The average global temperature for 2015-2019 is on track to be the warmest of any equivalent period on record, and July 2019 was the hottest month on record globally, a report released ahead of the UN Climate Action Summit 2019 in New York has found. The warmest five-year trend has especially affected large areas of the United States, including Alaska, eastern parts of South America, most of Europe and the Middle East, northern Eurasia, Australia and areas of Africa south of the Sahara.
The report ‘United in Science’ is a synthesis prepared by the Science Advisory Group of the summit. It has also found that greenhouse gases have reached “new highs”, heatwaves were the “deadliest” meteorological hazard in this period, and tropical cyclones led to the largest economic losses. Among its key findings:
GLOBAL TEMPERATURE: The average global temperature for 2015-19 is currently estimated to be 1.1°C above pre-industrial (1850-1900) times, the report said. Widespread and long-lasting heatwaves, record-breaking fires and other devastating events such as tropical cyclones, floods and drought have had major impacts on socio-economic development and the environment.
GREENHOUSE GASES: Levels of carbon dioxide, methane and nitrous oxide have reached new highs. The last time Earth’s atmosphere contained 400 parts per million carbon dioxide was about 3-5 million years ago. In 2018, the report said, global carbon dioxide concentration was 407.8 parts per million (ppm), 2.2 ppm higher than 2017. Preliminary data from a subset of monitoring sites for 2019 indicate that carbon dioxide concentrations are on track to reach or even exceed 410 ppm by the end of 2019.
In 2017, globally averaged atmospheric concentrations of carbon dioxide were 405.6 ppm, methane at 1859 parts per billion (ppb) and nitrous oxide at 329.9 ppb. These values constitute, respectively, 146%, 257% and 122% of pre-industrial levels (pre-1750). The growth rate of carbon dioxide averaged over three consecutive decades (1985-1995, 1995-2005 and 2005-2015) increased from 1.42 ppm/yr to 1.86 ppm/yr and to 2.06 ppm/yr.
However, the report notes that emissions from the US and the European Union have declined over the past decade, while growth in China’s emissions have slowed significantly compared to the 2000s. Indian emissions are the fourth highest and are “growing strongly at annual rates in excess of 5%, albeit starting from a much lower base of per capita emissions.”
HEATWAVES: The report notes that heatwaves affected all continents and set many new national temperature records. It also mentions the heatwave that struck the subcontinent in mid-2015 where 2,248 deaths were reported in India, and 1,229 in Pakistan. “The 2019 summer saw unprecedented wildfires in the Arctic region with 50 megatons of carbon dioxide emitted into the atmosphere in June alone,” the report says.
PRECIPITATION: The effects of climate change were also seen on precipitation levels in the 2015-2019 period when compared to the five years preceding that. The average precipitation totals were higher in the latter period than in the former in large regions in southern South and North America, eastern Europe and most of Asia. “In contrast, less precipitation fell in large parts of Europe, south-west and southern Africa, northern North America and a large part of South America, the Indian Monsoon region, and northern and western Australia,” the report states.
SEA ICE: Arctic summer sea-ice extent has declined at a rate of approximately 12% per decade during 1979-2018, the report said. The four lowest values for winter sea-ice extent occurred between 2015 and 2019. Overall, the amount of ice lost annually from the Antarctic ice sheet increased at least six-fold between 1979 and 2017. Glacier mass loss for 2015-2019 is the highest for any five-year period on record.