| 英文摘要: | Even if carbon emissions are reduced drastically in the next decade the amount of carbon already stored in the atmosphere would lead to the occurrence of extreme thermal events every three to four years between 2040 and 20801, 2. This time lag on the effect of reducing emissions suggests that the benefits of carbon emission reduction on the health of coral reefs will be noticeable only in the long term2, 3, 4. Here, we use a spatially explicit ecosystem model to compare the potential ecosystem benefits that Caribbean and Pacific reefs could gain from reductions in carbon emissions, and the timescale of these benefits. We found that whereas the effect of a reduction in emissions on Caribbean reefs will be modest and realized only in the long term (more than 60 years), Pacific reefs would start to show benefits within the first half of this century. Moreover, it seems that Pacific reefs have the potential to maintain their ecological integrity and ecosystem state in the mid- to long term if carbon emissions are reduced, but only if plate-like corals are present. Since the early 1990s climate change has been identified as one of the main threats to coral reefs1. It has been shown repeatedly that the frequency and intensity of extreme thermal events will increase nonlinearly over the next 100 years2, 5. Owing to the large pool of greenhouse gas (GHG) already stored in the atmosphere from decades of emissions, and lags in the ability of Earth systems to reabsorb these excesses, legacy impacts will be felt for years even if emissions are reduced drastically in the near future5, 6. Even under climate scenarios that require strong and immediate emission reductions (reducing emissions to 1980s level by 2020, Representative Concentration Pathway (RCP) 2.6), there will still be extreme thermal events every three to four years between 2040 and 2080; only towards the end of the century will the frequency of these events start to decline2, 5, 6. Therefore, it is not clear how long it will take for the reduction in thermal stress to translate into an improvement in ecosystem state. Furthermore, the potential for synergistic effects and ecological feedbacks from the multiple stressors impacting reefs—such as overfishing, hurricanes, reduced calcification, and sedimentation—increase the risk of coral reefs losing resilience by the time the potential benefits of reducing GHG emissions are realized7. Most of the projections of the effect of thermal stress on coral reefs are based on the frequency and intensity of predicted future thermal disturbances1, 8, but relatively few studies have attempted to predict the ecosystem-level consequences in detail9, 10, 11, 12. In particular, spatially explicit models that incorporate multiple coral taxa and their vital rates, as well as multiple ecological mechanisms (for example, herbivory and productivity), have mainly been applied to reefs in the Caribbean3, 4, 13. These studies support the idea that reducing emissions will have only a small positive effect in the state of Caribbean reefs in the short to mid-term, with a predicted coral cover of less than 10% for most Caribbean reefs, and with coral cover trajectories that do not start to trend up by the end of the twenty-first century. However, available evidence, in terms of observed recovery rates14, suggest that Pacific reefs have far greater resilience than those in the Caribbean. Thus, it is possible that Pacific reefs may respond earlier and more strongly to a change in climate policy. Here, we present a spatially explicit ecosystem model for Pacific coral reefs and examine their response to alternate climate scenarios. We also compare the behaviour of Pacific reefs against those of the Caribbean, using a similar model from that region. The model includes six representative coral growth forms of the Pacific, each with different life history traits (Fig. 1). Model parameterization combines 40 published articles and new empirical data in addition to the 26 publications used in the parameterization of the Caribbean model. Full descriptions of parameters and model sensitivity analysis are provided in Supplementary Methods and Supplementary Analysis, respectively. Model performance was validated by reproducing 18 observed recovery trajectories from 14 reefs, spanning more than 1,200 km along the Great Barrier Reef (GBR; Fig. 2a).
|
