The Marine Mammal Climate Change Protection Act of 2026 amends the Marine Mammal Protection Act of 1972 to establish a framework for conserving marine mammals threatened by climate change. It mandates the Secretary of Commerce, in consultation with the Marine Mammal Commission, to identify and list marine mammal species and population stocks in U.S. waters that are likely to experience population decline or reduced carrying capacity due to climate change within 20 years, or 100 years for Endangered Species Act-listed species. For each listed species or stock, the Secretary must develop a climate impact management plan (CIMP) within 18 to 30 months. These plans will outline comprehensive strategies for conservation and recovery, focusing on increasing resiliency, reducing human impacts like fisheries interactions, and managing prey species. Other federal agencies are required to utilize their authorities to support these CIMPs and ensure their actions do not conflict with the plans' objectives. The bill also establishes a monitoring program within NOAA to track climate change's adverse effects on marine mammals, improve predictive models, and assess their contribution to carbon reduction. It directs the Secretary to publish regulations for listing climate-impacted species, emphasizing that a lack of quantitative data should not prevent such listings. Furthermore, the bill requires considering climate impacts when estimating potential biological removal levels in stock assessments and authorizes appropriations for its implementation.