Page 25 - FAO-IPCC Expert meeting on climate change

Direct climate impacts on land-ecosystems and food provision
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1.1.3 Aquaculture
Climate change impacts on aquaculture and inland fisheries directly as a result of the rise in sea level, salinity of water, drought, floods, water scarcity and changing rainfall patterns, all of which depend on location. Climate shocks can cause substantial loss of fish stocks, extinction of species and loss of infrastructure, all of which lead to dependent populations becoming particularly vulnerable. There is far less research into climate impact on inland fisheries and aquaculture compared with major crops. Moreover, there is a need to better understand the links between climate impacts on inland fish species and nutrition. These issues should be included in vulnerability assessments which are of necessity context-specific.
1.2 Climate impacts mediated through soil, water and ecosystem services
1.2.1 Climate and soil health
A number of soil processes can be affected by climate change, resulting in erosion, soil leaching, soil organic carbon loss, salinization and nutrient loss. Climate warming can cause a loss of vegetation and lower the water table within the soil, thus increasing the decomposition of organic matter in the soil and promoting the release of soil carbon dioxide (CO2) into the atmosphere. These effects differ across regions and are more pronounced in hotspots, such as peatlands where drainage can lead to a large loss of CO2 as a result of the decomposing of soil organic matter. While an increase in CO2 may enhance crop productivity, the extent to which this may occur depends on the limitations of soil nutrients.
Climate change can also exacerbate soil erosion by water. According to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) in tropical croplands, it is estimated around 20 tonnes per hectare
per annum of soil are lost, caused by heavier precipitation and drought, reducing canopy cover and increasing soil erosion. In Europe, studies on soil erosion show that higher precipitation is expected to increase between 15−35 percent (under the RCP4.5 scenario) and soil erosion will worsen in southern Europe, a region that is already vulnerable to it.
A critical element of soil health is its nutrient status. It is known that many soils around the world have a huge excess
of phosphorus owing to continuous fertilization, notably in parts of Brazil, China, Europe and the United States. In many other regions, however, there is a serious phosphorus deficit which is expected to be exacerbated by climate change. Heavy precipitation causes phosphorus loss and increases the risk of eutrophication, impairing water quality and transferring phosphate to waterways. Land degradation increases erosion and phosphorus loss. Low soil moisture from climate change reduces the uptake of plant phosphorus; however, it is possible that a rise in the level of CO2 could counter that effect by increasing the development of mycorrhizal and the uptake of phosphorus.
Extensive agricultural systems are more vulnerable to reduced soil health under climate change. Soils from dry lands, peatlands, delta, flat plains and mountain areas are subject to higher health risks. In dry lands, land degradation
is well documented and is expected to become worse. Decreased precipitation leads to a reduction of canopy
cover and changes local climates which, in turn, result in an alteration in the level of albedo and cause roughness, evapotranspiration and the release of atmospheric dust. As a further consequence, as erosion increases, nutrients are transported elsewhere and there is a loss of fertility. Global warming also has the potential to change the type of vegetation, shifting it from semi-arid grasslands to shrub land and precipitating the erosion of soil and local decomposition, followed by a loss of soil productivity and weaker soil health.
As a result of climate change, the negative impact of a decline in soil health on crop yields may occur sooner, including areas that are temperate and which practice intensive agriculture systems. In France, where long-term research has taken place, there is evidence of a substantial loss of soil organic carbon, 90 percent of which is caused by the climate scenario and 10 percent by a change in land use. Approximately 25 percent of the total carbon organic stock is lost to climate change. Similar findings have occurred in the state of New South Wales, Australia, although these results vary by location with some areas gaining soil organic carbon and others losing it. This evidence, however, is sensitive to assumptions regarding the level of CO2 concentration in the atmosphere. When CO2 concentration in the air is accounted for, some of the carbon is captured in the soil. This suggests a possible role for soils as carbon sequester.
FAO-IPCC Expert meeting on climate change, land use and food security