Summary of CO2 and Climate
CONTENTS
Change Related studies.
[From CO2Science.org]
(1) Fifty Years of Precipitation over China
(2) A 500-Year Precipitation History From the Bavarian Forest
(3) The Timing of North American Spring and Autumn Bird Migrations
(4) Effects of Elevated Temperature and CO2 on Wheat
Fifty Years of Precipitation Over China
Reference
Zhai, P., Zhang, X., Wan, H. and Pan, X. 2005. Trends in total precipitation and frequency of daily precipitation extremes over China. Journal of Climate 18: 1096-1108.
What was done
The authors performed a series of analyses on daily precipitation data from 530 stations across mainland China over the period 1951-2000.
What was learned
Precipitation trends computed on an annual and seasonal basis were shown to vary by region in terms of both strength and sign. Some stations exhibited positive trends, some showed negative trends, still others showed no trend at all. For the whole of mainland China, the area-averaged time series of annual total precipitation anomalies showed a non-statistically significant decreasing trend of 1.03 mm per decade, which is consistent with an earlier study by Zhai et al. (1999) who examined trends from 296 stations for the period 1951-1995.
What it means
Overall, there has been no significant change in total annual precipitation over China during the second half of the 20th century, which finding does not support climate-alarmist claims of increased rainfall as a result of unprecedented CO2-induced global warming.
Reference
Zhai, P.-M. and Ren, F.-M. 1999. On change of China's maximum and minimum temperatures in 1951-1990. Acta Meteor. Sin. 13: 278-290.
A 500-Year Precipitation History
From the Bavarian Forest
Reference
Wilson, R. J., Luckman, B. H. and Esper, J. 2005. A 500 year dendroclimatic reconstruction of spring-summer precipitation from the lower Bavarian Forest region, Germany. International Journal of Climatology 25: 611-630.
What was done
Two versions of a March-August precipitation chronology were developed from living and historical tree-ring widths for the Bavarian Forest region of southeast Germany for the period 1456-2001. The first version, standardized with a fixed 80-year spline function (SPL), was designed to retain decadal and higher frequency variations, while the second version used regional curve standardization (RCS) to retain lower frequency variations.
What was learned
Significant year-to-year and decadal variability was seen in the SPL chronology, where March-August precipitation varied on these shorter time scales. However, there did not appear to be any trend toward wetter or drier conditions over the 500-year period. The RCS reconstruction, on the other hand, better captured lower frequency variation, suggesting that March-August precipitation was substantially greater than the long-term average during the periods 1730-1810 and 1870-2000 and drier than the long-term average during the periods 1500-1560, 1610-1730 and 1810-1870.
What it means
According to the authors, their RCS reconstruction is the "first dendroclimatic reconstruction in Europe to capture such low-frequency information and indicates that traditionally derived [tree ring] reconstructions in the region are missing important low-frequency signals." In light of these findings, we expect more studies will utilize the RCS method to further unlock the secrets of precipitation trends and variability over the past millennium and beyond by better capturing lower frequency variations on multi-decadal, centennial and millennial time scales. Only then will we have a valid benchmark to compare the instrumental record against; and only then will we be able to determine if recent precipitation trends are anthropogenically-forced or merely natural fluctuations induced by non-anthropogenic phenomena.
The Timing of North American Spring
and Autumn Bird Migrations
Reference
Mills, A.M. 2005. Changes in the timing of spring and autumn migration in North American migrant passerines during a period of global warming. Ibis 147: 259-269.
What was done
Using data collected at Long Point Bird Observatory on the north shore of Lake Erie in Ontario, Canada over the period 1975-2000, the author investigated whether there had been changes in the timing of spring and autumn migrations of 13 species of birds that might be viewed as ecological responses to global warming. Specifically, he analyzed for trends in the day of first arrival in the spring, and in the days of first, second and third quartile arrivals in the spring, as well as like departures in the autumn.
What was learned
All thirteen species exhibited earlier trends in the date of first arrival in the spring. However, when subjected to stringent thresholds of statistical analysis, only one species was considered to exhibit a definite trend. Spring quartile analyses were not nearly as universal. Only nine of the thirteen species trended toward an earlier arrival date, while four trended toward a later arrival date; and of the nine that trended toward an earlier arrival date, only two were statistically significant, leaving the author to conclude that "most individuals of most species cannot conclusively be said to have migrated in 2000 earlier than their 1975 ancestors." Furthermore, analysis of the quartile means revealed no significant phenological change by bird sex - male or female. With respect to autumn trends, five species showed delayed migration, two showed advanced migration and six exhibited no trend.
What it means
In pondering the results of his analysis, Mills writes that "caution should be exercised in drawing broad conclusions about changes in migration phenology" with respect to global warming. He notes, for example, that using first arrival dates to characterize migration systems "can be problematic because they are data from one tail of a distribution, they comprise a mostly male population and they may not correlate well with the balance of the migration period." He also notes that "changes do not appear to be universal in spring, and change in that season is (a) considerably less than that suggested by [first arrival date] analysis and (b) both less complex and less common than that exhibited during autumn migration." Consequently, global warming - if it is even occurring at all - seems not to be causing major alterations in bird migration dates on the north shore of Lake Erie.
Effects of Elevated Temperature and CO2 on Wheat
Reference
Bencze, S., Veisz, O. and Bedo, Z. 2005. Effect of elevated CO2 and high temperature on the photosynthesis and yield of wheat. Cereal Research Communications 33: 385-388.
What was done
Three varieties of winter wheat (Emma, Martina and Mezofold) were grown in controlled environment chambers under ambient (375 ppm) and elevated (750 ppm) CO2 at a min, max and mean temperature regime of 10,12 and 10.7°C, respectively. In addition, twelve days after the average heading date, several plants were subjected to fifteen days of elevated temperatures (min/max/mean of 20, 35 and 25.2°C ) in an effort to assess the combined effects of elevated CO2 and temperature on wheat growth and yield.
What was learned
The temperature treatment accelerated the aging process in the three wheat varieties, but concurrent atmospheric CO2 enrichment generally helped them maintain a higher and longer level of photosynthetic activity during grain-filling and maturation. As a result, the authors report that the CO2-enriched plants "suffered less damage from heat stress and produced a higher yield than at the ambient level." What is more, in the case of the Emma cultivar, the extra CO2 supplied to the plants meant the difference between life and premature death, since by the end of the 15-day high-temperature treatment, the plants growing in ambient air were dead, while the plants growing in elevated CO2 were able to survive for a few more days.
What it means
In a future world of higher atmospheric CO2 concentrations, wheat crops should be better able to withstand the stress of high temperature, suffering less damage and producing greater yields.
