arXiv:2610.27143v1 Announce Type: new Abstract: Rising temperatures due to climate change will reduce power system transmission capacity. This reduction will interact with an ongoing shift from static to time-varying transmission rating standards. Previous research has yet to disentangle the effects of changing rating standards and climates on investment decisions. We quantify transmission investment needs for the Western U.S. power system (WECC) through mid-century under climate change and three rating standards: static ratings (SLR), ambient-adjusted ratings (AAR), and dynamic line ratings (DLR). By embedding alternative rating standards and high-resolution future weather data into a generation and transmission expansion model, PyPSA-USA, we find WECC will lose 1-3% of its transmission capacity across potential future climates under static ratings by mid-century, necessitating a 1-5% increase in transmission investment. Adoption of AAR or DLR eliminates most (81-99%) of the adaptation-driven transmission capacity needs, and further reduces aggregate transmission investments (by up to 31%). Additionally, we demonstrate that planning with time-varying ratings does not increase investment variability for individual lines under climate uncertainty relative to planning with static ratings. Our results emphasize the value and practicality of considering alternative rating standards in climate adaptation planning.