Changing Climate Report of the Carbon Dioxide Assessment Committee (1983) / Chapter Skim
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DETECTION AND MONITORING OF CO2-INDUCED CLIMATE CHANGES
DETECTION AND MONITORING OF CO2-INDUCED CLIMATE CHANGES
Pages 292-382
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From page 292... ...
To the extent that one can judge from scanty data, southern hemisphere temperatures have increased more steadily by about the same amount. ^n view of the relatively large and inadequately explained fluctuations over the last century, we do not believe that the overall pattern of variations in hemispheric or global mean temperature or associated changes in other climatic variables yet confirms the occurrence of temperature changes attributable to increasing atmospheric CO?
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From page 293... ...
The quantitative reliability of these inferences is unknown. Despite these difficulties, a number of investigators, employing various combinations of data and methodology, have related the global or hemispheric mean temperature record with indices of turbidity and solar radiance and with estimates of the effect of increasing CO2.
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From page 294... ...
Given the inertia created by the ocean thermal capacity and the level of natural fluctuations, we expect that achieving statistical confirmation of the C02-induced contribution to global temperature changes so as to narrow substantially the range of acceptable model estimates may require an extended period. Improvements in climatic monitoring and modeling and in our historic data bases for changes in CO2, solar radiance, atmospheric turbidity, and other factors may, however, make it possible to account for climatic effects with less uncertainty and thus to detect a CO2 signal at an earlier time and with greater confidence.
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From page 295... ...
Can we make the required measurements? Initial application of these criteria leads to the list of recommended variables for monitoring given below: Priority First Second Monitoring Causal Factors by Measuring Changes in C02 concentrations Volcanic aerosols Solar radiance "Greenhouse" gases other than CO2 Stratospheric and tropospheric ozone Monitoring Climatic Effects by Measuring Changes in Troposphere/surface temperatures (including sea temperatures)
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From page 296... ...
Collection of the desired observations will require a healthy global observing system, of which satellites will be a major component. Satellites can provide or contribute to long-term global measurements of radiative fluxes, planetary albedo, snow/ice extent, ocean and atmospheric temperatures, atmospheric water content, polar ice sheet volume, aerosols, ozone, and trace atmospheric components; a well-designed and stable program of space-based environmental observation is essential if we are to monitor the state of our climate.
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From page 297... ...
. tThe thermal inertia of the oceans, and not delayed crossequatorial transport of CO2, is now believed to be important in delaying the temperature response of the southern hemisphere (Climate Research Board, l979; CO2/Climate Review Panel, l982)
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From page 298... ...
298 3 3 C \ CO 41 to -H to rji 4J 10 rH kl C .H 41 Qi 41 -H rH § § 41 1 -e ki 41 oi a • a 4J o 4J a -U 0 O id U H D kl CO tO C rH 4J 4J X 41 CO rH -H o 41 • a oi to 0 w rg 0 rH 4J Oi-H C Oi • 10 C CO rH O C 41 U CO -H rH tO -H -H -H Techni X
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From page 299... ...
299 II 3 r-4 M (O c 41 k i ia to S3 s 41 CJi oi 3 4J -H -H •H H 10 *
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From page 300... ...
300 North temperate zone Tropical South temperate zone 60° N to 50° S 1880 1900 I 1920 YEAR 1940 1960 Sub-arctic 60°-73° N North temperate zone Tropical South temperate zone 60° N to 50° S 1860 1960 FIGURE 5.l Reconstructions of changes in surface air temperature for different latitude regions by Callendar (l96l) applying (top)
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From page 301... ...
Although present climate model simulations indicate a sensitivity about half that found by Plass, they do project smaller temperature increases in the southern hemisphere (due presumably to ocean inertia and albedo effects) , provide for regions of both increasing and decreasing precipitation, and indicate that there should indeed be a large polar amplification of the CO2-induced global temperature increase.
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From page 302... ...
