IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability Crops and livestock

Changes in crop phenology provide important evidence of responses to recent regional climate change (Table 1.10). Such changes are apparent in perennial crops, such as fruit trees and wine-making varieties of grapes, which are less dependent on yearly management decisions by farmers than annual crops and are also often easier to observe. Phenological changes are often observed in tandem with changes in management practices by farmers. A study in Germany (Menzel et al., 2006c) has revealed that between 1951 and 2004 the advance for agricultural crops (2.1 days/decade) has been significantly less marked than for wild plants or fruit trees (4.4 to 7.1 days/decade). All the reported studies concern Europe, where recent warming has clearly advanced a significant part of the agricultural calendar.

Table 1.10. Observed changes in agricultural crop and livestock.

Agricultural metric Observed change Location Period References 
Phenology Advance of stem elongation for winter rye (10 days) and emergence for maize (12 days)  Germany  1961-2000  Chmielewski et al., 2004 
Advance in cherry tree flowering (0.9 days/10 years), apple tree flowering (1.1 days/10 years) in response (-5 days/°C) to March/April temperature increase  1951-2000 Menzel, 2003 
Advance in beginning of growing season of fruit trees (2.3 days/10 years), cherry tree blossom (2.0 days/10 years), apple tree blossom (2.2 days/10 years) in agreement with 1.4°C annual air temperature increase 1961-1990 Chmielewski et al., 2004 
Advance of fruit tree flowering of 1-3 weeks for apricot and peach trees, increase in spring frost risks and more frequent occurrence of bud fall or necrosis for sensitive apricot varieties South of France 1970-2001 Seguin et al., 2004 
Management practices, pests and diseases Advance of seeding dates for maize and sugarbeet (10 days) Germany 1961-2000 Chmielewski et al., 2004 
Advance of maize sowing dates by 20 days at 4 INRA experimental farms France  1974-2003 Benoit and Torre, 2004 
Advance of potato sowing date by 5 days, no change for spring cereals Finland 1965-1999 Hilden et al., 2005 
Partial shift of apple codling moth from 2 to 3 generations South of France  1984-2003 Sauphanor and Boivin, 2004 
Yields Lower hay yields, in relation to warmer summers  Rothamsted UK  1965-1998 Cannell et al., 1999 
Part of overall yield increase attributed to recent cooling during growing season: 25% maize, 33% soybean USA county level 1982-1998 Lobell and Asner, 2003 
Decrease of rice yield associated with increase in temperature (0.35°C and 1.13°C for Tmax and Tmin, respectively, during 1979 to 2003) Philippines 1992-2003 Peng et al., 2004 
Livestock Decrease of measured pasture biomass by 20-30% Mongolia 1970-2002 Batimaa, 2005 
Decline of NDVI of the third period of 10 days of July by 69% for the whole territory 1982-2002 Erdenetuya, 2004 
Observed increase in animal production related to warming in summer and annual temperature Tibet 1978-2002 Du et al., 2004 

Since the TAR, there has been evidence of recent trends in agro-climatic indices, particularly those with a direct relationship to temperature, such as increases in growing season length and in growing-degree-days during the crop cycle. These increases, associated with earlier last spring frost and delayed autumn frost dates, are clearly apparent in temperate regions of Eurasia (Moonen et al., 2002; Menzel et al., 2003; Genovese et al., 2005; Semenov et al., 2006) and a major part of North America (Robeson, 2002; Feng and Hu, 2004). They are especially detectable in indices applicable to wine-grape cultivation (Box 1.2). In Sahelian countries, increasing temperature in combination with rainfall reduction has led to a reduced length of vegetative period, no longer allowing present varieties to complete their cycle (Ben Mohamed et al., 2002).

However, no detectable change in crop yield directly attributable to climate change has been reported for Europe. For 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).

Box 1.2. 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 (Duchêne 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 Duchêne 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).