Michael Mann has an editorial on Scientific American’s site putting the well known 2.0C limit in perspective for the upcoming climate talks in Paris.

Mann makes a number of important points in his essay (read it here: Meeting a Global Carbon Limit Is Cheaper Than Avoiding One) but there is one point that I want to underscore.

The key factor is that there are technological innovations and economies of scale that emerge only in the course of actually doing something.

Here’s the thing. Let’s say you were suddenly in charge of one trillion dollars of money that could be used to address climate change. What would you spend the money on? Here are some suggestions.

1) Build machines that take CO2 out of the air.

2) Invest in the “next generation” of nuclear reactors.

3) Purchase a huge amount of deforested land and re-forest it.

4) Divide the money up among numerous research groups to develop as yet unknown clean energy technologies that may save us.

All those things are potentially good ideas, and we should probably think about doing all of them at some level. But that is not how you should spend your trillion dollars. The way you should spend your trillion dollars is to underwrite the cost of converting as many homes and businesses as you can to using passive geothermal heating and cooling, and to install photovoltaic on the roofs. Some of the money could also be used to switch internal combustion engines over to electric. Why do these things first? Because they are low hanging fruit. The results would be immediate. A home that uses passive geothermal will use about half, or less, of the fossil carbon for that purpose. A home that has fully deployed PV panels on the roof can cover the electricity for all of that home’s commuting costs and run the heating and cooling system, and a few other things, for much of the year. And so on. As long as our landscape is characterized by buildings with roofs that serve mainly to convert sunlight into heat, we can buy out that sunlight, harness it, and move towards a greater percentage of clean energy very very quickly.

At the same time, of course, we do want to do research on new technologies, perhaps even carbon capture (though I think that should be way down on the list). But there is so much we can do with existing technologies addressing existing needs. As Mann put it, “The obstacle is not a physical one—it is one of political and societal will.”