In a recent blog discussion with some unusually astute folks who are still concerned about human warming, the thread came to a dead-end at satellites and thermometers. It became clear that the real crux of the climate debate between well-studied people boils down to whether one believes the satellite or the surface temperature time series.
So what are the differences?
Here is the NASA Goddard surface index in red and the UAH satellite index in green from 1975. The surface index is from about five feet off the ground at weather stations and the satellite measures the entire lower atmosphere up to about the height of Mt. Whitney so one expects it to be generally lower and it is. They agree pretty well with no systematic discrepancies until recently.
Here I added triple running mean filters, linear trend lines, and the Berkeley land only data for kicks. Once again pretty much what one expects except the land data has a hotter trend and goes way out to lunch and out of phase with the others in 2010 (the data is cautioned as preliminary).
Here we zoom in to examine the systematic recent differences that begin in 2013. The trend lines are headed in different directions. Which to believe? If you look carefully at the second graphic you can see that there was only one time previously in the late eighties when the vectors diverged in sine.
There is the specter of data adjustments. They have occurred in both datasets but the surface adjustments have the disturbing habit of always cooling the past and warming the recent.
Here is what NOAA acknowledges.
Here is what Tony Heller finds since 2012. As you can see the changes are very small, but adding .07C to the GISS surface data would account for the divergence since 2013.
One can get the idea from this crude rotation of the plot.
The issue is critical because when atmospheric warming is negligible, the atmosphere makes no contribution to ocean warming. The atmosphere cannot warm the ocean directly because IR radiation from greenhouse gasses penetrates no deeper than the micron scale skin of water surfaces and the ocean is always warmer than the atmosphere. The atmosphere can only warm the ocean by increasing in warmth itself and thereby slowing the rate of ocean cooling.
So either the atmosphere is significantly warming or it is not. Either it is contributing to ocean warming or it is not. Two sets of measurements, two different results, enormous consequences, the crux of the climate debate.