This chapter presents an overview of climate changes, and assesses the potential effects on giant kelp and associated organisms. The earth's climate is changing at an unprecedented rate, and many predictions are critical about the consequent changes on ecosystems. In regard to the ocean, the major physical variables of change are likely to be temperature, wave forces, sea level, and pH from increasing atmospheric CO₂. The potential changes to kelp forest ecosystems are far less certain and largely assumed, due not only to the unpredicted and complex ways that climate variables may act on species and their interactions, but also in how they may act in a more direct way on giant kelp itself with its complex requirements and physiological-ecological responses across its life stages.