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Observed Increase in the Pollutants

Since the dawn of the industrial era, several trace gases have been increasing in the atmosphere. Recent advances in chemical measurements have helped document the rate of increase of the trace gas concentrations. The concentrations continue to increase at significant rates as shown in Figure 16.1 for carbon dioxide (C02), methane (CH4),

Testimony given in hearings before the Committee on Energy and Natural Resources, U.S. Senate, One-hundredth Congress, first session, on the Greenhouse Effect and Global Climate Change, 9-10 November 1987. This testimony is based largely on "Climate— Chemical Interactions and Effects of Changing Atmospheric Trace Gases," by V. Ramanathan, L. Callis, R. Cess, J. Hansen, I. Isaksen, W. Kuhn, A. Lacis, F Luther, J. Mahlman, R. Reck, and M. Schlesinger.

Figure 16.1

Observed TVace Gas Increases Over a Decade: 1975-1985

Figure 16.1

Observed TVace Gas Increases Over a Decade: 1975-1985

C02 CH4 N20 CCU CF2C12 CFCla CH3CCI3

Natural Gases Synthetic Gases

C02 CH4 N20 CCU CF2C12 CFCla CH3CCI3

Natural Gases Synthetic Gases

Observed trace gas increases over a decade from 1975 to 1985. C02 data are taken from Bolin et al., 1987, and all others are taken from Rasmussen and Khalil, 1986.

nitrous oxide (N20), carbon tetrachloride (CC14), chlorofluorocarbons (CFC), CFC-11 and CFC-12, and methyl chloroform (CH3CC13). The industrial sources for these gases as well as several others that have been detected in the atmosphere are given in Figure 16.2. Studies of the chemical balance of the land-ocean-atmosphere system provide compelling arguments for attributing the observed increases to human activities such as: fossil fuel consumption, deforestation, refrigerants, propellants, and numerous others.

Scientific concern for the climatic effects of an increase in the atmosphere concentration of C02 dates back to the nineteenth century. It is only within the last decade that we have become aware that human activities are causing an increase in the atmospheric concentrations of not only C02 but several other trace gases as well.

The Greenhouse Effect

The gases shown in Figure 16.1 trap the infrared (IR) radiation, also known as heat radiation, emitted by the surface of the earth which would have otherwise escaped to space. It is this trapping of the IR

radiation which is referred to as the greenhouse effect, particularly since the gases let the solar radiation (visible light) penetrate to the surface. The synthetic trace gases are significantly more effective than others in enhancing the greenhouse effect. For example, adding one molecule of CFC-11 and CFC-12 to the atmosphere can have the same radiative effect as adding 10,000 molecules of C02.

A Vigorous Climate

An increase in the concentration of the greenhouse gases leads to increased trapping of IR radiation and thus causes an excess of radiative energy available to drive the climate system. This excess energy will alter global and regional climate patterns since radiative energy (solar and IR) is the fundamental energy source for climate and the winds in the atmosphere and the oceans. The result, according to the theory, is a vigorous climate system. For example, the excess radiative energy will warm the oceans. The warmer oceans will evaporate more moisture. The excess moisture in the atmosphere will increase global rainfall. Hence, a greenhouse-rich atmosphere will be warmer, more humid, and wetter. However, because of nonlinear interactions between radiative heating and atmospheric circulation, the warming and rainfall changes will not be uniform, but will vary significantly with latitude, region, and season. In essence, shifts in the climate patterns should be anticipated.

Predicted Climate Changes

• The decadal increase in the greenhouse forcing from the decade of 1850 to that of 1980 as well as from the projected increases are shown in Figure 16.3. The rate of decadal increase of the total radiative heating of the planet is now about five times greater than the mean rate for the early part of this century. Non-C02 trace gases in the atmosphere are now adding to the greenhouse effect by an amount comparable to the effect of C02 increase.

• The cumulative increase in the greenhouse forcing until 1985 has committed the planet to an equilibrium warming of about 1 to 2.5°C. The 2.5°C is based on the sensitivity of three-dimensional climate models.

