TLDR
Scientists have created a new, more accurate record of how Earth's surface temperature has changed since 1850. This updated record shows that the world has warmed more than earlier estimates suggested, especially in the Arctic and other hard-to-measure places.
Summary
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1 Study Aim
The primary aim of this paper is to introduce and describe HadCRUT5, an updated global surface temperature data set. The authors seek to improve estimates of near-surface temperature changes from 1850 to 2018 by using more comprehensive land and sea measurements, better corrections for changes in how temperatures were recorded, and advanced statistical methods to fill in gaps where data are missing. The study also aims to provide a clearer understanding of uncertainties in temperature records and to compare the new data set with previous versions and other independent analyses. This study set out to make a better, more complete record of Earth's temperature changes by using improved data and smarter ways to handle missing information.
2 Study Design
The research team combined updated sea-surface temperature (SST) data from ships and buoys with near-surface air temperature data from weather stations on land. They used two main approaches: one that only includes locations with direct measurements, and another that uses a statistical method called Gaussian process regression (a way to estimate values in unmeasured areas based on nearby data) to fill in gaps. Both versions are provided as 200-member ensembles, which means they include many possible versions to show uncertainty. The study also compared HadCRUT5 to other major temperature data sets and used advanced error models to account for different sources of uncertainty, such as changes in measurement methods and incomplete coverage. The researchers built a new temperature record by combining land and ocean data, then used math to estimate temperatures in places without measurements, checking their results against other records.
3 Findings
The study reveals that HadCRUT5 shows a greater increase in global average temperature since 1850 than previous versions, especially in the 21st century. This is mainly due to better representation of warming in the Arctic and improved corrections for biases in sea-surface temperature measurements. The new statistical infilling method reduces uncertainty by making better use of available data, especially in regions with few observations. HadCRUT5's results are more consistent with other independent temperature records, increasing confidence in our understanding of global warming. However, the authors note that uncertainty remains for the 19th century and in areas with very limited data, such as parts of the southern hemisphere and polar regions. They recommend continued efforts to digitize old records and improve observational coverage to further reduce uncertainty in future updates. The new temperature record shows the world has warmed more than we thought, especially in the far north, but there are still some uncertainties in places with little data.