Background
The authors write that "as stressors accumulate across global to local scales, some combine to produce synergistic effects which cause changes of disproportionate ecological magnitude," and they suggest that "it would be particularly useful to understand whether the synergistic effects of global and local stressors could be alleviated, leading to slower change or faster recovery, if conditions under the control of local management alone were managed (i.e., nutrient pollution)."

What was done
In broaching this important question, Falkenberg et al. state that they "utilized field-based mesocosms to manipulate CO2 (i.e., forecasted global concentrations) and nutrients (i.e., local pollution) to test the hypothesis that, where synergies exist, reducing one contributing stressor would limit the effect of the other." And so it was that in testing this hypothesis, they chose to consider "the response of turfing algae, which can displace kelp forests on urbanized coastlines."

What was learned
The three Australian researchers say they demonstrated that "by reducing a locally determined stressor (i.e., nutrient pollution), its synergistic effects with a globally determined stressor (i.e., CO2 enrichment) on turf-forming algae may be substantially reduced."

What it means
In the concluding sentence of their paper's abstract, Falkenberg et al. state that "these results suggest that in the face of changing climate (e.g., ocean acidification), the management of local stressors (e.g., water pollution) may have a greater contribution in determining the dominant state than current thinking allows." Or as they put it in the concluding sentence of the body of their paper, "these results suggest that in the face of changing climate (e.g., ocean acidification), effective management of local stressors (e.g., water pollution) may have a greater contribution in determining natural habitats than currently anticipated."

Either way one looks at it, the marine environment wins.