Decadal forecasts, also called 'near-term' climate predictions, range up to a decade ahead. Predictions account for natural variability and climate change as these are expected to be of similar size in many parts of the world. Forecasts are experimental, so at this early stage of development expert advice is needed to assess the reliability of regional predictions.
Decadal forecasts are designed to predict fluctuations in the climate system over the next few years. They take into account natural variability as well as human influences. This is achieved by initialising climate models with observations of the current climate state, in addition to specifying changes in radiative forcing due to greenhouse gases, aerosols (both volcanic and man-made), and solar variability. Further details can be found in a Met Office article about the basis of decadal forecasting.
The latest Met Office decadal forecast presented here was started from the observed sea surface temperature pattern shown in Figure 1, along with similar observations of temperature and salinity below the ocean surface, and atmospheric winds, temperatures and surface pressure. The temperatures in Figure 1 show a weak La Niña pattern in the tropical Pacific, relatively cool conditions in the Southern Ocean, and warm conditions in the North Atlantic.
Figure 1: Observed sea surface temperature differences (°C) relative to 1981-2010 for October 2013. These, together with similar observations below the ocean surface, have been used as starting conditions for the decadal forecast.
The following maps (Figure 2) show the difference between the predicted geographical distribution of temperatures over the period November 2013-October 2018 and 1981-2010 averages. Diagram A is the most likely forecast outcome. Diagrams B and C indicate the range of forecast temperatures, such that we expect only a 10% chance of temperatures at a particular location being less than those in B, and only a 10% chance of temperatures higher than in C. Note that these ranges are for each individual location. The chances of these limits being met everywhere are very small, so the complete patterns shown in diagrams B and C are very unlikely to be realised.
Figure 2: Forecast (A) maps of surface temperature differences (°C) relative to 1981-2010 for the 5-year period November 2013 to October 2018. Forecasts consist of 10 ensemble members starting from November 2013. The probable range is diagnosed from the ensemble spread, and shown as the lower (B) and upper (C) limits for each 5° grid box, such that there is a 10% chance of the observations being cooler than (B), and a 10% chance of the observations being warmer than (C). Note that the actual anomaly patterns in (B) and (C) are unlikely to occur since extreme fluctuations would not be expected at all locations simultaneously. Lower panels (D, E, F) show the equivalent forecasts issued in December 2012 for the period November 2012 to October 2017 relative to 1981-2010.
Spatial patterns suggest more warming over land than ocean, and at high northern latitudes. There is some indication of continued cool conditions in the Southern Ocean, and of a developing cooling in the north Atlantic sub-polar gyre. Uncertainties in the forecast are considerable: for the period 2014-2018 most regions are expected to be warmer than the average of 1981 to 2010, but regional cooling is possible over much of the Pacific, North Atlantic and Southern Oceans, and over some land regions. The updated forecast (Figure 2 A-C) is very similar to the forecast issued a year ago (Figure 2 D-F).
Averaged over the five-year period 2014-2018, global average temperature is expected to remain between 0.17°C and 0.43°C (90% confidence range) above the long-term (1981-2010) mean (see blue shading in Figure 3 below).
The warmest individual year in the 160-year Met Office Hadley Centre global temperature record is 2010, with a temperature of 0.26°C above the 1981-2010 mean. The forecast of continued global warming is largely driven by continued high levels of greenhouse gases. However, the forecast initially remains towards the lower end of the range simulated by CMIP5 models that have not been initialised with observations (green shading), consistent with the recent pause in surface temperature warming. Changes in the exchange of heat between the upper and deep ocean appear to have caused at least part of the pause in surface warming, and observations suggest that the Pacific Ocean may play a key role. For further discussion on the surface warming pause see the Met Office report on the recent pause in warming.
Figure 3: Observed (black, from Hadley Centre, GISS and NCDC) and predicted (blue) global average annual surface temperature difference relative to 1981-2010. Previous predictions starting from November 1960, 1965,... 2005 are shown in red, and 22 Coupled Model Intercomparison Project phase 5 (CMIP5) model simulations that have not been initialised with observations are shown in green. In all cases, the shading represents the probable range, such that the observations are expected to lie within the shading 90% of the time. The most recent forecast (blue) starts from November 2013. All data are rolling annual mean values. The gap between the black curves and blue shading arises because the last observed value represents the period November 2012 to October 2013 whereas the first forecast period is November 2013 to October 2014.
Retrospective forecasts have been made from numerous dates in the past. Some of these are shown in the top global annual temperature forecast figure (red shading from 1960, 1965, ... 2005). Generally, the forecasts predict rises in temperatures similar to those observed (black curves). Many facets of the variability, such as the record warming caused by the large 1997-1998 El Niño and the cooling caused by the 2008 La Niña, are largely within the range of the predictions (red shading).
The following maps (Figure 4) compare observed (A) and forecast (B) surface temperatures (°C) for November 2008 to October 2013 relative to the 1981-2010 long-term average. Forecasts were made starting from November 2008. Stippling shows regions where the observed temperatures do not lie within the predicted range (5-95%) of the forecast. The forecast correctly predicted enhanced warming over high northern latitudes, and in most regions the observations lie within the predicted range. However, the predicted temperatures are too warm in the tropical Pacific Ocean and over parts of China, and too cold over the southern Atlantic and Indian oceans.
Figure 4: Observed (A) and forecast (B) maps of surface temperature differences (°C) relative to 1981-2010 for the 5-year period November 2008 to October 2013. Forecasts consist of 4 ensemble members starting from November 2008. The stippling shows where the observations lie outside the 5-95% confidence interval of the forecast ensemble.
Last updated: 19 September 2014