Institute report. For example, surface temperature measurements indicated that 1990 was by far the warmest year on record; however, the satellite data show that it was only the fourth warmest in thirteen years. According to the IPCC, the warming trend revealed by satellite data is only one third that seen by surface and balloon measurement. It is often stated that IPCC publications support the premise that there is a consensus among scientists that human-induced climate change will occur and that there will be catastrophic consequences. However, a recent Gallup Poll of 400 experts drawn from the American Geophysical Union and the American Meteorological Society does not show any such consensus. Who are we to believe? Those who foreordain a global catastrophe as a result of climate change fail to note that many scientific observations contradict their predictions of doom. Predictions of substantial warming in the United States over the last 50 years, when carbon dioxide concentrations increased, did not prove true. Substantially greater warming in the Northern compared to the Southern hemisphere has not occurred. Substantially greater warming at higher latitudes has not appeared. None of the changes predicted by the models actually occurred. Even if increased concentrations of greenhouse gases are likely to cause changes in atmospheric and oceanic temperatures and weather patterns, there is no valid basis for the hysteria that is being generated by some organizations about global warming. Sound science, not science driven by a political agenda, must provide the cornerstone for a sound response to the potential for climate change. We cannot allow ourselves to be pressured to act on inaccurate data which grabs headlines. We made that mistake with acid rain. Numerous scientists gained national attention by asserting that lakes in the Adirondacks were dying from acid rain. The warning was echoed by so called "public interest" groups. The National Acid Precipitation Assessment Program (NAPAP) launched a 10-year program that won praises for its scientific research; however little effort was made to define policyrelated research priorities. By the time the NAPAP results were in, the Congress had completed action of the 1990 Clean Air Act Amendments. Little attention was given to NAPAP's observation that many of the early scientific claims about aquatic damage were exaggerated. If we are not careful we are going to make that mistake again. We are going to produce a lot of good climate change science, but it is not going to be timely or relevant to the policy decisions that the United States and other nations face over the next decade. The prime source of irrationality in environmental regulation is not the lack of strategic planning but the politically induced errors and distortions. In addition to acid rain, this was the problem with the alar crisis, or asbestos, or dioxins, or even the Love Canal. Centralized strategic planning by national governments, never mind under an international climate change treaty, does nothing to address this problem, and may in fact exacerbate it. Examples of piecemeal environmental engineering, such as a climate change treaty based on the control of only one greenhouse gas-carbon dioxide-by only the developed nations, provide not firm defense against regulatory overreaction. The Federal government is undertaking a multi-year, multibillion-dollar research program. However, the bulk of research efforts on reducing greenhouse gases is focused only on carbon dioxide. Other greenhouse gases, such as methane and nitrogen oxides, and the effects of water vapor and sulfur oxides, have received comparatively little attention. Greater attention should be focused on integrated research that is responsive to the needs of policy-makers. There are actions that can be taken by the United States and other nations that are good from the standpoint of energy policy and preventative from the standpoint of climate change. Such actions should be taken and many of them are already being taken by the United States. Others are contained in S. 2166 as passed by the Senate. As advances are made in the science of climate change an appropriate strategy can be formulated that takes into consideration the economic, social and energy consequences of action. Mr. Chairman, I would like to submit for the record several statements and articles, and the recent Marshall Institute update on global warming. Length of the Solar Cycle: An Indicator of Solar E. FRIIS-CHRISTENSEN AND K. LASSEN It has recently been suggested that the solar irradiance has varied in phase with the 80- to 90-year period represented by the envelope of the 11-year sunspot cycle and that this variation is causing a significant part of the changes