The variations in greenhouse gas concentrations present in the atmosphere are known by comparing the modeled evolution during astronomical cycles with the observed paleoclimatic changes. The comparisons allowed scientists and researchers to observe climate change and then gave an independent estimate of changes in the concentration of greenhouse gases. The most notable changes from using this measurement are the concentration of carbon dioxide and methane, as these gases are stored in peat, tundra, and ocean sediments in colder climates, and are released into the atmosphere in a warmer climate. Carbon dioxide and methane are released, leading to a warming effect. Computer modeling is able to provide strong evidence that the role of greenhouse gases in changing past climate will further affect the future.