Retrospective multiyear climate forecasts from the Climate Analysis Forecasting Ensemble System

The Challenge

Delivering better climate forecasts on the annual to decadal climate time scale is a recognised grand challenge in climate science and a focus of the World Climate Research Program. This project will make a valuable contribution to this international effort by using the capabilities Pawsey provides to help generate novel sets of annual to decadal climate forecasts and to apply innovate analysis to extract utility from these forecasts.

The Solution

We have developed the Climate Analysis Forecast Ensemble (CAFE) system (O’Kane et al. 2021a and b) and we are using the system to explore the benefits to the forecast skill of:
1) more sophisticated ways to assimilate ocean, sea ice and atmospheric observations to determine the initial climate state;
2) novel ways to generate the perturbations of the climate state for delivering multiyear ensemble forecasts.

Both approaches are well developed, and we recently published our 96-member ensemble climate reanalysis product (CAFE60) to characterise the climate since 1960 (O’Kane et al. 2021a and b). We have used a subset (10-members) of CAFE60 as initial conditions for decadal climate forecasts run every Nov 1 from 1960. The forecast dataset has now been supplement by 96-member decadal forecasts every November 1 and May 1 from 1980 to 2020. These additional forecasts provide a large ensemble with a wealth of information to characterise extremes in the current climate (e.g. Squire et al., 2021 submitted). Squire et al. showed the extreme bushfire weather of 2019-2020 was a 1 in 200 year event but not the most extreme event we simulated in our large ensemble of forecasts (Figure 2).

The Outcome

Using the nationally important Pawsey infrastructure we have enhanced the CSIRO contribution to the World Meteorology Organisation (WMO) annual to decadal climate forecasting effort (https://hadleyserver.metoffice.gov.uk/wmolc/). CSIRO, with the support of Pawsey, is the only recognised centre from the Southern Hemisphere and the only centre that has provided a large ensemble of forecasts (96-members) to this international effort. As a WMO forecasting centre, Australia research is connected to international leaders in climate forecasting. Further, it will enable CSIRO to redirect some of the Northern Hemisphere efforts to climate prediction features of interest to Australia

The forecast dataset is already being used to assess regional climate extremes (Tozer et al., 2020) that may help Hydro Tasmania better manage their water resources. Further, the research team is now exploring how to use our forecast products to improve stock management in the Eastern Tuna and Billfish Fishery.

Most of our effort to date has been directed at producing the forecast datasets, and we are increasingly directing our effort towards extracting useful information from unique datasets.

As part of our contribution to the WMO annual to decadal predictions the following outlook was provided (Figure 1).

Executive Summary of the WMO annual to decadal predictions made on Nov. 1 2020:
• Annual mean global (land and sea) mean near-surface temperature is likely to be at least 1°C warmer than preindustrial levels (defined as the 1850-1900 average) in each of the coming 5 years and is very likely to be within the range 0.9 – 1.8°C
• It is about as likely as not (40% chance) that one of the next 5 years will be at least 1.5°C warmer than preindustrial levels and the chance is increasing with time
• It is very unlikely (10%) that the 5 year mean annual global near-surface temperature for 2021-2025 will be 1.5°C warmer than preindustrial levels
• The chance of at least one year exceeding the current warmest year, 2016, in the next five years is 90%
• Over 2021-2025, almost all regions, except parts of the southern oceans and the North Atlantic are likely to be warmer than the recent past (defined as the 1981-2010 average)
• Over 2021-2025, high latitude regions and the Sahel are likely to be wetter than the recent past
• Over 2021-2025 there is an increased chance of more tropical cyclones in the Atlantic compared to the recent past
• In 2021, large land areas in the Northern Hemisphere are likely to be over 0.8°C warmer than the recent past
• In 2021, the Arctic (north of 60°N) is likely to have warmed by more than twice as much as the global mean compared to the recent past
• In 2021, southwestern North America is likely to be drier than the recent past whereas the Sahel region and Australia are likely to be wetter

References cited:
O’Kane, T. J. et al. CAFE60v1: A 60-year large ensemble climate reanalysis. Part II: Evaluation. Journal of Climate 1–62 (2021) doi:10.1175/JCLI-D-20-0518.1.

O’Kane, T. J. et al. CAFE60v1: A 60-year large ensemble climate reanalysis. Part I: System design, model configuration and data assimilation. Journal of Climate 1–48 (2021) doi:10.1175/JCLI-D-20-0974.1.

Squire, D. T. et al. Likelihood of unprecedented drought and fire weather during Australia’s 2019/2020 megafires. submitted to Nature Climate Change, 17.

Tozer, C. R. et al. Assessing the representation of Australian regional climate extremes and their associated atmospheric circulation in climate models. Journal Of Climate 33, 1227–1245 (2020