The climate in 2011

The natural variability of our climate is driven in large part by the El Niño Southern Oscillation (ENSO) in the tropical Pacific Ocean. In the El Niño phase, global temperature tends to rise, whereas in the La Niña phase it tends to fall.

The natural variability of our climate is driven in large part by the El Niño Southern Oscillation (ENSO) in the tropical Pacific Ocean. In the El Niño phase, global temperature tends to rise, whereas in the La Niña phase it tends to fall.

Global near-surface temperature in 2011 compared to the 1961-1990 average Global near-surface temperature in 2011 compared to the 1961-1990 average The persistence of the very strong La Niña this year means that 2011 will not figure as highly as 2010 in the ranking of warmest years and is currently lying just outside the top ten in the Met Office's record. However, global temperature so far this year is higher than it was during the La Niña events in 2008 and 1999-2000.

It appears that a 'double-dip' La Niña is developing. The first dip is one reason why global temperature is lower this year and the second dip could mean we see this pattern repeated in 2012.

Regional variability in 2011 has been marked, with lower than normal temperatures over large areas of the eastern Pacific Ocean but warmer than average conditions over the Arctic. Global near-surface temperature Global near-surface temperature While there are difficulties in monitoring temperature in the Arctic because of sparse observations, the strength of warming is evidenced, at least in part, by the near-record minimum levels of summer sea ice in the region.

Regardless of the strength of regional variation in temperature in any given year, it's important to view the world as a whole when considering how the climate is changing.

It's also important to understand how short-term temperature trends - such as those associated with La Niña and El Niño - can temporarily run counter to, or augment, changes happening over the longer term. The Met Office Hadley Centre and University of East Anglia temperature series provides that longer view, identifying the trend that overlies short term variability.

Arctic sea ice

Arctic sea ice summer minimum extent for the record low year 2007 outlined in blue and 2011 in green. In both cases, the long-term average extent is shown by the grey shaded area. Arctic sea ice summer minimum extent for the record low year 2007 outlined in blue and 2011 in green. In both cases, the long-term average extent is shown by the grey shaded area. The Arctic summer sea ice minimum extent reached near-record levels in 2011, falling to an estimated 4.3 million km2 in early September according the National Snow and Ice Data Center in the US. This was largely as a result of prevailing weather patterns.

The low ice extent for 2011 continues pattern of low summer ice extents observed since 2007 and the downward trend evident over the previous 15 years. It is important, however, to place the observed loss in the context of climate model simulations.

Periods of rapid ice loss are not unusual in climate models, but based on model results, there is no reason to expect the rapid rate of loss to continue unabated. Climate models show that there could be decadal periods of relatively small loss of Arctic sea ice in summer, and there is no clear indication from our models that what we are seeing represents a tipping point in Arctic sea ice extent. Indeed, models show that the Arctic sea ice is recoverable with decreases in global temperature. 

Low levels of sea ice in the Arctic may have implications for atmospheric circulation patterns outside the region. For example, there is emerging evidence that European climate may be affected through a large part of the year.

The relative importance of sea ice conditions and other factors, such as solar variability and ENSO, in producing colder than average winter conditions across Europe is a focus of research at the Met Office.

La Niña and global rainfall patterns

The cycle of El Niño and La Niña in the tropical Pacific Ocean affects not only global temperatures, but can also drive some dramatic changes in rainfall patterns in different parts of the world.

The severe drought across the Horn of Africa, covered extensively by the media throughout spring 2011, arose in part from the failure of the 'short' autumn rains in 2010.

There is a strong influence of the ENSO at play here, with La Niña conditions contributing to the failure of this wet season in East Africa. Sea-surface temperatures across the Indian Ocean are another influence on rainfall in the region.

Typically, 2009 and 2010 followed this pattern with the El Niño of 2009 resulting in a wet year and the very strong La Niña a year later culminating in a very dry autumn season.

Met Office model-based seasonal predictions of the ENSO cycle have proved to be consistently good, and therefore provide valuable information to climate scientists in the region when preparing regional and national seasonal outlooks. Advancing the application of climate-model-based seasonal forecasts is one objective of the Climate Science Research Partnership between the Met Office and the UK's Department for International Development.

Last updated: 18 September 2013