The oceans have nourished our species for millennia, but we sure have a funny way of showing our appreciation. Overfishing, pollution, climate change, acidification—I could go on. The sea has always been an indispensable tool for transportation and sustenance, and we’re in danger of breaking that tool beyond repair.

Yet the ocean also presents a unique, and perhaps overlooked, opportunity to fight climate change. But where to start? Do you invest in coastal habitat restoration to absorb more CO2, or in renewable energy like offshore wind farms to cut emissions in the first place? Or rather more extreme, do you cover the ocean surface with white foam to bounce solar radiation back into space, what’s known as geoengineering? What’s worth the time and effort and money, and what will just make matters worse?

An international team of scientists just took a big swing at helping address those questions. Their new review, published in Frontiers in Marine Science, looked at more than 1,000 studies of potential oceanic solutions to climate change. The goal was to quantify not only what might be the most effective way to go about things, but how feasible the technologies are. The researchers identified 13 different strategies and scored them on eight different criteria, including efficiency and the duration of the effects.

“The ocean is a very important actor in the climate system,” says lead author and ocean scientist Jean-Pierre Gattuso of France’s Laboratoire d'Océanographie de Villefranche. “It is a victim of climate change with regard to warming and acidification. But it's also a source of solutions.”

The bright spots in this evaluation? Strategies like coastal vegetation restoration, which helps suck up CO2, are already proven to be effective. So keep that up. Same with renewable energy and coral reef conservation. Among the murkier bits? It may sound fun and mad-sciencey to manipulate marine clouds to brighten them and reflect light back into space, thus cooling the seas, but the technology is far from proven, and it would do nothing to address ocean acidification (a consequence of increased CO2 uptake).

“Likewise the fertilization of the oceans using iron,” says Gattuso. Iron helps encourage the growth of phytoplankton, plant-like organisms that sequester CO2. Folks have even proposed doing this to create more food for fisheries, sparking controversy. “But we also know that there are many disbenefits, like it drives the oceans to low-oxygen concentrations, which is a problem for animals.” That on top of it not addressing the acidification problem.

On the other hand, what the study found to be extremely effective is the preservation of habitats like seaside mangrove forests and saltmarshes. More trees allow an ecosystem to capture more CO2 (to be clear, humans must significantly reduce CO2 emissions in the first place, and quickly—trees alone won’t solve our problems). Robust mangrove forests act as bulwarks against storm surges as well. Also on the vegetation front, growing more seaweed could locally reduce acidification.

Another strategy that scores high marks in the study is renewable energy, like wave energy converters, which could, at least in theory, provide twice the amount of energy humans need. And let’s not forget about coastal wind power. “If one covers the whole North Atlantic with offshore windmills, we could generate enough energy for the entire planet,” says Gattuso. “It has very few negative effects, so it's really something that stands out in our evaluation.”

Where things get trickier, though, are the more daring solutions like solar radiation management. Say you want to experiment with spreading some kind of light-colored foam on the surface of the ocean. Because it’s lighter than the ocean itself, it makes the sea reflect solar radiation instead of absorbing it, thus (theoretically) cooling the water. But to be effective (again, this is very theoretical) you’d need to spread the stuff over vast distances—an acre of coverage won’t do you any good. You might succeed in cooling the sea, but you might also end up altering the weather patterns for your country and your neighbors. They may not take too kindly to that.