Figure 16.2

Greenhouse Gases: Dominant Sources and Sinks, Average Atmospheric Residence Time, 1980 Global Average Mixing Ratio, and Probable Concentration Range for the

Year 2030

Year 1980

Year 2030 Probable

Estimated

Global

Global Average

Average

Average

Concentration,

Residence

Mixing

ppb

Chemical

Chemical

Dominant

Dominant

Time,

Ratio,

Probable

Possible

Group

Formula

Source*

Sink*

years

ppbt

Value

Range

Remarks§

Carbon dioxide

C02

N, A

0

2

339 x 103

450 x 103

Based on a 2.4% per year increase in anthro

pogenic C02 release rates over the next 50 years.

Nitrogen

N,0

N, A

S(UV)

120

300

375

350-450

Combustion and fertilizer sources.

compounds

nh3

N, A

T

0.01

<1

<1

Concentration variable and poorly characterized.

(NO + N02)

N, A

T(OH)

0.001

0.05

0.05

0.05-0.1

Concentration variable and poorly characterized.

Sulfur

cso

N, A

T(0, OH)?

1(?)

0.52

0.52

Sources and sinks largely unknown.

compounds

CS2

N, A

T

K?)

<0.005

<0.005

Sources uncharacterized.

so2

A(?)

T(OH)

0.001

0.1

0.1

0.1-0.2

Given the short lifetime, the global presence of

S02 is unexplained.

h2s

N

T(OH)

0.001

<0.05

<0.05

Fully

CF4(F14)

A

1

>500

0.07

0.24

0.2-0.31

Aluminum industry a major source.

fluorinated

empile)

A

1

>500

0.004

0.02

0.01-0.04

Aluminum industry a major source.

species

sf6

A

1

>500

0.001

0.003

0.002-0.05

Chlorofluoro-

CC1F3(F13)

A

S(UV), 1

400

0.007

0.06

0.04-0.1

All chlorofluorocarbons are of exclusive man-

carbons

CC12F2(F12)

A

S(UV)

110

0.28

1.8

0.9-3.5

made origin. A number of regulatory actions are

CHC1F2(F22)

A

T(OH)

20

0.06

0.9

0.4-1.9

pending. The nature of regulations and their

CC13F(F11)

A

S(UV)

65

0.18

1.1

0.5-2.0

effectiveness would greatly affect the growth of

CF,CF2C1(F115)

A

S(UV)

380

0.005

0.04

0.02-0.1

these chemicals over the next 50 years.

CC1F2CC1F2(F114)

A

S(UV)

180

0.015

0.14

0.06-0.3

CC12FCC1F2(F113)

A

S(UV)

90

0.025

0.17

0.08-0.3

Chlorocarbons

CH,CI

N(O)

T(OH)

1.5

0.6

0.6

0.6-0.7

Dominant natural chlorine carrier of oceanic ori

CH2CI2

A

T(OH)

0.6

0.03

A popular reactive but nontoxic solvent.

CHC1,

A

T(OH)

0.6

0.01

0.03

0.02-0.1

Used for manufacture of F22; many secondary

sources also exist.

CC14

A

S(UV)

25-50

0.13

0.3

0.2-0.4

Used in manufacture of fluorocarbons; many

other applications as well.

CH,C1CH2C1

A

T(OH)

0.4

0.03

0.1

0.06-0.3

A major chemical intermediate (global produc

tion = 10 Tg/yr); possibly toxic.

CH3CC13

A

T(OH)

8.0

0.14

1.5

0.7-3.7

Nontoxic, largely uncontrolled degreasing sol

C2HC13

A

T(OH)

0.02

0.005

0.01

Possibly toxic, declining markets because of sub

stitution to CH3CC13.

C2C14

A

T(OH)

0.5

0.3

0.07

0.03-0.2

Possibly toxic, moderate growth owing to substi

tution to CH3CC13.

