Cultivating climate literacy among students allows them to understand, communicate, and make informed decisions about the weather, climate, functions, and impacts. Next Generation Science Standards (NGSS Lead States, 2013) and the Essential Principles for Climate Literacy (NOAA, 2009), partnered with science education reform, have created teaching and learning opportunities about Earth's climate and GCC in formal K-12 classrooms. However, teachers still report feeling challenged in understanding Earth's climate system, underprepared in teaching it, describing GCC instruction as a low priority (Hestness et al., 2011; Plutzer et al., 2016). We engaged in a 3-year, NSF-funded project to design and implement a new, 3-week curriculum unit designed around an online, computer-based global climate modeling tool to address this need. Based on HS-ESS3-5 (NGSS, 2013), this geoscience curriculum engages students in an authentic exploration of the Earth's climate and GCC using the Easy Global Climate Model(EzGCM) grounded in authentic NASA climate data. We followed two secondary science teachers over three years, using a combination of interviews, classroom observations, and daily reflections to access 1) In what ways do teachers implement the project curriculum? 2) How and why do they implement it in the ways that they do? and 3) How teachers' implementation changes during the project? Our findings from this longitudinal mixed-methods study show that in Y1, while the project curriculum was primarily built to highlight the practice of using climate models, teachers focused on describing model construction. However, while this remained true for one teacher across all three years, the other teacher made significant changes to her implementation during the project. During all three years, both teachers brought external resources than those explicitly written for the CliMES curriculum. These findings have implications for curriculum design, teacher professional development, and how secondary science teachers can support student learning about Earth'sEarth's climate.