"There are no scalable alternative fuels or technologies available today capable of taking the place of fossil fuels and offering society what those energy sources provide," he wrote in a blog in October.
Despite his concerns, Cerf said he believes that the internet's multi-stakeholder status has kept the web "evolvable, scalable, and has invited creativity".
"Most of the projects are funded by grants from donors, but since last year we have partnered with financial institutions who are providing loans to pay for future sanitation projects," says Ebrahim. "This came after we definitively proved that the projects are bankable, profitable and scalable".
Do you think models like these are scalable?
The situation boils down to this: fossil fuel is immensely useful, valuable and politically important, yet if we want to avoid taking unacceptable risks with the planet we need to leave most of that fuel in the ground – either forever or at least until there's an affordable and scalable way to stop the exhaust gases building up in the atmosphere.
However, it has abandoned for now attempts to help firms recruit employees from among Coursera's students, because catering to the different needs of each employer was "not a scalable model", says Ms Koller.For Udacity, in contrast, working with companies to train existing and future employees is now the heart of its business model.
Assets under management disappear and the patient building process has to start all over again.Nigel Wightman of Titanium Asset Management points out that in active management (ie, trying to beat an index) investment is not really scalable.
This is both the most effective option and the most "scalable", since a hotter Earth would simply require a bigger or more opaque parasol.The other ideas suffer from fundamental limits that stop them being scaled up indefinitely.
Fixing homeless people up as wireless hotspots doesn't seem like a scalable idea, but as an attention-getting experiment, well, why not?
The trick, he explains, is to abandon "handcrafted" teaching methods for scalable ones: online course materials and tutors; star teachers' lessons broadcast by satellite; tightly specified franchise agreements with hundreds of local teaching centres staffed by moderators.
