Climate indicators

The monthly series of mean CET begins in 1659 and is currently the longest available instrumental record of temperature in the world. The daily CET time-series begins in 1772. Since 1974 the data have been adjusted by 0.1 °C to 0.3  °C to allow for urban warming.

Daily and monthly maximum and minimum CET have been calculated for the period beginning 1878. For the most recent period, provisional daily versions of maximum, minimum and mean CET (dashed) are calculated from a network of weather stations reporting twice daily. These initial estimates are replaced by quality controlled daily values from a fixed network of high quality climate stations when they become available.

In general, night-time temperatures have increased throughout the 20th century and recent winters have seen fewer frosts.

The monthly time-series of England and Wales total precipitation (EWP) begins in 1766. The series is currently based on weighted averages of daily observations from a network of stations in five regions. It is the longest instrumental series of this kind in the world. Daily data begin in 1931. Data are available for EWP and for nine individual regions of the UK, including Scotland and Northern Ireland.

This graph shows how summer and winter rainfall over England and Wales have changed since 1873.

The North Atlantic Oscillation (NAO) is a phenomenon associated with fluctuations in temperatures, rainfall and storminess over much of Europe, especially in winter. When the NAO is 'positive' in winter, westerly winds are stronger or more persistent, northern Europe tends to be warmer and wetter than average and southern Europe colder and drier. When the NAO is 'negative' in winter, westerly winds are weaker or less persistent, northern Europe is colder and drier and southern Europe warmer and wetter than average. One of the simplest definitions of the NAO is that it is the difference in pressure at sea-level between the Azores and Iceland.

The global and hemispheric near-surface temperature series are calculated from regular measurements of air temperature at fixed long-term land stations and from sea-surface temperatures.

The global near-surface temperatures can also be given as the differences from the average values at the beginning of the 20th century. The final value for an incomplete year (green bar) is a preliminary value. Please note that until June the final value is not likely to be representative of the year as a whole. This is due to higher variability in the northern hemisphere during the winter period and the frequently different behaviour of later parts of the year.

This graph shows how independently measured sea-surface temperature, air temperature from fixed long-term stations over land and air temperature over the oceans have followed similar trends through time. The data have been filtered to show the longer-term fluctuations.

The El Niño Southern Oscillation (ENSO) phenomenon is a large-scale, natural fluctuation of the ocean-atmosphere system centred across the tropical to sub-tropical Indo-Pacific region. Through teleconnections to higher latitudes in both hemispheres, ENSO impacts can extend to near-global dimensions during strong phases of its El Niño or La Niña extremes.

Warm El Niño events in the eastern equatorial Pacific Ocean in 1982-83, 1987, and 1997-98 coincided with global warmth, but El Niño events are often followed by cooler La Niña events as in 1985, 1988 and 1998-99. SSTs have been extracted from an area between 150° W and 90° W, 5° N and 5° S.

Regions of the Earth's surface experiencing warmer or cooler than normal conditions can be easily identified from surface temperature charts. These monthly charts are produced using in situ observations of sea surface temperature measured from ships and buoys and air temperature data gathered at a global network of land stations.

The temperatures of the troposphere and stratosphere are routinely measured by weather balloons and satellites. The troposphere has generally warmed since the 1960s, whereas the stratosphere has cooled.