Journalists produce news, and a powerful tool they have is the choice of sources for articles, selecting from a wide variety of organizations and individuals. The "balance norm'' has been an important principle guiding journalism, emphasizing objectivity in reporting and covering opposing perspectives. However, recent changes in newsroom revenue models, staff demographics, and Trump's attacks on the mainstream media challenge this norm. This paper empirically examines how individual and political factors affect journalists' citation patterns for climate change articles in six major U.S. newspapers for 2012-2022. We construct the most comprehensive dataset of news source citations using large language models and use the DIME data to measure article slant. We extracted nearly 89,000 sources from approximately 17,000 news articles on climate change. The volume of articles on this topic increased sharply after 2018, a trend primarily driven by more liberal media outlets such as the New York Times and the Washington Post. For the sources extracted, we categorize them into various types, including academics, bureaucrats, businesses, and nonprofit organizations. U.S. government sources. There is variation across media outlets in terms of the sources they rely on. We document how the characteristics of individual journalists correlate with source citation patterns. We collect data on journalist-level characteristics, focusing on their education and experience. Our findings reveal that journalists with less experience and elite education increasingly write articles with a greater leftward slant. Additionally, we show that Trump's presidency has led to more ideologically polarized articles, especially among the most left-leaning journalists.