<P> Dendroclimatology is the analysis of tree ring growth patterns to determine past climate variations . Wide and thick rings indicate a fertile, well - watered growing period, while thin, narrow rings indicate a period of lower rainfall and less - than - ideal growing conditions . </P> <P> Analysis of ice in a core drilled from an ice sheet such as the Antarctic ice sheet, can be used to show a link between temperature and global sea level variations . The air trapped in bubbles in the ice can also reveal the CO variations of the atmosphere from the distant past, well before modern environmental influences . The study of these ice cores has been a significant indicator of the changes in CO over many millennia, and continues to provide valuable information about the differences between ancient and modern atmospheric conditions . </P> <P> Remains of beetles are common in freshwater and land sediments . Different species of beetles tend to be found under different climatic conditions . Given the extensive lineage of beetles whose genetic makeup has not altered significantly over the millennia, knowledge of the present climatic range of the different species, and the age of the sediments in which remains are found, past climatic conditions may be inferred . </P> <P> Similarly, the historical abundance of various fish species has been found to have a substantial relationship with observed climatic conditions . Changes in the primary productivity of autotrophs in the oceans can affect marine food webs . </P>

What factors cause changes in temperature from place to place