THE IMPACTS OF CLIMATE CHANGE
Agriculture is a human activity that is extremely sensitive to climate change. Most crop yields are driven down (or up, depending on the latitude) by only a slight increase in temperature. Warmer temperatures lead to a proliferation of pests and weeds, which may well reduce yields even further.
Carbon dioxide (CO2), one of the greenhouse gases (GHGs) causing climate change, is essential for plant growth. In general, higher CO2 concentrations in the atmosphere lead to increased agricultural production as the higher CO2 concentrations tend to improve plants’ water-use efficiency and photosynthesis rates. But certain humidity and heat-related conditions, along with the presence or absence of certain nutrients, could end up limiting or wiping out the benefits of CO2 fertilization altogether.
Agriculture also depends on the stability of water reserves. However, since current scenarios predict either drought or flooding, climate change may affect the availability of water resources. Climate change could also result in major forest fires and alter seasonal periodicity.
DIAGNOSING THE WORLD’S ILLS
Around the world, analysts demonstrate that climate change will affect agriculture and human food security more negatively than positively. Production will drop off in the developing countries, particularly in southern Asia, where irrigated crops will face sharp declines. Prices will rise for the main agricultural products (rice, wheat, corn and soya), as well as for animal feed, resulting in higher meat prices.
By 2050, the developing world is projected to see total calorie availability drop below 2000 levels. This will lead to a 20% increase in child malnutrition as compared to a “no climate change” scenario.
Soil erosion is one of the phenomena contributing to significant reductions in food productivity.
Global agriculture is grappling with the most daunting of challenges: soil damage as a result of erosion, soil exhaustion, saturation and solute accumulation. And these causes are directly linked to agricultural practices. But with climate change, these factors will be accompanied by variations in soil carbon content, leaching of soil nutrients and abnormal runoff.
Soil erosion, which threatens agricultural productivity and viability, will increase in certain regions due to climate change, particularly during the extreme climate events most forecasting models anticipate. This phenomenon will be exacerbated if producers decide to cut their losses by converting “green cover” to cropland. Certain areas may also experience a reduction in their protective snow cover, thus increasing the exposure of their soils.
In a climate change scenario for 2020‒2050, it is impossible to predict the impact weeds, insects and pathogens will have on agriculture. All of these factors are temperature- and humidity-sensitive. Certain organisms are also sensitive to CO2 concentrations in the atmosphere. However, various assumptions can be made of what is more than likely to occur (Figure 1).
AGRICULTURE IS RESPONSIBLE
Like it or not, agriculture is one of the top greenhouse gas emitters of all human activities. In global terms, the agricultural sector’s contribution to climate change accounts for 17% to 32% of all GHG emissions. In scientific terms, this works out to between 8.5 and 16.5 Pg CO2-eq.
The widespread use of agrochemicals as part of intensive global agriculture is also fuelling climate change. Agrochemical production is a source of GHG emissions in its own right that adds to agricultural emissions. Worldwide, the quantity of GHG emissions attributable to fertilizer manufacturing is estimated at 0.6% to 1.2%. These emissions primarily stem from carbon dioxide released into the atmosphere during fertilizer manufacturing. Nitrate production, in particular, gives off nitrous oxide, another GHG also emitted by virgin or fallow soils, as well as by livestock.
Furthermore, the sources of GHG emitted by animal farming include ruminants (cattle), manure, agrochemicals, etc. Dairy cows alone are directly responsible for 16% of methane emissions released into the atmosphere around the world. Methane is a product of incomplete digestion by ruminants during gastroenterological fermentation. Just one cow can emit from 100 to 500 litres of methane per day.
Dairy cows account for 16% of methane emissions released into the atmosphere. Their contribution to human nourishment is, however, incalculable.
The populations of developing countries tend to adopt the food habits of the industrialized world, namely increased consumption of meat products. This growing demand for meat follows economic growth curves in these countries and will result in a proliferation of farms engaged in intensive livestock production. In turn, this will cause GHG emissions to increase.
GHG emissions are also generated by other agricultural factors, including changes in land use, deforestation to create farmland, expansion of agriculture into tropical rainforests, increased use of mineral fertilizers worldwide, tilling, seeding, use of synthetic fertilizers, harvesting and irrigation.
FALLIBLE CLIMATE MODELS
Researchers from around the world have developed a number of climate forecasting models. We selected two of these models. In addition to having a global focus, our two choices are noted for the likelihood of their predictions and for their underlying criteria. Paradoxically, these criteria also corroborate the differences between the two models, so they can be used together to develop a “wet” and a “dry” scenario.
The models were developed by the National Center for Atmospheric Research (NCAR), located in Boulder, Colorado, and the Commonwealth Scientific and Industrial Research Organisation (CSIRO), located in Kingston, Australia.
The “wet” and “dry” scenarios were created by NCAR and CSIRO respectively. Both models forecast significantly higher temperatures by 2050. This expected increase should result in more extensive evaporation of water around the globe and more precipitation.
According to the NCAR scenario (“the wet scenario”), precipitation will increase by 10% on average, while the CSIRO scenario (“the dry scenario”) foresees an increase of only 2%.
The two scenarios differ appreciably. The NCAR projects an increase in average maximum temperatures that is twice that forecast by the CSIRO. In general, the NCAR predicts more precipitation than does the CSIRO.
It is interesting to note that, despite the relentless work of the researchers and scientists at these renowned institutions, not to mention other organizations such as the GFDL, GISS, OSU and UKMO, the substantial differences between their climate models show the fallibility of the modeling tools currently in use and clearly illustrate the limits of our ability to understand and predict global climate behaviour.
- Comprehensive Economic and Trade Agreement (CETA), www.plandaction.gc.ca/sites/default/files/pdfs/web_inbrief-final-fre.pdf
- Commonwealth Scientific and Industrial Research Organisation (CSIRO), www.csiro.au
- Geophysical Fluid Dynamics Laboratory (GFDL), www.gfdl.noaa.gov
- Goddard Institute for Space Studies (GISS), www.giss.nasa.gov
- Greenpeace, www.greenpeace.org/canada/Global/canada/report/2008/1/agriculture-contribution-changements-climatiques-resume-fr.pdf
- International Food Policy Research Institute (IFPRI), www.ifpri.org/fr
- National Center for Atmospheric Research (NCAR), http://ncar.ucar.edu
- Oregon State University (OSU), http://oregonstate.edu
- Food and Agriculture Organization (FAO) of the United Nations, www.fao.org
- Natural Resources Canada: www.rncan.gc.ca
- United Kingdom Meteorological Office (UKMO), www.metoffice.gov.uk/climate-change