It is very likely that 2017 will be one of the three hottest years on record, with many high-impact events including catastrophic hurricanes and floods, debilitating heatwaves and drought. Long-term indicators of climate change such as increasing carbon dioxide concentrations, sea level rise and ocean acidification continue unabated. Arctic sea ice coverage remains below average and previously stable Antarctic sea ice extent was at or near a record low.
The WMO statement – which covers January to September – was released on the opening day of the United Nations climate change conference (COP23) in Bonn, Germany. It includes information submitted by a wide range of UN agencies on human, socio-economic and environmental impacts as part of a drive to provide a more comprehensive, UN-wide policy brief for decision makers on the interplay between weather, climate and water and the UN global goals.
“The past three years have all been in the top three years in terms of temperature records. This is part of a long term warming trend,” said WMO Secretary-General, Petteri Taalas. “We have witnessed extraordinary weather, including temperatures topping 50 degrees Celsius in Asia, record-breaking hurricanes in rapid succession in the Caribbean and Atlantic reaching as far as Ireland, devastating monsoon flooding affecting many millions of people and a relentless drought in East Africa.
“Many of these events – and detailed scientific studies will determine exactly how many – bear the tell-tale sign of climate change caused by increased greenhouse gas concentrations from human activities,” he said.
Patricia Espinosa, Executive Secretary of UN Climate Change, which is hosting the Bonn conference, said: “These findings underline the rising risks to people, economies and the very fabric of life on Earth if we fail to get on track with the aims and ambitions of the Paris Agreement”.
“There is unprecedented and very welcome momentum among governments, but also cities, states, territories, regions, business and civil society. Bonn 2017 needs to be the launch pad towards the next, higher level of ambition by all nations and all sectors of society as we look to de-risk the future and maximise the opportunities from a fresh, forward-looking and sustainable development path,” she added.
Extreme events affect the food security of millions of people, especially the most vulnerable. A review of the Food and Agriculture Organisation (FAO) found that, in developing countries, agriculture (crops, livestock, fisheries, aquaculture and forestry) accounted for 26% of all the damage and loss associated with medium to large-scale storms, floods and drought.
According to the World Health Organisation (WHO), the global health impacts of heatwaves depend not only on the overall warming trend, but on how heatwaves are distributed across where people live. Recent research shows that the overall risk of heat-related illness or death has climbed steadily since 1980, with around 30% of the world’s population now living in climatic conditions that deliver prolonged extreme heatwaves. Between 2000 and 2016, the number of vulnerable people exposed to heatwave events has increased by approximately 125 million.
In 2016, 23.5 million people were displaced during weather-related disasters. Consistent with previous years, the majority of these internal displacements were associated with floods or storms and occurred in the Asia-Pacific region. In Somalia, more than 760,000 internal displacements have been reported, according to the UN High Commissioner for Refugees and International Organisation for Migration (IOM).
The latest International Monetary Fund (IMF) World Economic Outlook indicates that adverse consequences are concentrated in countries with relatively hot climates and which are home to close to 60% of current global population.
Global temperatures in 2017
Global mean temperature for the period January to September 2017 was 0.47°±0.08°C warmer than the 1981-2010 average (estimated at 14.31°C). This represents an approximately 1.1°C increase in temperature since the pre-industrial period. Parts of southern Europe, including Italy, North Africa, parts of east and southern Africa and the Asian part of the Russian Federation were record warm and China was the equal warmest. The northwestern USA and western Canada were cooler than the 1981-2010 average.
Temperatures in 2016 and, to an extent, 2015, were boosted by an exceptionally strong El Niño. 2017 is set to be the warmest year on record without an El Niño influence. The five-year average 2013-2017 is provisionally 0.40°C warmer than the 1981-2010 average and approximately 1.03°C above the pre-industrial period and is likely to be the hottest on record.
The WMO statement is based on five independently maintained global temperature data sets. WMO now uses 1981-2010 instead of the previous 1961-1990 baseline as it is more representative of current climatic conditions and allows for more consistent reporting of information from satellite and reanalysis systems (some of which do not extend back to 1960) alongside more traditional data sets based on surface-observations. The change in the baselines has no influence on trend analysis.
