Those making major decisions on how to address climate change, against a backdrop of global economic instability, require reliable estimates of how the climate may change in the future. This information is mainly provided by Earth System Models (ESMs) which describe the important physical, dynamical and biogeochemical processes in the climate system. However, despite their complexity, and great advances over recent decades, they remain simplified representations of the real earth system and are associated with a number of errors that reduce the reliability of future climate projections. Therefore improving the realism of European ESMs is vital in order to provide the most reliable estimates of future climate change to decision makers allowing them to make informed policy decisions at national, European and international levels.

 


Highlights: Investigating the North Atlantic 'hole'

hole close up imageWhile paleoclimatic data and recent measurements indicate the existence of rapid changes of Sea Surface Temperature (SST) in the North Atlantic, very few studies have looked at the possibility of such abrupt variations in the models participating in CMIP5. The EMBRACE WP5 team are leading a detailed analysis of the existence of abrupt changes in simulations from more than 30 models participating in CMIP5. Alongside other important topics like the potential Amazon dieback, the WP5 team have focused on the rapid changes in the North Atlantic.


In particular, they have looked at the so-called “North Atlantic hole”, an area located approximately to the south of the Greenland tip and where data from the last century (see recent Figure 1 from IPCC AR5 Summary for Policymakers below), and the CMIP5 simulations for the coming century, show a cooling while almost all of the rest of the globe is warming. 

altered wg1 spm fig 1

When looking at how the sea surface temperature (SST) changes over time at the location of the hole, it is clear that the transition can be abrupt, with changes of more than 1°C in less than 20 years. To illustrate this transition, the Figure below  shows the behaviour of SST in the model MIROC5, one of eight models among thirty-two that indicates this type of abrupt transition using the RCP4.5 scenario. In this particular model, the transition occurs as early as 2010 and ends in 2020. This can occur later in other models, but also earlier, in historical simulations (in GFDL-ESM2G for instance).

The model exhibiting the largest changes is FIO-ESM with a cooling starting in 2030 and reaching more than 2°C within 40 years. The team is currently investigating the causes of this pattern, which may implicate variations in the Atlantic Meridional Overturning Circulation but also rapid changes in the sub polar gyre, which is now recognised for its potential for bi-stable behaviour. As work progresses, WP5 will share any interesting results with the EMBRACE and wider scientific community, and a wider audience through the project website.

Find out more about the other aspects of WP5's work here

 

 

Examples of research areas targeted by EMBRACE

 

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