www.metoffice.gov.uk/media/pdf/8/c/Changes_In_The_Climate_System.pdf
Summary
Changes are occurring in some of the leading patterns of global climate variability, altering the risk of regional climate impacts worldwide and affecting decadal rates of global warming.
El Niño is now well underway and is growing in strength. This is likely to have widespread regional impacts and to continue to contribute to raised global average temperatures this year and next year.
On longer timescales, the Pacific Decadal Oscillation has been negative in recent years and this has been linked to a slowing of the rate of global warming. Changes in the North Pacific suggest that the PDO may now be entering its positive phase, but because understanding of what drives the low frequency behaviour of the PDO is limited and its predictability appears to be low, a definitive statement on its future state is not yet possible.
The Atlantic Ocean has been warm in recent years but is now showing the first signs of a switch to cooler conditions, consistent with observed changes in the deeper ocean circulation. Widespread impacts around the Atlantic basin are likely if this continues.
While global surface warming slowed from the end of the 20th century, our best estimates of global mean temperature for 2015 are at or near record levels, and this is consistent with climate predictions for similarly high values that we made last year (http://www.metoffice.gov.uk/news/releases/archive/2014/2015-global-temp-forecast). Record or near record temperatures last year and so far this year, along with the expected warming effects of El Niño, mean that decadal temperature trends are likely to increase. Barring a large volcanic eruption or a very sudden return to La Niña or negative AMO conditions which could temporarily cool climate, ten year global average warming rates are likely to return to late 20th century levels within the next two years. Nevertheless, the slowdown in warming is still an active research topic and trends over a longer (15 year) period will take longer to respond.
Further long-term global warming is expected over the coming decades but variations of climate worldwide from year to year or decade to decade will always depend on the subsequent variations in the patterns of climate variability described in this report.
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