temperature increase in the interval 30-250 years B.P. (Cermak et al., 1992). When reassessing the anomalous curvature observed in the Cuban temperature profiles, it was felt that the ramp/step model may be too simple and hence more advanced SVD technique was applied. All Cuban "spaghetti-type" GST histories (Figure 94) resemble the results reported by Pollack and Huang (1998, 2000) for cumulative interpretation of worldwide borehole dataset, namely the fact that the twentieth century has been the warmest of the past five centuries (see Section 3.2). Present characteristic warming rate amounts over 0.5 K/100 years since 1900; additional warming of 0.5 K came as a contribution of the four previous centuries (1500-1900).
As in the case of the Czech and other regional investigations (see, e.g., Figure 33, Chapter 2 or Figure 77 of this chapter), the Cuban spaghetti diagram is confusing only at the first sight. Certain climatic trend can be delineated when all occurrence times of the individual extremes in the GST curves are plotted as a frequency-time diagram. Figure 95 illustrates the climate reconstruction as a histogram of times of relative temperature maxima ("warm" events) and occurrences of relative temperature minima ("cold" events), regardless of their possible magnitude, grouped in 50-year long intervals. The colder sixteenth to eighteenth centuries together with the recent one or two centuries of temperature recovery and most recent warming are well documented. The mean value of the twentieth century warming for Cuba amounts to 2.2 ± 0.5K. This value appears quite high in comparison with the amounts lesser than 1K obtained, e.g., for Utah and Texas (Table 7); however, it coincides well with the warming rates reported at other Caribbean islands by Singh (1997), even when Singh's data refer shorter time span of the last 40 or 50years only. The rate of detected warming at Puerto-Rico, Jamaica, Bahamas, Guadeloupe and Trinidad amounted to 0.8-4.6 K/100 years.
Cuba is relatively small and narrow; thus, its climate is strongly influenced by the surrounding Atlantic Ocean/Caribbean Sea. According to Hansen et al. (1996), at lower latitudes (approximately between 24°N and 24°S) there is an extensive sustained warming over almost the entire tropical oceans. While global mean surface temperature has risen by about 0.5 K over the last 100 years, the temperature rise in the Caribbean region seems to be somewhat higher, at least 1K (Singh, 1997). On the other hand, the natural climate variability is masked in this region by high apparent GST warming, a product of systematic clearing of the original tropical forest and consequent exposure of the land to intense solar radiation which increased the surface temperatures by several degrees of Celsius tracing thus the advancement of colonization of the island during the last century.
The above-mentioned examples from the North American continent have demonstrated the possibility of the geothermal method for the investigation of recent warming to complete other climate information in the regions where GST reconstructions represent the only available data on the past climate detection. Numerous examples of the recent warming also exist in Eurasia. The paleoclimatic reconstructions using borehole temperature-depth profiles were performed in a broad international co-operation among several European countries. Even arranged in not so dense network as in North America GST histories in Eurasia represent wide amount of climatologic data captured in regions from Atlantic to Pacific Ocean. Most of the calculated GST histories clearly confirmed a general recent warming in the last 200 years. However, because climate of the continent exhibits considerable spatial variability, especially in its European-Atlantic sector, systematic areal trends in the warming amplitude could not have been detected. Thus, further on only the most important GST reconstructions over Eurasia are briefly mentioned.
Evidences of the recent warming in Europe are less. They are rather clustered in several countries and show less pronounced amplitude than that detected in North America.
Data from the Czech Republic and Finland were described in detail in the previous section. Clauser and Mareschal (1995) have inferred the climatic trends of the past 250 years using temperature logs measured in several boreholes of southeastern Germany. Obtained results indicate two main episodes in the averaged GST history, namely cooling that continued from 1750-1800 to 1930-1950 followed by mutual changing of short oscillations of the cold and warm with amplitudes of 0.2-0.5 K. This course of climatic history coincides well with the meteorological SAT records in the area and with independent GST reconstructions for boreholes located in Western Bohemia. Ground temperature histories were inverted from temperature logs measured in two deep boreholes in central France (Mareschal and Vasseur, 1992; see also Section 3.5). Except two remote climatic episodes, this study has identified recent warming over the past 150-200 years. All suitable borehole temperature logs from mainland Portugal were collected and analyzed to assess corresponding GST histories. Results have been compared with the meteorological data (Correia and Safanda, 1999). Extracted GST histories revealed long-term warming that started at the end of the nineteenth century. Further investigations of the T-z profile measured near Evora (Southern Portugal) have indicated warming of about 1 K from the second half of the last century to the middle of the 1990s (Correia and Safanda, 2001). The rate of this warming increased in the recent 10-15 years. Obtained results agree well with the trends observed on almost 150-year long meteorological SAT series recorded at the Lisbon meteorological station.
