The insights that can be gained by studying ancient temperature trends are limited, however.

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The scientists did the study to put the global temperature trends into a long-range perspective, Marcott said.

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Only during the last quarter of the century was there an appreciable correlation between greenhouse gas trends and global temperature trends.

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As you can see in the graph to the right, the temperature trends from the PI strongly correlate with that from MLOST.

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After all, what do pre-industrial world temperature trends have anything to tell us about the effect of man-made Co2 on 20th century temperatures?

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The global temperature trends since then have followed not rising CO2 trends but the ocean temperature cycles of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO).

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Before they can make much progress in confirming that suggestion, climatologists need a stream of reliable data on worldwide temperature trends, both at the surface and in the atmosphere.

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That lack of association between temperature trends and CO2 has continued over the last century, as the up and down pattern of global temperatures over the past 100 years does not follow the upward climb of CO2 as the industrial revolution has expanded globally.

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The study points to human activity as the cause, because of the suddenness of the shift in temperature which appears to be out of whack with long-term trends.

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