Warm-Season Annual to Decadal Temperature Variability for Hokkaido, Japan, Inferred from Maximum Latewood Density and Ring Width Data

We present a warm season (April–September) temperature reconstructionfor Asahikawa, north central Hokkaido, Japan for AD 1557–1990. The reconstruction, which accounts for 34% of the temperature variancefrom 1925–1990, is based on maximum latewood density data from Saghalinspruce (Picea glehnii) growing at timberline (1340–1390 m) at MountAsahidake, Hokkaido. We only present a high frequency (prewhitened or white noise) version of the reconstruction because there is an unexplained offset in the mean between the actual and estimated temperature data for an earlier period of overlap from 1891–1924. The coldest summer in the reconstruction is 1718, forwhich the estimated value is 12.89 ° C, nearly four standard deviations (SD) below the mean. A colder-than-average year is reconstructed for 1641 (13.30° C, nearly 3 SD below mean), following the eruption of Komagatake, Hokkaido which began in July, 1640. The Asahikawa density chronology, shows decadal modes of variation with statistically significant spectral peaks prior to around 1850. A tree-ring width chronology for this same site (AD 1532–1990) is in phase with a tree-ring width record from centralKamchatka prior to around 1850, but out of phase since that time. This pattern suggests, as has been hypothesized for temperature-sensitive tree-ring records from the eastern Pacific sector (Alaska and Patagonia), that a decadal mode of climate variation was more dominant in the Pacific sector prior to about 1850, after which a higher frequency (ENSO-type) mode may have become more pronounced, at least until recent decades. Additional data from the northwestern Pacific is needed to compare to these findings.     

The Stable Carbon Isotope Ratio of Biogenic Emissions of Isoprene and the Potential Use of Stable Isotope Ratio Measurements to Study Photochemical Processing of Isoprene in the Atmosphere

A technique was developed that allows the determination of the stable carbon isotope ratio of isoprene in air. The method was used for a limited number of ambient measurements as well as laboratory studies of isoprene emitted from Velvet Bean (Mucana pruriens L. var. utilis), including the light and temperature dependence. The mean stable carbon isotope ratio ( ¹³C) of isoprene emitted from Velvet Bean (Mucana pruriens L. var. utilis) for all our measurements is –27.7 ± 2.0 (standard deviation for 23 data points). Our results indicate a small dependence of the stable carbon isotope ratios on leaf temperature and photosynthetic photon flux density (PPFD). The light dependence is 0.0026 ± 0.0012/( mol of photons m^–2 s^–1) for the studied range from 400 to 1700 mol of photons m^–2 s^–1. The temperature dependence is 0.16 ± 0.09/K. On average, the emitted isoprene is 2.6 ± 0.9 lighter than the leaf carbon. An uncertainty analysis of the possibility to use stable carbon isotope ratio measurements of isoprene for estimates of its mean photochemical age suggests that meaningful results can be obtained. This is supported by the results of a small number of measurements of the stable carbon isotope composition of ambient isoprene at different locations. The results range from approximately –29 to –16. They are consistent with vegetation emissions of isoprene that is slightly depleted in ¹³C relative to the plant material and enrichment of ¹³C in the atmosphere due to isotope fractionation associated with the reaction with OH-radicals. The stable carbon isotope ratio of ambient isoprene at locations directly influenced by isoprene emissions is very close to the values we found in our emission studies, whereas at sites located remote from isoprene emitting vegetation we find substantial enrichment of ¹³C. This suggests that stable carbon isotope ratio measurements will be a valuable, quantitative method to determine the extent of photochemical processing of isoprene in ambient air.     

Adaptation, Spatial Heterogeneity, and the Vulnerability of Agricultural Systems to Climate Change and CO2 Fertilization: An Integrated Assessment Approach

In this paper we develop economic measures of vulnerability to climate change with and without adaptation in agricultural production systems. We implement these measures using coupled, site-specific ecosystem and economic simulation models. This modeling approach has two key features needed to study the response of agricultural production systems to climate change: it represents adaptation as an endogenous, non-marginal economic response to climate change; and it provides the capability to represent the spatial variability in bio-physical and economic conditions that interact with adaptive responses. We apply this approach to the dryland grain production systems of the Northern Plains region of the United States. The results support the hypothesis that the most adverse impacts on net returns distributions tend to occur in the areas with the poorest resource endowments and when mitigating effects of CO₂ fertilization and adaptation are absent. We find that relative and absolute measures of vulnerability depend on complex interactions between climate change, CO₂ level, adaptation, and economic conditions such as relativeoutput prices. The relationship between relative vulnerability and resource endowments varies with assumptions about climate change, adaptation, and economic conditions. Vulnerability measured with respect to an absolute threshold is inversely related to resource endowments in all cases investigated.     

Spatial Response to Major Volcanic Events in or about AD 536, 934 and 1258: Frost Rings and Other Dendrochronological Evidence from Mongolia and Northern Siberia: Comment on R. B. Stothers, ‘Volcanic Dry Fogs, Climate Cooling, and Plague Pandemics in Europe and the Middle East’ (Climatic Change, 42, 1999)

Hypothesized large-scale climatic extremes require verification from distantregions in order toconfirm the magnitude and timing of such events. Three of the most massivehypothesized volcanic events of the past two millennia, occurring in or aboutAD 536, 934 and1258, had profound climatic and demographic repercussions over much of Europe,the MiddleEast, and other areas, according to historical accounts recently described inStothers (1998, 1999,2000) as well as other research. Here we report on frost ring and otherdendrochronologicalevidence derived from a 1738-year tree-ring chronology from Mongolia andmillennial-scaletree-ring data from northern Siberia which demonstrate that these three eventsmay have alsoimpacted conditions in these distant regions.