in the global temperature. This interpretation has been criticized for statistical reasons and because there are no observations that indicate significant changes in the solar irradiance. A set of data that supports the suggestion of a direct influence of solar activity on global climate is the variation of the solar cycle length. This record closely matches the long-term variations of the Northern Hemisphere land air temperature during the past 130 years. M UCH SCIENTIFIC EFFORT HAS been exercised in order to understand the effects on climate of the release of increased quantities of CO2 into the atmosphere. Because realistic experiments on a global scale are not possible, verification of physical theories have relied on model simulations or observations. Model simulations are limited by the necessary assumptions, and observations suffer from the lack of sufficiently long time series of fundamental quantities. One of the most fundamental quantities in relation to the terrestrial climate is the sun's radiation. This is one of the parameters of which we have the least exact knowledge. Eddy (1) pointed out that apparent long-term relations between solar activity and certain indicators of the global climate might be caused by changes in the solar irradiance. Only recently, however, during the satellite era, have reliable measurements of the variability of the sun's irradiance been obtained (2), but these measurements Danish Meteorological Institute, Lyngbyvej 100, DK. 2100 Copenhagen Ø. 698 for the temperature increase during the 130-year period is less than 1%, which is consistent with the magnitude of the long-term trend that could be derived from the measurements of the solar irradi ance. Correlations regarding sun-weather relations have traditionally been attacked for two main reasons. The first, and perhaps most serious one, is the lack of a physical mechanism that could lead to the claimed relations. The second has been the poor statistical significance of the correlations. Kelly and Wigley (5) argued that the required change in the sun's energy output are for a time scale shorter than a solar largely exceeds the changes that are sugcycle. Reid (3) discussed a striking similarity between the globally averaged sea-surface temperature (SST) and the long-term record of solar activity, as represented by the 11-year running mean Zürich sunspot number. He pointed out that although not identical, the two time series had several features in common. Most noteworthy was the prominent minimum in the early decades of this century, the steep rise to a maximum in the 1950s, a brief drop during the 1960s and early 1970s followed by a final rise, which apparently has not stopped. Reid used these observations to show that the solar irradiance may have varied by approximately 0.6% from 1910 to 1960 in phase with the 80- to 90-year cycle (the Gleissberg period) represented by the envelope of the 11-year solar activity cycle. To estimate the response of the upper ocean to changes in the solar constant, Reid used a simple one-dimensional ocean thermal model of Hoffert et al. (4). He found that the necessary range of variation in the solar constant required to account gested by direct measurements. On the basis of directly measured irradiance data from the short time period of satellite measurements, Foukal and Lean (6) constructed a model of the total solar irradiance variation between 1874 and 1988. Variations of less than 1.1 W/m2, which is less than 0.1% of the total output, were predicted. However, they explicitly noted that additional low-frequency changes in the irradiance might be present that could not be deduced from the limited series of irradiance data. Even for a change in the solar energy output compatible with the value estimated by Reid, model calculations by Kelly and Wigley (5) indicated that solar forcing is unlikely to have accounted for more than a small part of the observed temperature variation. An important reason for this conclusion was the limited statistical correlation between the two time series used by Reid. There is, however, no a priori reason to believe that the long-term changes of solar irradiance are perfectly represented by the number of sunspots. In this paper we pre SCIENCE, VOL. 254 Fig. 1. Northern Hemisphere temperature anomalies from 1861 to 1989 (right-hand scale). The symbols (*) represent average values of the temperature record corresponding to individual solar cycles from solar maximum to solar maximum and from solar minimum to solar minimum, respectively. The second curve (+) shows the corresponding 11-year running mean values of the Zürich sunspot number (left-hand scale). For both curves, the abscissas of the plotted points correspond to the central time of the individual solar cycles. 