A census of the biomass on Earth is key for understanding the structure and dynamics of the biosphere. However, a global, quantitative view of how the biomass of different taxa compare with one another is still lacking. Here, we assemble the overall biomass composition of the biosphere, establishing a census of the ≈550 gigatons of carbon (Gt C) of biomass distributed among all of the kingdoms of life. We find that the kingdoms of life concentrate at different locations on the planet; plants (≈450 Gt C, the dominant kingdom) are primarily terrestrial, whereas animals (≈2 Gt C) are mainly marine, and bacteria (≈70 Gt C) and archaea (≈7 Gt C) are predominantly located in deep subsurface environments. We show that terrestrial biomass is about two orders of magnitude higher than marine biomass and estimate a total of ≈6 Gt C of marine biota, doubling the previous estimated quantity. Our analysis reveals that the global marine biomass pyramid contains more consumers than producers, thus increasing the scope of previous observations on inverse food pyramids. Finally, we highlight that the mass of humans is an order of magnitude higher than that of all wild mammals combined and report the historical impact of humanity on the global biomass of prominent taxa, including mammals, fish, and plants.

https://www.pnas.org/content/pnas/115/25/6506.full.pdf

The biomass distribution on Earth

Climate tipping points occur when change in a part of the climate system becomes self-perpetuating beyond a warming threshold, leading to substantial Earth system impacts. Synthesizing paleoclimate, observational, and model-based studies, we provide a revised shortlist of global “core” tipping elements and regional “impact” tipping elements and their temperature thresholds. Current global warming of ~1.1°C above preindustrial temperatures already lies within the lower end of some tipping point uncertainty ranges. Several tipping points may be triggered in the Paris Agreement range of 1.5 to <2°C global warming, with many more likely at the 2 to 3°C of warming expected on current policy trajectories. This strengthens the evidence base for urgent action to mitigate climate change and to develop improved tipping point risk assessment, early warning capability, and adaptation strategies. Description Getting tipsy Climate tipping points are conditions beyond which changes in a part of the climate system become self-perpetuating. These changes may lead to abrupt, irreversible, and dangerous impacts with serious implications for humanity. Armstrong McKay et al. present an updated assessment of the most important climate tipping elements and their potential tipping points, including their temperature thresholds, time scales, and impacts. Their analysis indicates that even global warming of 1°C, a threshold that we already have passed, puts us at risk by triggering some tipping points. This finding provides a compelling reason to limit additional warming as much as possible. —HJS Global warming greater than 1.5°C could trigger multiple climate tipping points. INTRODUCTION Climate tipping points (CTPs) are a source of growing scientific, policy, and public concern. They occur when change in large parts of the climate system—known as tipping elements—become self-perpetuating beyond a warming threshold. Triggering CTPs leads to significant, policy-relevant impacts, including substantial sea level rise from collapsing ice sheets, dieback of biodiverse biomes such as the Amazon rainforest or warm-water corals, and carbon release from thawing permafrost. Nine policy-relevant tipping elements and their CTPs were originally identified by Lenton et al. (2008). We carry out the first comprehensive reassessment of all suggested tipping elements, their CTPs, and the timescales and impacts of tipping. We also highlight steps to further improve understanding of CTPs, including an expert elicitation, a model intercomparison project, and early warning systems leveraging deep learning and remotely sensed data. RATIONALE Since the original identification of tipping elements there have been substantial advances in scientific understanding from paleoclimate, observational, and model-based studies. Additional tipping elements have been proposed (e.g., parts of the East Antarctic ice sheet) and the status of others (e.g., Arctic summer sea ice) has been questioned. Observations have revealed that parts of the West Antarctic ice sheet may have already passed a tipping point. Potential early warning signals of the Greenland ice sheet, Atlantic Meridional Overturning Circulation, and Amazon rainforest destabilization have been detected. Multiple abrupt shifts have been found in climate models. Recent work has suggested that up to 15 tipping elements are now active (Lenton et al., 2019). Hence it is timely to synthesize this new knowledge to provide a revised shortlist of potential tipping elements and their CTP thresholds. RESULTS We identify nine global “core” tipping elements which contribute substantially to Earth system functioning and seven regional “impact” tipping elements which contribute substantially to human welfare or have great value as unique features of the Earth system (see figure). Their estimated CTP thresholds have significant implications for climate policy: Current global warming of ~1.1°C above pre-industrial already lies within the lower end of five CTP uncertainty ranges. Six CTPs become likely (with a further four possible) within the Paris Agreement range of 1.5 to <2°C warming, including collapse of the Greenland and West Antarctic ice sheets, die-off of low-latitude coral reefs, and widespread abrupt permafrost thaw. An additional CTP becomes likely and another three possible at the ~2.6°C of warming expected under current policies. CONCLUSION Our assessment provides strong scientific evidence for urgent action to mitigate climate change. We show that even the Paris Agreement goal of limiting warming to well below 2°C and preferably 1.5°C is not safe as 1.5°C and above risks crossing multiple tipping points. Crossing these CTPs can generate positive feedbacks that increase the likelihood of crossing other CTPs. Currently the world is heading toward ~2 to 3°C of global warming; at best, if all net-zero pledges and nationally determined contributions are implemented it could reach just below 2°C. This would lower tipping point risks somewhat but would still be dangerous as it could trigger multiple climate tipping points. The location of climate tipping elements in the cryosphere (blue), biosphere (green), and ocean/atmosphere (orange), and global warming levels at which their tipping points will likely be triggered. Pins are colored according to our central global warming threshold estimate being below 2°C, i.e., within the Paris Agreement range (light orange, circles); between 2 and 4°C, i.e., accessible with current policies (orange, diamonds); and 4°C and above (red, triangles).

