The ocean plays a critical role in moderating climate change by absorbing excess heat and carbon dioxide, but this comes at the cost of significant changes in its chemistry and physics. The study compares two emission scenarios: RCP2.6, which aligns with the Copenhagen Accord's goal of limiting global warming to less than 2°C, and RCP8.5, representing a business-as-usual trajectory of carbon emissions. Under RCP8.5, the ocean will be much warmer and more acidic by 2100, with severe impacts on marine ecosystems, biodiversity, and human societies. The paper highlights the urgent need for ambitious carbon emission reductions to minimize these impacts. Ocean acidification, warming, and deoxygenation have profound effects on marine life, including coral reefs, shell-forming organisms, and fish populations. These changes threaten ecosystem services such as coastal protection, fisheries, and tourism, as well as human health and economic stability. The study emphasizes that current emission levels are already causing detectable impacts, and without significant reductions, these effects will worsen. The paper calls for immediate action to reduce emissions and protect marine ecosystems, stressing that the ocean's ability to absorb carbon is declining as emissions increase. The findings underscore the importance of integrating ocean-related issues into climate policy to ensure sustainable development and protect vulnerable communities.The ocean plays a critical role in moderating climate change by absorbing excess heat and carbon dioxide, but this comes at the cost of significant changes in its chemistry and physics. The study compares two emission scenarios: RCP2.6, which aligns with the Copenhagen Accord's goal of limiting global warming to less than 2°C, and RCP8.5, representing a business-as-usual trajectory of carbon emissions. Under RCP8.5, the ocean will be much warmer and more acidic by 2100, with severe impacts on marine ecosystems, biodiversity, and human societies. The paper highlights the urgent need for ambitious carbon emission reductions to minimize these impacts. Ocean acidification, warming, and deoxygenation have profound effects on marine life, including coral reefs, shell-forming organisms, and fish populations. These changes threaten ecosystem services such as coastal protection, fisheries, and tourism, as well as human health and economic stability. The study emphasizes that current emission levels are already causing detectable impacts, and without significant reductions, these effects will worsen. The paper calls for immediate action to reduce emissions and protect marine ecosystems, stressing that the ocean's ability to absorb carbon is declining as emissions increase. The findings underscore the importance of integrating ocean-related issues into climate policy to ensure sustainable development and protect vulnerable communities.