Telescopes are not low polluting.  Where they mine the materials to build TMT?  Out of the ground?  Does it pollute when it digs these materials out of the ground?  Do it pollute our environment shipping it to where ever it will end up?  The chemicals used where it will be built be environmentally friendly?  There was an oil spill on the current TMT site from one of the bulldozers.  So calling a telescope low polluting is not true.