September 2019 was the warmest such month on record, tying the old record set in 2016, according to the Copernicus Climate Change Service, an organization funded by the European Union that tracks global temperatures. This makes September the fourth straight month "to be close to or breaking a temperature record," according to an agency statement.

Based on Copernicus' data, which uses computer models fed with billions of observations from air, land and sea, June 2019 set a record high for that month, July 2019 was the warmest month ever recorded, and August 2019 was the second-warmest such month globally. Other agencies, including NASA and NOAA, are expected to release their monthly data, which will be based on other methods, during the next one to two weeks.

According to Copernicus, September was about 1.02 degrees above the 1981-2010 average for the month, and about 1.2 degrees above the preindustrial level. It was also slightly warmer, by about 0.04 degrees, than September 2016, which had been the warmest such month on record. The small margin between the two years indicates the two months are statistically tied, according to Copernicus's statement.

Importantly, the warmth this year occurs in the absence of a strong El Niño event in the tropical Pacific Ocean. El Niño is a natural climate cycle that tends to boost global temperatures by bringing more ocean heat to the surface and adding it to the atmosphere as well. A powerful El Niño occurred in 2015 and 2016, contributing to the record heat at that time.

Regions that were particularly warm in September included the central and eastern United States, where many cities saw their hottest September on record. In addition, large portions of the Arctic had above-average temperatures stemming in part from an extensive sea-ice melt. Much of Europe was also above average for the month, whereas southwestern Russia and parts of Antarctica saw much below-average temperatures, the Copernicus analysis found.

"The recent series of record-breaking temperatures is an alarming reminder of the long-term warming trend that can be observed on a global level. With continued greenhouse gas emissions and the resulting impact on global temperatures, records will continue to be broken in the future," said Jean-Noël Thépaut, director of Copernicus at the European Center for Medium-Range Weather Forecasts, in a statement.

The Northern Hemisphere had its hottest summer on record since 1880, according to NOAA data released last month. The five hottest summers in the Northern Hemisphere, which contains most of the world's land masses and population, have each occurred during the past five years. It's almost 100 percent certain that 2019 will be a top-five warmest year, NOAA found.