More efficient phosphorus use can avoid cropland expansion.

Global projections indicate that approximately 500 Mha of new arable land will be required to meet crop demand by 2050. Applying a dynamic phosphorus (P) pool simulator under different socioeconomic scenarios, we find that cropland expansion can be avoided with less than 7% additional cumulative P fertilizer over 2006-2050 when comparing with cropland expansion scenarios, mostly targeted at nutrient-depleted soils of sub-Saharan Africa. Additional P fertilizer would replenish P withdrawn from crop production, thereby allowing higher productivity levels. We also show that further agronomic improvements such as those that allow for better (legacy) P use in soils could reduce both P outflows to freshwater and coastal ecosystems and the overall demand for P fertilizer.

Nitrogen futures in the shared socioeconomic pathways 4.

Humanity's transformation of the nitrogen cycle has major consequences for ecosystems, climate and human health, making it one of the key environmental issues of our time. Understanding how trends could evolve over the course of the 21st century is crucial for scientists and decision-makers from local to global scales. Scenario analysis is the primary tool for doing so, and has been applied across all major environmental issues, including nitrogen pollution. However, to date most scenario efforts addressing nitrogen flows have either taken a narrow approach, focusing on a singular impact or sector, or have not been integrated within a broader scenario framework - a missed opportunity given the multiple environmental and socio-economic impacts that nitrogen pollution exacerbates. Capitalizing on our expanding knowledge of nitrogen flows, this study introduces a framework for new nitrogen-focused narratives based on the widely used Shared Socioeconomic Pathways that include all the major nitrogen-polluting sectors (agriculture, industry, transport and wastewater). These new narratives are the first to integrate the influence of climate and other environmental pollution control policies, while also incorporating explicit nitrogen-control measures. The next step is for them to be used as model inputs to evaluate the impact of different nitrogen production, consumption and loss trajectories, and thus advance understanding of how to address environmental impacts while simultaneously meeting key development goals. This effort is an important step in assessing how humanity can return to the planetary boundary of this essential element over the coming century.

Future global pig production systems according to the Shared Socioeconomic Pathways.

Global pork production has increased fourfold over the last 50 years and is expected to continue growing during the next three decades. This may have considerable implications for feed use, land requirements, and nitrogen emissions. To analyze the development of the pig production sector at the scale of world regions, we developed the IMAGE-Pig model to describe changes in feed demand, feed conversion ratios (FCRs), nitrogen use efficiency (NUE) and nitrogen excretion for backyard, intermediate and intensive systems during the past few decades as a basis to explore future scenarios. For each region and production system, total production, productive characteristics and dietary compositions were defined for the 1970-2005 period. The results show that due to the growing pork production total feed demand has increased by a factor of two (from 229 to 471Tg DM). This is despite the improvement of FCRs during the 1970-2005 period, which has reduced the feed use per kg of product. The increase of nitrogen use efficiency was slower than the improvement of FCRs due to increasing protein content in the feed rations. As a result, total N excretion increased by more than a factor of two in the 1970-2005 period (from 4.6 to 11.1 Tg N/year). For the period up to 2050, the Shared Socio-economic Pathways (SSPs) provide information on levels of human consumption, technical development and environmental awareness. The sustainability of pig production systems for the coming decades will be based not only on the expected efficiency improvements at the level of animal breeds, but also on four additional pillars: (i) use of alternative feed sources not competing with human food, (ii) reduction of the crude protein content in rations, (iii) the proper use of slurries as fertilizers through coupling of crop and livestock production and (iv) moderation of the human pork consumption.

Reducing emissions from agriculture to meet the 2 °C target.

More than 100 countries pledged to reduce agricultural greenhouse gas (GHG) emissions in the 2015 Paris Agreement of the United Nations Framework Convention on Climate Change. Yet technical information about how much mitigation is needed in the sector vs. how much is feasible remains poor. We identify a preliminary global target for reducing emissions from agriculture of ~1 GtCO2 e yr-1 by 2030 to limit warming in 2100 to 2 °C above pre-industrial levels. Yet plausible agricultural development pathways with mitigation cobenefits deliver only 21-40% of needed mitigation. The target indicates that more transformative technical and policy options will be needed, such as methane inhibitors and finance for new practices. A more comprehensive target for the 2 °C limit should be developed to include soil carbon and agriculture-related mitigation options. Excluding agricultural emissions from mitigation targets and plans will increase the cost of mitigation in other sectors or reduce the feasibility of meeting the 2 °C limit.