysis. As a rcsult, a stable C02 dominated atmosphere came into existcncc (scc also Habcr 1965). The high C02 concentration could have strongly promoted the greenhouse effect. Due to a rising temperature, water evaporation would have bcen further enhanced, with its additional promotion of the GHE and atmosphcric tcmpcrature rise until a hot earth would have emerged, envclopcd by a water vapor cloud and C02 dominated atmosphere. (For comparison, planct Venus built up a hot and stable COz atmosphere of ca 450" C). But planct earth took a completely different turn in the development of life, probably already slowly bcginning under the reduced CH4/NH3 atmosphere, whcre NH3 was decomposed, releasing N2 into thc aunosphcre, whilc excessive C 0 2 precipitated with Ca, Mg or Fc, which were dissolved by weathering procedures (without oxygen participation) in thc marine basins (not the least enclosed in phytoplancton). Thus, only a moderate GHE occurred due to water vapor and C02 built up, increasing carth's mean temperature by 33" C from - 1 8" C to +15" C (Arrhcnius 1896). This is a temperature level suitable for the liquid state of water and thc colloidal state within living organisms. Other conditions supported the sustainability of life as well, such as: 1 ) the Van Allen belt (the magnetosphere); 2) the shield against cosmic radiation; 3) similarly, the ozone shield for absorption of UV light; 4) the earth magnctic field, although changing its polarity rcpcatcdly in the course of earth history, giving furlher radiation protcction and orientation; 5 ) the high altitude cirrus clouds, heating the atmosphere; 6) the lower altitudc vapor saturated clouds exerting a cooling effect; 7) the inclined earth axis (23.5"), producing annual seasons of climate; 8) the earth rotation, causative for day and night change for regeneration of the metabolisms; and 9) the atmospheric currents for transportation of moisture, heat and dissipation of products of pollution.
4
H.W. Scharpenseel and P . Becker-Heidmann
Soil and humus formation, CO, and 0, trends
&M
0 Quaternary Ter t iar y
.
70
. 140
.
180
-
225
. 275
345
'
. 400
.
440
. 490
Cretaceous Jurassic
plus humus of Angiosperms
Triassic Permian Carbonian Devonian
first complete soil cover plus humus of Gymnosperms
Silurian Ordovician Cambrian
'
580
C02 trend decreasing 0 trend increasing
Fig. 1.1
Soil and humusformation in earth is history
Life on earth was slowly turning the N/C02 atmosphere into a N/O atmosphere. The 0 2 concentration increased by almost one order of magnitude (Fig. 1.1) during the last ca 600 million years, that is since the beginning of terrestrial plant growth (the Phanerozoic; flowering plants, the angiosperms since just ca 150 million years) . This is mainly the effect of oxygen release during the photosynthesis process of organic matter production from CO2, and 0 and H from H20, previously dissociated by sunlight energy (light reaction of photosynthesis). The slow development of our oxygen rich atmosphere after exhaustion of the enormous demand for marine and terrestrial Fe-oxidation is shown in Fig. 1.2. Meanwhile the total free oxygen pool in the atmosphere and dissolved in the oceans is estimated to amount to 1.3 x 1021 g. Most of the biologically produced oxygen, at present ca 3.3 x 1017g of 0 2 per year (corresponding with ca 1.2 x lOI7 g of C per year by terrestrial photosynthesis) plus ca 1.3 x 1017 g of 0 2 per year (corresponding with ca 5 x 10l6 g of C consumed by marine photosynthesis), is bound in the earth crust as metal oxide, sulfate, silicate, and carbonate and represents about 6 x g of oxygen (Chem. Ind. 1987). Considering the high reactivity of oxygen, its existence as free 02-gas in the atmosphere is possibly only the result of constant new 0 2 production and
5
Historical overview of the greenhouse effect
addition. Without replenishment by photosynthesis, our atmospheric oxygen may
be consumed in about 3000 years due to oxidation processes in the earth crust
(Haber 1965, 1971). But also atmospheric C02 needs replacement outside the biochemical cycle of photosynthesis and respiration due to consumption of C02 by silicate weathering, where from 2 molecules of C02 involved in the bicarbonate reaction always only one is returned to the atmosphere, whereas the second one is precipitated as carbonate, which would use up the present atmospheric CO2-pool in about 10.000 years (2 COz + H 2 0 + CaSi03 t Ca2' + 2 HCO3- + Si02) (Berner and Lasaga 1990). Similarly the gas exchange pump of the oceans induce C02 intake to replace C02 of precipitated carbonate. After longtime involvement of the geochemical cycle, these carbonates may under high pressure and temperature be subjected to metamorphic processes and eventually release the C02 through volcanism or expulsion by subduction zones.
