Pop quiz: What causes mass planetary extinction events? Asteroids—yep. Volcanic explosions—those too. But the biggest cause of extinction events right now and in the foreseeable future? PEOPLE.

A new study examined what the ocean will look like in the future if we keep burning all the fossil fuels we can lay our hands on. And if we do, the future for the ocean is grim indeed. The researchers applied powerful Earth system models that faithfully recreate the behavior of the ocean, land and atmosphere to game out the future.

The researchers found that unchecked fossil fuel burning will cause a mass extinction event in the ocean in the far future. By 2300, ocean warming and dwindling oxygen will eliminate the huge diversity of marine life that has filled the ocean for the past 50 million years. The authors have compared what’s in store to a period that geoscientists call “The Great Dying.” This was the largest mass extinction in Earth’s history some 250 million years ago driven by a huge upswing in planetary volcanic activity. About 90% of all marine life and 70% of all terrestrial life went extinct as a result.

Yep, you heard that right. If we don’t get our act together fast, humans will be directly responsible for The Next Great Dying.

But the researchers also showed that there is still hope for the ocean. If we cap planetary warming to less than 2°C, losses of marine species will be minimized. At 1.5°C it would be even better, as it would protect stony corals and other species that are at greatest risk. But limiting planetary warming to that level requires immediate, decisive shifts away from the most-polluting behaviors that have put our global society on this path.

What will we do to save the ocean we love?

Will we upend our bad habits, our greed and our obsession with convenience to reimagine what our global society can be? Are we brave enough to rapidly embrace the solutions that are ready now that will help us do this? The science is clear, many technologies are available and the cost of using them continues to drop.

So many ocean-based solutions exist already to help transform the future. We can decarbonize our transportation and manufacturing, and transition to renewable energy sources both on land and in the ocean. By investing in people and communities (particularly those suffering the most from climate change), we can create a society built around the common good instead of immediate profit for a few. Ocean Conservancy is working hard on these and other climate solutions.

The alternative is to continue the short-sighted habits that the previous few generations hooked us on and be responsible for the next great planetary extinction. Technically, we have a choice—but to me, there is only one answer. Climate action is essential. Take action today by urging our leaders to act on climate now and avoid this devastating future for our ocean.