, the change in global average surface temperature (the most closely scrutinized model result) due to doubled C02 concentration is likely to be between l.5 and 4.5°C, with more physically comprehensive models giving results in the range of 2 to 3.5°C.
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From page 303... ...
. As a result of these limitations, the primary indicator used in diagnostic studies of climate has been the change in surface air temperature during the last hundred years.
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From page 304... ...
While .some investigators have attempted to develop data bases of global and polar temperature change, the most used indicator has been the change in northern hemisphere average surface air temperature. Comparison of the temperature records compiled by several investigators shows that not only has temperature fluctuated but also that the temporal pattern of the temperature anomalies is not uniquely established (Figure 5.3)
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From page 305... ...
Southern latitudes (23.60S-90"S) 1880 1900 1920 1940 YEAR 1960 1980 FIGURE 5.4 Reconstruction of surface-air-temperature anomalies for various latitude bands by Hansen et al.
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From page 306... ...
Their results, however, should be considered as only an initial examination of the SST data in that their averaging techniques for handling gaps in the record raise many questions. An additional complication in using available temperature records to estimate temperature changes induced by increasing CO2 concentrations is that the records do not extend back to before the time that CO2 concentrations began to rise.
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From page 307... ...
To attribute climatic changes to causal factors requires adequate data bases for the changes in each causal factor, as well as for the climate state itself, over a period sufficiently long that changes attributable to the causal factors are comparable with the level of natural variability. Moreover, for carbon dioxide the record is not yet adequate.
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From page 308... ...
) in global mean equilibrium surface temperature between l850 and the period l96l-l980.
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From page 309... ...
Averaging period of volcanic aerosol loading Definitions of major volcanoes and of the number of volcanoes considered Assumptions about size distribution of volcanic particles and of chemical composition of gaseous emissions, leading to ad hoc adjustments Assumptions regarding lifetime and distribution of aerosol due to season, latitude, and height of injection of volcanic dust and gases Circularity caused by estimation of dust loading from observations of subsequent temperature change high northern latitude volcanoes often cited as missing by other investigators -- but strangely not evident in the core record. The recent Smithsonian compilation of volcanoes has also greatly expanded the number of volcanoes considered (Simkin et al., l98l)
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From page 310... ...
10 -l 1 1 1 1 1 1 -- -- r (V) stratospheric loading by volcanic activity Adjusted to northern hemisphere 120-yr average V 4.2x1 (olons 1850 1870 1890 1910 1930 1950 1970 UJ C DC O / Si CC I30 20 10 y o Krakatoa Bandai San, Ritter Island 4 Awu 4 Mont Pelee, Soufriere Santa Maria Shtyubelya Sopka Katmai 1880 1900 0 LU > 1920 YEAR 1940 1960 0 = 1 50 X UJ Q - 100 UJ i 150 200 250 J_ 1890 1910 1930 YEAR 1950 1970 FIGURE 5.6 Estimates of stratospheric aerosol loading by (top)
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From page 311... ...
The apparent inverse relationship occurs because direct radiation measures the clarity of the stratosphere whereas aerosol optical depth measures the lack of clarity. 5.2.2.3 Relating Causal Factors and Climatic Effects Even given precise records of how the climate has varied and the history of the important causal factors, a number of problems arise in attributing appropriate components of the climatic fluctuations of the last l00 years to the various causal factors, the remainder of the fluctuations being assumed to be natural (or, more properly, natural
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From page 312... ...
and Bryson (l980) both indicate that they use the same surface-air-temperature record and similar actinometric measures of stratospheric transmissivity, their different approaches to relating the causal factor to the induced climatic change lead them to very different conclusions about whether there has or has not been a temperature increase attributable to increasing CO2 concentrations.
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From page 313... ...