100 80 60 20 sent a set of data that supports the idea that a change in solar activity could be related to global temperature. Both solar activity and temperature records are subject to serious deficiencies. The land and sea-surface temperature records show similar behavior, but the SST record as well as the air temperatures over the ocean show a lag of several years relative to the land temperature. Reid (7) concluded that the lack of the long-term consistency between the two curves suggests that there was some slowly varying systematic error in one or the other, or in both, time series. A lag of the SST could, however, be explained by a significant response time of the ocean to possible changes in solar forcing. The Northern Hemisphere land temperature record presented by Hansen and Lebedeff (8) and Jones et al. (9) is probably the most reliable indicator of the global temperature because it is based on the largest systematic set of temperature measurements. Therefore, we have used the land air temperature for the Northern Hemisphere, expressed as anom. alies relative to the interval 1951 to 1980, smoothed by Jones [see (10)]. From the plotted time series (Fig. 1), it is apparent that the variation of the Northern Hemisphere land air temperature has some similarity with the 11-year smoothed sunspot number, as was also the case for the SST record shown by Reid. But the data show that the land air temperature record leads the sunspot record. Therefore, if a relation between solar activity changes and surface temperature is to be maintained, the smoothed sunspot number cannot be a usable index of solar forcing. 0.3 0.1 0.0 +-0.1 -0.2 -0.3 -0.4 -0.5 1880 1900 1920 1940 1960 1980 2000 Year Temperature anomaly (°C) to the series of individual sunspot maximum 0.2 and minimum epochs. This particular filter was selected because it has been generally used in the determination of long-term trends in solar activity, but the use of a different filter would not change the results significantly, as long as the short-term variations related to the 11-year cycle and shorter periods are removed. For the last two * extrema, the available data do not allow full smoothing. Therefore, we filtered the second to last extrema by estimating the next extremum (because this is included in the filtering with a weight of one-eighth only); the last extrema express the unfiltered epochs. The consistency between the independent determinations of the cycle length based on the epochs of maximum and minimum of the sunspot number, respectively, indicates that the sunspot cycle length may be associated with a physically meaningful index of solar activity. sunspot number returns to near zero at each 11-year minimum, the 11-year geomagnetic activity variations are superposed on a long-term variation of similar amplitude including a nearly monotonic increase from 1900 to 1950. From the statistical relation between geomagnetic activity and satellite measurements of the solar wind velocity, Feynman and Crooker (11) estimated that solar wind velocities were low at the beginning of the century. A plausible physical mechanism for a direct effect on climate of a varying solar wind has not yet been demonstrated, however. But the observed long-term variation in solar energy output by means of the solar wind suggests that similar long-term changes in other manifestations of solar energy output may have occurred. A different solar parameter showing long-term changes is the length of the sunspot cycle. This parameter is known to vary with solar activity so that high activity implies short solar cycles whereas long solar cycles are characteristic for low activity levels of the sun. Gleissberg (12) demonstrated that the variation occurred in a systematic manner with a long-term periodicity of 80 to 90 years, now known as the Gleissberg period. We determined the length of the sunspot cycle using epochs of maxima and minima found by the secular smoothing procedure introduced by Gleissberg (12) (Fig. 2). This procedure corresponds to the application of a low-pass filter with coefficients 1, 2, 2, 2, 1 The introduction of this parameter of solar activity instead of the smoothed sunspot number removes the apparent lag of the solar activity curve relative to the surface temperature (Fig. 2). Furthermore, a strikingly good agreement between these two curves is revealed. There is a close association between the two curves in the up-going trends from 1900 to 1940 and since 1970, as well as in the important decrease from 1945 to 1970. For the total data, this approach gives a much closer fit to the temperature data than that for the smoothed sunspot number obtained by Reid (7). We therefore find that this agreement supports (although it does not prove) the