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In page Global surface temperature:

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When scientists explored the trapped gas in the ice core bubbles, they found that the methane concentration in Greenland ice core is significantly higher than that in Antarctic samples of similar age, the records of changes of concentration difference between Greenland and Antarctic reveal variation of latitudinal distribution of methane sources.[3] Increase in methane concentration shown by Greenland ice core records implies that the global wetland area has changed greatly over past years.[4] As a component of greenhouse gases, methane plays an important role in global warming. The variation of methane from Greenland records makes a unique contribution for global temperature records undoubtedly.[citation needed]