Hot end to our hottest decade

2019 was the second warmest year on record, according to the World Meteorological Organisation’s consolidated analysis of leading international datasets.

2016 remains the warmest because of the added impact of a very strong El Niño event.

Average temperatures for the five-year (2015-2019) and 10-year (2010-2019) periods were the highest on record.

Since the 1980s, each decade has been warmer than the previous one. This trend is expected to continue, the WMO statement says, because of record levels of heat-trapping greenhouse gases in the atmosphere.

Averaged across the five data sets used in the consolidated analysis, the annual global temperature in 2019 was 1.1 degrees Celsius warmer than the average for 1850-1900, used to represent pre-industrial conditions.

“On the current path of carbon dioxide emissions, we are heading towards a temperature increase of 3 to 5 degrees Celsius by the end of century,” says WMO Secretary-General Petteri Taalas.

Temperatures are only part of the story, the WMO adds. The past decade has been characterised by retreating ice, record sea levels, increasing ocean heat and acidification, and extreme weather.

These have combined to have major impacts on the health and well-being of both humans and the environment, as highlighted by WMO’s Provisional Statement on the State of the Global Climate in 2019, which was presented at the UN Climate Change Conference, COP25, in Madrid. The full statement will be issued in March 2020.

More than 90% of the excess heat is stored within the world’s ocean, and so ocean heat content is a good way to quantify the rate of global warming. 

A new study published this week with data from the National Oceanic and Atmospheric Administration/National Centre for Environmental Information and the Institute of Atmospheric Physics showed that ocean heat content was at a record level in 2019.

The past five years are the top five warmest years in the ocean historically with modern instruments, and the past 10 years are also the top 10 on record.

WMO uses datasets from the US National Oceanic and Atmospheric Administration, NASA’s Goddard Institute for Space Studies, the UK’s Met Office Hadley Centre and the University of East Anglia’s Climatic Research Unit, UK.

It also uses reanalysis datasets from the European Centre for Medium Range Weather Forecasts and its Copernicus Climate Change Service, and the Japan Meteorological Agency.

This method combines millions of meteorological and marine observations, including from satellites, with models to produce a complete reanalysis of the atmosphere. The combination of observations with models makes it possible to estimate temperatures at any time and in any place across the globe, even in data-sparse areas such as the polar regions.

The spread between the five data sets was 0.15 degrees with both the lowest (1.05 degrees) and the highest (1.20 degrees) being more than 1 degree warmer than the pre-industrial baseline.