However, his departure from the programme would pose huge challenges for the BBC.
The turmoil across the Middle East has opened a vast range of opportunities for al-Qaida, but expansion poses huge challenges, too.
The sheer volume of information, and the internationalisation of terrorist networks mediated through modern telecommunications, poses huge challenges for national security agencies, in terms of resourcing alone.
But the donor community's insistence on digging wells, as well as the fierce competition to win philanthropic grants, posed huge challenges for Water.org's staff.
Their styles pose huge challenges to batsmen, but the strains created on their bodies mean that both have recently decided to limit themselves to shorter forms of the game in the hope that they can prolong their injury-plagued careers.
This posed huge challenges for the visual-effects team, led by Mr Letteri.And so to PandoraActors performing as Na'vi wore motion-capture suits in the usual way, and their scenes were performed in a warehouse where reflective items were entirely absent, to prevent any interference.
None of these reforms is easy, and all will take time to produce results, but governments around the world should press ahead with them.As this special report will explain, the changes now under way will pose huge challenges not only to governments but also to employers and individual workers.
Deputy Environmental Commissioner David Leff said: "The only thing they lobster die-off and the fish kill have in common is they pose huge challenges to the investigating scientists since they inevitably involve many complex, interrelated environmental and ecological factors, and many scientific disciplines.
Climate change and increasing urbanization pose huge challenges in managing urban planning for a sustainable future.
Flexible air-breathing hypersonic vehicles feature significant uncertainties which pose huge challenges to robust controller designs.