4 B I L L I O N Y E A R S AGO
3 TO
Primordial m l m o ~ p h e r e
Formallon 01
co2
S o l u l l o n O d 0, I " w a t e r
S O l U l l O " I " "11*,
4
B I L L I O N Y E A R S AGO
0, I n
water
CA
2 B I L L I O N Y E A R S AGO
Formillon 01
0, I n w a t e r
T B ~ l d S l I 1 ~l 1l x a l l o n 01
0,
......~
CA
0 5 B I L L I O N Y E A R S AGO
T e r r e $ t r i a l o r m ~ t i a n0 1
0, R I S E
0,
I N ATMOSPHERE
IIIIII
0 2
0 A C T E A IA
W E AT H E R I N G
CaCO, A
I
Fig. I .2
Fe*O 3
-
MUD
,
History of oxygen formation and dynamics
This gas exchange process would exhaust atmospheric C02 in about 300,000 years (Bemer and Lasaga 1990). Planet earth, its atmosphere and biosphere become vitally predetermined by the consequences of the vast but slow geochemical and faster biochemical cycle, which however represents a much smaller carbon compartment.
6
H.W. Scharpenseel and P . Becker-Heidmann
FEATURES OF THE BIOCHEMICAL CYCLE Only carbonaceous materials, produced by abiotic processes till ca 3 billion years ago are exclusively geochemical (Rankama 1948). All others also have a biochemical component. The organic matter residues of living organisms are preserved almost exclusively in aquatic sediments as carbonates or in contact with shales and clay minerals. The latter as clay domains provide also the matrix for organo-mineralcomplexation of younger or even today's terrestrial organic matter (Aylmore and Quirk 1960; Theng and Scharpenseel 1975; Theng 1979) (Fig. 1.3). 70-
60-
50I
P
E" 40-
1
H m i c acid concentration (mg/rnl)
Fig. 1.3
Isotherms at 20°C f o r the adsorption of 14 C-humid acid by montmorillonite saturated with diflerent cations (Theng and Scharpenseel 1975)
Most of recent as well as ancient sediment's organic matter stcms from phytoplancton and bacteria (Bordowsky 1965; Murphy et al. 1966); this forms the major sink of organic C and of CO2. Sediments, produced by precipitation, such as evaporites and carbonates, rarely contain large amounts of allochthonous organic matter. Detrital rocks like sandstone or shales engulf, usually diagenetically formed, relatively stable, secondary polymerized compounds, such as humic acids as oxidative or kerogene as reductive products (Tappan and Loeblich, ref. Welte 1963). Both together represent the major organic carbon sink
Historical overview of the greenhouse effect
7
at a level of ca 3.6 x loi5t, compared with petrol or coal with stocks of the order of 10l2- l O I 3 t only (Degens 1967). Finally, climatic and tectonic events have a great influence on the organic compound production and preservation, e.g. bituminous sequences often seem to be related to orogenic phases or epimgenic oscillations with corresponding eustatic lifts, trans- and regressions (Bitterli 1963). The C02 and 0 2 balance in ocean water and in the atmosphere changed with the organic matter production in the course of earth history, with its carbonate precipitation as well as the emergence of higher plants and animals (Tappan and Loeblich, ref. Welte 1969). During sediment diagenesis organic matter supports the microbial metabolism and it exerts influence on chemical reactions through pH and Eh changes, especially those involving C02 - SO2 CH4. After microbial activity terminates, chemical interactions with the inorganic matrix occur, leading to complexation and chelation, and reactive chemical groups like carboxyl, hydroxyl, and amino groups are released. The origin of life is believed to have occurred in an aquatic milieu, which provides more continuity due to less zoographic isolation than terrestrial life which developed later. According to Schilder (1956), 63 among 68 animal classes live in a marine environment, but, due to geographic/ecologic isolation in terrestrial environments, the differentiation in species is more pronounced, comprising ca 83 % of all known animal species. The transition from marine to land based life, that contributed most to an oxygenation of the atmosphere and that became a major sink for C02 excess in the biochemical cycle, must have begun preferably in marginal shelf fringes of the epipelagial, the euphotic zone, mostly under tidal influence, such as in marshy or mangrove environments and in shallow littorals. Since organisms sustaining the