Table 1.

High-priority research questions to motivate a research agenda for diagnosing ACES across a wide range of systems and scales.

Research questions
Ecological systems may show ACES in some dimensions but not others
—What constitutes sufficient observational evidence for detecting past or current ACES? —Are ACES becoming more common, both within and across ecosystems? —Are some dimensions of ecosystems (e.g. composition, structure, function) more prone to ACES than others, and if so, why? —How well can early warning signs be applied to different dimensions of real-world ecosystems? —How do ACES translate through levels of organization (e.g. species to ecosystems) and trophic networks?
Trends in climate extremes may be more likely to trigger ACES than trends in mean climate
—How is variance in drivers of abrupt change changing over time? —How are the magnitude, duration and frequency of climate extremes changing over time and space? —What types or sequences of extremes are likely to produce ACES? —Under what conditions do climate extremes produce ACES? —What ecosystems (globally) are most sensitive to climate extremes, and why?
Interactions among multiple drivers often produce ACES
—How do deterministic and stochastic drivers interact to produce ACES? —What factors increased the frequency and extent of ACES in the past (e.g. using palaeoecological records of change)? —Did changes in climate make past ACES inevitable? —Are drivers of abrupt change shared or distinct among different ecosystems? —How will ongoing climate change interact with other changing drivers, including disturbances and extreme events, to produce ACES and alter ecosystem trajectories?
Contingencies matter (a lot) for ACES
—How is ecological memory changing across different systems? —To what degree are ACES dependent on adjacent or synchronous events? —When does heterogeneity increase or decrease the likelihood of ACES, and does spatial heterogeneity (transient havens, refugia) buy time for systems to adapt to changing climate? —How do slow processes mask or amplify ecological responses to rapid climate change? —What is the role of subcontinental to global teleconnections (e.g. climate, trade) in generating ACES?
Tipping points are key (but not the only) causes of ACES
—Are threshold changing, and if so, which ones and why? —What feedbacks stabilize new states, and what changes are reversible versus irreversible, or desirable versus undesirable? —What are the key tipping elements within ecological systems and at different scales? —When thresholds are exceeded, are effects likely to cascade through ecosystems and produce additional ACES? What feedbacks dampen or amplify the likelihood of tipping cascades? —Do tipping points necessarily follow a particular sequence, and what happens if that sequence is disrupted? Can changes in the timing of different tipping points reduce the likelihood of cascades?