Southern South America (particularly in Argentina), western China, and parts of southeast Asia were wetter than average. January to September was the wettest on record for the contiguous United States. Rainfall was generally close to average in Brazil, and near to above average in northwest South America and Central America, easing droughts associated with the 2015-16 El Niño. The 2017 rainy season saw above-average rainfall over many parts of the Sahel, with flooding in some regions (especially in Niger).
All-India rainfall for the 2017 monsoon season (June to September) was 5% below average. However, above-average rainfall in the northeast, and adjacent countries led to significant flooding.
The Canadian Prairies, the Mediterranean region, Somalia, Mongolia, Gabon and southwestern South Africa all received lower rainfall than average. Italy had its driest January to September on record.
Ice and snow:
Arctic sea-ice extent was well below average throughout 2017 and was at record-low levels for the first four months of the year, according to the National Snow and Ice Data Center and the Copernicus Climate Change Service. The Arctic annual maximum extent in early March was among the five lowest in the 1979-2017 satellite record, and according to the NSIDC’s data was record low. The five lowest maximum extents have occurred since 2006.
A strong and persistent low pressure system over the central Arctic helped to inhibit ice loss during the summer months. The Arctic sea ice extent minimum in mid-September was 25- 31% below the 1981-2010 average, and among the eight smallest minimum extents on record. The ten smallest minimum extents have all occurred since 2007.
Antarctic sea ice extent was also well below average. The annual minimum extent in early March was record low, and the annual maximum extent in mid-October was at or near record low levels. Sea ice conditions in the Antarctic have been highly variable over the past several years with the record large sea ice extents occurring as recently as 2015.
Northern Hemisphere snow cover extent was 10.54 million square km, near the median value in the 1967-2017 satellite record.
The Greenland ice sheet saw an increase of more than 40 billion tons of ice due to above-average snowfall and a short melt season. Despite the gain in overall ice mass this year, it is only a small departure from the declining trend, with the Greenland ice sheet having lost approximately 3,600 billion tons of ice mass since 2002.
The global mean sea level (GMSL) is one of the best climate change indicators. Global mean sea level has been relatively stable in 2017 to date, similar to levels first reached in late 2015. This is because the temporary influence of the 2015-16 El Niño (during which GMSL peaked in early 2016 at around 10 millimeters above the 2004-2015 trend) continues to unwind and GMSL is reverting to values closer to the long-term trend. Preliminary data indicate that a rise in GMSL may have started to resume from July-August 2017 onwards.
Global sea surface temperatures are on track to be among the three highest on record. Global ocean heat content in 2017 to date has been at or near record high levels. Elevated tropical sea surface temperatures which contribute to coral bleaching were not as widespread as during the 2015-16 El Niño. But some significant coral bleaching did still occur, including the Australia’s Great Barrier Reef. UNESCO reported in June that all but three of the 29 coral reefs with World Heritage listing had experienced temperatures consistent with bleaching at some point in the 2014-2017 period.
According to the Intergovernmental Oceanographic Commission of UNESCO the ocean absorbs up to 30% of the annual emissions of anthropogenic CO2 in the atmosphere, helping to alleviate the impacts of climate change on the planet. However, this comes at a steep ecological cost, as the absorbed CO2 changes acidity levels in the ocean. Since records at Aloha station (north of Hawaii) began in the late 1980s, seawater pH has progressively fallen, from values above 8.10 in the early 1980s to between 8.04 and 8.09 in the last five years.
Ocean acidification is directly influencing the health of coral reefs and the survival and calcification of several key organisms. These have cascading effects within the food web and impact aquaculture and coastal economies.
The rate of increase in CO2 from 2015 to 2016 was the highest on record, 3.3 parts per million/year, reaching 403.3 parts per million. Global average figures for 2017 will not be available until late 2018. Real-time data from a number of specific locations indicate that levels of CO2, methane and nitrous oxide continued to increase in 2017.
