|
ATMOSPHERIC CARBON DIOXIDE
<br />The concentration of C02 in Earth's atmosphere has increased
<br />during the past century, as shown in Figure 17. The magnitude of
<br />this atmospheric increase is currently about 4 gigatons (Gt C) of car-
<br />bon per year. Total human industrial COz production, primarily from
<br />use of coal, oil, and natural gas and the production of cement, is cur-
<br />rently about 8 Gt C per year (7,56,57). Humans also exhale about 0.6
<br />Gt C per year, which has been sequestered by plants from atmo-
<br />spheric C02.Office air concentrations often exceed 1,000 ppm C02.
<br />To put these figures in perspective, it is estimated that the atmo-
<br />sphere contains 780 Gt C; the surface ocean contains 1,000 Gt C;
<br />vegetation, soils, and detritus contain 2,000 Gt C; and the intermedi-
<br />ate and deep oceans contain 38,000 Gt C, as C02 or C02 hydration
<br />products. Each year, the surface ocean and atmosphere exchange an
<br />estimated 90 Gt C; vegetation and the atmosphere, 100 Gt C; marine
<br />biota and the surface ocean, 50 Gt C; and the surface ocean and the
<br />intermediate and deep oceans, 40 Gt C (56,57).
<br />So great are the magnitudes of these reservoirs, the rates of ex-
<br />change between them, and the uncertainties of these estimated num-
<br />bers that the sources of the recent rise in atmospheric C02 have not
<br />been determined with certainty (58,59). Atmospheric concentrations
<br />of C02 are reported to have varied widely over geological time, with
<br />peaks, according to some estimates, some 20-fold higher than at
<br />present and lows at approximately 200 ppm (60-62).
<br />Ice-core records are reported to show seven extended periods dur-
<br />ing 650,000 years in which COz, methane (CHq), and temperature
<br />increased and then decreased (63-65). Ice-core records contain sub-
<br />stantial uncertainties (58), so these correlations are imprecise.
<br />In all seven glacial and interglacial cycles, the reported changes in
<br />C02 and CHq lagged the temperature changes and could not, there-
<br />fore, have caused them (66). These fluctuations probably involved
<br />temperature-caused changes in oceanic and terrestrial COZ and CH4
<br />content. More recent C02 fluctuations also lag temperature (67,68).
<br />In 1957, Revelle and Seuss (69) estimated that tempera-
<br />ture-caused out-gassing of ocean C02 would increase atmospheric
<br /> 4U
<br />a
<br /> 0~
<br />~
<br />' ~s
<br />a ~ ~
<br />O
<br />
<br />U
<br />
<br />0
<br />M
<br />~.
<br />..
<br />U a
<br />a6
<br />~
<br />4
<br />2
<br />8
<br />F ®
<br />Measured Estlmahd Meswred Aataretk Global
<br />la by ReveNe in
<br />Ice Cores In 1957 Sea Water
<br />Figure 16: Temperature rise versus COZ rise from seven ice-core measured
<br />interglacial periods (63-65); from calculations (69) and measurements (70)
<br />of sea water out-gassing; and as measured during the 20th and 21st centuries
<br />(10,72). The interglacial temperature increases caused the COz rises through
<br />release of ocean CO2. The COZ rises did not cause the temperature rises.
<br />In addition to the agreement between the out-gassing estimates and mea-
<br />surements, this conclusion is also verified by the small temperature rise dur-
<br />ing the 20th and 21st centuries. If the COZ versus temperature correlation
<br />during the seven interglacials had been caused by COz greenhouse wamvn
<br />then the temperature rise per COZ rise would have been as high during the
<br />20th and 21st centuries as it was during the seven interglacial periods.
<br />Antarctk Ice Core Temperature
<br />meow 3oaese Ia,80!
<br />Reported Ice Core Abe (Years Before Present)
<br /> C02 Rise During Seven Interglacials Was
<br /> Ocean Out-gassing Caused by Tempernture Rise
<br />During Seven Ocean
<br />Interglacials Out-gassing
<br />
<br />During 20tb
<br />and 2
<br />1s
<br />t Centuries
<br />.