biochemical cycle by photosynthesis (C02 consumption) and respiration (C02 release) survive in evolutionary processes, due to their capability to adopt flexibly to environmental changes and to find ecological niches or refuges, the eco/geographical boundaries governing the distribution of species are constantly shifting due to climate changes as well as to tectonic effects. This applies particularly to stenothermic animal species requiring a narrow temperature regime. In biomes, animal life usually is more flexible and stretches further into critical environments than growth of vegetation (Wurmbach 1971). The spread of terrestrial life has also been largely influenced by plate tectonics in conjunction with the dissolution of Pangaea, the Gondwana and Europe-Angara drifting with the corresponding climate changes. In this context, the most striking process of soil degradation, a land fossilization and lateritic cuirass formation, occurred due to changed erosion and drainage patterns. These cuirasscs represent an extreme form of humid tropical weathering under the changing climate of the floating Gondwana subcontinents (mainly Jurassic to Oligocene) (Valeton 1984). A sporadic soil blanket (pers. comm. Dudal 1990)
8
H . W . Scharpenseel and P . Becker-Heidmann
existed probably since the end of thc Silurian, a soil continuum came into being some time after the cold spell during the Permian.
IMPACTS OF GEOCHEMICAL AND BIOCHEMICAL CARBON CYCLE A comparison of the magnitudes of the compartments of carbon in the (bio)geochcmical (exchange of C between sediments, atmosphere, biosphere and ocean) and biochemical (organic matter production, respiration, turnover) cycle shows the dominance in pool size of the former, which over geological time pcriods is all decisive with its enormous buffer capacity (Table 1.1). Shortcuts in the biochemical cycle and short-term excessive inputs may produce a flicker, strong enough though for consequences on the GHE, the earth temperature, the prccipitation and the circulation, which may damage or even exterminate species causativc of the disturbance. Thus, in our short historical span we can not rely on the buffcr capacity of the large but slow gcochcmical cycle to neutralize the consequcnces of our mistakes. Table 1.1
Comparison of carbon pool sizes in biochemical and geochemical cycle*
Componcnts CaC03 in sediments CaMg (CO& in sediments Organic sediments (kerogcne) HCOf and C032- dissolved in sea Fossil fuel (coal, gas, oil) Dead soil biomass (humus) C02 in atmosphere Living biomass (plant, animals) * Data slightly modified from Berner and
C-amount in 10'2 t of c 35,000 25,000 15,000
42 5
2 0.72 0.56 Lasaga 1990.
LIFE ON EARTH, A CARBON TRIP Lifc on earth is on a carbon trip. We must get aware of the need for changing course in time to avoid an erratic trip back into chaos, from which evolution made us ascend. Looking at the biochemical carbon cycle (Fig.1.4). about 115 to 120 x l O I 5 g of C are turned over annually in the terrestrial ecosystems by photosynthesis and inversely by respiration through the bio- and pedosphere. Worrysome is the surplus due to respiration of ca 1.5 x lOI5 g of C from annual land clearing (slash and bum) as well as the 5.5 x l O I 5 g of C from
9
Historical overview of the greenhouse effecr
combustion of fossil fuel, which are adding up at a ca 50% rate to the 720 x 10'5 g of C in the atmospheric carbon pool. However, recent results of Esser (1990) suggest that the C-sink due to C02 fertilization is already overcompenzating the C02 source from forest clearing (ca. 1.5 Gt C y - l from 10 to 15 mil. ha of clearing a year). Principally, carbon oxidation products, C02 and CH4, although being greenhouse active trace gases, are minor in importance compared with water vapor (1:5) in generating the temperature rising greenhouse effect of 33"C, lifting the surface temperature from -18°C to +15"C. According to Ramanathan (1989) as well as Raval and Ramanathan (1989), the total natural 33°C greenhouse effect generated by water vapor plus C02 equals 155 Wm-2 (ca 145 W at clear sky, 180 W at cloudy sky). Doubling of the C 0 2 concentration would add ca 4 Wm-2 only; human activities so far have enhanced the GHE of the atmosphere by ca 1.5 % only.