Extreme Events and Impacts
The North Atlantic had a very active season. The Accumulated Cyclone Energy (ACE) index, a measure of the aggregate intensity and duration of cyclones, had its highest monthly value on record in September.
Three major and high-impact hurricanes occurred in the North Atlantic in rapid succession, with Harvey in August followed by Irma and Maria in September. Harvey made landfall in Texas as a category 4 system and remained near the coast for several days, producing extreme rainfall and flooding. Provisional seven-day rainfall totals reached as high as 1,539 mm at a gauge near Nederland, Texas, the largest ever recorded for a single event in the mainland United States.
It was the first time two Category 4 hurricanes (Harvey and Irma) made landfall in the same year in the USA. Irma had winds of 300 km/h for 37 hours – the longest on the satellite record at that intensity and spent three consecutive days as a Category 5 hurricane, also the longest on record. Like Irma, Maria also reached category 5 intensity and caused major destruction on a number of Caribbean islands. In mid-October, Ophelia reached major hurricane (category 3) status more than 1,000 kilometers further northeast than any previous North Atlantic hurricane. It caused substantial damage in Ireland, whilst winds associated with its circulation contributed to severe wildfires in Portugal and northwest Spain.
The WMO Expert Team on Climate Impacts on Tropical Cyclones found that, whilst there is no clear evidence that climate change is making the occurrence of slow-moving, land-falling hurricanes such as Harvey more or less frequent, it is likely that human-induced climate change makes rainfall rates more intense, and that ongoing sea-level rise exacerbates storm surge impacts.
Exceptionally heavy rain triggered a landslide in Freetown, Sierra Leone in August, killing more than 500 people. Freetown received 1459.2 mm of rain in two weeks, about four times higher than average. Heavy rainfall contributed to a landslide in Mocoa, southern Colombia, in April, with at least 273 deaths reported.
Many parts of the Indian subcontinent were affected by monsoonal flooding, despite overall seasonal rainfall being near average. The most serious flooding occurred in mid-August in eastern Nepal, northern Bangladesh and nearby northern India. Mawsynram (India) received more than 1,400 mm from August 9 to 12. Rangpur (Bangladesh) received a month’s worth of rain (360 mm) on August 11 to 12. More than 1,200 deaths were reported in India, Bangladesh and Nepal, whilst more than 40 million people were displaced or otherwise affected. The WHO indicated that in Bangladesh alone, more than 13 000 cases of waterborne diseases and respiratory infections were reported during three weeks in August, whilst extensive damage was reported to public health facilities in Nepal.
Flooding affected many parts of Peru in March, killing 75 people and making 70,000 homeless. The FAO reported that there were significant crop production losses, particularly maize. Flooding of this type typically affects Peru during the late phase of El Niño events. Whilst there was no Pacific-wide El Niño during 2017, sea surface temperatures near the Peruvian coast in March were 2°C or more above average and similar to El Niño values.
Major flooding occurred mid-year in parts of southern China, especially within the Yangtze River basin. Peak totals from 29 June to 2 July topped 250 mm. Fifty-six deaths were reported and economic losses were estimated at more than $5 billion.
Heavy rain affected the western United States in January and February caused substantial flooding, numerous landslides and the evacuation of tens of thousands of people. It was the wettest winter on record for Nevada, and the second-wettest for California.
Parts of east Africa continued to be seriously affected by drought. Following well-below-average rainfall in 2016, the 2017 “long rains” season (March to May) was also dry in many parts of Somalia, the northern half of Kenya, and southeastern Ethiopia.
FAO reported that in Somalia, as of June 2017, more than half of the cropland was affected by drought, with herds reduced by 40-60% since December 2016. WFP estimates that the number of people on the brink of famine in Somalia has doubled to 800,000 since February 2017, with half the country needing assistance. WFP has confirmed that more than 11 million people are experiencing severe food insecurity in Somalia, Ethiopia and Kenya.
From November 2016 to mid-June 2017, more than 760,000 drought-related internal displacements in Somalia were recorded by the Protection and Return Monitoring Network (PRMN), a United Nations High Commissioner for Refugees (UNHCR) led project.