suggestion of a direct solar activity influence on global temperature. The temperature record is only available for the last 130 years, which is about 1.5 cycles of a possible 80- to 90 year oscillation. The official Zürich sunspot number, however, extends back to 1715, and it is therefore possible to calculate the smoothed sunspot cycle length from 1740. This in principle allows a comparison between the length of the solar cycle and a parameter that could be regarded as a reasonable estimate of the 120 1880 1900 1920 1940 1960 1980 2000 Year REPORTS 699 global temperature. One parameter covering this long time period is an index of the North Atlantic sea ice, which is known to show similar long-term variations. Although the individually measured extensions of sea ice suffer from a number of different influences and probably cannot be used directly as a temperature index, it seems reasonable that the absence of considerable amounts of ice would be associated with relatively high global, or at least hemispheric, average temperatures. We therefore compared (Fig. 3) the smoothed sunspot cycle lengths and a 22year running mean of the extent of sea ice around Iceland (13, 14). The comparison clearly shows that each maximum in the long-term solar activity around 1770, 1850, and 1940 has been accompanied by a corresponding minimum in the 22year running mean value of the extent of sea ice around Iceland. We have presented observations that support the suggestion by Eddy (1) and Reid (3) that long-term changes in the solar activity influence the terrestrial climate. Using a perhaps more suitable parameter of the terrestrial climate than the one used by Reid, namely the Northern Hemisphere land air temperature difference and a possibly more direct indicator of long-term solar activity, namely the solar cycle length, we were able to improve the goodness of fit relative to that obtained by Reid. Kelly and Wigley (5) argued that a change in the solar constant is unlikely to have accounted for more than a small fraction of the observed warming in global mean surface temperature since the mid19th century. They used data compatible with the data used by Reid (3) to investigate temperature changes simulated in a model of the climate system, and they extended their analysis over a range of different climate sensitivities and solarforcing scaling factors. They examined the departure of the observed temperature 700 0.4 0.2 0.0 -0.21 1960 -0.4 Fig. 3. (Top) 22-year running mean of the amount of sea ice around Iceland from 1740 to 1970 during summer months (represented by the number of weeks when ice was observed). (Bottom) Smoothed sunspot cycle lengths from 1740 to 1970 (left-hand scale) and Northern Hemisphere temperature (right-hand mean scale). from the modeled one for the various processes. Their results indicated that since the mid-19th century, the influence of the enhanced greenhouse effect on global mean temperature has almost certainly dominated over direct influence of solar variability. A major contribution to the enhanced greenhouse effect is due to a nearly exponential increase in the concentration of CO2 in the atmosphere. Although the Northern Hemisphere temperature record includes a significant net increase during the last 130 years, which could partly be caused by the increased greenhouse effect, the temperature record does show a considerable departure from this long-term trend from 1940 to 1970. During these years the temperature decreased, simultaneously with a decrease in solar activity as indicated by the variation of solar cycle length (Fig. 2). The use of the solar cycle length as a measure of solar activity instead of the 11-year running mean of the sunspot number would significantly affect the analysis by Kelly and Wigley (5). The high correlation between the two series, based on intervals of increasing as well as decreasing temperatures, could reduce the importance of measured greenhouse gases relative to the direct influence of solar variability. This result would not necessarily indicate that an increased greenhouse effect does not exist -it could just mean that other effects may be counteracting the greenhouse effect. In particular it has been debated whether increased cloudiness due to increased global pollution could have a cooling influence on the climate, similar to the effects due to volcano eruptions, as discussed by Lamb (15). A different argument against the suggestion of solar irradiance changes as causes of climate changes is the question of whether the available satellite observations of the solar irradiance could be used as an indication of long-term chan several indications that ther quency changes in the solar are not yet distinguishable lite data. Reid (7) referred lished by