Dieter Gerten’s research while affiliated with Humboldt-Universität zu Berlin and other places

Six of nine planetary boundaries are currently transgressed, many related to human land use. Conversion of sizeable land areas to biomass plantations for Bioenergy with Carbon Capture and Storage (BECCS) – often assumed in climate mitigation scenarios to meet the Paris Agreement – may exert additional pressure on terrestrial planetary boundaries. Using spatially-explicit, process-based global biogeochemical modelling, we systematically compute feedstock production potentials for BECCS under individual and joint constraints of the planetary boundaries for nitrogen flows, freshwater change, land system change and biosphere integrity (including protection of remaining forests), while reserving current agricultural areas for meeting the growing global demand for food, fodder and fibre. We find that the constrained BECCS potential from dedicated Miscanthus plantations is close to zero (0.1 gigatons of carbon dioxide equivalents per year under mid-century climate for Representative Concentration Pathway (RCP) 4.5). The planetary boundary for biosphere integrity has the largest individual effect, highlighting a particularly severe trade-off between climate change mitigation with BECCS and ecosystem preservation. Ultimately however, the overall limitation results from the joint effect of all four planetary boundaries, emphasizing the importance of a holistic consideration of Earth system stability in the context of climate change mitigation.

Tropical convection anomaly could serve as a crucial driver of global atmospheric teleconnections and weather extremes around the world. However, quantifying the dominances of convection anomalies with regional discrepancies, relevant for the variations of global atmospheric circulations, remains challenging. By using a network analysis of observation-based CMAP rainfall and ERA5 reanalysis datasets, our study reveals that El Niño-like convection is the most primary rainfall pattern driving the global circulation variations. Furthermore, we find that the global climate relevance of El Niño-like convection will be doubled by the end of this century, as projected consistently by 23 climate models. Such “rich nodes get richer” phenomenon in the network science is probably attributable to the dipolar rainfall changes over the western-central Pacific, coupled with the projected El Niño-like sea surface temperature changes. This study highlights the dominant role of El Niño-like convection on the global climate variations, especially under the future changing climate.

Two new control variables are suggested for quantitatively assessing the core planetary boundary for functional biosphere integrity: 1) Human appropriation of net primary production (HANPP) and 2) a metric for ecological disruption (EcoRisk). HANPP is a measure of the pressure exerted on the biosphere by removing energy otherwise available to ecosystem processes. EcoRisk indicates ecological disequilibrium through changes in vegetation structure and biogeochemical state variables as a measure of more general ecological disruption. We use simulations with the Dynamic Global Vegetation Model LPJmL to map the status of these variables at a spatial resolution of 0.5◦ x0.5◦ and quantify their temporal evolution since the year 1600. We additionally quantify local thresholds using a newly developed methodology at grid-cell scale by comparison with independent indicators for biosphere integrity. We find that EcoRisk and HANPP are good predictors of degradation as measured by a variety of global ecological datasets. We finally combine both indicators into a meta-metric, and aggregate results globally to a planetary boundary status based on the land area showing a transgression of the local thresholds relative to the preindustrial state. We find that the local boundary is currently transgressed on 69% of the global ice-free land surface, with 44% already at high risk of degradation.

Pronounced spatial disparities in heatwave trends are bound up with a diversity of atmospheric signals with complex variations, including different phases and wavenumbers. However, assessing their relationships quantitatively remains a challenging problem. Here, we use a network-searching approach to identify the strengths of heatwave-related atmospheric teleconnections (AT) with ERA5 reanalysis data. This way, we quantify the close links between heatwave intensity and AT in the Northern Hemisphere. Approximately half of the interannual variability of heatwaves is explained and nearly 80% of the zonally asymmetric trend signs are estimated correctly by the AT changes in the mid-latitudes. We also uncover that the likelihood of extremely hot summers has increased sharply by a factor of 4.5 after 2000 over areas with enhanced AT, but remained almost unchanged over the areas with attenuated AT. Furthermore, reproducing Eastern European heatwave trends among various models of the Coupled Model Intercomparison Project Phase 6 largely depends on the simulated Eurasian AT changes, highlighting the potentially significant impact of AT shifts on the simulation and projection of heatwaves.

