GOOGLE EARTH INTERFACE FOR CRUTEM5 LAND TEMPERATURE DATA

About CRUTEM

CRUTEM is a dataset derived from air temperatures near to the land surface recorded at weather stations across all continents of Earth. It has been developed and maintained by the Climatic Research Unit since the early 1980s, with funding provided mostly by the US Department of Energy. The lead scientist for most of this work was Professor Phil Jones, though many colleagues have also contributed. In recent years, the Met Office Hadley Centre (MOHC) have also been involved, especially in the regular updating of the operational version of CRUTEM (current version CRUTEM5). CRUTEM has been combined with the MOHC's dataset of sea surface temperatures to provide a near-global dataset of temperatures across Earth's surface, called HadCRUT. For example, the current version HadCRUT5 combines CRUTEM5 and HadSST4. These datasets have been widely used for assessing anthropogenic climate change.

The latest version of CRUTEM is available in text and netCDF formats at the Climatic Research Unit and at the Met Office Hadley Centre.

IMPORTANT: on some Macs, running Mac OS X 10.10.0 or later, choosing to view a larger annual or seasonal plot may crash Google Earth when you try to go "Back to Google Earth". One work-around (April 2016) is to select/tick "Show web results in external browser" under the "General" tab in your Mac's Google Earth preferences.

What is this for?

To facilitate direct access to visualisations and the underlying data values, the CRUTEM land surface air temperature dataset is made available via Google Earth. An online rendition of the dataset -- the weather station monthly temperature data and their locations, the grid-box monthly temperature anomalies, and seasonal and annual timeseries graphs of all these data -- is accessed via an overlay written in Keyhole Markup Language (KML). The KML file overlays these locations onto the three-dimensional representation of the Earth provided by the Google Earth software, enabling the dataset to be explored and accessed interactively and graphically. This significantly enhances the accessibility of this key climate dataset, whether for exploring the data and extracting regional information for research and teaching, or for identifying any errors or limitations, without the need to develop bespoke software to analyse the data. Given that the Google Earth software is freely available and has been downloaded more than one billion times this represents an important additional dissemination route for the CRUTEM dataset.

How do I use it?

If you don't already have the Google Earth Pro app installed, then follow these instructions to install it.

When you have clicked the KML file above, choose to open it with Google Earth. You will then see a dark and light grey (previously green and red) checkerboard over the Earth. These are the boxes that we have weather station data in (note that sea surface temperatures are not included in CRUTEM, only in HadCRUT). You can click any grey box you choose and it will show the annual temperature anomaly timeseries for that grid box, plus clickable links to seasonal images and the grid-box data. There is also a link called "Stations": clicking this will show the approximate locations of all weather stations in our archive for that grid box with marker pins and the ID/name of the station. You can click any station pin to see the annual temperature timeseries for that station, and to access the seasonal images and the station data itself. The data files are in a suitable format to import into a spreadsheet: save them and then open as comma-deliminated (CSV) files.

References

The primary reference for the CRUTEM5 dataset, which should be cited whenever CRUTEM5 data are used, is:

The primary reference for the CRUTEM4 dataset, which should be cited whenever CRUTEM4 data are used, is:

If you use the information provided by this Google Earth interface, then please also acknowledge our work by citing:

Notes (Questions & Answers)

1. Q. What if I haven't got Google Earth on my computer/device?
   • A. You could install it, or try another Earth browser, or import the KML file into Google Earth web or Google Maps (we cannot provide any support of assistance).


2. Q. Is the entire weather station database included?
   • A. All weather stations that are used in the final CRUTEM5 dataset are included. Some weather stations do not have sufficient measurements during the 1961-1990 reference period to be used. Of these unused stations, those that are in grid boxes for which CRUTEM5 does have data (from other stations in the box with longer records) are included, while those in grid boxes with no CRUTEM5 data are not. The full station database can be obtained from here.


3. Q. Why are weather stations in the wrong locations?
   • A. The information we currently have about the latitude/longitude of each station is limited to 1 decimal place, so the station markers could be a few kilometres from the actual location. This is adequate for the construction of the CRUTEM gridded and global temperature records, because they do not depend on the precise location of each station. WMO/GCOS have asked member states to provide more accurate location details in future initiatives.


4. Q. Why do the grid-box temperature graphs appear to contain more years with data than the station temperature graphs within the same grid box?
   • A. For the station temperature graphs, complete data are required to form an annual or seasonal average (i.e. 12 full months or 3 full months, respectively). For the grid-box temperature anomaly graphs, annual or seasonal averages are shown even if up to one third of the individual monthly values are missing. The reason for the different approach is that seasonal variations can be large and therefore an annual-mean value could be biased significantly higher if a winter month value was missing. For the absolute values shown for the station temperature graphs, complete data are required to avoid such artefacts. For the grid-box data, all values are temperature anomalies and the conversion to anomalies removes the mean seasonal cycle, so any bias in the results due to a small number of missing values is likely to be much smaller.


5. Q. For a small number of stations, there is no annual temperature graph shown when the station marker is clicked (for example, some stations in the grid box containing Baghdad, Iraq). Why?
   • A. If there is only one year or less with complete data, then an annual temperature graph has not been drawn for that station. The "Data" link shows the raw data, where this can be verified. The "Seasonal image" link may show seasonal temperature graphs if there are complete data for more than one year in at least one season. These stations are not used for constructing the gridded CRUTEM dataset because they do not have sufficient observations during the reference period.
   
   
6. Q. What does the 'Station markers' legend mean and can I hide it?
   • A. The different station markers are designed to help you find stations with long records, early data and/or recent data. The legend in the bottom left shows the marker colours used to distinguish weather stations according to the quantity of data they have. It you want to find the longer stations, choose the darker markers. Some markers also include a black star if they have at least 12 monthly values in the last 3 years or a black circle if they have a useful amount of data before 1900. If they have both pre-1900 data and recent data they will only be marked by a black star, but they will have a darker colour marker because they are a long record. To hide the legend, open the 'Gridboxes' folder in the 'Places' section of Google Earth Pro, and untick 'Legend:Stations'.