Decadal forecast 2017

Forecast issued in January 2018. The forecast will next be updated in January 2019. Further discussion and background information can be found in this research news 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 skill and 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

• Averaged over the five-year period 2018-2022, forecast patterns suggest enhanced warming over land, and at high northern latitudes. There is some indication of continued cool conditions in the Pacific sector of the Southern Ocean and enhanced warming in the Atlantic sector of the Southern Ocean. Current relatively cool conditions in the North Atlantic sub-polar gyre are predicted to return to more normal conditions with potentially important climate impacts over Europe, America and Africa.
• During the five-year period 2018-2022, global average temperature is expected to remain high and is very likely to be between 0.96°C and 1.54°C above the pre-industrial average period from 1850-1900.  This compares with an anomaly of +1.14 ± 0.1 °C observed in 2016, currently the warmest year on record. There is a small (~10%) chance of one year temporarily exceeding 1.5°C. These high global temperatures are consistent with continued high levels of greenhouse gases.

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 anthropogenic), 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 and temperatures. The temperatures in Figure 1 show a moderate La Niña pattern in the tropical Pacific, unusually warm conditions in many other regions, but especially near the Arctic sea ice edge, relatively cool conditions in parts of the Southern and Indian Oceans, and warm conditions over the tropical and subtropical North Atlantic but with some colder temperatures in the mid-latitude North Atlantic.

Observed sea surface temperature

Figure 1: Observed sea surface temperature differences (°C) relative to 1981-2010 for October 2017. 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 2017-October 2022 relative to 1981-2010 averages. Diagram A shows 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.

Spatial patterns suggest enhanced warming is likely over much of the globe, especially over land and at high northern latitudes. There is some indication of continued relatively cool conditions in the Pacific sector of the Southern Ocean, and of enhanced warming in the Atlantic sector of the Southern Ocean. Uncertainties in the forecast are considerable: for the period 2018-2022 most regions are expected to be warmer than the average of 1981 to 2010, but regional cooling is possible especially over parts of the Southern Ocean and the North and East Pacific. Further forecasts from other international modelling centres are available from the multi-model decadal forecast exchange.

During the five-year period 2018-2022, global average temperature (see blue shading in Figure 3 below) is expected to remain between 0.96°C and 1.54°C (90% confidence range) relative to  pre-industrial conditions represented by the period 1850 to 1900 (0.35°C to 0.93°C above the 1981-2010 mean) with a small (~10%) chance of one year temporarily exceeding 1.5°C. The warmest individual year in the 160-year Met Office Hadley Centre global temperature record is 2016 with a temperature of 1.14 ± 0.1 °C relative to pre-industrial conditions. Averaged over the whole five-year period 2018-2022, global average temperature is expected to be between 1.10°C and 1.40°C relative to pre-industrial conditions (0.49°C to 0.79°C above the 1981-2010 mean).

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 pre-industrial conditions represented by the period 1850-1900. Previous predictions starting from November 1960, 1965, ..., 2010 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 2017. 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 2016 to October 2017 whereas the first forecast period is November 2017 to October 2018.

The forecast is for continued global warming largely driven by continued high levels of greenhouse gases. However, other changes in the climate system, including a moderate La Niña in 2018 and longer term shifts in both the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO), are also contributing. Near record temperatures are predicted during the coming five years, although La Niña is expected to cool 2018 slightly, consistent with the Met Office 2018 global mean temperature forecast. 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 negative PDO or negative AMO conditions which could temporarily cool climate, ten year global average warming rates are likely to be similar to late 20th century levels over the next few years. The recent slowdown in surface warming now appears to be at an end following a run of very warm years since 2014. For further discussion on the surface warming slowdown see the Met Office reports on the recent pause in warming and on the recent resumption of high warming rates.

Verification

The following maps (Figure 4) compare observed (A) and forecast (B, issued in December 2012) surface temperatures (°C) for November 2012 to October 2017 relative to the 1981-2010 long-term average. Forecasts were made starting from November 2012 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.

The forecast issued five years ago predicted enhanced warming over high northern latitudes, and cooling in parts of the Southern Ocean and the North Atlantic sub-polar gyre. Although there are differences in the precise magnitude and location of anomalies the observations generally lie within the forecast uncertainty range. However, the forecast was generally cooler than observed in the Southern Ocean, the North Atlantic sub-polar gyre and the North Pacific.