According to astronomer Dr Roger Angel, at the University of Arizona, the trillions of mirrors would have to be fired one million miles above the earth using a huge cannon with a barrel of 0.6 miles across.
The gun would pack 100 times the power of conventional weapons and need an exclusion zone of several miles before being fired.
Despite the obvious obstacles - including an estimated $350 trillion (£244trn) price tag for the project - Dr Angel is confident of getting the project off the ground.
He said: "What we have developed is certainly effective and a method guaranteed to work.
"Tests are ongoing but we expect to be ready to launch within 20 or 30 years time. Things that take a few decades are not that futuristic."
Dr Angel has already secured NASA funding for a pilot project and British inventor Tod Todeschini, 38, was commissioned to build a scaled-down version of the gun.
He constructed the four-metre long cannon in his workshop in Sandlake, Oxfordshire, for a TV documentary investigating the sun shield theory.
He said: "The gun was horrendously dangerous. This was the first gun I'd ever built.
"I knew I could put it together safely but at the end of it all I didn't know what I was going to get.
"It was immensely dangerous. I was attempting to build a gun to produce 1,500G of force but it ended up creating about 10,000G and we had to turn the power down.
"Most weapons used by the army produce 100Gs of force so our gun was about 100 times more powerful.
"The main danger was electrocution because it used enough power to boil 44,000 kettles.
"If you were working with normal levels of electricity you could get a shock and be fine, but if you got a shock off this you would be dead - no question.
"We've proved it's possible to build a scaled-down version of the gun needed to get these lenses into the air so it's just a matter of scaling up the designs for the real thing."
If Dr Angel's sun shield is successful he says the mirrors will last 50 years before needing to be replaced.
"What you are talking about is a project which will stop global warming for centuries to come," he said.
"At the moment the sums involved sound huge but in the greater scheme of things it's a price worth paying.
"Over 50 years the mirrors will become damaged and therefore fresh lenses will need to be fired into space to ensure the shield is constant."
Dr Angel, who pioneers solar energy, is developing cheaper methods of making the lenses to bring the cost of the project down.
In the meantime researchers at the University of Victoria, Canada, are testing the sun shield theory by using computer simulations of the project.
Dr Angel's sun shield theory will feature on Ways to Save the Planet on the Discovery Channel at 7pm on Sunday.