It’s warmer than average. But what is average?

WMO scientists explain the important of global climate monitoring and its value for decision-making in a blog post published by the UK's Met Office.

The heat of summer is upon us, and there is much talk about how it is warmer than average – certainly in many parts of Europe. But what is average?

Well. It’s complicated. And this is why we need global coordination and support.

The World Meteorological Organization helps monitor the Earth’s climate on a global scale to provide the best possible science to support decision-making.

In order to assess whether a given day, week, month or year is warmer or wetter than average, we use a 30-year baseline, known as ‘Climatalogical Standard Normals’. These are averages of climatological data over a 30-year period, 1 January 1981–31 December 2010, 1 January 1991–31 December 2020, and so forth. It’s important to use a long-term average because of the natural variability in our climate.

Rising atmospheric concentrations of greenhouse gases are changing the Earth’s climate much faster than before, and therefore WMO has agreed that the standard 30-year reference period has to be updated every decade in order to better reflect the changing climate and its influence on our day-to-day weather experience.

This is vital for operational decision-making in climate-sensitive sectors and industries such as water management, energy, agriculture and viticulture (production of grapes). They need up-to-date information for forecasting of peak energy load, crop selection and planting times, transport planning and schedules, and much more.

A new baseline

Until the end of 2020, the most current and widely used standard reference period for calculating climate normals was the 30-year period 1981-2010. WMO’s recent Executive Council recommended that the new 30-year baseline, 1991-2020, should be adopted globally and pledged support to Members to help them update their figures.

The United States of America and many countries in Europe have already switched to the new baseline, aided by today’s increasingly powerful computers and climate data management systems making it much easier to conduct more frequent updates, which involve analysing massive amounts of climate data.

But for developing countries, which have significant gaps in their data collection and processing capacity, this poses a real challenge. Just 70 out of 193 Members submitted their Climate Normals (CLINO) for the period 1991–2020 – less than 37%. This raises the concern of meeting the deadline for completing the CLINO collection in 2023.

“Missing CLINO 1991–2020 will seriously hamper the quality of Members’ and WMO products and services. Operational monitoring and prediction products, such as El Niño/La Niña monitoring, State of Climate reports, seasonal forecasts etc. will suffer from a non-delivery of updated CLINO. These products will lose their modern relevance for various application sectors as a result of the changing climate,” comments Omar Baddour, Head of WMO Climate Monitoring and Policy Division.

“An urgent collective action involving Members, WMO Secretariat, Technical Commissions and Regional Associations is needed to accelerate Members’ data submission and collection,” he says.

Ian Lisk from the Met Office and president of the WMO Services Commission agrees. “The Climate Normals dataset is used for a wide range of applications all over the world. It is also worth highlighting that there are also fixed historical reference periods that are used to benchmark climate change monitoring. The WMO Reference Period for long-term climate change assessment is based on the period 1961-1990 whilst the pre-industrial reference period, 1850-1900, is used by WMO and IPCC as the baseline for estimating past and future global temperature increases.”

He goes on to add that, “The WMO Services Commission is currently developing guidance on good practices for the use of climate normals and other reference period baselines to support the improved communication of climate change related information.’’

Consolidated data

WMO uses six international datasets for temperatures – HadCRUT.5.0.1.0 (Met Office, UK), NOAAGlobalTemp v5 (USA), NASA GISTEMP v4 (USA), Berkeley Earth (USA), ERA5 (ECMWF) and JRA-55 (Japan).

In 2021, the Met Office and the University of East Anglia upgraded their long-running HadCRUT dataset, including better coverage in data-sparse areas such as the rapidly warming Arctic. This provides more accurate estimates of global, hemispheric and regional temperature changes. The previous version, HadCRUT4, showed less warming than other global temperature data sets. HadCRUT5 is now more consistent with these other datasets during recent decades and shows slightly more warming than most of them do over the full period since 1850. 

Thus, the average global temperature in 2021 was about 1.11°C (± 0.13) above the pre-industrial level. The warmest year on record remains 2016, when the average global temperature was 1.29°C above the pre-industrial era because of a combination of a powerful El Niño event and global warming.

With each passing year, the chance of us reaching the 1.5°C lower limit of the Paris Agreement increases. Continued climate monitoring is therefore vital to inform mitigation policy and to guide us in our efforts to adapt to climate change.