They have various methods. One of the common ones is analyzing ice core samples. The ice sheets are accumulated over the years so each layer on ice sheets is from a certain historical period (much like tree trunks.) By analyzing the chemical status of the ice core on each layer, they can extract data, such as temperature, about a certain period.
How do they estimate temps so long ago? What data do they use?
They have various methods. One of the common ones is analyzing ice core samples. The ice sheets are accumulated over the years so each layer on ice sheets is from a certain historical period (much like tree trunks.) By analyzing the chemical status of the ice core on each layer, they can extract data, such as temperature, about a certain period.