Such complications as arise in relating volcanic eruptions to the temperature response also arise in attempting to relate other causal factors to temperature change. In some cases, these complications can be resolved by just expanding the models to include omitted, but important, processes and domains or to treat the transient as opposed to the equilibrium response; in other cases, the complications can only be resolved by improving existing data bases (e.g., extending the temperature record back in time)
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From page 315... ...
3l5 ai 5 E k i -a 10 I 41 a 10 n jSljl *
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From page 317... ...
3l7 O 10 4J C to cn Q 10 c k i J3 .H ii iii i • - i i i i § 10 O u rH 0 M C CO 4J O CO OL, + 1+1 rH 0, o1 « <0 C 41 ,2 T1 u S'S 5 •rt W 10 3 U 0 1 -- .
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From page 318... ...
Closer examination of a few of these studies shows more clearly the uncertainties and discrepancies that are involved, although identifying the exact causes of these disagreements is beyond the scope of this report. In comparing the various studies, consideration should be given to how well their choice of causal factors is able to explain the major features of the climate of the last hundred years as indicated by almost all available data sets, including the warmth of the northern hemisphere from l920 to l950 and the relatively steady warming of the southern hemisphere.
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From page 319... ...
They looked in the 50-60° N latitude band where the spatial coverage of the records is quite good and where equilibrium climate models predict that the temperature changes should be largest. Their results were negative (i.e., they found no statistically significant signal emerging from the noise)
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From page 320... ...
the anomaly is slightly less. Although most authors use the northern hemisphere temperature record as a basis for evaluation of the relationship between causal factors and climate changes, Hansen et al.
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From page 321... ...
. Oliver compares his results with the northern hemisphere temperature record and Hansen to the global temperature record.
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From page 322... ...
Although Mitchell (l96l) had found some agreement with the observed temperature record up to l940 if he considered temperature changes due to both C(>2 and time-averaged sunspot number, these factors could not explain the later cooling that was observed.
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From page 323... ...
uses umbral/penumbral ratio as an indicator of solar radiance and compares with global temperature change. (Bottom)
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From page 324... ...
(a) The maximum variation of Hansen et al.'s global temperature record is about 0.5°C, whereas Gilliland's northern hemisphere temperature record has a range of about 0.9°C.
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From page 325... ...
Fitted (Volcano + 1880 1890 1900 1910 1920 1930 1940 1950 YEAR 1960 1970 1980 FIGURE 5.ll Comparison of the observed change in surface air temperature and model predictions of the change in temperature when considering the increase of CO2 concentrations and changing stratospheric aerosol loading.
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From page 326... ...
• • Observations I I 1880 1900 1920 1940 YEAR 1960 1980 FIGURE 5.l2 Comparison of the observed change in surface air temperature and model predictions of the change in temperature when considering the increase of C02 concentrations and changes in solar irradiance and stratospheric aerosol loading.
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From page 327... ...
They have been very helpful in raising questions, suggesting relationships, and identifying gaps in our data bases and observational approach, and we cannot preclude the chance that at least one may be correctly relating causal factors and temperature changes. However, contrasting causal components of the climate change and differences in data bases make it difficult to accept the results as reinforcement of the general hypothesis of the C02-induced climate shift.
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From page 328... ...
2. The global mean temperature record has been reconstructed from a relatively short and geographically limited set of observations, primarily over land areas of the northern hemisphere.
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From page 329... ...
2. Improvement in the accuracy and representativeness of the temperature record through incorporation of marine data and continued attention to influences such as urbanization.
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From page 330... ...
For example, one might anticipate that the pattern of tropospheric temperature changes caused by turbidity variations due to volcanic aerosols would differ from those caused by the more globally uniform variations of CO2. While the notion of an index that would unequivocally reveal the influence of CO2 on climate is indeed enticing, its practical application does not appear immediately feasible.
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From page 331... ...
. Estimation of the climatic change expected to result from increased CO2 depends on climate models that address the processes and scales of interest.
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From page 332... ...
