Press Release No. 997
For use of the information media
Not an official record
Scientists urge more frequent updates of 30-year climate
baselines to keep pace with rapid climate change
Heidelberg, Germany, 9 July 2014 – The WMO Commission for Climatology has recommended that governments adopt a two-tier approach to updating the 30-year baselines that scientists and meteorological services use to monitor the weather and climate and make comparisons to past conditions.
Because the climate varies naturally from year to year, climatologists use standard 30-year averages of temperatures, precipitation and other variables to put, for example, the magnitude of a current heatwave or rainstorm into historical context. These 30-year historical periods are called “climate normals” and can be calculated at the local, national or global levels.
Climate normals are presently updated once every 30 years, so that the current official climate normal period is still 1961-1990. However, rising atmospheric concentrations of greenhouse gases are changing the Earth’s climate much faster than before. As a result, decision-makers in climate-sensitive industries may be basing important decisions on information that may be out of date.
In response, many national weather services have started to use the more recent 30-year period of 1981-2010 to give people a more recent context for understanding weather and climate extremes and forecasts. These weather services also view the 1981-2010 baseline as more useful for other operational services, such as forecasts of peak energy load and recommendations on crop selection and planting times. One consequence of this is that different researchers and weather services are using different baselines, which results in inconsistent comparisons.
Together with an array of other decisions and recommendations on climate data, monitoring and science, the WMO Commission for Climatology is therefore recommending that WMO adopt a new global standard of making decadal updates of climate normals for most purposes, while at the same time maintaining the 1961-1990 period as a stable reference for monitoring long-term climate variability and change.
Under this proposal, all countries would start using the period 1981-2010. This period would be updated every 10 years, so that the 30-year climate normal to be used in the 2020s would be 1991-2020. This approach would satisfy modern needs for current information and standardize weather and climate information and forecasts around the world.
Maintaining 1961-1990 as the base period for monitoring and assessing long-term climate variability and change would promote a better understanding of changes over the course of this century and beyond. The 1961-1990 reference period would be retained for climate change purposes until there is a compelling scientific case for changing it.
The proposed new technical regulation on “Calculating Climatological Standard Normals Every 10 Years” will be forwarded for consideration and adoption by the World Meteorological Congress. The Congress, which is the governing body of the World Meteorological Organization, will meet in Geneva from 25 May to 12 June 2015.
Today’s increasingly powerful computers and climate data management systems now make it much easier to conduct more frequent updates, which involve analyzing massive amounts of climate data. Another advantage of decadal updates is that they will make it possible to incorporate data from newly established weather stations into the normals more rapidly.
The WMO Commission for Climatology promotes international cooperation in climatology and the use of climate information and knowledge for supporting sustainable development, environmental protection and operational climate services. It also advises and guides the activities of the World Climate Programme, through the World Climate Applications and Services Programme, and the World Climate Data and Monitoring Programme.
Other issues discussed at the 3-8 July Heidelberg meeting of the Commission included future priorities and progress on key initiatives. For example, the initiative on centennial observing stations promotes efforts to build a sustained and long-term record of climate observations. Another initiative is facilitating the real-time international exchange of multi-annual to decadal climate predictions.
Weather, Climate and Water
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