CARBON CYCLE
l
120
I
A
n 2'
B'OSPHERE + PEDOSPHERE
i...ca.?3P..!!.!v!na.! .......
$.
C6 2000 (dead)
ca 100
ca 60
01
,
5"
DEPOSITS 5000 i ......COAL, . ...........OIL, .........GAS ............................................ SEDIMENTS/LITHOSPHERE 66 000 000 o,2 from l o r e s t a n d sol1 d e g r a d a t i o n
ca 100
OCEAN SURFACE WATER c a 700 ................................................................... DEEPER OCEAN WATER c a 37000
l r o m c o a l , 011.
gas combusllon
a m o u n t s ~n G I ( I O " ~ ) , f l u x e s i n G I I ~
Fig. 1.4
Carbon compartments in biochemical and geochemical cycle
But the increments of C02, CH4, as well as the other radiatively active trace gases, such as the CFCs, N20 and tropospheric ozone, are wholly or to greatest extent the product of anthropogenic activities. Human civilization was in its earlier phases sustained by the direct products of photosynthetic C reduction and
10
H.W. Schorpenseel and P.Becker-Heidmann
photolysis of water (Calvin 1962). Since beginning craftsmanship and industrialization it progressively built up a dependency on minable and consumable forms of organic matter, produced mainly throughout the last 350 million years, such as coal, kerogene/petrol and methane. While the first scientists, expressing the vision of an expanding greenhouse effect with temperature and in consequence an eustatic sea level rise (Arrhenius 1896; Callendar 1938; Flohn 1941, cited in Lausch 1989) found little attention or enthusiastic response, at present an almost overheated scientific climate and preferably apocalyptic predictions thtcaten to misinterpret the real facts, needs and situative, curative potentials. We also should not ignore the main trend of decreasing C02 concentration over most of the geochemical and biochemical evolutionary phases of the past, with at least five times the present level still during Tertiary times and about 200 ppm after fluctuations during glacial and interglacial periods at the end of last Wisconsin-, Wurmian-, Weichselian glacial. Since even the present 350 ppm are at the lower end of the plant physiologically suitable C02 range, could there have been an acute C02 deficiency developing, and the C02 rise since begin of industrialization in reality being beneficial in our endeavour to increase food production for the growing world population ? The temperature rise of 0.7"C since 1860 and a sea level rise of about 17 cm are acknowledged by most climate research units, but a highly rated group of scientists from the G.C. Marshall Institute in Washington, D.C. draws attention to a better correlation between the observed trend in temperature and the solar activity/sun spot activity than the more commonly considered increasing C02 concentration (ref. Economist Vol. 313, No. 7633, 1989). R.S. Lindzen from M.I.T. Boston a.0. reported to be expecting nominal temperature increases only. Other critical observations focus in many different ways on the overestimation of the C02 concentration change and neglect of the importance of changes in atmospheric moisture level, which, as mentioned before, is undisputed the major promoter of the basic greenhouse effect. While the determination to reduce the release of the other greenhouse active trace gases, such as CH4, N 2 0 , CFCs, tropospheric ozone (see overview in Table 1.2) is apparently worldwide accepted, a production oriented pedologist/plant nutritionist can argue, whether the rise of C02, which is expected to enhance especially C3 photosynthetic efficiency and to improve the water economy of plants due to closing of stornatal aperture with increasing C02 concentration, which even under rising temperature and water evaporation may also conserve precious water (Schleser and Kirstein 1990), would be really all that bad. Fig. 1.5 shows the wide range of C02 concentration versus light intensity capable of increasing photosynthetic efficiency. The relative effect of increasing C02 on the major cultivated plants as well as the most obnoxious weeds requires thorough attention.
