What term describes the variations in climate over a period ranging from 10 to 30 years?

The term that describes the variations in climate over a period ranging from 10 to 30 years is the Pacific Decadal Oscillation (PDO). The PDO is a long-term climate pattern that affects the ocean temperatures in the Pacific Ocean and influences weather and climate variations over decades. It is recognized for its impact on climate conditions across the Pacific region, as well as effects on weather patterns in North America and other parts of the world. This oscillation can lead to significant shifts in temperature and precipitation patterns, which can last for several decades, making it distinct from shorter-term variations.

In contrast, global warming refers to the long-term increase in Earth's average surface temperature due to human activities and does not focus specifically on the multi-decadal variations. Climate oscillation is a broader term that can encompass various types of climate fluctuations, but does not specifically indicate the timed scale mentioned in the question. Seasonal variability highlights changes in weather patterns that occur within a year, which is not relevant to the longer time frame of 10 to 30 years. Thus, the Pacific Decadal Oscillation is the most accurate choice for this specific time frame of climate variation.