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Thomas observed a graph showing changes in Earth's glaciers. After looking at the graph, he came to a conclusion about Earth's climate and stability. Based on the graph below, what conclusion did Thomas make about Earth's climate?

Earth's climate goes through short-term cycles of cooling and warming.

Earth's climate goes through long-term cycles of cooling and warming.

Earth's climate appears to be cooling over a period of time.

Earth's climate appears to be irregularly cooling and warming.