Climate Change Impacts on Canadian Agriculture

1
Climate Change Impacts on Canadian Agriculture

• R.F. Grant
• Dept. of Renewable Resources, Univ. of Alberta,
  Edmonton,Alberta

2
Climate Change Impacts - Positive

• Higher concentrations of atmospheric CO2 (Ca)
  raise CO2 fixation rates and hence plant
  productivity
• Doubled Ca raises plant growth by 30 (C3) and
  10 (C4)
• This rise is smaller if nutrients are limiting
• Higher Ca lowers transpiration rates and hence
  water requirements
• Doubled Ca lowers water requirements by 15 - 25
• This reduction is larger if nutrients are
  limiting
• Higher temperatures raise CO2 fixation rates,
  lengthen growing season
• Plant productivity increases with mean annual
  temperature to 15oC
• Higher temperatures accelerate mineralization,
  nutrient uptake

3
Climate Change Impacts - Negative

• Higher temperatures raise evaporation rates and
  hence water requirements
• 3.5oC increase raises water requirements by 25.
• Offsets reduction in water requirements from
  higher Ca
• more rapid soil drying during mid-continental
  summers can cause greater risk of agricultural
  drought, forest fires, and decreased quality and
  quantity of water in reservoirs.
• However higher temperatures are also expected to
  cause higher precipitation (3.5oC rise in
  temperature ? 8-10 rise in precip.)
• Precipitation may become more variable, which
  reduces productivity, increases erosion.
• Effects of variable rainfall on productivity can
  be reduced by soil and water conservation
  practices that maintain SOM and improve WUE.

4
Climate Change Impacts - Negative

• Higher temperatures raise respiration rates and
  hence C loss to atmosphere
• Offsets C gain at mean annual temperatures
  greater than 15oC
• More frequent heat waves over most land areas can
  cause heat stress in livestock and crops
• Higher minimum temperatures allow expanded ranges
  for pests and diseases of humans, livestock and
  crops (e.g. grasshoppers, potato beetle).

5
Climate Change Impacts on Agricultural Geography
during the 21st Century Key points

• Frost free season will be extended by 40 days.
• Growing seasons are already lengthening by 1 to 3
  days per decade in northern regions
• May need longer-maturing, heat-tolerant crop
  varieties
• Seeding dates of annual crops will be 3 weeks
  earlier
• Regrowth of perennial crops will start 2-3 weels
  earlier and critical fall harvest dates will be
  2-3 weeks later
• Spring wheat will be replaced by winter wheat
  through most of the prairies
• Corn may replace other cereals and soybean may
  replace canola through the southern and central
  prairies
• Ponderosa pine may replace lodgepole pine in
  foothills forests.

6
Climate Change Impacts on Agricultural
Productivity during the 21st Century Key points

• Average yields of canola and cereals in western
  Canada will increase from current levels by 10
  to 30 by the end of the century
• This increase will be larger in central and
  cooler regions (e.g. Peace River) and less in
  warmer regions (e.g. southern Saskatchewan)
• The size of this increase depends upon the
  amounts by which temperature and precipitation
  rise
• e.g. in southern Saskatchewan if temperature
  rises by 3oC and precipitation does not rise,
  then average yields will rise only marginally,
  but their variability will increase insurance,
  storage.
• But if temperature rises by 6oC and precipitation
  does not rise (worst case scenario), then average
  yields will decline and crop failure will become
  more frequent
• Grassland productivity will increase by 20 to
  25
• Changes in species composition (e.g. C3 to C4)
  may be an issue

7
Climate Change and Land Use in the 21st Century

• Much of the increased agricultural productivity
  from climate change in N. America will be
  realized by northward expansion of cultivation
• Possibly as much as 60Mha, depending on emission
  scenario
• But northern soils are largely luvisolic, with
  fertility limitations to agriculture
• This expansion will be offset by loss of
  cultivable area in most regions of Africa and in
  NE Brazil and Australia.