Originally published on ScienceBlogs.
By Greg Laden
Look at the graph at the top of the post.
This is a graph from the now famous Exxon documents that date to 1981, explaining how Exxon scientists were projecting global warming with continued release of the greenhouse gas CO2 into the atmosphere. There is a lot written about that work which remained secret until just a few days ago. The timing of this expose is interesting because it comes at about the same moment as a call to use US RICO laws to investigate and possibly prosecute those who seem to have been conspiring for a long time muddy the waters about the science of climate change in order to put off taking action that might financially hurt Big Petrol. (See also this.)
There are several interesting things about this graph. First, it was made in the 1980s, which proves that an IBM Selectric can make graphs. But never mind that. The graph shows the range of global surface temperature (vertical axis) over time (horizontal axis) in the past and future. If there was no effect from the human generated greenhouse gas CO2, global surface temperature would range, and had previously ranged, between about a half a degree C (Kelvin in the graph, but one degree K is one degree C) above and below a hypothetical baseline. However, given the influence of human generated greenhouse gas, the temperature rises.
When I saw this graph, I was reminded of several other graphs, such as the current surface temperature graphs showing rather shocking warming over the last few decades (since the Exxon graph was first typed). I was also reminded of the IPCC projections for warming, and the Hockey Stick graph of Mann, Hughes and others. It is notable that Exxon scientists, even before the marriage of the increasingly refined paleo-record with the increasingly detailed instrumental record that clearly demonstrated global warming, essentially had it right.
So I decided to see how right they were. To do this I made a graph that I’ll call a “Thumbsuck Estimate” (a phrase I picked up working in South Africa) of what the instrumental record of global surface warming, the IPCC projections, and Exxon ca 1981 indicated. My source graphs, other than the one shown above, included a graph of NOAA’s instrumental record (moving 12 month average) put together by my colleague John Abraham to include the most recent data:
And the graph found in Michael Mann’s book, “Dire Predictions” showing the instrumental record and the various IPCC projections.
For all three graphs, I estimated the center line of the variation indicated (the midpoint of the range shown on the Exxon graph, the midpoint of the range of IPCC estimates, the midpoints of relevant clusters of observed temperature values from NOAA) using simple interpolation with the help of a graphic application with moveable guides. I then recorded the available numbers (using years that matched across the graphics) in a spreadsheet, and specified for each data series a second order polynomial. The reason I used the second order polynomial is simply that the data consist of two parts, the background (roughly, pre-industrial though not quite) variation in surface temperature, and the upward swing of surface temperatures under anthropogenic global warming. By using the polynomial I’d get a curve that approximated this transition without using fancy statistics. Thumbsuck methodology.
This is the graph I got:
Notice that Exxon 1981 had it right. The revelations of the Exxon research, and the fact that it was kept secret and all that, is an interesting story. And, that story will develop over coming days, week, and months. But I don’t want to lose track of the other story, in some ways even more interesting. How surprised should we be, after all, that a major corporation would both look into and ignore, possibly even repress, the science associated with their primary activity? Not at all, really. But what is surprising is that we (and by “we” I mean scientists who have studied climate change) have understood the basic problem for a very long time, and decades of research have confirmed early findings, and of course, added important details.
With respect to the existential nature of global warming, we knew then what we know now, in broad outline.
There are some great uncertainties associated with anthropogenic climate change. For example, we don’t know how much sea levels will ultimately rise, or how long that will take. We don’t actually know in detail what will happen to specific coastlines that are inundated. We don’t know everything we need to now about how weather, especially as it relates to important endeavors such as food production, will change. We know it has already changed and will change more, but we can’t at this point confidently predict exactly what will happen, where, and when. And there are other things we don’t know.
But the basic relationship between greenhouse gasses and surface temperature rise, given a certain (not small but not huge) amount of variability, is something we do have a good idea of. Our knowledge of this problem predates concerted efforts by science deniers to distract, ignore, and avoid the science. The actual amount of surface temperature increase given a certain amount of CO2 and other greenhouse gasses added to the atmosphere is of course subject to multiple variables, and I don’t want to give the impression that we know the precise march of surface temperatures over time. But if you stand back a way, squint just a little, and look at what science could have said in 1981 and what it says now, they are pretty much the same.
See also this from Weather Underground
Reprinted with permission.
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