The environmental consequences of climate-driven agricultural frontiers

Mountains of USA and Canada have the greatest frontier area (0.1 and 0.9 million km2, resp- ectively). Frontiers on the fringes of Australian and African deserts are the result of projected increases in precipitation, for which there is relatively low GCM agreement, including diver- gent trends in sign of precipitation change among GCMs. This makes conclusions about potential for agricultural expansion in these areas highly uncertain. In contrast, there will be a small loss of existing crop area. We estimated that about 0.2% of existing crop area will become unsuitable for all modelled crops without irrigation or other intensive inputs for RCP 8.5 2060–2080 scenario. Environmental impacts of climate-driven agricultural frontiers Environmental impacts from climate-related agricultural land use change include impacts on climate services (e.g., reduction in carbon storage), the effects of agricultural pollution on downstream areas, and degradation of natural habitats with attendant loss of biodiversity [47–52]. The most significant impact is likely reduction in climate services provided by carbon storage in frontiers soils, particularly in the extensive high latitude frontiers. Climate services impact The total amount of carbon that resides in the top 1 m of soil under agricultural frontiers has a median value of 632 GtC (gigatons of carbon) (RCP 8.5, ensemble) and 539 GtC (RCP 4.5, ensemble), with a minimum RCP 8.5 ensemble value of 400 and a maximum value of 991 GtC (Table 2). This is equivalent to 47–116% of all carbon currently in the Earth’s atmosphere

(Fig 2). Release of carbon from high latitude soils due to warming is already of major concern but may be small relative to the amounts of carbon that might be released if these areas come under cultivation [53]. Fig 1. Global climate-driven agricultural frontiers for RCP8.5 2060–2080. Areas that transition from no current suitability for major commodity crops to suitability for one or more crops are depicted in blue, while currently uncultivated areas that transition to suitability for multiple major commodity crops are shown in red. Intensity of color indicates the level of agreement between simulations driven by different GCMs for the RCP 8.5 radiative concentration pathway. Terrestrial areas in white are either currently suitable for at least one modeled crop or, not suitable for any modeled crops in the projected climatic conditions. Suitability under current and projected climates is defined as universal agreement of suitability methods (EcoCrop, Maxent, Frequency of Extreme Temperatures). https://doi.org/10.1371/journal.pone.0228305.g001 The environmental consequences of climate-driven agricultural frontiers PLOS ONE | https://doi.org/10.1371/journal.pone.0228305 February 12, 2020 6 / 19