/pdf/exceeding-1-5degc-global-warming-could-trigger-multiple-1idank94.pdf

Exceeding 1.5°C global warming could trigger multiple climate tipping points

The boreal forest, one of the largest biomes on Earth, provides ecosystem services that benefit society at levels ranging from local to global. Currently, about two-thirds of the area covered by this biome is under some form of management, mostly for wood production. Services such as climate regulation are also provided by both the unmanaged and managed boreal forests. Although most of the boreal forests have retained the resilience to cope with current disturbances, projected environmental changes of unprecedented speed and amplitude pose a substantial threat to their health. Management options to reduce these threats are available and could be implemented, but economic incentives and a greater focus on the boreal biome in international fora are needed to support further adaptation and mitigation actions.

https://www.alachuacounty.us/Depts/epd/EPAC/AAAS%20Boreal%20forest%20health%20and%20global%20change%20-%20819.full.pdf

Boreal forest health and global change

The response of the terrestrial carbon cycle to climate change is among the largest uncertainties affecting future climate change projections. The feedback between the terrestrial carbon cycle and climate is partly determined by changes in the turnover time of carbon in land ecosystems, which in turn is an ecosystem property that emerges from the interplay between climate, soil and vegetation type. Here we present a global, spatially explicit and observation-based assessment of whole-ecosystem carbon turnover times that combines new estimates of vegetation and soil organic carbon stocks and fluxes. We find that the overall mean global carbon turnover time is 23(+7)(-4) years (95 per cent confidence interval). On average, carbon resides in the vegetation and soil near the Equator for a shorter time than at latitudes north of 75° north (mean turnover times of 15 and 255 years, respectively). We identify a clear dependence of the turnover time on temperature, as expected from our present understanding of temperature controls on ecosystem dynamics. Surprisingly, our analysis also reveals a similarly strong association between turnover time and precipitation. Moreover, we find that the ecosystem carbon turnover times simulated by state-of-the-art coupled climate/carbon-cycle models vary widely and that numerical simulations, on average, tend to underestimate the global carbon turnover time by 36 per cent. The models show stronger spatial relationships with temperature than do observation-based estimates, but generally do not reproduce the strong relationships with precipitation and predict faster carbon turnover in many semi-arid regions. Our findings suggest that future climate/carbon-cycle feedbacks may depend more strongly on changes in the hydrological cycle than is expected at present and is considered in Earth system models.

