Scientists looking for a reason for the current "pause" in global warming believe they may have found the culprit in Pacific and Atlantic ocean cycles that have a major impact on Northern Hemisphere temperatures.
Following a big increase since industrialization global temperatures have been rather flat since 2000. Prompting some to claim that global warming was down to natural cycles. Research from Penn State University suggests that the pause is down to a combination the Atlantic Multidecadal Oscillation (AMO) and the Pacific Multidecadal Oscillation (PMO) and if these swing back global warming could come back with a vengance. The 'flattening' of global surface temperatures observed over the past 15 years or so is due to the artificial warming, from excess carbon dioxide emissions, being balanced by the cooling caused by the shift in the PMO and a neutral shift for the AMO. If the human-caused warming trend is largely being masked by this recent strong 'down-trend' in the PMO, an upswing in the oscillation would not only remove the mask, allowing the true warming trend to show through, but it could augment the trend to a dangerous extreme.