SCHLEIFER, Stanley; BORENSTEIN, Samuel; KHANDAKER, Nazrul I.; HUANG, Che-Tsao; CHATURGAN, Thakur; LIANG, Feng C.; JO-RAMIREZ, Mario; FLORES, Dorean J.; PERSAUD, Poonraj; and LEBOURNE, Selwyn
Many scientists in the field of earth and environmental science believe that much of the increase in earth surface temperatures, measured during the 20th century, is due, for the most part, to anthropogenic increases in the atmospheric concentration of infrared active gases, (methane, oxides of nitrogen, chlorofluorocarbons, and particularly carbon dioxide). [Hansen et. Al., 1998] Others still believe that recent global warming may be a manifestation of natural cycles that are not anthropogenic. [NRC, 1982] The authors have done an analysis of available meteorological data, which may add to the growing body of information addressing this question. In this study, we attempt to isolate carbon dioxide as a factor in the recent global warming.
During the winter time in either the Northern or the Southern Hemisphere of the earth, surface temperatures, all other things being equal, will decrease while the heat lost to space by radiation exceeds the heat gained by insolation (i. e. heat absorbed at the surface of the earth due to solar radiation, per unit area per unit time). At the end of this period, surface temperatures will be at their minimum for a given year. As the solar altitude increases after the winter solstice, insolation increases until it equals heat loss. This is the time on minimum temperature. After this time, insolation exceeds heat loss and surface temperatures begin to increase. During the summer, surface temperatures rise while insolation exceeds radiative heat loss. After the summer solstice, as the solar altitude decreases, insolation decreases. When radiative heat loss equals insolation, surface temperatures are at their maximum. Subsequently, as sun altitude and insolation continue
to decrease, surface temperatures decrease.
The concentration of carbon dioxide in the earth’s atmosphere has been increasing since the beginning of the Industrial Revolution.3 If an augmented greenhouse effect, due to increasing atmospheric carbon dioxide concentration, has been a significant factor producing recent global warming, then this should be indicated by a change in the interval of time between the time of maximum insolation (i.e. the summer solstice for either the Northern or the Southern Hemisphere), and the time of maximum surface temperature in the mid latitudes of that hemisphere, as well as the interval of time between minimum insolation (i.e. the winter solstice for either the Northern or the Southern Hemisphere), and the time of minimum surface temperature in the mid latitudes of that hemisphere. Specifically, the interval of time from the winter solstice to the time of minimum surface temperature in a northern hemisphere, mid-latitude land area should decrease and the interval of time from the summer solstice to the time of maximum surface temperature in a northern hemisphere, mid-latitude land area should increase. However, the magnitude of Figure 1 Insolation and Heat Loss by Long Wave Radiation this effect should not be as great during the Northern Hemisphere summer as during the Northern Hemisphere winter because of the reduction in atmospheric carbon dioxide due to increased photosynthesis during the Northern Hemisphere summer. (See figure 1.)
Figure 1: Insolation and Heat Loss by Long Wave Radiation
The authors have examined surface air temperature data from mid-latitude, continental areas to see if there has been a significant change in the interval of time between the summer solstice and the time of maximum surface temperature and the winter solstice and the time of minimum surface temperature, during periods of changing global surface temperatures, as predicted by the above hypothesis. Mid-latitude, continental areas were chosen for this study because the effects on air temperatures, due to changes in the heat budget at the surface of the earth are most easily observed in these areas. [Lutgens & Tarbuck, 1998]
It should be noted that similar changes in “lag time”, to those illustrated above, between the solstices and times of maximum and minimum temperatures, respectively, would also result from increasing insolation or increasing retention of heat at the surface of the earth due to causes other than a carbon dioxide enhanced greenhouse effect. However, if this increased heat retention is due to increasing atmospheric carbon dioxide concentrations, then it would be mitigated during the Northern Hemisphere summer as discussed above, when atmospheric concentrations of carbon dioxide are reduced by increased photosynthesis. In figure 2, below, the low points, or troughs in atmospheric carbon dioxide concentration, occur during the Northern Hemisphere summer. Therefore, the effect on the “lag time”, discussed above, should be reduced or eliminated during the Figure 2 Globally Averaged Atmospheric Carbon Dioxide Concentration Showing Seasonal Variation (Data from Mona Loa Observatory, Hawaii) Northern Hemisphere summer if it is primarily due to the effect of carbon dioxide as an infrared active gas.
