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Climate bulletin - July 2017

Summary of the world's climate in July 2017

The global average temperature for July 2017 as estimated from the HadCRUT. data set was 0.65±0.18°C above the 1961-1990 average. Globally, July 2017 was one of the seventeen warmest Julys on record but most likely the fourth warmest. Global temperature data sets maintained by NASA GISS, NOAA NCEI, Berkeley Earth and C3S also show that July was a very warm month globally. July was nominally between 1st and 4th warmest in these data sets. Sea-surface temperatures across the breadth of the tropical Pacific were near average indicating neutral ENSO conditions.

The global average land temperature for July 2017 was 1.08 ± 0.28°C above the 1961-1990 average. For global land areas July 2017 was nominally the warmest July on record and very likely one of the top thirteen.  Unusual warmth – temperatures exceeding the 90th percentile for the month – was recorded across western parts of the US and Canada, areas of Central America, Alaska, many areas of Africa where observations are available, Madagascar, Australia (where average daily maximum temperatures for July beat the previous record by a clear margin), southern India, Iceland and in a band running from the Mediterranean, through the Middle East to China and Japan.  Few areas were unusually cold with temperatures below the 10th percentile. These were small areas in ain the southeast of Brazil and southern China. An unusual cold spell from 14-21 July affected Argentina and neighbouring countries.

The global average sea-surface temperature for July 2017 was 0.54 ± 0.08°C above the 1961-1990 average, nominally the fourth warmest on record and very likely between second and tenth warmest. Sea surface temperatures in the tropical Pacific were near average, indicating neutral ENSO conditions. Areas of unusually warm SST included: the western Pacific, two bands around 30°N and 30°S in the Pacific, the Mediterranean and large areas of the Indian Ocean (except an area just west of Australia). The tropical Atlantic, Gulf of Mexico and western north Atlantic were much warmer than average in July. SSTs in the Atlantic hurricane Main Development Region (MDR) were warmer than average, with SSTs in some areas exceeding the 98th percentile. Areas of unusually low SST included limited regions of the southeast Pacific, south Atlantic and eastern Indian Ocean. Another area of below average SST – where historical coverage is too low to accurately assess the significance of current anomalies – was an extended area in the Atlantic sector of the Southern Ocean which has persisted for several months and has been spreading slowly east.

As in May, April and June, 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. 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 in a band running from Ireland (it was the wettest July at Shannon airport since 1946) and the UK, across Germany into eastern Europe and Russia. Parts of Norway and Sweden and southeast Europe were also wetter than average. Northwest Canada saw higher than average rainfall totals in July as did parts of the southwest and northeast US, eastern Brazil, New Zealand, areas of the Arabian Peninsula, western China, areas of Southeast Asia, including Vietnam and parts of Indonesia. Above average rainfall caused flooding in Gujarat in western India and heavy rain caused flooding in northeast India early in the month. In Japan, heavy rains lead to flooding in the north of the main island, Honshu.

Drier than average conditions were recorded: along the west coast of the US and areas of southern Canada; large areas of Brazil, Bolivia and Paraguay; Portugal; Italy; southern France (which has also been affected by wildfires) and parts of the Balkans. Austria found itself on the boundary between wet conditions to the north and dry conditions in the south. Australia was drier than average in the south, and much wetter than average in parts of the Northern Territory.

Based on data from the HadISST. data set and from the National Snow and Ice Data Center, the Northern Hemisphere (Arctic) sea ice extent in July 2017 was likely to have been between the 3rd and 7th least extensive in the satellite record for July. There is some uncertainty in the ranking as a number of years have very similar extents. Southern Hemisphere (Antarctic) sea ice extent was nominally the least extensive or 2nd least extensive July on record in both data sets. Sea-ice extent in the Antarctic has been unusually low since late last year likely due to high remnant sea-surface temperatures following the El Niño and unusual atmospheric circulation [link to paper]. For more details and analysis of the ice extents including updates throughout the summer, see the sea-ice monitoring brief.


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