The first step should be to identify the climatic parameters whose responses to increased CO2, individually or in combinations, are likely to be significant. Atmospheric model studies suggest that likely candidates are the tropospheric and surface air temperature (which should rise)
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From page 333... ...
, it is important that simulations be made with comprehensive GCMs in which the significance of any climatic changes due to changes in solar radiation can be determined and, if possible, differentiated from those due to other factors. This information will help us to interpret monitored climate records in terms of signals due to variations in incoming radiation, aerosol loading, or greenhouse gas concentrations and residual changes that may contain a signal attributable to increased CO2.
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From page 334... ...
Stratospheric ozone Tropospheric ozone B Primary parameters for monitoring the effects of climate change Atmosphere Global temperature Mean surface air temperature Tropospheric temperature distribution Stratospheric temperature distribution Radiation Upward terrestrial and reflected solar radiation at the top of the atmosphere Cloud and water vapor Precipitable water content of the atmosphere Equivalent emission temperature (cloudiness)
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From page 335... ...
Table 5.9 lists the trace gases with potentially important radiative, climatic, or chemical effects. We further limit our consideration to external factors that might induce hemispheric or global temperature changes of magnitude 0.l K or greater over about a century and to a lesser extent according to feasibility of monitoring.
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From page 336... ...
336 TABLE 5.8 Principal Anthropogenic Sources of Trace Gases and Aerosols Anthropogenic Source Comments Gas C02 00 Hydrocarbons C2H4, for example Chlorocarbons CH, N20 NO, NO2 Sulfur Compounds OCS, CS2 S02 Ozone Aerosols Fossil fuel combustion Internal combustion engines Internal combustion engines Refrigerants, solvents, propeHants Internal combustion engines, industry, change in land use Combustion, fertilizer manufacture Internal combustion engines, aircraft Fossil fuel conversion Possibly large biospheric component Those of concern entirely man-made Large component from biological activity Large natural component from biological activity High-flying aircraft are an upper-tropospheric and lower-stratospheric source Volcanoes are an intermittent source of sulfur Combustion Anthropogenic contribution is from chemical reaction of other trace gases Sulfate Silicate or car bon-conta in ing Conversion from S02 and other sulfurbearing compounds Combustion, soil erosion Most important for stratospheric aerosols Diesel engines especially, closely tied to land use roughness, and surface thermal characteristics by desertification, urbanization, and extension of agriculture (e.g., Charney, l975; Sagan et al., l979; Potter et al., l975, l980) are not included because effects of such changes appear to be primarily regional and because of the difficulty of developing a data base.
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From page 337... ...
337 41 co W • *
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From page 338... ...
Although water vapor and albedo feedback mechanisms are a function of global mean temperature, for a moderate warming, temperature change (AT) is nearly linearly proportional to radiative flux, so that where ATd is the expected temperature change for doubling, and [CO2]
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From page 339... ...
Spatial Coverage and Resolution of Additional Measurements Required. The present global network provides adequate coverage and resolution of CO2 concentration for purposes of detection of climatic changes.
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From page 340... ...
, size distribution, scattering phase function, and optical depth of the stratospheric aerosols. Surface-temperature changes associated with potential radiative perturbations of climate were calculated by various research groups.
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From page 341... ...
Volcanic eruptions have been related to climatic changes since a suggestion by Benjamin Franklin in l784 (cf. Pollack et al., l976a)
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From page 342... ...
(l98l) suggest a 0.5°C global average surface temperature rise associated with a hypothetical 0.3% increase in the solar constant.
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From page 343... ...
A doubling of ^o concentrations would also decrease the total ozone column by as much as l5% (World Meteorological Organization, l98l) through the catalytic reactions of N2O-produced nitrogen oxides with ozone; the change in O3 concentration would also have climatic effects.
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From page 344... ...
Because of its long lifetime, N2O in the troposphere is well mixed, to within 5 ppbv, i.e., l.7% of its mean (World Meteorological Organization, l98l)
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From page 345... ...
