Page 90 - Climate Change and Food Systems

climate change and food systems: global assessments and implications for food security and trade
Since 2012/13, new climate change predictions have become available from the climate models and contributed to the IPCC’s Fifth Assessment, published in 2014. GCMs participating in the CMIP5 have progressed in a number of ways since the CMIP3 that supported the Fourth Assessment.7 Their use of stochastic initial conditions and parameters will result
in more outputs being expressed in terms of probabilities that quantify model uncertainties (McFarlane). CMIP5 models also are refining
both their spatial and temporal scales to report climate changes in daily increments at grids as small as 50 km (Easterbrook). Finer resolutions reduce the potential for errors associated with downscaling techniques. Researchers are trying to improve the capacity of models to develop projections for near-term (over the next three decades) and intermediate decadal time periods. This is challenging because in the nearer term, chaotic weather events and anomalies such as
El Nino become more important in determining climate conditions. Earth system models that describe the carbon feedback cycle will have a greater role than previously (Flato). Perhaps the most important change under the CMIP5 is the redefinition of the emission scenarios. Instead of the approach taken in the SRES process, which describes the effects of different combinations of human activity on projected emissions, the new set of scenarios specify low, medium and high RCPs of GHG concentration levels that have been described in the open literature (Moss, et al. 2010; van Vuuren et al. 2011, Easterbrook) (Figure 3). These emission levels may result from many kinds and combinations of human activities, including effective mitigation.
The latest generation of GCMs, with improved capabilities in modelling SRESs, suggest that climate change may be experienced sooner and the effects may be more extreme than predicted by the CMIP3. Findings from the Massachussets Institute of Technology’s JPM model, published
in 2009, describe a mean surface warming in 2091–2100 of 4.1C to 5.1C relative to 1990, compared to 2.4C in their previous 2003 study, and a 90 percent probability of surface warming of between 3.5 to 7.4 degrees (Sokolov, 2009). Their more recent projection builds on modelling improvements and takes into account additional influences on the environment, including the cooling provided by 20th-century volcanoes. Using a high-resolution, century-scale model
of the United States, Diffenbaugh et al. (2011) project that 21st-century summer warming will permanently emerge prior to 2020 over most areas of the continental United States. Diffenbaugh and Scherer (2011) use observational data and the CMIP3 generation of SRES A1B output to analyse how soon the world will experience the onset of permanently higher temperatures. They project that many tropical regions in Africa, Asia and South America will experience unprecedented summer heat by 2040. The most immediate increase
will occur in the tropics, with up to 70 percent
of seasons in 2010–2039 exceeding late 20th- century maximums. Onset will be slower in areas of the United States, Europe and China.
Betts et al. (2011) use a GCM to simulate SRES A1F1, the highest emission scenario, which was not examined by the GCMs used in the Fourth Assessment. They project a global warming of 4C relative to pre-industrial temperatures as soon as the early 2060s. Sanderson et al. (2011) explore the impacts of future emission levels that are
about double those projected in SRES A1F1, but which are consistent with the highest levels now appearing in the published literature. They project a mean global warming of over 5C relative to 1990,
a complete loss of arctic summer sea-ice by 2070 and an additional 43 percent sea level rise due to thermal expansion above A1FI levels by 2100. In counterpoint, Shindell, et al. (2012), using a GCM model developed to more fully account for the countervailing effects of a number of climate change forcings,8 identify 14 simple and affordable measures
7
See the CMIP-5 website at http://cmip-pcmdi.llnl. gov/cmip5/
8
The term climate change “forcing” (often used interchangeably with radiative forcing or CO2 forcing) refers to the effect of increased CO2 concentration
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