Large-landscape conservation can play a key role in advancing nature-based climate mitigation solutions at scale. The Yellowstone to Yukon Conservation Initiative (Y2Y) has been working for over 30 years to protect and connect North America’s transboundary Rocky Mountain region so that people and nature can thrive. More recently, Y2Y has focused on understanding and protecting the climate regulating benefits of this carbon-rich region. This talk presents Y2Y’s efforts to quantify and map carbon storage and sequestration characteristics across the 1.3 million square kilometre Y2Y region, to assess key threats to nature-based climate mitigation, and to safeguard priority areas in ways that maximize carbon protection as well as other socio-ecological co-benefits. The presentation demonstrates the out-sized climate regulating benefits of the Y2Y region and invites comparative analyses from other mountain areas globally.