(l98l) calculated a surface temperature change of 0.65 K
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From page 346... ...
Estimated precision for CFCl3 and CF2Cl2 measurements are 2-5% (World Meteorological Organization, l98l)
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From page 347... ...
However, Ramanathan (l980) has shown that changes in the vertical ozone distribution can have a significant effect on surface temperature, even if the total ozone column does not change.
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From page 348... ...
However, major uncertainties exist in both the existing Umkehr network and satellite measurements. Only about l8 stations currently make regular Umkehr measurements; only 3 of these stations are in the southern hemisphere.
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From page 349... ...
Most stations are located in continental areas at middle latitudes in the northern hemisphere. Consequently, it is difficult to estimate global total ozone when there are vast areas of the world (mostly in the southern hemisphere)
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From page 350... ...
5.3.3.l.8 Tropospheric Ozone Sensitivity. Although only 5-l0% of the total column amount of ozone is in the troposphere, a uniform percentage change in tropospheric ozone can have about the same effect on surface temperature as the same percentage change in stratospheric ozone.
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From page 351... ...
5.3.3.2 Atmospheric Parameters The atmosphere is the part of the climate system with the least thermal inertia and, therefore, the part that can respond most quickly to the radiative effects of increasing CO2 concentrations. Climate models have focused most attention on the changes that increasing CO2 concentrations will induce in the atmosphere, and it is therefore quite appropriate to look first to the atmosphere for any evidence of CO2-induced climate changes.
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From page 352... ...
Satellites are potentially powerful tools for monitoring these parameters. However, interpretation of most satellite measurements to the accuracy required to explain temperature changes of a few tenths of a degree appears difficult, as this requires that absolute changes in the radiation budget of the order of 0.2% over a period of years be detected.
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From page 353... ...
. Depending on assumptions of temperature sensitivity to increases in CO2 concentration and ocean thermal lag, an increase of atmospheric CO2 concentration to between 400 and 450 ppm should raise the global average surface air temperature distinctly beyond the expected natural fluctuations of surface temperature.
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From page 354... ...
However, further improvement of the accuracy of sea-surface temperature determination is required in order to improve estimates of surface air temperature. 5.3.3.2.2 Tropospheric Temperature Distribution Sensitivity.
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From page 355... ...
. The results from these studies suggest that the signal-to-noise ratio of the C02induced warming of zonal mean surface air temperature is at a maximum in middle latitudes in summer when the magnitude of natural temperature fluctuation is relatively small.
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From page 356... ...
Rate of Change. Since the thermal coupling between the stratosphere and troposphere is relatively weak, the response time of stratospheric temperature is not prolonged by the large thermal inertia of oceans as is the case with respect to the tropospheric temperature.
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From page 357... ...
Models indicate that total precipitable water will increase, seasurface temperature will increase, sea ice and snow cover will change, and stratospheric temperature will decrease as CO2 rises. Climate models cannot reliably tell us, at present, the impact of CO2 change on cloud amount, height, and type, although we know that key parameters for cloud formation, such as the water content of the atmosphere and the atmospheric lapse rate, will change.
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From page 358... ...
Observation of this parameter will, therefore, help to confirm whether the numerical models are properly simulating the role of water vapor processes in contributing to climatic change. Rate of Change.
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From page 359... ...
Spatial Coverage and Resolution of Additional Measurements Required. A data set based on satellite measurements of atmospheric water vapor (whether direct or indirect)
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From page 360... ...
Signal-to-Noise Ratio. Since the temperature change for doubled CO2 is expected to be about 3°C, one might estimate that global mean equivalent emission temperature should be measured to an accuracy of a few tenths of a degree.
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From page 361... ...
Typical residence times of solid precipitation in the various reservoirs are approximately l0-l to l year for seasonal snow cover, l-l0 years for sea ice, and l03-l0^ years for ground ice and ice sheets. In each case certain
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From page 362... ...
