Would lower maximum motorway speed help reduce CO2-emissions?
If so, that would be an obvious support for an initiative like Climate Speed.
In 2010 Mattijs Otten and Hiub van Essen from CE Delft in Holland wrote a paper on the subject. Read about it and download their paper here.
In 2011 the European Environment Agency worked with the same question. Read about it here. (Unfortunately their pdf-report seems impossible to download, but anyway.)
So, does a speed reduction reduce CO2-emissions? Yes, it really does. And a speed reduction also reduces many other emissions (if not all) and strengthens traffic security in many ways.