Abstract
The impact of climate change on Sahel precipitation is uncertain and has to be widely documented. Recently, it has been shown that Arctic sea ice loss leverages the global warming effects worldwide, suggesting a potential impact of Arctic sea ice decline on tropical regions. However, defining the specific roles of increasing greenhouse gases (GHG) concentration and declining Arctic sea ice extent on Sahel climate is not straightforward since the former impacts the latter. We avoid this dependency by analysing idealized experiments performed with the CNRM-CM5 coupled model. Results show that the increase in GHG concentration explains most of the Sahel precipitation change. We found that the impact due to Arctic sea ice loss depends on the level of atmospheric GHG concentration. When the GHG concentration is relatively low (values representative of 1980s), then the impact is moderate over the Sahel. However, when the concentration in GHG is levelled up, then Arctic sea ice loss leads to increased Sahel precipitation. In this particular case the ocean-land meridional gradient of temperature strengthens, allowing a more intense monsoon circulation. We linked the non-linearity of Arctic sea ice decline impact with differences in temperature and sea level pressure changes over the North Atlantic Ocean. We argue that the impact of the Arctic sea ice loss will become more relevant with time, in the context of climate change.
Highlights
As a consequence of climate change induced by human activities, Arctic sea ice is projected to disappear in summer at the end of the twenty-first century (Massonnet et al 2012; Stroeve et al 2012) leaving an ice-free ocean
The greenhouse gases (GHG) concentration is projected to increase leading to a dramatic decline of the Arctic sea ice, and even to its almost complete melting in late summer and early autumn by the end of twenty-first century
Recent studies based on coupled simulations have reported that Arctic sea ice decline could impact high and mid-latitudes, and tropical areas, such as the Sahel (Chiang and Bitz 2005; Kang et al 2008; Deser et al 2015; Blackport and Kushner 2016; OU17; Smith et al 2017)
Summary
As a consequence of climate change induced by human activities, Arctic sea ice is projected to disappear in summer at the end of the twenty-first century (Massonnet et al 2012; Stroeve et al 2012) leaving an ice-free ocean. The mechanism proposed by Smith et al (2017) involves a warming of the North Atlantic Ocean leading to a reinforced atmospheric circulation This is illustrated by Talento and Barreiro (2017) that have performed idealised numerical experiments in which a temperature increase of several degrees was prescribed at high latitudes to the model. Arctic sea ice loss is associated with an increase in surface air temperature (SAT), larger in autumn and early winter than during the preceding summer (Screen et al 2013; Deser et al 2015), resulting in a delay in phase of the SAT annual cycle at high latitudes (Mann and Park 1996; Dwyer et al 2012) This delay is found at lower latitudes (Dwyer et al 2012), impacting the seasonality (e.g. phase) of tropical precipitation (Dwyer et al 2014). What are the mechanisms involved in this relation? Is the impact of Arctic sea ice loss depending on the level of GHG concentration?
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