. Climate research indicates that doubling the C02 concentrations will lead to a significant reduction in the extent of snow cover and sea ice with perhaps, if the warming persists, melting and deterioration of the major polar ice sheets.
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From page 363... ...
Budd (l975) calculates from empirical data in Antarctica that an annual change of l°C in mean temperature corresponds to a 70-day variation in the duration of sea ice at the margin and a 2.5° latitude variation in maximum extent.
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From page 364... ...
Spatial Coverage and Resolution of Additional Measurements Required. Satellite measurements allow routine integration of the areal extent of sea ice in both hemispheres.
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From page 365... ...
. In the short-run CO2-induced climate changes could result in either positive or negative transient mass balance changes of the ice sheets, depending on regional shifts in temperature and precipitation.
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From page 366... ...
Few data are available on the extent of melt features on ice shelves, on calving rates of iceberg, or on the response of ice shelves to climatic changes. Spatial Coverage and Resolution of Additional Measurements Required.
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From page 367... ...
Of the parameters identified by these authors, which include sea level, sea temperatures, salinity, and ocean circulation patterns, the first two seem most appropriate for monitoring the possible effects of C02-induced warming. Changes in sea level, though not driven by thermal expansion alone, may be the best indicator of the global change in ocean temperature, because an observational network exists, at least in the northern hemisphere, and sea-level data are representative of integrated, rather than point, measurements.
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From page 368... ...
Rate of Change. Rises in sea level in response to projected induced warming will be slow, but much more rapid than recent historic rates.
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From page 369... ...
The effect is most pronounced in high latitudes. As with sea level, change in sea-surface temperature resulting from this air temperature increase should be global in nature.
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From page 370... ...
The demonstrated accuracy of the spaceborne sea-surface temperature systems still remains inadequate to resolve the signals as observed by direct measurement. For studies of warming, accuracies of from 0.l to 0.5°C are needed, but this accuracy has not yet been achieved.
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From page 371... ...
Second "Greenhouse" gases Snow and sea-ice covers other than CO2 Polar ice-sheet mass balance Stratospheric and Sea level tropospheric ozone 5.3.4.2 Measurement Networks The key to a successful monitoring strategy is a global observation system. Satellites are a major component of such a system, and it is essential to be able to continue monitoring without interruption on a long-term basis the radiative fluxes, the planetary albedo, snow and ice extent, and sea-surface temperatures and to improve the spaceborne measurements of tropospheric and stratospheric temperatures, precipitable water content of the atmosphere, mass balance of the polar ice sheets and sea level, as well as aerosols, ozone, and other atmospheric constituents.
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From page 372... ...
Unfortunately, the C02-induced climatic changes calculated from the various current climate models continue to show substantial differences. In order to develop an effective monitoring strategy, it is essential that further intensive efforts be made to improve climate models by validating them against the observed structure and behavior of the oceanatmosphere system and to make effective use of model improvements.
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From page 373... ...
. Stratospheric aerosols and climatic change.
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From page 374... ...
. Volcanic activity and climatic changes.
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From page 375... ...
. Solar, volcanic, and C02 forcing of recent climatic changes.
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From page 376... ...
. Variations in surface air temperatures: Part l.
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From page 377... ...
. A statistical study of the likely influence of some causative factors on the temperature changes since l665.
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From page 378... ...
. Changes in global surface temperature from l880 to l977 derived from historical records of sea surface temperature.
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From page 379... ...
. Climatic effects of anthropogenic trace gases.
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From page 380... ...
. A Review of Climate Model Simulations of CO2-Induced Climatic Change.
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From page 381... ...
. The empirical analysis of CO2 influence on the modern changes of the mean annual Northern Hemisphere surface air temperature.
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From page 382... ...
35. World Meteorological Organization, Geneva, 85 pp.
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