In DepthClimate

Ocean cycles sidelined in 20th century temperature record

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Science  31 May 2019:
Vol. 364, Issue 6443, pp. 814
DOI: 10.1126/science.364.6443.814

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For decades, scientists have chalked up early swings in 20th century temperature to the planet's internal variability—in particular, a climatic pacemaker called the Atlantic Multidecadal Oscillation (AMO), said to warm and cool the ocean. But researchers are increasingly questioning whether the AMO played the dominant role once thought. A new study has found that it is now possible to explain the record almost entirely without the AMO. After correcting for the distinct effects of pollution hazes over land and ocean and for flaws in the temperature record, the researchers found that the interplay of greenhouse gases and atmospheric pollution almost single-handedly shaped the climate. Although the study could have reached different conclusions with different assumptions, outside researchers have conceded that the idea of regular multidecade cycles in the ocean is getting harder to defend.