Brominated

CH,Br

N

T(OH)

1.7

0.01

0.01

0.01-0.02

Major natural bromine carrier.

and iodated

CBrF3(F13Bl)

A

S(UV)

110

0.001

0.005

0.003-0.01

Fire extinguisher.

species

CH2BrCH2Br

A

T(OH)

0.4

0.002

0.002

0.001-0.01

Major gasoline additive for lead scavenging; also

a fumigant.

CH2i

N

T(UV)

0.02

0.002

0.002

Exclusively of oceanic origin.

Hydrocarbons,

CO, and H2

ch4

N

T(OH)

5-10

1650

2340

1850-3300

A trend showing increase over the last 2 years has

been identified.

c2 h6

N

T(oh)

0.3

0.8

0.8

0.8-1.2

Predominantly of auto exhaust origin.

c2h2

A

T(oh)

0.3

0.06

0.1

0.06-0.16

No trend has been identified to date.

c3h8

N

T(OH)

0.03

0.05

0.05

0.05-0.1

No trend has been identified to date.

CO

N, A

T(OH)

0.3

90

115

90-160

No trend has been identified to date.

h2

N, A

T(SL, OH)

2

560

760

560-1140

Ozone

o3

N

T(UV,

0.1-0.3

F(Z)

12.5%

A small trend appears to exist, but data are insuf

(Tropospheric)

SL, O)

ficient.

Aldehydes

HCHO

N

T(OH, UV) 0.001

0.2

0.2

Secondary products of hydrocarbon oxidation.

CH3CHO

N

T(OH, UV) 0.001

0.02

0.02

1980 concentration estimated from theory.

*N: natural; A: anthropogenic; O: oceanic; S: stratosphere; UV: ultraviolet photolysis; T: troposphere; OH: hydroxyl radical removal; I: ionospheric and extreme UV and electron capture removal; and SL; soil sink.

tThese concentrations are integrated averages; for chemicals with lifetimes of 10 years or less, significant latitudinal gradients can be expected in the troposphere; for chemicals with extremely short lifetimes (0.001-0.3 years), vertical gradients may also be encountered. $These values are not used in the present assessment. §Also see text for details.

*N: natural; A: anthropogenic; O: oceanic; S: stratosphere; UV: ultraviolet photolysis; T: troposphere; OH: hydroxyl radical removal; I: ionospheric and extreme UV and electron capture removal; and SL; soil sink.

tThese concentrations are integrated averages; for chemicals with lifetimes of 10 years or less, significant latitudinal gradients can be expected in the troposphere; for chemicals with extremely short lifetimes (0.001-0.3 years), vertical gradients may also be encountered. $These values are not used in the present assessment. §Also see text for details.

(Source: Ramanathan et al., 1985.)

Figure 16.3

0.20

0.16

0.12

0.04

Decadal Increments of Greenhouse Forcing

CFCs str. h20

CFCs str. h20

CFCs str. h20

n2o

CFCs str. h20

c03

V

12.8

Fl2

ppm

ch4

n2o

l 1

15.6 ppm

f

Fl2

n2o

ch4

1850-1960 (per decade)

1960s

1970s

1980s

Decadal Increments of Greenhouse Forcing (1990-2030)

CFCs str.

CFCs str. ho i

CFCs: str.

17.7 ppm n2o ch, co3

20.6 ppm

1990s

2000s

2010s

2020s

Decadal additions (see Editor's Note below)to global mean greenhouse forcing of the climate system. The (ATS)0 is the computed temperature change at equilibrium (t for the estimated decadal increases in trace gas abundances, with no climate feedbacks included. Formulas for (ATs) as a function of the trace gas abundances are given by Lacis et al„ 1981. (a) Past additions. Except for 03 and stratospheric H20, the estimated trace gas increases are based on measurements, as discussed in the text. (b) Future additions.

Editor's Note: This Figure depicts the greenhouse forcing (in degrees C) due to the additions of greenhouse gases per decade. The expected increases in average global surface temperatures are greater than the climate forcing because of feedbacks, primarily increases in atmospheric water vapor associated with warming. As Ramanathan notes in his text, the 1980s greenhouse forcing of about 0.08°C from C02, and an equal amount from the other greenhouse gases, leads to an increase in average global temperature of between 0.2 and 0.5°C per decade.

