It is one of the most encouraging truisms of the entire clean tech sector that the vast majority of the technologies required to deliver a low carbon economy are already in existence.

This week we've seen countless examples of the extent to which zero and low carbon technologies are not only technically feasible but already fully operational. From zero carbon homes to biofuel powered flights, electric cars to highly efficient solar cells many of the solutions to climate change are already up and running.

The big question - in fact the only question that matters in the wake of the news that concentrations of carbon dioxide in the atmosphere are at frightening high levels - is how quickly these technologies and thousands more like them can make the transition from technical feasibility to economic viability.

A few months back I caught up with Jan van Dokkum, chief executive of fuel cell specialist UTC Power, who underscored the scale of the challenge faced by those firms developing these clean technologies. He said that anyone visiting the company's offices could go out into the parking lot and go for a spin in a zero emissions fuel cell powered car that in terms of performance was easily the equal of pretty much anything on the road today. The only problem was that it costs hundreds of thousands of dollars.

And, as he explained, in many ways it would be ridiculous to expect it to cost much less when you consider that the incumbent auto manufacturers are churning out millions of cars a year, while those pioneering fuel cell technologies are producing mere hundreds, or in some cases tens, of vehicles.

The problem for these firms is developing the economies of scale that will allow their technologies to become cost competitive, while simultaneously ousting incumbent competitors with established manufacturing operations and supply chains.

And yet, if they can build up the requisite economies of scale clean tech firms can find themselves in a position where the environmental, health and life time cost benefits of many green technologies means they will be able to grow surprisingly quickly.

Toyota, for example, announced this week that it has now sold a million Prius' worldwide and hopes to have annual sales of over a million within the next five years or so.

Meanwhile, Van Dokkum said this week that UTC is just a couple of years away from delivering a fuel cell powered bus that, when running costs are taken into account, will be cheaper than diesel alternatives. Similarly, Cisco this week unveiled the second generation of its video conferencing suite at a price point a massive 90 per cent below the first generation version.

Making that economies of scale breakthrough and attaining cost competitiveness will typically require vast investment, but as Toyota has proven if it can be achieved the rewards can be vaster still.

Right, I'm off to find a green gauntlet to throw at the feet of Boris Johnson.

Have a good weekend,

James