11
Historical overview of the greenhouse effect
Table 1.2
Greenhouse active and other (polluting)trace gases, basic pool sizes
Trace gases
% share of antrogenic
GHE
co2
50 19 17 8 6 Residence time Concentration 100 y 350 ppm
co
1 - 6 months
CH4 CFCs (ClOx -radicals)
10 Y 50 - 150 y
100-150ppb N 40-80 ppb S (N, S. hemisphere) 1.7 ppm 0.2 - 0.3 ppb
170 y few days only
0.31 ppm 0 - 100 ppb
co2 CH4 CFCs 0 3 (tropospheric) N20
Components
N20
NOx (NO, NO21 0 3 (stratospheric) 0 3 (tropospheric)
OH (atmospheric)
so2
Atmospheric C-pool Photosynthesis (terrestr.) Soil organic matter pool Ocean C-cycle flux
Fossil fuel C
few seconds only
10 ppm (35 km) 0.02 ppm (0.1 ppm max.) < O.oooO1 ppb
GHE-rising potential of trace gases rel. to c02 1 32 14 - 17,000 2000 150 Increase per year (1800->280, 1950>310); ca. 0.5% variable 1.1 % (18 ppb) 5% 4% 0.3 % (ca 1 ppb) 0.2 - 0.3 % (stratospheric)
0.5 %
50 ppb (max.) 740 bil t 115 bil t (ca 1/2 respired, ca. 1/2 Wmpo@ 1.8 x 10l2 t
38.5 x 10l2 t (3x 109tpery precipitated as carbonate) 5 - 10 x 1012 t
The vegetation belt, which may be particularly affected by increasing heat and drought, the inigation-dependent and responsive sub-tropics, may hopehlly
12
H.W. Scharpemeel and P . Becker-Heidmann
replenish water deficits by stepped up sea water distillation, which may become technically feasible in nearer future. Besides, the leading Russian climatologist from Leningrad, M.I. Budyko (ref. Spiegel 1990) expects even for the (semi)arid tropics more rainfall and a vegetation cover similar to that of the Pliocene. Increase of temperature and precipitation in the boreal belt could bear grave consequences due to enhancement of organic matter decomposition and consequent COs release, but may also hold unforeseeable opportunities to increase agricultural production in vast areas of so far low productive boreal lands, which may even become important carbon sinks (see for more details Chapters 16 and 17). The catalogue of pros and contras of effects of climate change is certain to expand. Net photosynthetic rate for different light intensities and C 0 2 concentrations Rp (mg C O P / q m
I Fig. 1.5
I
s)
I light Intens.. Rp net photosynth. r a t e
Influence of light intensity and CO;, on photosynthesis. (modified from Mengel and Kirkby 1979,acc. to Warren-Wilson 1969)
We should be critically alert towards the climate change syndrome, but as critically open to the more constructive and may be even optimistic arguments before destroying productive structures without having replacements in panic, through poorly conceived legal actions as well as preventive or curative measures, . The most important reaction, though, should be to prepare t k follow-up phase of a mixed hydrogen plus carbon trip. In geological times the geochemical cycle is absolutely dominating and decisive for CO2 concentration and its influence on temperature. However, the anthropogenic shortcut of the
H k l o r i c a l overview of the greenhouse effect
13
biochemical cycle that we practice with wasteful consumption of fossil fuel reserves, with rising population and living standards, may suffer under t k unsentimental regime of natural processes, such as temperature and sea-level rise, to destroy our species and civilization (only a fast forgotten flicker in earth history), We must therefore concentrate all our efforts on the development of the photovoltaic hydrogen technology for replacement of C-based fossil fuels, as well as on the methodology for use of sun energy in desalination of sea and brackish ground water to stabilize life and productivity in the (semi)arid lands.
