This book provides a foundational overview of climate change, focusing on its impact on natural systems, human activities, and diseases. It discusses key natural variables influencing the Earth's climate, such as greenhouse gases, Earth's orbital variations, and solar radiation, which have shaped temperatures over millennia. However, recent decades have seen accelerated changes largely driven by human activities, particularly fossil fuel combustion and industrial agriculture, resulting in increased carbon dioxide, methane, and nitrous oxide emissions. These emissions contribute to global warming and ocean deoxygenation, which affect aquatic life by altering species' metabolism, growth, reproduction, and survival. Adaptation strategies, like modifying agriculture and constructing coastal defenses, offer temporary relief, but significant change depends on mitigation measures such as geoengineering. This book is designed as an introductory resource for students interested in climate change research, with an emphasis on the intersection of climate change and disease dynamics.