CROP YIELD DECLINE
As average global temperatures have risen, mid- to upper-latitude regions have been experiencing disproportionate warming in the range of 1.5 to 2.5 C, when compared to a base period of 1981 to 2010.[1] Because of this trend, agriculture should increasingly become possible in regions north of which they were formerly impractical. But the benefits of this phenomenon will most likely be outweighed by the damage done to crop productivity resulting from the increasing incidence of drought, insect pests, and flooding in lower latitudes.[2]
The graph above is from the 2014 IPCC Synthesis Report,[3] and summarizes projections for global crop yield increases versus declines in comparison with late 20th Century levels. The 2020-2029 range shows projections for yield increases at a peak of approximately 50%, still slightly below projections for yield decreases during that period. In future periods the trends diverge, with projections for increasing yields dropping to 30% in the 2030-2049 period, while projections for decreases rise to 70%. By the end of the 21st century, yield increase projections comprise only one fifth (~20%) of those for yield decline.
Note the trend line in yellow marking rising low values for percentage of drought area globally. (Source: nasa.gov)
If these projections prove accurate, the expenses of crop yield decline should accumulate in proportion to climate disruption. Costs will be borne by governments treating malnutrition and providing emergency subsidies to the agriculture industry. Mass migration from drought-stricken areas could also complicate geopolitics and potentially affect global markets.[4] Ripple effects from a destabilized commodities sector could raise prices throughout the supply chain, which would be passed on to businesses and consumers, while compromising investment portfolios. When these potential drawbacks are considered, the benefit of arable regions’ expanding northwards seems minor by comparison.
[1] https://www.ncdc.noaa.gov/sotc/global/201713
[2] http://www.foodsystemprimer.org/food-production/food-and-climate-change/
[3] http://www.ipcc.ch/pdf/assessment-report/ar5/syr/SYR_AR5_FINAL_full_wcover.pdf [p. 15]
[4] http://www.businessinsider.com/effects-of-climate-change-2014-6
(Projections for 2030 concerning crops worldwide)