Planetary Health Research Digest
Authors: Sam Hinsley
Journal: The Lancet Planetary Health (2021)

Changes to forest cover, whether expansions or contractions, have major impacts on local biodiversity. The resulting ecosystem disruptions can affect human health, particularly through zoonotic and vector-borne diseases. Serge Morand (CNRS & CIRAD, Montpellier University, France) and Claire Lajaunie (INSERM, Aix-Marseille University, France) used World Bank data on national forest cover and the GIDEON database of infectious disease outbreaks between 1990 and 2016 to investigate whether changes in forest cover are associated with increases in vector-borne and zoonotic diseases. In tropical areas, deforestation was associated with zoonotic and vector-borne diseases, with increases in oil palm cultivation particularly associated with increases in vector-borne diseases. Conversely, in temperate areas, increases in forest cover were associated with increased zoonotic and vector-borne diseases. The authors call for greater protection of biodiversity and human health by preserving existing forests and improving management of new or expanding forests. Although the 82% of farms worldwide are less than 2 hectares in size, around 78% of farmed land is on larger farms. The benefits and trade-offs of larger and smaller farms in terms of their productivity and environmental impacts are debated. Vincent Ricciardi (University of British Columbia, Canada) and co-authors conducted a systematic review and meta-analysis of studies comparing small and large farms. They found that, overall, the literature suggested that smaller farms had higher yields and greater crop and non-crop biodiversity. No significant differences were found in terms of profits, resource-use efficiency, or greenhouse gas emission intensity. The authors suggest that, while many differences are context-specific, investment in smallholders should be a key strategy in achieving international biodiversity and sustainable development goals. Radiative forcing is the imbalance in radiative energy in the atmosphere resulting from, for example, increases in the concentration of greenhouse gases in the atmosphere, and it is this imbalance that leads to surface temperature increases. Directly measuring the degree of radiative forcing remains difficult though, with previous estimates coming from atmospheric models. Ryan Kramer (NASA Goddard Space Flight Center, USA) and co-authors used the radiative kernels technique with satellite observations to separate out radiative forcing from other radiative changes. Between 2003 and 2018, instantaneous radiative forcing increased by 0·53 W/m2 (SD 0·11), which the authors link to increasing greenhouse gas concentrations and reductions in emissions of reflective aerosols, providing directly observed evidence of anthropogenic activities affecting the Earth's energy budget. As well as providing further evidence of anthropogenic climate change, the authors conclude that their method could be useful to monitor climatic responses to greenhouse gas mitigation efforts. Ensuring equitable human development without further destabilising the Earth's natural systems is perhaps the greatest challenge of our time. Navigating these seemingly opposing objectives will require a detailed understanding of the trade-offs and synergies between development and environmental targets. Johan Rockström (Potsdam Institute for Climate Impact Research, Germany) and co-authors propose a conceptual framework to identify a path to the future that is both safe—ie, the stability of the Earths system is preserved and enhanced—and just—ie, nature's benefits, risks, and responsibilities are shared fairly across the world. This “safe and just corridor” will be defined by target ranges for biophysical variables based on whichever is stricter of the “safe” and “just” targets. By outlining how safe and just targets might be defined, the authors set up a way forward for research into how such targets might be implemented at different scales.