This section includes a review of impacts on agriculture, production forestry, and marine fisheries.

15.2.3.1. Agriculture

Most global climate change scenarios indicate that higher latitudes in North America would undergo warming that would affect the growing season in this region. For example, estimates of increases in the frost-free season under climatic change range from a minimum of 1 week to a maximum of 9 weeks (Brklacich et al., 1997a). For the Prairies, Ontario, and Quebec, most estimates suggest an extension of 3-5 weeks. Estimated temperature increases for the frost-free season in Ontario and Quebec are mostly between 1.5 and 5.0°C, and agricultural moisture regimes show an even broader range of estimates, indicating precipitation changes for the Prairies and Peace River regions ranging from decreases of 30% to increases of 80% (Brklacich et al., 1997a).

Although warmer spring and summer temperatures might be beneficial to crop production in northern latitudes, they may adversely affect crop maturity in regions where summer temperature and water stress limit production (Rosenzweig and Tubiello, 1997). Predicted shifts in thermal regimes indicate a significant increase in potential evapotranspiration, implying increased seasonal moisture deficits. Modeling studies addressing the southeast United States have shown that changes in thermal regimes under conditions of doubled CO₂ would induce greater demand for irrigation water and lower energy efficiency of production (Peart et al., 1995).

Table 15-3: Range of climate change scenario impacts on agriculture.
Crop Yield (% change from current)		Cropped Area	Change in Soil Carbon/Soil Quality	Pesticide Expenditures6 (% change)	Irrigated Acreage	Livestock Production
Canada1		Increase3 and decrease4	Increase5	Corn +10 to +20	Increase7	Decrease8
- Smallgrains	-24 to +14a
	-35 to +66b
	-75 to +73c			Wheat -15 to +15
	-17 to 0d
	+21 to +124e
				Potato + 5 to +15
US2
- Spring Wheat	+17 to +23
- Winter Wheat	-9 to +24			Soybean and Cotton +2 to +5
- Corn	+11 to +20
- Soybean	+7 to +49
- Sorghum	+32 to +43
- Potato	+7 to +8
- Citrus       (oranges/grapefruit)	+13 to +40
1 Data pertain to (a) Peace River/agricultural margin; (b) Alberta, Saskatchewan, Manitoba; (c) Ontario, Quebec; and (d) Atlantic region [adapted from Brklacich et al., 1997a; based on scenarios from pre-1995 versions of four GCMs (CCC, GFDL, GISS, and UKMO) with different crop models (FAO and CERES), assuming no adaptation and no CO2 fertilizer effects]. Data for note (e) represents yields of corn, spring and winter wheat, and canola [from McGinn et al., 1999; based on CCC model (results also show growing degree days increase by 50%)]. 2 Weighted average yield impact for crops grown under dryland conditions with adaptation, percentage change from base conditions (Reilly et al., 2000). Results based on simulations at 46 sites of current major production representing changes in climate predicted by the CCC, Hadley Centre, and Pacific Northwest National Laboratory models, and calculated using 20-yr averages centered around the year 2030, with an atmospheric CO2 concentration of 445 ppm; crop yields were simulated by the DSSAT models (Tsuji et al., 1994). 3 For Alaska and northwestern Canada (Mills, 1994), and Peace River region, northern Ontario, and Quebec in northern Canada (Brklacich et al., 1997b). 4 For example, in citrus production in the southeastern United States, if risk of freeze damage increases with climate change (Miller and Downtown, 1993), area in cropland decreased 5-10% (Reilly et al., 2000). 5 If soil conservation practices (e.g., no tillage, increased forage production, higher cropping frequency) implemented as mitigation strategies (TAR WGIII). 6 Reilly et al. (2000) results based on simulations at 45 sites of current major production representing changes in climate predicted by the CCCM and Hadley Centre models, and calculated using 20-yr averages centered around 2090, with an atmospheric CO2 concentration of 660 ppm. 7 Irrigated acreage estimated to increase by 0.8-7.3Mha in the United States (Adams et al., 1990). 8 Direct effects include warmer temperatures, which are estimated to suppress livestock appetite. If quality or supply of forage/feed grains is altered, production may be more affected by changes in pasture and grain prices (Adams et al., 1999).

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