The latest report on climate change is a mixed bag for Canadian farmers – longer and warmer growing seasons on the plus side, but negative effects from the more intense weather events, plant and animal stress, disease and insect infestation.
In early February, the first Working Group of the United Nation’s Intergovernmental Panel on Climate Change (IPPC) released its latest assessment on where our climate is at, and where it’s going (see April issue of Better Farming). Two months later, on Good Friday, the IPCC’s second Working Group released the sequel that sought to address the related question, “so what?”
By all indications, the final discussions between lead science experts and government representatives to the Working Group II meeting were complex, poorly facilitated and bogged down by the filibustering of several obstructionist countries – especially China and Saudi Arabia. Finally, after an all-nighter that lasted until 10:30 on the morning of Good Friday, a significantly watered down Summary for Policy Makers (SPM) report emerged.
Many of the science experts involved expressed frustration with both the process and the results, pointing to the marked difference between the results presented in the technical summary that the experts had prepared with that which finally appeared in the working group’s SPM.
Despite such concerns about the accuracy of the SPM, the full IPCC “impacts” report upon which it was based gives some good indications of how a future rise in global temperatures and related changes in weather behaviour might affect us in the decades to come. For Canadian agriculture, not surprisingly, it’s a good news-bad news story.
The good news is that a rise in average temperatures means longer and warmer growing seasons for Canada and other countries located in the colder regions of habitable Earth. Everything else being equal, this suggests higher crop productivity. Added to this is the direct fertilization effect of higher CO2, particularly for C3-type plants. C3 plants such as trees include more than 95 per cent of the plant species on earth. C3 species continue to increase photosynthesis with rising CO2. Plants such as sugar cane and corn known asC4, don’t. Reduced stomata openings under high CO2 conditions also result in lower moisture loss due to evapotranspiration, and hence improved drought tolerance. Read more
Averages and “everything else being equal,” however, are seldom good criteria of how the real world works. There are a number of factors that are likely to offset and perhaps even reverse some of the gains provided by increased growing degree days and the CO2 fertilization effects. Particularly important is the projected increase in extreme weather conditions – more intense rain, longer and more severe droughts, and heat waves. Furthermore, the risks of disease and insect infestation are likely to increase under warmer climates. That’s the bad news.
Chapter 5 of the new Working Group II report, written by a team of experts from 15 different countries, provides some added details of impacts on agricultural systems. They conclude, among other things, that:
Plant stress due to heat waves, moisture deficits or exposure to high surface ozone levels – the latter an increasing problem in eastern North America – may in some regions largely mitigate or offset the direct beneficial effects of CO2 fertilization on crops. Impacts on crop yields are, however, very dependent on when these stresses occur during the crop growth cycle. For example, heat stress during the flowering stage of plants can reduce the size, number and of seeds that they produce, while it would have much less impact during the final maturation stage.
Research results on the combined effects of elevated CO2 concentrations and warmer temperatures suggest increased problems in future decades with weed control, and a significant increase in crop damage from pest herbivores.
Intense precipitation events can cause significant damage to crops and exacerbate soil erosion. Most climate models indicate that the number and intensity of such events will increase under warmer climates. A U.S. study suggests that crop losses there, due to excessive moisture events could double to $3 billion per year by 2030.
Intense weather events may also lower long-term yields by making the timing of field applications more difficult, thus reducing the efficiency of farm inputs.
While more precipitation is expected to fall in the form of extreme events, total summer precipitation in mid-latitudes is expected to decrease.Furthermore, the period of time between precipitation events is expected to become longer. Moisture stress is also added through the enhanced surface evaporation and vegetation evapotranspiration caused by higher temperatures. Hence, there is an enhanced risk of crop damage or loss due to severe drought events. While increased irrigation is one option for adapting to this challenge, competition for water use from other users will also increase.
Heat stress will also affect the feed intake and productivity of livestock, both on pastures and when confined.
Despite these concerns, the international community generally views Canadian farmers as winners in the climate change sweepstakes – as long as the magnitude and rate of warming remains modest (less than 2-3C). In other words, the pluses are likely to initially more than offset the minuses. Furthermore, Canadian farmers can useexperience, anticipatory knowledge, advanced technologies and disaster relief programs (such as crop insurance) to help adapt to the projected changes, capitalizing on the pluses and mitigating the minuses.
Many others around the world will be less prepared to cope. For example, in low latitude regions – where there are far more people to feed and there is far less margin for survival – warmer temperatures have no benefits and lots of penalties. Drier conditions can turn regions that are already arid into deserts. Water stress in much of the tropics is expected to increase dramatically.
Furthermore, given the poverty that pervades most of these countries, their capacity to adapt is minimal. For them, even a 1C warming is potentially catastrophic.