Undergraduate biology educators strive to understand how to best teach students the concepts of climate change. The root of this understanding is the establishment of what students know about climate change. This research aims to describe undergraduate biology students' conceptions of climate change and their argument practices and associated cognitive biases in how they think about the topic. We used qualitative conception interviews to obtain data from 26 American biology undergraduate students who predicted how climate change would affect a forested ecosystem after an average of 1° increase in Fahrenheit (0.5°C change) over 25 years. Through deductive coding, we found the majority of students' predictions agreed with expert ideas. However, the students used various argument strategies (i.e., Reasoning and Cognitive Biases) in defending their choices, including Ecological Explanations, Observations, Anchoring, and Contrast Effects.