/pdf/global-covariation-of-carbon-turnover-times-with-climate-in-5gs1udmgw0.pdf

Global covariation of carbon turnover times with climate in terrestrial ecosystems

The carbon balance of tropical ecosystems remains uncertain, with top-down atmospheric studies suggesting an overall sink and bottom-up ecological approaches indicating a modest net source. Here we use 12 years (2003 to 2014) of MODIS pantropical satellite data to quantify net annual changes in the aboveground carbon density of tropical woody live vegetation, providing direct, measurement-based evidence that the world’s tropical forests are a net carbon source of 425.2 ± 92.0 teragrams of carbon per year (Tg C year –1 ). This net release of carbon consists of losses of 861.7 ± 80.2 Tg C year –1 and gains of 436.5 ± 31.0 Tg C year –1 . Gains result from forest growth; losses result from deforestation and from reductions in carbon density within standing forests (degradation or disturbance), with the latter accounting for 68.9% of overall losses.

https://science.sciencemag.org/content/sci/358/6360/230.full.pdf

Tropical forests are a net carbon source based on aboveground measurements of gain and loss

AIM: To infer a forest carbon density map at 0.010 resolution from a radar remote sensing product for the estimation of carbon stocks in Northern Hemisphere boreal and temperate forests. 

LOCATION: The study area extends from 300 degrees N to 800 degrees N, covering three forest biomes -- temperate broadleaf and mixed forests (TBMF), temperate conifer forests (TCF) and boreal forests (BFT) -- over three continents (North America, Europe and Asia). 

METHODS: This study is based on a recently available growing stock volume (GSV) product retrieved from synthetic aperture radar data. Forest biomass and spatially explicit uncertainty estimates were derived from the GSV using existing databases of wood density and allometric relationships between biomass compartments (stem, branches, roots, foliage). We tested the resultant map against inventory-based biomass data from Russia, Europe and the USA prior to making intercontinent and interbiome carbon stock comparisons. 

RESULTS: Our derived carbon density map agrees well with inventory data at regional scales (r2 = 0.70-0.90). While 40.7 +/- 15.7 petagram of carbon (PgC) are stored in BFT, TBMF and TCF contain 24.5 +/- 9.4 PgC and 14.5 +/- 4.8 PgC, respectively. In terms of carbon density, we found 6.21 +/- 2.07 kg C/m2 retained in TCF and 5.80 +/- 2.21 kg C/m2 in TBMF, whereas BFT have a mean carbon density of 4.00 +/- 1.54 kg C/m2. Indications of a higher carbon density in Europe compared with the other continents across each of the three biomes could not be proved to be significant. 

MAIN CONCLUSIONS: The presented carbon density and corresponding uncertainty map give an insight into the spatial patterns of biomass and stand as a new benchmark to improve carbon cycle models and carbon monitoring systems. In total, we found 79.8 +/- 29.9 PgC stored in northern boreal and temperate forests, with Asian BFT accounting for 22.1 +/- 8.3 PgC.

/pdf/carbon-stock-and-density-of-northern-boreal-and-temperate-2v8arjxhnk.pdf

Carbon stock and density of northern boreal and temperate forests

The aim of this report is to illustrate by means of a series of case studies the implementation of mapping and assessment of forest ecosystem services in different contexts and geographical levels. Methodological aspects, data issues, approaches, limitations, gaps and further steps for improvement are analysed for providing good practices and decision making guidance. The EU initiative on Mapping and Assessment of Ecosystems and their Services (MAES), with the support of all Member States, contributes to improve the knowledge on ecosytem services. MAES is one of the building-block initiatives supporting the EU Biodiversity Strategy to 2000.

Mapping and assessment of forest ecosystems and their services : Applications and guidance for decision making in the framework of MAES

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Carbon stock and density of northern boreal and temperate forests

Mapping and assessment of forest ecosystems and their services : Applications and guidance for decision making in the framework of MAES