Biophysical and economic limits to negative CO2 emissions

Abstract

NATURE CLIMATE CHANGE | ADVANCE ONLINE PUBLICATION | www.nature.com/natureclimatechange 1 D espite two decades of effort to curb emissions of CO 2 and other greenhouse gases (GHGs), emissions grew faster during the 2000s than in the 1990s 1 , and by 2010 had reached ~50 Gt CO 2 equivalent (CO 2 eq) yr −1 (refs 2,3). The continuing rise in emissions is a growing challenge for meeting the international goal of limiting warming to less than 2 °C relative to the pre-industrial era, particularly without stringent climate policies to decrease emissions in the near future 2-4 . As negative emissions technologies (NETs) seem ever more necessary 3,[5][6][7][8][9][10] To have a >50% chance of limiting warming below 2 °C, most recent scenarios from integrated assessment models (IAMs) require large-scale deployment of negative emissions technologies (NETs). These are technologies that result in the net removal of greenhouse gases from the atmosphere. We quantify potential global impacts of the different NETs on various factors (such as land, greenhouse gas emissions, water, albedo, nutrients and energy) to determine the biophysical limits to, and economic costs of, their widespread application. Resource implications vary between technologies and need to be satisfactorily addressed if NETs are to have a significant role in achieving climate goals.options, to be able to decide which pathways are most desirable for dealing with climate change.There are distinct classes of NETs, such as: (1) bioenergy with carbon capture and storage (BECCS) 11,12 ; (2) direct air capture of CO 2 from ambient air by engineered chemical reactions (DAC) 13,14 ; (3) enhanced weathering of minerals (EW) 15 , where natural weathering to remove CO 2 from the atmosphere is accelerated and the products stored in soils, or buried in land or deep ocean [16][17][18][19] ; (4) afforestation and reforestation (AR) to fix atmospheric carbon in biomass and soils [20][21][22] ; (5) manipulation of carbon uptake by the ocean, either

Emissions reduction: Scrutinize CO2 removal methods

“…Existing insights from agriculture, geoscience and mineral extraction enable more informed assessments of the feasibility and acceptability 3-6 of these approaches. Yet it is crucial to know more about the permanence of carbon storage for biologically based methods, and the environmental impacts that might result if such approaches are used at vast scale [4][5][6] .…”

“…It has fallen to other groups to review insights and gaps in our understanding of the influence of CO 2 -removal techniques on ecology [3][4][5] ; to make broad assessments of climate-engineering schemes 6 ; and to carry out comparative modelling studies 7 .…”

Regional Climate Projections

“…Strong mitigation scenarios, including potential use of negative emission technologies, are likely to significantly alter land use (Smith et al 2016) and therefore impact climate through an alternative pathway from atmospheric composition. Climate evolutions also undergo a natural internal variability at a timescale of a decade to several decades.…”

Geoengineering: neither economical, nor ethical—a risk–reward nexus analysis of carbon dioxide removal

“…The most risky aspect of BECCS, however, is not the CCS part but the bio-energy (BE) part where the production of bio-energy feedstock may seriously interfere with land and water use (Fajardy and Mac Dowell 2017;Smith et al 2016). …”