| 英文摘要: | To the Editor —
Our ecosystems and the services they provide are increasingly being degraded by multiple and interacting pressures. Humans are using geoengineering to mitigate their effects, even though it commonly addresses acute symptoms of single pressures. Barrett et al.1 discuss the benefits, problems and geopolitical consequences of proposed geoengineering to alleviate the effects of climate change by injecting sulphate into the stratosphere. This is an untried, global measure, the efficacy of which is difficult to predict2. However, geoengineering is already being applied in fresh waters, at smaller scales, using additives to alleviate the effects of either local nutrient enrichment or regional acid deposition3. Lessons from these and other freshwater management experiences provide empirical evidence to reinforce the conclusions of Barrett et al. Here, we highlight the need to consider feedbacks between ecosystems and the pressures acting on them beyond the potential interactions in their Fig. 1.
Barrett et al.1 discuss various environmental problems that stratospheric sulphate injection cannot solve, such as Antarctic ice loss and indirect effects on precipitation. Similarly, in fresh waters, phosphorus reduction using geoengineering will not alter the widespread effects of nitrogen enrichment4. Barrett et al.1 point out that geoengineering will not return the climate to past conditions. The same is also true in lakes for phosphorus removal, and for natural or artificial recovery from acidification, where multiple pressures produce novel ecosystems5. Mitigation of climate change by sulphate injection could reduce the pressure on politicians to lessen carbon emissions. In fresh waters, there is a similar concern that geoengineering will reduce the pressure on regulators to manage nutrient loss from the catchment3.
These limitations seem to be common across scales, but there are also positive and negative feedbacks of geoengineering that are difficult to predict. For example, a cooled climate may alleviate eutrophication symptoms in fresh waters, such as cyanobacterial blooms or the effects of rapid expansion of non-native species from warmer areas6. A decrease in phosphorus following rapid phosphorus control using geoengineering in fresh waters is likely to favour a decrease in methane ebullition from lakes to the atmosphere7. Altering weather may change catchment productivity, which is also linked to carbon dioxide losses to the atmosphere from lakes8. Both climate mitigation and phosphorus control are likely to reduce coastal fish stocks, compounding the negative socioeconomic effects of overfishing9.
Management of climate systems may cause geopolitical problems that benefit some nations at the expense of others1. Similarly, in fresh waters, although the scale of effect is smaller, the projected financial burden of meeting the European Water Framework Directive through geoengineering is equally large (that is, about US$100 billion; ref. 3). The need to consider transboundary environmental and geopolitical conflicts across connected ecosystems has been acknowledged for both climate1 and freshwater systems10. However, negotiations will be required, during which the financial burden of 'the polluters' may be balanced with the resultant financial gain of 'the polluted'. For fresh waters, the benefits of geoengineering to alleviate eutrophication symptoms are likely to be constrained to the region in which the managed system is situated, whereas the benefits of geoengineering to alleviate climate change symptoms may, arguably, be much wider in scale2.
Geoengineering is mitigation, rather than adaptation, and continual and costly treatment of chronic symptoms will be required if the root causes of the problems (for example, nutrient loading and greenhouse-gas emissions) are not addressed11. We call for a more comprehensive long-term perspective when planning environmental management at this scale. |