As they prepared to publish their findings, the researchers felt uneasy. Their study showed two very different future outcomes for ocean life depending on whether greenhouse gas emissions were reduced or continued at current levels. The title of the study seemed to only emphasize the negative aspects of their results, so they added a word to highlight the possibility of avoiding the bleak scenario described in their findings. The most recent research published in Science on Thursday, titled "Avoiding Ocean Mass Extinction From Climate Warming," highlights the critical juncture humanity is currently facing. The decisions made now regarding greenhouse gas emissions will have a profound impact on the future of life on Earth, despite the potential consequences seeming distant. According to the scientists' projections under a high emissions scenario, continued pollution from fossil fuel burning could lead to a level of ocean species loss by 2300 comparable to the five mass extinctions in Earth's history, including the event that caused the extinction of the dinosaurs. Penn, a postdoctoral researcher at Princeton, described his reaction to a graph comparing past extinctions with a grim forecast as more of an "oh, my God" moment rather than an "aha" moment. Scientists found that reducing emissions to stay within the upper limit of the Paris climate agreement could decrease ocean extinction risks by over 70%. In this scenario, climate change would result in about 4% of species being lost by the end of the century. Deutsch emphasized the significant impact our choices have on the environment. While transitioning away from coal towards wind and solar energy could prevent the worst-case scenario, the continued use of oil and gas is causing emissions to rise, putting the world off track to meet the lower-emissions scenario projected by scientists. The recent study expands on Deutsch and Penn's previous research by developing a computer simulation that examines the most severe extinction event in Earth's history around 252 million years ago. Known as "the Great Dying," this event resulted in the loss of over 90% of species in the oceans due to global warming caused by volcanic eruptions. The oceans experienced a decrease in oxygen levels, leading to fish dying from heat stress, asphyxiation, or both. The computer model revealed higher extinction rates at the poles than in the tropics, a finding that was supported by the fossil record. The scientists used a complex model to predict the impacts of global warming caused by human activity, considering factors such as sunlight, clouds, ocean and air currents, and chemical interactions among heat, oxygen, water, and air. They also examined potential shifts in fish habitats and estimated survivability thresholds. The study focused on warming and oxygen loss, but noted that ocean acidification and other consequences could exacerbate species loss. The ocean has historically served as a buffer against climate change by absorbing carbon dioxide and heat from human activities like burning fossil fuels and deforestation. The provision of that service has resulted in negative consequences. The ocean experienced its highest temperature and lowest oxygen levels last year since the beginning of human record-keeping. Alterations in the ocean's chemical composition are currently endangering fish populations, while coral reefs are rapidly deteriorating. Deutsch frequently hears questions about how dire the situation is. "If we fail to take action, we are in serious trouble." Countries are still not close to taking the necessary actions to prevent catastrophic climate change. UN Secretary-General António Guterres recently warned that the goal of limiting global warming to 1.5 degrees Celsius since preindustrial times is in jeopardy. The International Energy Agency has stated that countries must immediately halt new fossil fuel projects, but they have not done so. The recent conflict in Ukraine has led to calls for increased drilling for energy security. Scientists Deutsch and Penn compare their situation to the ignored scientists in the movie "Don't Look Up," where a comet symbolizes climate change. Like in the film, the world is at a crucial juncture, with current generations having a significant role in shaping the future. Deutsch emphasized the importance of understanding the responsibility that comes with great power, particularly in relation to future generations and all other life on the planet. Pippa Moore, a marine science professor at Newcastle University, praised the study for its comprehensive analysis of the impact of climate change on marine ecosystems. She warned that without significant efforts to reduce greenhouse gas emissions, marine species could face significant shifts in habitat and potential extinction events comparable to past mass extinctions. Brad Plumer provided additional reporting for this article.