Tuesday, July 12, 2011

Global Map of Precipitation Changes Expected by 2040 Due to Climate Change

The following map is from the BIS report, "International Dimensions of Climate Change." [pdf] The map shows the projected change in annual mean precipitation (mm per year) for 2040, relative to 1970-1999.*

Then, below, the "agriculture" section has been excerpted from the report.

  • Ensemble modelling carried out for this project signals a decrease in precipitation in parts of the Amazon region, southern Africa and Southeast Asia by the 2040s.
  • Decreased precipitation to a lesser extent is also predicted over this timescale for the Mediterranean and eastern Australia, although agreement across the ensemble is lower in these areas.
  • The high latitudes of North America, Europe and Central and North Asia are more likely to experience increased precipitation by the 2040s, but the projections for increases in central Africa and Asia have a lower confidence due to a lower level of agreement across different simulations within the ensemble.
  • By 2100 a smaller decrease in precipitation over the Amazon, Africa, and Southern Europe is projected in the aggressive mitigation scenario than under the medium emissions scenario.
  • Rainfall-driven runoff is an important contributor to global freshwater supplies, and by the 2040s water availability is therefore projected to decline in the Amazon region, southern Africa and Southeast Asia, although North America, South and East Asia may experience increases in runoff.
  • Runoff projections also take evaporation into account, which is predicted to generally increase in a warming world.
  • Evaporation may be counteracted to an extent by rising levels of atmospheric CO2 causing a decrease in water loss from plants to the atmosphere, although there is considerable uncertainty about the extent of this effect.
*The projection is the member of the ensemble with the median change in annual mean precipitation averaged over the land surface selected from an ensemble of 17 scenarios with variants of the HadCM3 climate model.

Some of the largest impacts of climate change are likely to occur in agricultural commodities, where, for some crop types, there is likely to be a mix of positive and negative impacts by the 2040s. The 2011 Foresight Report The Future of Food and Farming found that the extent to which a rise in atmospheric concentrations of CO2 will interact with plant physiology and so affect agricultural productivity is highly uncertain.

Some studies have indicated that some plants (known as C3 plants, including wheat, rice, soya, potatoes and oilseed rape) are able to benefit physiologically from higher concentrations of CO2 in the atmosphere, independent of other environmental conditions. Any benefits from CO2 will only occur if plant growth is not limited by other factors, including water and nutrient availability, as well as biotic stress caused by pest attack, diseases and competition from weeds.

Other possible benefits, strongly influenced by location and existing conditions, include the expansion of areas suitable for crop production, longer growing seasons, and, for some regions, potential increases in rainfall. However, benefits will be more than offset by some of the predicted negative impacts of climate change, such as changes in precipitation patterns, more frequent droughts in some regions, increased stress in crop, animal and fish production systems in response to extremes in temperature, and the reduced reliability of water availability.

It has been proposed that, by 2050, there will be, on average, 18% less water available worldwide for agriculture, due to pressures from environmental flow requirements (EFR), and municipal and industrial water demands.

Beyond the 2040s, the negative consequences of climate change on agriculture are expected to become increasingly significant, particularly the effects of extremes of heat and water availability. Sea level rise and any changes in the intensity of storms could also have serious consequences for agricultural productivity. In the short term, climate change could affect the security of supply and price of some agricultural commodities more than others, and this may encourage nations to protect their own agricultural markets through subsidies or export bans.

For example, the Met Office assessment commissioned for this project highlights the particular sensitivity of rice crops to climate change, compared with more temperate crops such as wheat and barley. Some regions that are currently very suitable for particular crops, such as the warm, wet conditions found in Southeast Asia for rice cultivation (in 2008, around a third of global rice production was from India and Bangladesh), may not be so in the future, while other areas could become more suitable for these crops as regional temperatures increase and precipitation patterns change.

Natural variability of the climate may continue to cause fluctuations in agricultural commodity prices, leading to sharp fluctuations in food production. Food price volatility would be exacerbated if some countries focused on more immediate national concerns, and implemented protectionist responses that inhibit usual market adjustments. This was the outcome of the Russian ban on exporting wheat from August to December 2010, which followed a severe drought and wildfires.

Periods of food price volatility disproportionately affect low-income countries and poor communities in all countries. Between 2005 and 2009, the rate of increase in hunger jumped to 25 million per year, and the number of hungry people reached 915 million in 2009. By the beginning of 2010 this figure was 1.02 billion, before falling back to 925 million.

Malnutrition on this scale, and any future potential increases, is likely to have significant impacts on UK humanitarian aid provision, and may interact with other drivers triggering localised unrest, requiring UK peacekeeping or stabilisation interventions.

As temperatures increase globally up to 2040, potential negative impacts are likely to include increases in heat stress in livestock, particularly during transportation. However, in some areas, such as Canada, regions of China and some parts of Europe, this impact is likely to be offset by decreases in the very coldest temperatures, which have an adverse effect on livestock.

Water availability is also important for livestock, and although changes in precipitation are uncertain, there is potential for water stress to limit livestock production in some areas, particularly Brazil, where there is some evidence from climate modelling for reduced precipitation and increased drought.

Sea level rise may also have a negative impact on livestock production where grazing land is situated in coastal regions. Changes in precipitation and water availability are projected to become more severe out to 2100, with an even stronger signal for drying over Brazil. These changes are present in both the medium emissions and aggressive mitigation scenarios, although more severe in the case of the former.

Agricultural pathogens, parasites and pests are also likely to be affected by climate change. Although poorly understood, there is evidence that climate change is changing disease distributions and their severity, as species are stressed by rising temperatures. For example, higher concentrations of atmospheric CO2 increases the risk of fungal infection with rice blast, and sheath blight, affecting crop production.

In livestock, modelling shows that some areas of sub-Saharan Africa are becoming increasingly suitable for the tick-borne disease East Coast Fever, one of the most significant in Africa, killing 1.1 million cattle and causing losses of $168 million each year. Predicted temperature increases are also likely to enhance the potential insect damage on vegetation growth and productivity in Europe.

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