Climate facts 2017 - The warmest non-El Niño year ever
2017 was one of the three warmest years on record. But even more important is the fact that it was the hottest year ever recorded without the warming effect of the natural climate oscillation, El Niño. All 17 years since 2001 rank among the 18 warmest years ever. And in all of this, scientists see a clear signal of climate change.
According to data in January 2018 from the US National Oceanic and Atmospheric Administration (NOAA), the global mean temperature in 2017 over land and sea surfaces exceeded the 20th century average of 13.9°C by 0.84°C. This makes the successive years 2014 to 2017 the four warmest in the measurement series since 1980. Also, 2017 was the third-warmest year, following on from the warmest-ever year of 2016, which was influenced by El Niño. It was also the warmest year without any influence from El Niño, which typically increases the global mean temperature. In this instance, the start of the year saw cool neutral and the end weak La Niña conditions.
On average, the greatest temperature anomalies occurred in central, northern and eastern parts of Asia, where temperatures during the winter and spring were already much too warm. Russia and China registered record high temperatures in the period January to September. It was also too warm in southern regions of North America and in Alaska – reflecting the significant temperature anomalies in the first and last few months of the year. The USA had its third-warmest year, while California experienced its hottest summer with a heatwave in August/September – thus providing one of the prerequisites for the severe forest fires later in the year.
Other land areas with positive temperature anomalies included eastern Australia, where parts of Queensland and New South Wales experienced their warmest year, with heatwaves in January/February 2017. It was also very warm in western Europe, and in parts of central and southern Europe. This was particularly so in March, then again during periods of extremely hot weather in June/July, and in southern Europe in August as well. Researchers have determined that, as a result of climate change, a hot summer like 2017 has become substantially more probable in the European Mediterranean area in comparison with the start of the 20th century. The probability is currently approximately 10% (World Weather Attribution, 2017).
There were also heatwaves in many other regions: at the start of the year in Argentina and Chile, and later in Pakistan, Iran and Oman, as well as in parts of China. The lower graph on page 60 shows that the global area affected each year by severe and extreme heat events in summer months has been steadily expanding since at least the 1990s. According to information from the World Health Organization, the average number of people annually exposed to heatwaves has increased by 125 million since 2000 (WMO, 2017).
The mean temperature in western Russia over the first ten months was slightly cooler than the 20th century average – the result of negative monthly anomalies in this region and neighbouring areas in the months of April, May, June, July and October. In April especially, western, central and eastern Europe, which had previously experienced unusually warm temperatures, came under the influence of polar and arctic air flows. This resulted in extensive frost damage in large parts of Europe, because the flowering and budding phases in fruit- and wine-growing regions were already well advanced following a warm spring.
In the equatorial Pacific, the first few months of the year saw contrasting sea surface temperatures, with tremendous heat off the coast of Peru and relative cool in more western areas. In February, March and at the start of April, this led to severe and destructive rainfall in northwestern regions of Peru, favoured by extreme humidity from the high rate of evaporation from the sea. The Peruvian weather service spoke of a “coastal El Niño” – an El Niño phase that has not fully developed. In addition, there is some evidence that this equatorial temperature pattern, as a result of teleconnection effects, contributed to an extremely early thunderstorm season in the USA, which caused billions of dollars in damage.
In Europe, the summer months saw an approximate north-south divide in terms of rainfall: in southern Europe from Portugal and Spain to southern France, and especially in Italy and parts of the Balkans, the weather was anomalously dry and generally too hot,contributing to numerous forest fires. In Portugal, the annual rainfall was only 60% of the long-term average, while the period from April to December was the driest since measurements began. Italy experienced the warmest January to August period on record and received just 64% of its normal rainfall. In more northerly regions of Europe, on the other hand, it was for the most part too wet. The north and northeast of Germany, for example, saw exceptionally heavy rainfall, while June in Scotland was the wettest since records began and parts of Scandinavia also experienced unusually wet conditions. The drought of 2016 continued in parts of East Africa, particularly in Somalia, but also in the north of Kenya and the southeast of Ethiopia. The drought in South Africa’s Western Cape province intensified.
In China, as in the year before, intense precipitation during the East Asian monsoon caused river flooding and damage in June and July in the Yangtze region. The South Asian summer monsoon, which for decades has been bringing increasingly heavy rainfall to places like central India, brought severe regional flooding to India, Nepal and Bangladesh until very late into the monsoon season in September. This season could be perceived as a glimpse into the future of monsoon systems: as climate change progresses further, the IPCC expects a more prolonged monsoon season, with a further increase in the variability and intensity of precipitation, as well as of 5-day rainfall amounts.
The threat to people and the need for increased resilience was highly evident in 2017 against the background of numerous heatwaves, droughts, forest fires and floods, as well as the extremely active hurricane season in the North Atlantic. We can no longer ignore the fact that climate change is the explanation for the clear long-term trend in global average
temperature, and is already having or will have an intensified effect on many of these weather extremes.
World Weather Attribution (2017): Euro-Mediterranean Heat – Summer 2017 (https://wwa.climatecentral.org/analyses/euro-mediterranean-heat-summer-2017/)
Coumou, D. & Robinson, A. (2013): Historic and future increase in the global land area affected by monthly heat extremes. Environ. Res. Lett. 8(3). doi:10.1088/1748-9326/8/3/034018
NOAA/NCEI (2018): Global Climate Report – Annual 2017
WMO (2017): WMO’s provisional statement on the state of the climate