REFERENCES Asimov, 1. (1984). Asimov’s new guide to science. Basic Books Publ., New York. Aylmore, L.A.G. and J.P. Quirk (1960). Domain or turbostratic structure of clays. Nature 187. 1046- 1048. Berner, R.A. and A.J. Lasaga (1990). Simulation des geochemischen Kreislaufs. Spektrum der Wissenschaft 5, 56. Bitterli, P. (1963). Aspects of the genesis of bituminous rock sequences. Geol. Mijnbouw. 42, 183-201. Bordovskij, O.K. (1965). Accumulation and transformation of organic substances in marine sediments. Marine Geology 3, 3-1 14. Calvin, M. and J.A. Bassham (1962). The photosynthesis of carbon compounds, W.A. Benjamin Inc., New York. Degens, E.T. (1967). Diagenesis of organic matter. In: Diagenesis in sediments, Larsen, G. and G.V. Chilingar, Eds., Elsevier, Amsterdam, chap. 7. Dudal, R. (1990). Global Soil Change, report of an IIASA-ISSS-UNEP Task Force Meet. on the Role of Soil Global Change, Chap. 3 (in print). Esser, G. (1990). Modeling global terrestrial sources and sinks of COz with special reference to soil organic matter. In: Soils and the greenhouse effect, A.F. Bouwman (Ed.) (1990). John Wiley and Sons, Chichester. Fond der Chemischen Industrie, Umweltbereich Luft (1987). Vol 22, p. 15. Haber. H. (1965. 1971). Die Entwicklungsgeschichte der Erde, Deutsche Verlags Anstalt, Stuttgart, p. 79, p. 208. Lausch, E. (1989). Treibhaus Erde. CEO (Gruner u. Jahr, Hamburg) 37,46-49. Mengel, K. and E.A. Kirkby (1979). Principles of Plant Nutrition. Int. Potash Institute, Bern, Switzerland, 233. Murphy, M, B. Nagy, G. Rouser, and G. Kritchevsky (1965). Analysis of sulphur compounds in lipid extracts from the Orguiel meteorite. J. A. Oil Chem. Soc. 43, 189.196. Ramanathan, V. (1989). Spurengase, Treibhauseffekt und weltweite Erwrmung, In: Das Ende des blauen Planeten ? Crutzen and Muller (Eds) Beck, Federal Republic of Germany, 6576. Rankama, K. (1948). New evidence of the origin of pre Cambrian carbon. Bull. Geol. Soc. Am. 59, 389-416. Raval. A. and V. Ramanathan (1989). Observational determination of the greenhouse effect. Nature 342, 758-761. Schilder, F.A. (1956). Lehrbuch der Allgemeinen Zoogeographie, Jena, German Democratic Republic. Schleser, G. and W. Kirstein (1989). Der Treibhauseffekt. Ursachen und Konsequenzen fur
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H.W. Scharpenseel and P . Becker-Heidmonn
Klima und Biosphre. Seminar Technik und Gesellschaft, KFA Jlich, Federal Republic of Germany (preprint). Spiegel (1990). M.I. Budyko - Interview. Der Spiegel, Hamburg, 1, 143. Theng, B.K.G. (1979). Formation and Properties of Clay Polymer Complexes, part 3, Chap. 12, 283-314. Theng. B.K.G. and H.W. Scharpenseel (1975). The adsorption of 14-C labelled humic acid by montmorillonite. Proc. Internatl. Clay Conf., Mexico City, 643-653. Valeton, I. (1983). Klimaperioden, lateritische Verwitterung und ihr Abbild in den synchronen Sedimentationsrumen. Z. Dtsche Geol. Ges. 134, 2. Warren-Wilson, I. (1969) Maximum yield potential. In: Transition from extensive to intensive agriculture with fertilizers, Proc. 7th Coll. Intern. Potash Institute, Bern, Switzerland, 34-56. Welte, D.H. (1969) Organic matter in sediments. In: Organic Chemistry, Springer, Berlin, 262-264. Wunderlich, H.G. (1968). Einfhrung in dic Geologie, Vol. 1, Exogene Dynamik. Bibliographisches Institut, Mannheim. Federal Republic of Germany. Wurmbach, U. (1971). Zoologie. Vol. 2, G. Fischer Verlag, Stuttgart.