Final answer:
Reliable instrumental climate records date back approximately 150 years. Before this period, indirect measures like ice cores and tree rings provide insights into Earth's climate history, including events such as the Medieval Warm Period and the Little Ice Age.
Step-by-step explanation:
Reliable instrumental records of climate are generally only available for the past approximately 150 years.
For Earth's climate record, scientists analyze indirect measures of climate such as ice cores, tree rings, glacier size, pollen counts, and ocean sediments to piece together a historical picture. These proxies have provided a vast amount of information about Earth's past climate, significantly before reliable instrumental records began in the late 19th century.
These methods have helped to identify notable past climate events such as the Medieval Climate Anomaly and the Little Ice Age and how they align with certain drivers of climate change, including the Milankovitch cycles and the effects of industrialization.