Climate change temperature trends

Climatic change may occur as fluctuations in means and/or extremes of climatic variables. Most studies of climatic change, however, focus almost exclusively on trends in mean values of climatic variables (usually temperature). In fact, a climatic shift also may be manifest as an increase or decrease in the frequency of occurrence of extremes. That is, episodes of drought or excessive rainfall or record high or low temperatures may become more or less frequent. Changes in frequency of extremes may occur with little or no concurrent change in means. 

Here we revisit two important topics in limnology just to show that climate change studies that only include data from lakes are not applicable to reservoirs. Firstly, we show that temperature trends in reservoirs and lakes cannot be interpreted in the same way. Secondly, we show that drivers of the deep-water oxygen content in reservoirs and lakes can be very different. This last analysis will be used in the following section as the starting point for a new framework for climate change impact studies in reservoirs. 

Fig. 4.14. Tracing climate change in the Miocene. Shown here are records of ice volume and temperature (based on foraminiferal S 0) and relative organic carbon burial (based on foraminiferal S C), compared with the CO2 estimates of Pagani et al. (1999), and tectonic events that may have affected ocean heat transport. Trends in CO2 are consistent with organic carbon burial and CO2 drawdown during the Monterey Excursion, but cannot explain the Miocene Climatic Optimum (MCO) or expansion of the East Antarctic Ice Sheet (EAIS).

Climate changes from the time ofthe disappearance of dinosaurs to our days have also been based up on deep-sea stable isotope data oxygen isotope data provide an insight into the temperature variations, while carbon isotope data are informative on the kind of global carbon cycle perturbation (Zachos 2001). These data suggest that the present conditions of temperature are similar to the late Middle Age. However, the trend toward higher temperatures is now more difficult to contrast because of the drastic deforestation and emission of gases. 

The most important (and controversial) conclusion by Jacobson (2002a, b) concerning the anthropogenic nature of present-day climate change is based on analysis of the SAT and SST combined data (i.e., on the secular trend of mean average annual global surface temperature, GST). In this connection, two questions arise ... 

Of the 19 LAII projects 3 are part of the International Tundra Experiment (ITEX), which looks at the response of plant communities to climate change. Three others are concerned with atmosphere processes, including weather patterns affecting snowmelt, Arctic-wide temperature trends, and water vapor over the Arctic and its relationship with atmospheric circulation and surface conditions. Another project deals with the response of birds to climate and sea level change at river deltas, and yet another studies the balance and recent volume changes of McCall Glacier in the Brooks Range. 

Karl T.R. (1998). Regional Trends and Variations of Temperature and Precipitation. In R.T. Watson, M.C. Zinyowera, and R.H. Moss (eds.), The Regional Impacts of Climate Change. Cambridge University Press, Cambridge, U.K., pp. 87-119. 

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