My office at the University of California, Santa Barbara, looks out over the coastline. The United States’ first set of offshore oil platforms dot the skyline, the source of the 1969 oil spill that started the modern environmental movement. Enormous cargo ships traverse an ocean mega-highway, bringing goods from around the world and occasionally striking and killing whales. Surfers ride waves, sailing boats head for the islands and, on clear days, the beaches crawl with sunbathers. Recreational fishers cast their lines from the pier, commercial fishers set lobster traps along the coast, and a small mussel farm is hidden below the water just offshore.

All of these activities are part of an intensifying ‘blue economy’, withdrawing value from the oceans that cover 71% of our planet. In many ways, this is a good thing. Shipping goods by sea is one of the most environmentally friendly ways to conduct global trade; farmed seafood is highly nutritious and often sustainable; offshore wind has the potential to generate huge amounts of green energy. But soon the already warming, already crowded ocean will reach the same points of no return that humans have reached on much of the land.

Indeed, aquaculture, or farming seafood, has increased about 5% each year for the past 30 years, and experts anticipate that this growth will continue for the next few decades. Offshore wind is rapidly expanding; the United Kingdom is building a 1,000-square-kilometre metropolis of wind turbines off its coast, and China quadrupled offshore wind production just last year, adding the equivalent of roughly 17 nuclear power plants. An even more enormous area for wind farms has been proposed off the US Atlantic coast, at 7,000 square kilometres, nearly the size of Puerto Rico. And by 2050, the amount of goods travelling by sea is expected to triple as a result of increasing global population, wealth and trade.

This is the dilemma at the centre of my research. For 20 years, I’ve studied how uses of the ocean cumulatively damage marine ecosystems, but also support vibrant human communities. From this work, I’ve come to feel there needs to be a collective deal to ensure that the economic benefits of the blue economy outweigh the ecological costs. I propose that any new ocean activities should be sustainable and also contribute to reduce pressure on the land.

There is precedent for such give-and-take deals. In the United States and elsewhere, developers who encroach on wetlands and streams must create or restore equivalent habitats elsewhere, often at ratios of two-to-one or significantly greater (for example, 10 hectares of new wetland for every hectare destroyed). Carbon credits operate in a similar way; fees paid for emissions can go towards planting forests or building renewable energy infrastructure.

A planetary deal of this kind should adhere to three constraints to be fair and effective.

First, insist on real gains — not coincidental ones. If coal-fired power plants are already being phased out, this shouldn’t count as a balancing factor for new offshore wind. If conservation easements already protect fallow farmland, this can’t work as the counterpoint to new aquaculture farms.

Second, actions need to be managed mainly through policy and regulations, not free markets. Left to their own devices, markets rarely incentivize sustainability or truly compensate for damage done to the environment. For example, evidence shows that increasing the amount of farmed fish in a free market does not reduce meat production.

Finally, large corporations should bear the brunt of the costs of the planetary deal. Encouraging small operators often improves environmental justice while increasing local livelihoods and economic security by keeping owners and workers local. Compensatory requirements should be proportionally less for these small operators and progressively more for larger ones, analogous to the way income tax works in much of the world.

So what might this planetary deal look like? For example, to receive a lease for a new 100-square-kilometre offshore wind farm, a company must restore twice as much coastal habitat. This restored habitat must be additional to any existing efforts to protect habitat, such as current global targets to protect 30% of land and sea.

Or, for a new commercial offshore fish farm, enough land used for livestock should be permanently fallowed to remove a volume of livestock equivalent to the intended fish production. Such ‘habitat credits’ could be traded in the same way as carbon credits. The cattle farmer would get paid a tradable credit per reduced cattle head and hectare; an aquaculture company would need to purchase that credit to cover the increase in fish production.

None of these options is politically easy — many will say that such policy and market regulation will slow progress and can be circumvented by determined bad actors — but in my opinion we must embrace them. They will require local, national and international coordination and enforcement, as well as public support. Science can help to inform and monitor effectiveness; government agencies will need to determinedly implement change. Moving forward with the blue economy without concomitant reductions in human pressures on both land and sea will simply sacrifice our oceans without planetary gain. That is no deal at all.