Fröhlich (16) ba satellite era measurements and balloons. From these dat ed that there was a real chang output from 1968 to 1978 which is about 0.3% of the Comparing this value with th in Fig. 2, it is seen that the c change in solar cycle length 1 1978 was about half of a yea change we can expect tha sponding change in the solar 1890 to 1984 was about 1 consistent with the number Reid (3). The observations we have p gest that long-term variation temperature are closely asso variations in the solar cycle le therefore appears to be a possi of long-term changes in the output of the sun. If this r related to a real physical mech is a possibility to determine the warming signal and predict lo mate changes by appropriate the sun's dynamics. Estimation ural variability of the Earth's cli causes are needed before any sion regarding anthropogenic made. REFERENCES 1. J. A. Eddy, Science 192, 1189 (1970 2. J. R. Hickey, B. M. Alton, H. Hoyt, Space Sci. Rev. 48, 321 ( Willson and H. S. Hudson, Nat (1988). 3. G. C. Reid, Nature 329, 142 (1987) 4. M. I. Hoffert, A. J. Callegari, C. Geophys. Res. 85, 6667 (1980). 5. P. M. Kelly and T. M. L. Wigley, N (1990). 6. P. Foukal and J. Lean, Science 247,5 7. G. C. Reid, J. Geophys. Res. 96, 283 8. J. Hansen and S. Lebedeff, ibid. 92, 1. Geophys. Res. Lett. 6, 767 (1988). 9. P. D. Jones et al., J. Climatol. Appl. 161 (1986). 10. Climate Change, The IPCC Scienti (Intergovernmental Panel on Clim World Meteorological Organization, tions Environment Programme, Gene 11. J. Feynman and N. U. Crooker, Nat (1978). 12. W. Gleissberg, Terrest. Magnet. Atmo 243 (1944). 13. L. Koch, Medd. Grenland 130, 3 (194 14. H. H. Lamb, Climate: Present, Past, an 2, Climatic History and the Future (M don, 1977). 15. H. H. Lamb, Weather, Climate, and H (Routledge, London, 1988). 16. C. Fröhlich, J. Geophys. Res. 92, 796 16 May 1991; accepted 6 August 199 SCIENCE GLOBAL WARMING UPDATE Recent Scientific Findings A report by the George C. Marshall Institute EXECUTIVE SUMMARY Recent findings analyzed by scientists associated with the George C. Marshall Institute indicate that theoretical estimates of the greenhouse effect have seriously exaggerated its importance. ● New Information on Global Temperatures. Computer studies indicate that the temperature of the earth should have risen rapidly in recent years as a result of large increases in the amount of carbon dioxide and other greenhouse gases in the atmosphere. However, precise satellite measurements of global temperature, reported in the last year, reveal that the temperature increase over the last decade has been far less than the computer studies had predicted. It is five times smaller than the increase quoted in the U.N. Intergovernmental Panel on Climate Change (IPCC). This result has important implications. The IPCC "best estimate" for greenhouse warming in the next century is 2.5°C. When the IPCC prediction is lowered by a factor of five to bring it into line with the satellite measurements, the result is a predicted warming of 0.5°C or less than one degree Fahrenheit. This small change would be indistinguishable from natural climate fluctuations. The satellite measurements enable us for the first time to put a quantitative limit on the size of the greenhouse effect. ● New Information on Sea Level Rise. Melting of the polar ice sheets and a catastrophic rise in sea level were widely regarded as possible consequences of the greenhouse effect. Here, too, recently published evidence contradicts earlier predictions. Examination of 130,000 years of geological records reveals that a temperature increase leads to more moisture in the air over polar regions, to greater snowfall, and to a thickening of the ice sheets rather than a thinning. The result is that more water is locked up in the polar ice sheets and the sea level falls by up to one foot directly opposite to earlier theoretical predictions. • The Penalty for a Five-Year Delay on CO2 Limits. Understanding of the greenhouse effect and its consequences is evolving rapidly. Important new findings are reported almost monthly. The U.S. is spending more than a billion dollars a year on climate research and major progress can be expected in the next few years, just as in the recent past. Scientists could have answers to many of the important questions in five years. How much difference to the environment would five years delay on CO2 limits make? Suppose the government waits five years to get more results before imposing limits on CO2 emissions? Calculations based on commonly assumed energy growth rates show that as a result the earth's temperature will rise by at most an additional tenth of a degree in the next century, compared to how much it would rise if we acted immediately to limit CO2 emissions. |