Climate change reduces biodiversity by shifting temperatures beyond what many species can tolerate, and this chapter explains how those changes are measured using the Mean Species Abundance (MSA) metric. MSA reflects the degree to which ecosystems remain intact, and the model quantifies how CO₂ emissions lower the abundance of plants, birds, and mammals. The pathway begins with greenhouse gases entering the atmosphere and trapping heat, which raises global temperatures. As climates warm, species lose suitable habitat within their bioclimatic zones, reducing the fraction of species that can remain in each location. The chapter links these global temperature increases to measurable MSA losses using a 100year time horizon. Each kilogram of CO₂ emitted contributes to a small but quantifiable reduction in biodiversity across the planet. The calculation combines global warming potentials and observed biodiversity responses to estimate climatedriven MSA loss. Because GLOBIO uses universal MSA relationships, changes in species abundance are treated consistently across regions, even though realworld ecosystems differ.