<br />/
<br />i
<br />
<br />a
<br />a
<br />C
<br />>~
<br />u
<br />u
<br />0
<br />U
<br />O
<br />U
<br />u
<br />a
<br />a
<br />0
<br />s
<br />leo
<br />3b'/. Increase 22•/. tncresse
<br />1
<br />Atmospherk Carbon Dioxide
<br />r~
<br />Gas
<br />World Hydrocarbon Used ~ 14
<br />Coal 1~
<br />19SY 199® 1959 2998
<br />Year
<br />a
<br />a
<br />U
<br />0
<br />F
<br />as
<br />
<br />Figure 17: Atmospheric COZ wncenhations in parts per million by volume,
<br />ppm, measured spectrophotometrically at Mauna Loa, Hawaii, between
<br />1958 and 2007. These measurements agree well with those at other locations
<br />(71). Data before 1958 are from ice cores and chemical analyses, which have
<br />substantial experimental uncertainties. We have used 295 ppm for the period
<br />1880 to 1890, which is an average of the available estimates. About 0.6 Gt C
<br />of COZ is produced annually by human respiration and often leads to con-
<br />centrations exceeding 1,000 ppm in public buildings. Atmospheric COZ has
<br />increased 22% since 1958 and about 30% since 1880.
<br />C02 by about 7% per °C temperature rise. The reported change dur-
<br />ing the seven interglacials of the 650,000-year ice core record is
<br />about 5% per °C (63), which agrees with the out-gassing calculation.
<br />Between 1900 and 2006, Antarctic COz increased 30% per 0.1 °C
<br />temperature change (72), and world COz increased 30% per 0.5 °C.
<br />In addition to ocean out-gassing, C02 from human use of hydrocar-
<br />bons is a new source. Neither this new source nor the older natural
<br />C02 sources are causing atmospheric temperature to change.
<br />The hypothesis that the C02 rise during the interglacials caused
<br />the temperature to rise requires an increase of about 6 °C per 30%
<br />rise in COz as seen in the ice core record. If this hypothesis were cor-
<br />rect, Earth temperatures would have risen about 6 °C between 1900
<br />and 2006, rather than the rise of between 0.1 °C and 0.5 °C, which
<br />actually occurred. This difference is illustrated in Figure 16.
<br />The 650,000-year ice-core record does not, therefore, agree with
<br />the hypothesis of "human-caused global warming," and, in fact, pro-
<br />vides empirical evidence that invalidates this hypothesis.
<br />Carbon dioxide has a very short residence time in the atmosphere.
<br />Beginning with the 7 to 10-year half-time of C02 in the atmosphere
<br />estimated by Revelle and Seuss (69), there were 36 estimates of the
<br />atmospheric COZ half-time based upon experimental measurements
<br />published between 1957 and 1992 (59). These range between 2 and
<br />25 years, with a mean of 7.5, a median of 7.6, and an upper range
<br />average of about 10. Of the 36 values, 33 are 10 years or less.
<br />Many of these estimates are from the decrease in atmospheric
<br />carbon 14 after cessation of atmospheric nuclear weapons testing,
<br />which provides a reliable half-time. There is no experimental evi-
<br />dence to support computer model estimates (73) of a COz atmo-
<br />spheric "lifetime" of 300 years or more.
<br />Human production of 8 Gt C per year of COZ is negligible as
<br />compared with the 40,000 Gt C residing in the oceans and biosphere.
<br />At ultimate equilibrium, human-produced C02 will have an
<br />insignificant effect on the amounts in the various reservoirs. The
<br />rates of approach to equilibrium are, however, slow enough that hu-
<br />man use creates a transient atmospheric increase.
<br />In any case, the sources and amounts of C02 in the atmosphere
<br />are of secondary importance to the hypothesis of "human-caused
<br />global warming." It is human burning of coal, oil, and natural gas
<br />that is at issue. COZ is merely an intermediate in a hypothetical
<br />mechanism by which this "human-caused global warming" is said to
<br />take place. The amount of atmospheric C02 does have profound en-
<br />vironmental effects on plant and animal populations (74) and diver-
<br />sity, as is discussed below.
<br />-6-
<br />
|