Planetary health research digest
Authors: Sam Hinsley
Journal: The Lancet Planetary Health (2020)

The EAT-Lancet Commission sets out six planetary boundaries for the food system, within which food production should operate to not jeopardise the sustainability of Earth system processes. The boundaries set targets for greenhouse gas emissions, nitrogen and phosphorus cycling, freshwater use, biodiversity loss, and land-system change at the global scale. Emma Moberg (Swedish University of Agricultural Sciences, Sweden) and co-authors used the EAT-Lancet boundaries and downscaled them to per-capita level in order to benchmark the environmental impacts of the Swedish diet against the boundaries. Similar to the global level, the average Swedish diet exceeded all boundaries except for water use. Sweden has established its own national environmental objectives including a set of indicators that the authors compared to the global indicators in the EAT-Lancet report. In their comparison of indicators, the authors noted that the boundaries did not account for factors such as chemical pollution or acidification, and that many aspects of the boundaries are too low in resolution to be useful in local contexts (eg, eutrophication impacts). To improve future tracking of diet sustainability, they call for improved record keeping during production and greater traceability for imported foods. Intertidal wetlands, the areas that are covered by sea at high tide and exposed to air at low tide, provide diverse habitats and many ecosystem services, such as shoreline stabilisation and storm protection. However, similar to other types of wetlands around the world, they are particularly vulnerable to anthropogenic environmental changes. The intertidal wetlands of China's continental coastline are no exception. Given the huge economic growth and development that have occurred in China since the opening up polices of the late 1970s, Song Song (Guangzhou University, China) and co-authors used historical satellite images to investigate how the distribution of intertidal wetlands has changed over this period. They found declines in the extent of the intertidal wetlands from 7848 km2 in the 1970s to 6017 km2 in 1995, which further declined to 4895 km2 in 2015, with Shandong and Jiangsu being the most affected provinces. Land reclamation was identified as the main cause of the seaward migration and width shrinkage of the intertidal wetlands over this period. Their results highlight the need to protect these vulnerable habitats, and the authors argue that protective legislation and education on ecosystem services could be ways to achieve this. Tropical forests act as carbon sinks, offsetting some of our GHG emissions. Many climate-driven vegetation models predict that this sink function will continue for several decades. The global terrestrial carbon sink does appear to be increasing, but evidence suggests that the sink strength of tropical forests could already be declining. Wannes Hubau (University of Leeds, UK) and co-authors analysed inventory data from 244 African and 321 Amazonian plots to investigate long-term changes in carbon sink strength of intact tropical forests and the drivers behind the change. They find that the sink strength of African forests remained stable until 2010, when it began to decline, in contrast to the previously documented decline in Amazonian forests since the 1990s. The divergence in sink properties was attributed to the extent to which fertilisation from the increasing concentration of atmospheric CO2 was outweighed by higher temperatures and drought, and internal forest dynamics triggering accelerated tree death. Carbon uptake by Amazon rainforests peaked in the 1990s while the African forests appear to have peaked around 2010, with declines predicted for both forests up to 2030. The authors point out that these findings indicate that peak carbon sequestration by these tropical forests occurred earlier than predicted, which means the date by which we need to achieve net zero greenhouse gas emissions will likely need to be brought forward. Protecting biodiversity in the face of human activity, especially when it results in changes to land use, is one of the biggest challenges facing the world. The Convention on Biological Diversity has proposed a target of conserving 30% of land and sea, but it is uncertain what degree of protection from extinction this will offer in light of future climate change. Lee Hannah (Moore Center for Science, USA) and co-authors used data on 289 219 species to map potential land conservation areas in the tropics that would minimise extinctions (up to 50% conserved land), and modelled the effects under two models of future climate change: a business-as-usual scenario (RCP 8.5) and one aiming to limit change to around 2°C (RCP 2.6). As expected, the greatest protection came at 50% conservation under RCP 2.6 with 72–82% reductions in extinctions, but even 30% conservation could reduce extinctions by 52–68% under the same scenario. The authors took species movements due to climate change into account in their spatial planning, and their findings show the importance of taking a strategic approach to conservation while also continuing efforts to minimise climate change itself.