Abrupt changes in Great Britain vegetation carbon projected under climate change

This is the final version. Available on open access from Wiley via the DOI in this recordPast abrupt ‘regime shifts’ have been observed in a range of ecosystems due to various forcing factors. Large-scale abrupt shifts are projected for some terrestrial ecosystems under climate change, particularly in tropical and high-latitude regions. However, there is very little high-resolution modelling of smaller-scale future projected abrupt shifts in ecosystems, and relatively less focus on the potential for abrupt shifts in temperate terrestrial ecosystems. Here, we show that numerous climate-driven abrupt shifts in vegetation carbon are projected in a high-resolution model of Great Britain's land surface driven by two different climate change scenarios. In each scenario, the effects of climate and CO2 combined are isolated from the effects of climate change alone. We use a new algorithm to detect and classify abrupt shifts in model time series, assessing the sign and strength of the non-linear responses. The abrupt ecosystem changes projected are non-linear responses to climate change, not simply driven by abrupt shifts in climate. Depending on the scenario, 374–1,144 grid cells of 1.5 km × 1.5 km each, comprising 0.5%–1.5% of Great Britain's land area show abrupt shifts in vegetation carbon. We find that abrupt ecosystem shifts associated with increases (rather than decreases) in vegetation carbon, show the greatest potential for early warning signals (rising autocorrelation and variance beforehand). In one scenario, 89% of abrupt increases in vegetation carbon show increasing autocorrelation and variance beforehand. Across the scenarios, 81% of abrupt increases in vegetation carbon have increasing autocorrelation and 74% increasing variance beforehand, whereas for decreases in vegetation carbon these figures are 56% and 47% respectively. Our results should not be taken as specific spatial or temporal predictions of abrupt ecosystem change. However, they serve to illustrate that numerous abrupt shifts in temperate terrestrial ecosystems could occur in a changing climate, with some early warning signals detectable beforehand.Natural Environment Research Council (NERC)Leverhulme Trus

Evidence of localised Amazon rainforest dieback in CMIP6 models

This is the final version. Available on open access from th European Geosciences Union via the DOI in this recordCode and data availability: The CMIP6 model output datasets analysed during this study are available online at https://doi.org/10.22033/ESGF/CMIP6.4507 (EC-Earth Consortium, 2019), https://doi.org/10.22033/ESGF/CMIP6.8473 (Krasting et al., 2018), doi10.22033/ESGF/CMIP6.6435 (Wieners et al., 2019), https://doi.org/10.22033/ESGF/CMIP6.10861 (Bethke et al., 2019), https://doi.org/10.22033/ESGF/CMIP6.7782 (Park and Shin, 2019), https://doi.org/10.22033/ESGF/CMIP6.9702 (Lee and Liang, 2020), and https://doi.org/10.22033/ESGF/CMIP6.5792 (Tang et al., 2019). Code used for analysis is available at https://doi.org/10.5281/zenodo.7038389 (Parry et al., 2022).Amazon forest dieback is seen as a potential tipping point under climate change. These concerns are partly based on an early coupled climate–carbon cycle simulation that produced unusually strong drying and warming in Amazonia. In contrast, the fifth-generation Earth system models (Phase 5 of the Coupled Model Intercomparison Project, CMIP5) produced few examples of Amazon dieback under climate change. Here we examine results from seven sixth-generation models (Phase 6 of the Coupled Model Intercomparison Project, CMIP6), which include interactive vegetation carbon and in some cases interactive forest fires. Although these models typically project increases in area-mean forest carbon across Amazonia under CO2-induced climate change, five of the seven models also produce abrupt reductions in vegetation carbon, which indicate localised dieback events. The northern South America (NSA) region, which contains most of the rainforest, is especially vulnerable in the models. These dieback events, some of which are mediated by fire, are preceded by an increase in the amplitude of the seasonal cycle in near-surface temperature, which is consistent with more extreme dry seasons. Based on the ensemble mean of the detected dieback events we estimate that 7±5 % of the NSA region will experience abrupt downward shifts in vegetation carbon for every degree of global warming past 1.5 ∘C.European Research Council (ERC)European Union Horizon 2020Engineering and Physical Sciences Research Council (EPSRC

Tipping points: Both problem and solution

This is the author accepted manuscript. The final version is available from Cell Press via the DOI in this recordOvershooting the Paris Agreement target of limiting warming to 1.5°C is now probable, making crossing several climate tipping point thresholds likely. Triggering positive tipping points can help reach the levels of decarbonization required to minimize both overshoot time and peak warming in order to avoid triggering climate tipping points, but urgent action is neededEuropean Research CouncilOptimal High Resolution Earth System Models for Exploring Future Climate Changes (OptimESM) projectEuropean Union’s Horizon 2020The Earth CommissionDARPA ACTM AIE program (DARPA-PA-21-04-02)Bezos Earth Fund

Shifts in national land use and food production in Great Britain after a climate tipping point

Climate change is expected to impact agricultural land use. Steadily accumulating changes in temperature and water availability can alter the relative profitability of different farming activities and promote land-use changes. There is also potential for high-impact ‘climate tipping points’, where abrupt, nonlinear change in climate occurs, such as the potential collapse of the Atlantic Meridional Overturning Circulation (AMOC). Here, using data from Great Britain, we develop a methodology to analyse the impacts of a climate tipping point on land use and economic outcomes for agriculture. We show that economic and land-use impacts of such a tipping point are likely to include widespread cessation of arable farming with losses of agricultural output that are an order of magnitude larger than the impacts of climate change without an AMOC collapse. The agricultural effects of AMOC collapse could be ameliorated by technological adaptations such as widespread irrigation, but the amount of water required and the costs appear to be prohibitive in this instance