Climategate (2/3): be careful what you model for because you might get it

In the previous post I showed how James Hansen at GISS NASA clearly over estimated global warming in the late 80’s due to the modeling choices he made. To make a point on how influential the choice of a model is, in this post I will make modeling choices that will allow us to claim that global warming can be explained as a fluke in a random process.

I like to explain the relationship between data and models saying that data is the shadow reality casts, and models are what we believe is casting the shadow. So once we have a model  we can use it to cast shadows (make predictions) like the one James Hansen did and could be read in 1986 newspapers:

Hansen predicted global temperatures should be nearly 2 degrees higher in 20 year. “Which is about the warmest the earth has been in the last 100,000 years.”

Interestingly James Hansen downgraded his prediction in a 1988 paper from the nearly two degrees higher to a one degree higher. Though to be fair I would not be surprised if media misquoted him; I might not trust scientists but I absolutely distrust media.

Anyhow, let’s now compare NASA’s prediction in this 1988 paper (in red) to what actually happened years later (in blue):

1988 NASA predictions on top of yearly average global temperature changes with major volcano activity and parts per million levels of CO₂

Data for this plot comes from the B.E.S.T and N.O.A.A.