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Climate bulletin - May 2017

Summary of the world's climate in May 2017

The global average temperature for May 2017 as estimated from the HadCRUT. data set was 0.65±0.16°C above the 1961-1990 average. Globally May 2017 was one of the ten warmest Mays on record and most likely the third warmest. Global temperature data sets maintained by NASA GISS, NOAA NCEI, Berkeley Earth and C3S also show that May was a very warm month globally. May was nominally 2nd or 3rd warmest in each of these data sets. Sea-surface temperatures in much of the tropical Pacific were near or slightly above average indicating neutral ENSO conditions. SSTs in the eastern Tropical Pacific, close to the coast of South America, which were much warmer than average in March and April, were much closer to average in May.


The global average land temperature for May 2017 was 0.94 ± 0.27°C above the 1961-1990 average. For global land areas May 2017 was nominally the 5th warmest May on record and very likely in the top fifteen.  Unusual warmth – temperatures exceeding the 90th percentile for the month – was recorded in: northwest Canada, areas of South America, including Brazil, parts of Central America and the Caribbean, Madagascar, parts of South Africa, and some islands in the Tropical Pacific. Unusually high temperatures (in places coupled with low rainfall) were also reported across an area extending from Iceland, through western Europe (both the UK and Spain had their second warmest May, Portugal its third warmest), the Mediterranean, north Africa, the Middle East (exceptional temperatures were recorded in Iran late in the month), western parts of India, Mongolia, China and Japan. Few areas were unusually cold with temperatures below the 10th percentile. These were: northwest Russia, an area of north-western Australia and a station on the northeast coast of Greenland.

The global average sea-surface temperature for May 2017 was 0.56 ± 0.09°C above the 1961-1990 average, nominally the third warmest on record and very likely one of the six warmest. Sea surface temperatures in the tropical Pacific were near average with some areas warmer than the long-term mean, indicating neutral ENSO conditions. The previous area of unusually high SST in the eastern Pacific, near the coast of South America, dissipated during May. Areas of unusually warm SST included: large areas of the North Atlantic and tropical Atlantic including the Caribbean; the Indian Ocean (except for the area to the west of Australia and Indonesia); areas of the Pacific, particularly west of the dateline and around 30°N and 30°S. Unusually-low SSTs were recorded in limited areas which included: an area to the southeast of Newfoundland, parts of the South Atlantic, an area to the west of Australia and Indonesia. Other areas of below average SST – where historical coverage is too low to accurately assess the significance of current anomalies – include an extended area in the Atlantic sector of the Southern Ocean which has persisted for several months.

As in April, there was a band of cooler-than-average waters in the North Pacific at around 45°N surrounded by areas of warmer-than-average waters. This pattern is characteristic of the positive phase of the Pacific Decadal Oscillation (PDO). Some measures of the PDO have been indicating a shift to its positive phase since the start of 2014. However, on short time scales, SST patterns associated with the PDO look very similar to those associated with El Niño. As ENSO conditions are currently neutral, this suggests a more persistent shift to the positive phase of the PDO. However, other indicators (e.g. the Tripole Index or TPI) have returned to near-neutral, so it is not yet clear. The negative phase of the PDO has been associated with a reduction in the rate of global temperature increase since the start of the millennium.

Higher than average precipitation totals (based on the monthly first-guess analysis by the Global Precipitation Climatology Centre, GPCC) were recorded across: southern Brazil and neighbouring countries; Oman and southeast Saudi Arabia; northern parts of India and western China; large areas of Russia. In Australia, an area crossing the base of the Cape York Peninsula saw higher than average rainfall, with some locations reporting their wettest May day on record . Parts of eastern Africa also received more rain than usual. In Sri Lanka, heavy rain led to flooding. Heavy rain across eastern areas of North America combined with melting snow lead to flooding in Quebec. Higher than average rainfall in Thailand and Cambodia saw flooding in Bangkok. Drier than average areas included: much of the rest of Australia; the Mediterranean, except Greece and Turkey; central Europe and the Baltic; parts of Southern Africa, southern Japan and Korea.

Based on data from the HadISST. data set and the National Snow and Ice Data Center in the US, Northern Hemisphere (Arctic) sea ice was nominally the 4th or 5th least extensive May on record. Southern Hemisphere sea-ice extent was nominally the 2nd or 3rd least extensive on record (May 1980 and May 1987 were comparable or had less extensive Antarctic sea ice). Sea-ice extent in the Antarctic has been unusually low since late last year. For more details and analysis of the ice extents including updates throughout the summer, see the sea-ice monitoring brief.



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