Studies based on the inversion of temperature records measured in boreholes of northwestern Italy showed that the average temperature prior to the beginning of the meteorological recording in the 1830s was surprisingly higher by 0.6 K than that of the 1973-1982 decade (Pasquale et al., 1998). The position of the country surrounded by the Mediterranean Sea implies strong effects of the local air circulation that cause high spatial and temporal climate variability. Further analysis of a suite of boreholes located in the Tyrrhenian as well as in the Adriatic sides of the country demonstrates that the trend of the temperature change on the western side of the Apennines chain differs from that on the eastern side. Since 1750 the western side shows temperature lower than that of the 1990s, with minimum values in the period 1930-1960, followed by an almost linear increase in the GST. Along the eastern side the temperature was always higher than that inferred for the 1970s, with maximum values in the period 1920-1940, which is followed by a sharp temperature decrease. Only since 1970-1980 a local warming phase has started (Pasquale et al., 2005).
Seven of the nine processed boreholes in northeastern Slovenia confirmed a warming of about 0.6-0.7K in the past 100 years; another 2km deep hole revealed a GST history of the past 20-30ka (Rajver et al., 1998). Inversion of precise temperature logs measured in 20 boreholes in Hungary revealed rather synchronous warming that culminated near 1850 and cooling since then (Bodri and Dovényi, 2004). Along the northern border of the country an opposite trend is observed. The GST reconstructions based on temperature logs measured in two Hungarian boreholes situated at the lowland of the Carpathian Mts. and two Slovakian boreholes located at some 100-120km distance NW of Hungarian holes gave quite coherent climatic histories showing cold period around 1800-1850 and pronounced warming since then. The GST histories obtained from seven holes in different regions of Romania indicated cooling during the last 150 years for the inner region of the Carpathian Mountains and warming at the same time in the Carpathian foreland. The reconstructions are consistent with the long-term air temperature records (Veliciu and Safanda, 1998).
Inversion results from 31 boreholes spread in a 1000km long, broad N-S oriented strip in the Urals region (Russia) confirmed cold climate conditions 0.5-1.0 K below the long-term mean which culminated in 1700-1750 A.D. followed by more than 1K recent warming consistent with a 160-year SAT record (Stulc et al., 1998; Golovanova et al., 2001). The Institute of Geology at Novosibirsk (Russia), giving partly contradictory results, reported first practical inversions. Borehole inversions from West Siberia showed last century GST increase of 1.5°C. The permafrost data from the northern regions confirmed a steady general GST increase by 1-5 K beginning in the fifteenth century. However, these results also revealed a slight decrease by 0.3-0.5K during the last century. Data from two holes drilled in the bottom of the Baikal Lake have also shown certain decrease in the bottom temperature since 1800 till 1910-1930, but a pronounced GST increase by up to 1.5-1.7 K in the last 50-70 years (Duchkov and Sokolova, 1998; see also the next section).
Twenty temperature logs measured between 1979 and 1986 are available from the territory of Kamchatka (Smirnov et al., 1991; Sugrobov and Yanovsky, 1993). Later as a part of the 3-year Japanese/Czech/Russian project "Reconstruction of the climatic change from borehole temperature profiles and tree rings in the Kamchatka Peninsula" (2000-2002), precise temperature measurements were performed in a number of holes (Yamano et al., 2002). This project primarily concentrated on obtaining high-quality temperature-depth profiles and verification of the previous measurements in the region. Temperature logs used for the GST reconstructions are shown in Figure 96. Figure 97 shows "spaghetti diagram" of the inverted GST histories. As expected, the recent approximately 200 years' temperature changes could surely be recovered. Calculated GST changes are in the range of 1.5-2K. Similar to examples described in Section 1.3 (Chapter 1), boreholes logged with the shift of time gave coherent GST histories. The scatter of all GST curves is somewhat higher and reflects different environmental conditions and history of the Kamchatka Peninsula. Their averaging revealed only the general turn to the warmer conditions from approximately 1950. Obtained results are in good agreement with existing SAT series. Jones et al. (1999) have presented global patterns of the surface temperature change over the past 150 years combined land and marine data on the 5° X 5° grid box basis. Figure 98 represents one box of this database and shows an estimate of the SAT changes for southern part of the Kamchatka Peninsula. The temperature anomaly time series, reliable back to the beginning of the twentieth century, exhibits marked period of warmth during the last 10-15 years of the record. A slow rise in temperature occurred from the turn of the century to the 1940s and then temperatures remained relatively stable until the second warming phase that began during the mid-1970s. Temperature trends over 1978-1997 were 0.05-0.1 K/year for all Kamchatka (significant at the 95% level). Similar warming trends were obtained for all Pacific Ocean at latitudes 40-60°N and in eastern Siberia (Rogers and Mosley-Thompson, 1995). It was this warming that Budyko (1977) and other climatologists have interpreted as the start of a new large-scale climate warming.
TEMPERATURE, deg.C 2 4 6 8 10 12 14 16 18 20
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