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Air temperatures influence our health, well-being, food security, economies and many other factors. Temperature excesses can cause cold or heat stress in humans, curb crop growth, adversely affect animal health and biodiversity, impact many businesses and even affect the functioning of infrastructure such as bridges and railways.
With climate change under way, there is a growing need to understand how changes to air temperature will affect us and our ecosystems in the coming years. However, for scientists to research this in-depth, a large amount of data is required on historical air temperatures across the globe.
While in some locations – for example, in weather stations and on board ships – air temperature records span decades, in many areas there is a noticeable lack of information. The EU-funded EUSTACE project is helping to fill this knowledge gap by using temperature estimates taken from satellite measurements to boost the amount of currently available data and helping to build up a record of global temperatures covering 166 years.
‘We have also used cutting-edge statistical methods to exploit the links between air temperature in different places and through time to estimate daily air temperatures in places and at times when we have neither direct measurements nor satellite estimates,” explains Nick Rayner, Met Office UK scientist and EUSTACE project coordinator.
Surface values
Across the globe, there are many regions where temperature records are lacking. Whilst Europe, North America and Australia can boast good records, those from most other continents, some parts of the oceans and the poles are not as complete.
However, this is where satellites are useful. They can provide information on, for example, the temperature of the Earth’s surface, or the surface of the ice in the Arctic, or the grass in the Prairies.
To estimate air temperatures using satellite information, scientists must first understand the relationships between traditional direct land and marine surface air temperature measurements and satellite measurements of temperatures of the land, ice, sea and lake surfaces.
The relationship between satellite-observed temperatures and direct air temperature records is affected by different things in different places. To overcome this barrier, EUSTACE researchers explored temperature records separately over land, ice and ocean, and then used their knowledge to estimate air temperatures using satellite measurements.
Mind the gaps
To provide an accurate picture of air temperature over time, measurements at weather stations needed to be verified for any jumps in the series that might have come from changes in the surroundings of the weather station, the instruments used, or the location of the station.
In particular, these changes can affect the extreme high or low temperatures recorded at the station, which means that scientists must ensure that the recordings are consistent before they can use the information. To achieve this, EUSTACE researchers developed a technique to automatically check the thousands of weather station records so as to flag up points in time where the measurements might contain a non-climatic change.
The project is still ongoing, but once the final results are available, they will improve our understanding of our vulnerability to daily variations in near-surface air temperature. Furthermore, they could be used to provide context for projections of future climate change, and to evaluate near-term predictions on seasonal to decade-long timescales, says Rayner.