• At the current observed rate of increase in the trace gases, the greenhouse warming of the globe increases by 0.2 to 0.5°C per decade. Hence, if emission of pollutants by human activities continues unabated, the predicted warming can exceed several degrees °C by the middle of the next century.

• The earth as a whole will be more humid and wetter.

• The warming will be amplified significantly in the polar regions due to melting of sea ice and snow cover.

• Because of feedbacks involving the radiation, water cycle, clouds, atmospheric winds, sea ice, and oceans, shifts in climate patterns can be anticipated.

Out-of-Equilibrium Climate and Timing of the Warming

The most important effect of the increase in the trapping of the IR radiation energy by the trace gases is to drive the climate system out of equilibrium with the incoming solar energy. Consequently, the world oceans, the distribution of sea ice, the clouds, the biosphere, and the land are all driven out of equilibrium with respect to the energy fluxes maintaining their present state.

The climate system cannot restore the equilibrium instantaneously, and hence the surface warming and other changes will lag behind the trace gas increase. Current models indicate that this lag will range between several decades to a century. However, analyses of temperature records of the last 100 years as well as proxy records of the paleoclimate changes indicate that climate changes can also occur abruptly instead of a gradual return to equilibrium as estimated by models. The timing of the warming is one of the most uncertain aspects of the theory.

Climate Extremes

Surface warming as large as that predicted by the models for the next century would be unprecedented because the present climate is just coming out of the peak of an interglacial. The earth's climate oscillates between glacial (ice age) and interglacial periods with a temperature variation of about 5°C. The last great ice age peaked between 14,000 to 22,000 years ago and warmed to an interglacial with the peak occurring around 5,000 years ago. Hence, a human-induced global warming of

5°C during an interglacial period would be beyond the range of extreme climates that have occurred during, at least, the last million years.

Major Uncertainties in the Predictions

The timing of the warming is one of the major uncertainties. Next is the role of climate feedbacks that govern the magnitude of the warming. One of the least understood is how clouds will respond to the climate change and how these changes, in turn, will influence the climate. The cloud feedback question arises because clouds are very powerful regulators of the radiative heating of the planet. The next potentially important feedback is the feedback between vegetation and climate. This feedback arises because the greenhouse effect significantly perturbs the cycling of water between the oceans, the atmosphere, and the continents.

Connections with the Ozone Problem

Roughly 85% of the ozone resides between 12 and 50 km, the region referred to as the stratosphere. The stratospheric ozone absorbs UV radiation from the sun, and hence regulates solar energy reaching the ground. Thus a decrease in stratospheric ozone allows more solar energy to penetrate to the ground, which would warm the surface. At the same time, ozone is a greenhouse gas, and hence a decrease in ozone would decrease the IR warming. The net climate effect of ozone changes in the stratosphere will depend on where in the atmosphere the ozone is destroyed. In addition, a decrease in stratospheric ozone would cause a severe cooling of the stratosphere and alter the stratospheric winds. The potentially strong destabilizing effect of a severe stratospheric cooling, occurring in conjunction with a lower atmosphere warming by the greenhouse gases, has not been factored into any current model studies.

Furthermore, tropospheric ozone is an important greenhouse gas. Changes in methane, carbon monoxide, and nitrogen oxides, through chemical reactions, can lead to an increase in tropospheric ozone which can cause an additional warming. The above examples are some of the emerging issues that increasingly suggest a strong coupling between the greenhouse and the ozone problems.

References for Figures

B. Bolin, B. R. Döös, J. Jaeger, and R. A. Warrick (eds.), The Greenhouse Effect, Climate Change and Ecosystems: A Synthesis of the Present Knowledge. Wiley, Chichester, In press. R. A. Rasmussen and M.A.K. Khalil, 1986, Science, 232, 1623-1624. A. Lacis et al„ 1981, Geophys. Res. Lett., 8, 1035-1038. V. Ramanathan et al„ 1985, Geophys. Res., 90, 5547-5566.

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Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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