Figure 2: Globally Averaged Atmospheric Carbon Dioxide Concentration Showing Seasonal Variation (Data from Mona Loa Observatory, Hawaii)
Surface temperature data was obtained from the NOAA NCEP-NCAR CDAS-1 DAILY Diagnostic above_ground temp: Temperature data online database. Information from November 1, 1950 to September 30, 2003 was used for this study. Interpolated daily temperatures, 2 meters above the surface, were obtained from the above source for a contiguous Eurasian land area from approximately 40 degrees East Longitude to 120 degrees East Longitude, and from approximately 30 degrees North Latitude to 60 degrees North Latitude. Data points are 1.875 degrees apart. The data obtained was loaded into a spreadsheet program for processing. (Microsoft Excel and Corel Quattro Pro programs were used.)
The arithmetic mean of the daily temperatures at the above grid points, corrected for surface area variation with latitude, was computed for each day of the data set.
To offset the effects of short term temperature variation, (noise), on the determination of seasonal temperature maxima and minima for the selected area, a 61 day traveling mean was computed and the day for which the time weighted temperature of the 30 days preceding equals that of the 30 days following, was taken as the time of minimum or maximum temperature (statistical coldest or warmest day, or crossover day), for the winter and summer (respectively) of each year of the data set. The interval of time, in days, between the an arbitrary date, selected in the fall and the spring and the crossover day was plotted for the summer and winter of each year in the data set.
Figure 3, below, clearly shows that the date of the statistical coldest winter day has gotten earlier, with time, during the second half of the 20th Century, in the study area. This is consistent with an increasing retention of heat, with time, during the winter season for the same period.
Figure 3: Eurasla Winter - Statistical Days to Coldest Days
Standard Error 1.28984141804254
Standard Deviation 9.39018726309513
Confidence Level (0.950000)
Figure 4: Eurasia Summer - Statistical Days to Warmest Day
Standard Error 0.435770232847071
Standard Deviation 3.20224414670741
Confidence Level ( 0.950000)
Figure 4, above, shows that the date of the statistical warmest summer day has not significantly changed, with time, during the second half of the 20th Century, in the same study area.
The results indicate that, in the study area, for at least the latter half of the 20th Century, global warming has occurred during the Northern Hemisphere winter and not during the Northern Hemisphere summer. This is consistent with anthropogenic increases in atmospheric carbon dioxide being a major factor in this global warming.
Increased photo-synthetic conversion of carbon dioxide during the Northern Hemisphere summer sequesters atmospheric carbon in the plant biomass, lowering carbon dioxide concentrations in the atmosphere. During the Northern Hemisphere winter, increased burning of fossil fuels and wood, both containing carbon, as well as the decay of dead vegetation, raise the atmospheric concentration of carbon dioxide. This would augment the “greenhouse effect” during the Northern Hemisphere winter and mitigate or diminish it during the Northern Hemisphere summer. This is consistent with the results of our study.
The data also indicate that things other than atmospheric carbon dioxide concentration have significantly influenced thermal equilibrium at the surface of the earth. Figure 2 shows a steady year to year increase in globally averaged atmospheric carbon dioxide concentrations from before 1960 to after 1990.
Figure 5, below [From Environmental Geology by Carla Montgomery, 5th Ed.], shows the estimated globally averaged rate of temperature change, on land areas from about 1885 to 1995, as computed by GHCN, Jones, and Hansen and Wilson. For the period of about 1960 to 1980, worldwide land temperatures were static or actually decreasing according to these studies. Since carbon dioxide concentrations were steadily increasing during this period, other factors clearly affected the thermal balance on the earth. This is reflected in the winter lag times for this period which are steady or increasing, as shown in figure 3. Thereafter, there was relatively rapid warming. This is reflected in figure 3 by rapidly decreasing lag times up to the end of the study period.
Figure 5: Worldwide (Land)
The mean slope of change in lag time to the statistically coldest days, derived from the winter data, is ~ -0.16 days per year. For the last 15 years of the study, which was a period of very rapid warming, the slope is ~ -1.3 days per year. These results support the basic hypothesis of this investigation. The time periods with the greatest negative rate of change of lag time to the coldest winter day correspond to the times of greatest global warming. However, there are many factors other than seasonal variations in atomospheric carbon dioxide concentration which may influence, and explain, the difference between the Northern Hemisphere summer and winter lag time patterns. The authors believe that among the most important of these may be seasonal variations in atmospheric water vapor content and cloud cover. The authors propose continuing research, using earth satellite derived data, as well as surface data, to investigate this possibility.
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