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- ItemThe limits to global-warming mitigation by terrestrial carbon removal(Hoboken, NJ : Wiley, 2017) Boysen, Lena R.; Lucht, Wolfgang; Gerten, Dieter; Heck, Vera; Lenton, Timothy M.; Schellnhuber, Hans JoachimMassive nearāterm greenhouse gas emissions reduction is a precondition for staying āwell below 2Ā°Cā global warming as envisaged by the Paris Agreement. Furthermore, extensive terrestrial carbon dioxide removal (tCDR) through managed biomass growth and subsequent carbon capture and storage is required to avoid temperature āovershootā in most pertinent scenarios. Here, we address two major issues: First, we calculate the extent of tCDR required to ārepairā delayed or insufficient emissions reduction policies unable to prevent global mean temperature rise of 2.5Ā°C or even 4.5Ā°C above preāindustrial level. Our results show that those tCDR measures are unable to counteract ābusinessāasāusualā emissions without eliminating virtually all natural ecosystems. Even if considerable (Representative Concentration Pathway 4.5 [RCP4.5]) emissions reductions are assumed, tCDR with 50% storage efficiency requires >1.1āGha of the most productive agricultural areas or the elimination of >50% of natural forests. In addition, >100āMtN/yr fertilizers would be needed to remove the roughly 320āGtC foreseen in these scenarios. Such interventions would severely compromise food production and/or biosphere functioning. Second, we reanalyze the requirements for achieving the 160ā190āGtC tCDR that would complement strong mitigation action (RCP2.6) in order to avoid 2Ā°C overshoot anytime. We find that a combination of high irrigation water input and/or more efficient conversion to stored carbon is necessary. In the face of severe tradeāoffs with society and the biosphere, we conclude that largeāscale tCDR is not a viable alternative to aggressive emissions reduction. However, we argue that tCDR might serve as a valuable āsupporting actorā for strong mitigation if sustainable schemes are established immediately.
- ItemThe biosphere under potential Paris outcomes(Hoboken, NJ : Wiley, 2018) Ostberg, Sebastian; Boysen, Lena R.; Schaphoff, Sibyll; Lucht, Wolfgang; Gerten, DieterRapid economic and population growth over the last centuries have started to push the Earth out of its Holocene state into the Anthropocene. In this new era, ecosystems across the globe face mounting dual pressure from human land use change (LUC) and climate change (CC). With the Paris Agreement, the international community has committed to holding global warming below 2Ā°C above preindustrial levels, yet current pledges by countries to reduce greenhouse gas emissions appear insufficient to achieve that goal. At the same time, the sustainable development goals strive to reduce inequalities between countries and provide sufficient food, feed, and clean energy to a growing world population likely to reach more than 9 billion by 2050. Here, we present a macroāscale analysis of the projected impacts of both CC and LUC on the terrestrial biosphere over the 21st century using the Representative Concentration Pathways (RCPs) to illustrate possible trajectories following the Paris Agreement. We find that CC may cause major impacts in landscapes covering between 16% and 65% of the global iceāfree land surface by the end of the century, depending on the success or failure of achieving the Paris goal. Accounting for LUC impacts in addition, this number increases to 38%ā80%. Thus, CC will likely replace LUC as the major driver of ecosystem change unless global warming can be limited to well below 2Ā°C. We also find a substantial risk that impacts of agricultural expansion may offset some of the benefits of ambitious climate protection for ecosystems.