Final answer:
Reliable instrumental records of climate are generally only available for the past few hundred years, but scientists can study Earth's past climate using proxies such as fossils, ice cores, tree rings, and sediment cores.
Step-by-step explanation:
Reliable instrumental records of climate are generally only available for the past few hundred years. However, scientists can indirectly study Earth's past climate by analyzing proxies, which are secondary sources of information such as fossils, ice cores, tree rings, and sediment cores. These proxies provide valuable insights into past climate conditions and help scientists understand long-term climate patterns.