Box 12 Wine and recent warming

Wine-grapes are known to be highly sensitive to climatic conditions, especially temperature (e.g., viticulture was thriving in England during the last medieval warm period). They have been used as an indicator of observed changes in agriculture related to warming trends, particularly in Europe and in some areas of North America.

In Alsace, France, the number of days with a mean daily temperature above 10°C (favourable for vine activity) has increased from 170 around 1970 to 210 at the end of the 20th century (Duchene and Schneider, 2005). An increase associated with a lower year-to-year variability in the last 15 years of the heliothermal index of Huglin (Seguin et al., 2004) has been observed for all the wine-producing areas of France, documenting favourable conditions for wine, in terms of both quality and stability. Similar trends in the average growing-season temperatures (April-October for the Northern Hemisphere) have been observed at the main sites of viticultural production in Europe (Jones, 2005). The same tendencies have also been found in the California, Oregon and Washington vineyards of the USA (Nemani et al., 2001; Jones, 2005).

The consequences of warming are already detectable in wine quality, as shown by Duchene and Schneider (2005), with a gradual increase in the potential alcohol levels at harvest for Riesling in Alsace of nearly 2% volume in the last 30 years. On a worldwide scale, for 25 of the 30 analysed regions, increasing trends of vintage ratings (average rise of 13.3 points on a 100-point scale for every 1°C warmer during the growing season), with lower vintage-to-vintage variation, has been established (Jones, 2005).

example, the yield trend of winter wheat displays progressive growth from 2.0 t/ha in 1961 to 5.0 t/ha in 2000, with anomalies due to climate variability on the order of 0.2 t/ha (Cantelaube et al., 2004). The same observation is valid for Asia, where the rice production of India has grown over the period 1950-1999 from 20 Mt to over 90 Mt, with only a slight decline during El Niño years when monsoon rainfall is reduced (Selvaraju, 2003). A negative effect of warming for rice production observed by the International Rice Research Institute (IRRI) in the Philippines (yield loss of 15% for 1°C increase of growing-season minimum temperature in the dry season) (Peng et al., 2004) is limited to a local observation for a short time period; a similar effect has been noted on hay yield in the UK (1°C increase in July-August led to a 0.33 t/ha loss) (Cannell et al., 1999). A study at the county level of U.S. maize and soybean yields (Lobell and Asner, 2003) has established a positive effect of cooler and wetter years in the Midwest and hotter and drier years in the North-west plains. In the case of the Sahel region of Africa, warmer and drier conditions have served as a catalyst for a number of other factors that have accelerated a decline in groundnut production (Van Duivenbooden et al., 2002).

For livestock, one study in Tibet reports a significant relationship of improved performance with warming in high mountainous conditions (Du et al., 2004). On the other hand, the pasture biomass in Mongolia has been affected by the warmer and drier climate, as observed at a local station (Batimaa, 2005) or at the regional scale by remote sensing (Erdenetuya, 2004).

1.3.62 Forestry

Here we focus on forest productivity and its contributing factors (see Section 1.3.5 for phenological aspects). Rising atmospheric CO2 concentration, lengthening of the growing season due to warming, nitrogen deposition and changed management have resulted in a steady increase in annual forest CO2 storage capacity in the past few decades, which has led to a more significant net carbon uptake (Nabuurs et al., 2002). Satellite-derived estimates of global net primary production from satellite data of vegetation indexes indicate a 6% increase from 1982 to 1999, with large increases in tropical ecosystems (Nemani et al., 2003) (Figure 1.5). The study by Zhou et al. (2003), also using satellite data, confirm that the Northern Hemisphere vegetation activity has increased in magnitude by 12% in Eurasia and by 8% in North America from 1981 to 1999. Thus, the overall trend towards longer growing seasons is consistent with an increase in the 'greenness' of vegetation, for broadly continuous regions in Eurasia and in a more fragmented way in North America, reflecting changes in biological activity. Analyses in China attribute increases in net primary productivity, in part, to a country-wide lengthening of the growing season (Fang and Dingbo, 2003). Similarly, other studies find a decrease of 10 days in the frost period in northern China (Schwartz and Chen, 2002) and advances in spring phenology (Zheng et al., 2002).

However, in the humid evergreen tropical forest in Costa Rica, annual growth from 1984 to 2000 was shown to vary inversely with the annual mean of daily minimum temperature, because of increased respiration at night (Clark et al., 2003). For southern Europe, a trend towards a reduction in biomass production has been detected in relation to rainfall decrease (Maselli, 2004), especially after the severe drought of 2003 (Gobron et al., 2005; Lobo and Maisongrande, 2006). A recent

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