evidence: Geological records show that there have been a number of large variations in the Earth’s climate. These have been caused by many natural factors, including changes in the sun, emissions from volcanoes, variations in Earth’s orbit and levels of carbon dioxide (CO2). [...] According to Milankovitch’s theory, these three cycles combine to affect the amount of solar heat that reaches the Earth’s surface and subsequently influences climatic patterns, including periods of glaciation (ice ages). The time period between these changes can be tens of thousands of years (precession and axial tilt) or more than hundreds of thousands of years (eccentricity). [...] Each of these factors contributes to changes in the Earth’s climate, but the way they interact with each other makes it more complicated. A change in any one of these can lead to additional and enhanced or reduced changes in the others.