Decadal forecast 2015

Outlook for global climate in the coming years

Forecast issued in January 2016. The forecast will next be updated in January 2017. Further discussion and background information can be found in this research article.

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 over this forecast period. Forecasts are experimental, so at this early stage of development expert advice is needed to assess the reliability of regional predictions.

Important

Long-range forecasts are unlike weather forecasts for the next few days.
Forecasts are for a range of possible conditions over a wide region and time period.

Summary

During 2015 our decadal prediction system was upgraded to use the latest high resolution version of our coupled climate model, consistent with our seasonal forecasts. This is in line with our aim to produce seamless forecasts as outlined in the Met Office science strategy.
Averaged over the five-year period 2016-2020, forecast patterns suggest enhanced warming over land, and at high northern latitudes. There is some indication of continued cool conditions in the Southern Ocean, and of relatively cool conditions in the North Atlantic sub-polar gyre. The latter is potentially important for climate impacts over Europe, America and Africa.
During the five-year period 2016-2020, global average temperature is expected to remain high and is likely to be between 0.28°C and 0.77°C above the long-term (1981-2010) average. This compares with an anomaly of +0.44 ± 0.1 °C observed in 2015, currently the warmest year on record on record. These high global temperatures are consistent with continued high levels of greenhouse gases and big changes that are currently underway in the climate system and were highlighted in a recent Met Office research news article.

Introduction

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.

During 2015 our decadal prediction system was upgraded to use the latest version of our coupled climate model, consistent with our seasonal forecasts. The forecasts and retrospective forecasts shown here have been updated to reflect this change.

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 strong El Niño pattern in the tropical Pacific, , unusually warm conditions in the North-East Pacific, relatively cool conditions in the Southern Ocean, and warm conditions over the subtropical North Atlantic but with some cooling in the mid-latitude North Atlantic.

Observed sea surface temperature

Figure 1:Observed sea surface temperature differences (°C) relative to 1981-2010 for October 2015. These, together with similar observations below the ocean surface, have been used as starting conditions for the decadal forecast.

Forecast

The maps below (Figure 2) show predicted temperatures over the period November 2015-October 2020 relative to 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 particular locations 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 global patterns shown in diagrams B and C are very unlikely to be realised.

Five-year mean forecast: mean, lower and upper estimates

Figure 2:Forecast (A) of surface temperature differences (°C) relative to 1981-2010 for the 5-year period November 2015 to October 2020. Forecasts consist of 10 ensemble members starting from November 2015. 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.

Spatial patterns suggest enhanced warming over land and at high northern latitudes. There is some indication of continued cool conditions in the Southern Ocean, and of relatively cool conditions in the North Atlantic sub-polar gyre. Uncertainties in the forecast are considerable: for the period 2016-2020 most regions are expected to be warmer than the average of 1981 to 2010, but regional cooling is possible over much of the Southern Ocean and the North Atlantic sub-polar gyre. Differences with our decadal forecast for 2014 are expected because the updated forecast has been made with an upgraded version of our model. Nevertheless, both forecasts suggest relatively cool conditions in the Southern Ocean and the North Atlantic sub-polar gyre although the magnitude of the anomalies is smaller in the updated forecast. Further forecasts from other international modelling centres are available from the multi-model decadal forecast exchange.

During the five-year period 2016-2020, global average temperature (see blue shading in Figure 3 below) is expected to remain between 0.28°C and 0.77°C (90% confidence range) above the long-term 1981-2010 mean (0.88°C to 1.37°C relative to pre-industrial conditions represented by the period 1850 to 1900). The warmest individual year in the 160-year Met Office Hadley Centre global temperature record is 2015 with a temperature of 0.44 ± 0.1 °C above the 1981-2010 mean. Averaged over the whole five-year period 2016-2020, global average temperature is expected to be between 0.42°C and 0.67°C above the 1981-2010 mean (1.02°C to 1.27°C relative to pre-industrial conditions).

Global annual temperature

Figure 3:Observed (black, from Met Office 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 model simulations, from the Coupled Model Intercomparison Project phase 5 (CMIP5), 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 2015. All data are rolling 12-month mean values. The gap between the black curves and blue shading arises because the last observed value represents the period November 2014 to October 2015 whereas the first forecast period is November 2015 to October 2016.

The forecast is for continued global warming largely driven by continued high levels of greenhouse gases. However, other changes in the climate system, including the largest El Niño since 1997 and longer term shifts in both the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO), are also contributing. Near record temperatures are predicted for the coming five years, consistent with the Met Office 2016 global mean temperature forecast. However, the recent run of consecutive record years is likely to end in 2017 as El Niño declines. The forecast remains towards the mid to upper end of the range simulated by CMIP5 models that have not been initialised with observations (green shading in Figure 3). Barring a large volcanic eruption or a very sudden return to La Niña or negative AMO conditions which could temporarily cool climate, ten year global average warming rates are likely to return to late 20th century levels within the next two years. Nevertheless, the recent slowdown in surface warming is still an active research topic and trends over a longer (15 year) period will take longer to respond. For further discussion on the surface warming slowdown see the Met Office reports on the recent pause in warming and on big changes underway in the climate system.

Verification

The following maps (Figure 4) compare observed (A) and forecast (B, issued in December 2010) surface temperatures (°C) for September 2010 to August 2015 relative to the 1981-2010 long-term average. Forecasts were made starting from September 2010 using the version of our forecast system at the time. Stippling shows regions where the observed temperatures lie outside the 5-95% range of the forecast.

Observations and five-year mean forecast from September 2010

Figure 4:Observed (A) and issued forecast (B) of surface temperature differences (°C) relative to 1981-2010 for the 5-year period September 2010 to August 2015. Forecasts consist of 20 ensemble members starting from September and June 2010. The stippling shows where the observations lie outside of the 5-95% confidence interval of the forecast ensemble.

The forecast issued five years ago predicted enhanced warming over high northern latitudes, and cooling in parts of the Southern Ocean and eastern tropical Pacific in broad agreement with the observations. Although there are differences in the precise magnitude and location of anomalies the observations generally lie within the forecast uncertainty range.