Abstract There is a dearth of assessments of temporal trajectories and spatial patterns of planetary boundaries (PBs – precautionary limits to human interference with nine critical Earth system processes). To facilitate such studies by a generic computation tool, we have developed the R-based, open-source software package ‘boundaries’. It allows to calculate and plot the statuses of different PBs (i.e. if, when, where, and how strongly they are transgressed), based on required variables provided from an external source. The pilot version 1.0 presented here is designed to use outputs from the LPJmL biosphere model, which dynamically simulates processes underlying the PBs for land-system change, freshwater change, nitrogen flows and biosphere integrity. From these data, boundaries derives the four PBs’ statuses at different scales (planetary and corresponding regional boundaries), in a transparent way, following the latest definitions. In an application, we visualise the past and current PB states. We strongly encourage users to enhance boundaries for processing outputs from other models and datasets. Keywords: planetary boundaries, LPJmL, Earth system, analysis software

The planetary boundaries framework defines a safe operating space for humanity. To date, these boundaries have mostly been investigated separately, and it is unclear whether breaching one boundary can lead to the transgression of another. By employing a dynamic global vegetation model, we systematically simulate the strength and direction of the effects of different transgression levels of the climate change boundary (using climate output from ten phase 6 of the Coupled Model Intercomparison Project models for CO2 levels ranging from 350 ppm to 1000 ppm). We focus on climate change-induced shifts of Earth’s major forest biomes, the control variable for the land-system change boundary, both by the end of this century and, to account for the long-term legacy effect, by the end of the millennium. Our simulations show that while staying within the 350 ppm climate change boundary co-stabilizes the land-system change boundary, breaching it (>450 ppm) leads to critical transgression of the latter, with greater severity the higher the ppm level rises and the more time passes. Specifically, this involves a poleward treeline shift, boreal forest dieback (nearly completely within its current area under extreme climate scenarios), competitive expansion of temperate forest into today’s boreal zone, and a slight tropical forest extension. These interacting changes also affect other planetary boundaries (freshwater change and biosphere integrity) and provide feedback to the climate change boundary itself. Our quantitative process-based study highlights the need for interactions to be studied for a systemic operationalization of the planetary boundaries framework.

Ecosystems are under multiple stressors, and impacts can be measured with multiple variables. Humans have altered mass and energy flows of basically all ecosystems on Earth towards dangerous levels. However, integrating the data and synthesizing conclusions is becoming more and more complicated. Here we present an automated and easy-to-apply R package to assess terrestrial biosphere integrity that combines two complementary metrics. (i)The BioCol metric that quantifies the human colonization pressure exerted on the biosphere through alteration and extraction (appropriation) of net primary productivity. (ii)The EcoRisk metric that quantifies biogeochemical and vegetation structural changes as a proxy for the risk of ecosystem destabilization. Applied to simulations with the dynamic global vegetation model LPJmL5 for 1500–2016, we find that large regions presently (period 2007–2016) show modification and extraction of >20 % of the preindustrial potential net primary production. The modification (degradation) of net primary production (NPP) as a result of land use change and extraction in terms of biomass removal (e.g., from harvest) leads to drastic alterations in key ecosystem properties, which suggests a high risk of ecosystem destabilization. As a consequence of these dynamics, EcoRisk shows particularly high values in regions with intense land use and deforestation and in regions prone to impacts of climate change, such as the Arctic and boreal zone. The metrics presented here enable spatially explicit global-scale evaluation of historical and future states of the biosphere and are designed for use by the wider scientific community, being applicable not only to assessing biosphere integrity but also to benchmarking model performance. The package will be maintained on GitHub and through that we encourage its future application to other models and data sets.

Heatwaves are projected to substantially increase almost without exception at a global scale, exacerbating worldwide heat-related risks in the future. However, understanding spatial heterogeneity of future heatwave changes and their origins remains challenging. By analyzing the output of various climate models from the Coupled Model Intercomparison Project Phase 6, we found pronounced spatial disparity of projected heatwave increases in the Northern Hemisphere, even outstretching ten-fold inter-regional differences in extreme heatwave occurrences, attributed primarily to future changes in heat-dome-like circulations and soil moisture-temperature coupling. Specifically, we found that by the end of the 21st century, the modulations of combined Pacific El Niño and positive Pacific Meridional Mode on magnified heat-dome-like circulations would be translated into summertime hotspots over western Asia and western North America. Amplified soil moisture-temperature couplings then further aggravate the heatwave intensity over these two hotspots. This study of future heterogeneous heatwave patterns provides supports for formulating impact-based mitigation strategies and efficiently addressing the potential future risks for climate extremes.