Marine ecosystems play a critical role in regulating the Earth’s climate, acting as vast carbon sinks, influencing weather patterns, and supporting global biodiversity. Oceans absorb over 90% of the excess heat generated by greenhouse gas emissions and sequester significant amounts of atmospheric CO₂ through biological and physical processes, such as phytoplankton photosynthesis and ocean circulation. However, climate change is profoundly affecting marine environments through rising sea temperatures, ocean acidification, deoxygenation, and shifting current systems. These changes threaten the structure and function of marine ecosystems, including coral reefs, mangroves, and polar habitats, with cascading effects on marine food webs, fisheries, and coastal communities. Protecting and restoring marine ecosystems is essential for climate resilience, carbon storage, and the preservation of ecological balance. Integrated ocean-climate policies, marine protected areas, and sustainable management practices are vital to safeguarding marine biodiversity and the ocean’s role in climate regulation.