Kenya declared the 2017 drought a national disaster. Nairobi faced water shortages that compelled city authorities to ration water, whilst cereal prices rose and GDP figures were hit.
An above-average wet summer season eased drought conditions in southern Africa. But localised drought intensified in the Cape Province.
Heavy winter rains in early 2017 eased long-term drought conditions in California, but resulted in some flooding, and contributed to vegetation growth which may have influenced the severity of wildfires later in the year.
Many parts of the Mediterranean experienced dry conditions. The most severe drought was in Italy, hitting agricultural production and causing a 62% drop in olive oil production compared to 2016. Rainfall averaged over Italy for January-August 2017 was 36% below average. It was also Italy’s hottest January-August on record, with temperatures 1.31°C above the 1981-2010 average. Other dry areas included many parts of Spain and Portugal.
The Democratic People’s Republic of Korea was affected by below-average rains, impacting key staple crops such as paddy and maize. In the Republic of Korea, rainfall from January to June was 51% below average, the lowest since national records began in 1973.
An extreme heatwave affected parts of South America in January. In Chile, numerous locations had their highest temperature on record, including Santiago (37.4°C). In Argentina, the temperature reached 43.5°C on 27 January at Puerto Madryn, the highest ever recorded so far south (43°S) anywhere in the world.
Much of eastern Australia experienced extreme heat in January and February, peaking on from February 11 to 12 when temperatures reached 47°C.
Exceptional heat affected parts of southwest Asia in late May. On May 28, temperatures reached 54.0°C in Turbat, in the far west of Pakistan near the Iranian border, and also exceeded 50°C in Iran and Oman. A temperature of 53.7°C was recorded at Ahwaz, Iran on June 29, and Bahrain experienced its hottest August on record.
The Chinese city of Shanghai and the Hong Kong Observatory reported new records of 40.9°C and 36.6 °C during summer.
In the Mediterranean, Cordoba in southern Spain experienced 46.9°C on July 12 and Granada 45.7°C on July 13. An extensive heatwave in early August led to temperature records in northern and central Italy, Croatia and southern France.
California had its hottest summer on record and extreme heat affected other western states. This culminated in a major heatwave at the end of August and early September, which included a record high temperature (41.1°C) at San Francisco.
Extreme heat and drought contributed to many destructive wildfires.
Chile had the most significant forest fires in its history during the 2016-2017 summer, after exceptionally dry conditions during 2016 followed by extreme heat in December and January.
Eleven deaths were reported, and a total of 614,000 hectares of forest were burnt, easily the highest seasonal total on record and eight times the long-term average. There were also significant fires during the 2016-2017 Southern Hemisphere summer in various parts of eastern Australia and in the Christchurch region of New Zealand, whilst the southern South African town of Knysna was badly affected by fire in June.
It was a very active fire season in the Mediterranean. The worst single incident occurred in central Portugal in June, with 64 deaths. There were further major fire outbreaks in Portugal and northwestern Spain in mid-October, exacerbated by strong winds associated with Hurricane Ophelia.. Other significant fires affected countries including Croatia, Italy and France.
The area burned in the contiguous United States from January to 19 October was 46% above the 2007-2016 average. The area burned in the western provinces of Canada was about eight times the 2006-2015 seasonal average and contributed to heavy smoke pollution. A wet winter, which allowed the heavy growth of ground vegetation, followed by a dry and hot summer, provided ideal conditions for high-intensity fires in northern California in early October. At least 41 deaths were reported, the worst loss of life in a wildfire in the United States since 1918.
Other noteworthy events
Severe cold and snow affected parts of Argentina in July. After heavy snow had fallen the previous day, the temperature reached −25.4°C in Bariloche on July 16, 4.3°C below the previous lowest temperature on record there. Other regions where record low temperatures occurred in 2017 included some locations in inland southeastern Australia in early July, where Canberra had its lowest temperature (−8.7°C) since 1971, and the Gulf region in the Middle East in early February.
The United States had its most active tornado season since 2011, with a preliminary total of 1,321 tornadoes in the January to August period, including the second-most active January on record.