This is a follow up to our continuing discussion of the possible implications of changes to mid-century global average temperatures for conclusions reached by the IPCC AR4, and how scientists react to such changes.

Over at Real Climate they pointed to the following figure as representing “a good first guess at what the change will look like” and asserted that it would have no meaningful implications for the trends in temperature rise since mid-century presented by the IPCC.

Since there was some disagreement here in the comments of an earlier post about how to interpret this graph, I have decided to simply replicate it and then see if I could exactly replicate the graph from the Independent. The data is available here.

The first thing to note is that the Independent graph has a major error which Real Climate did not point out. It says that the smooth curve represents a 5-year average, when in fact, it actually represents a 21-point binomial filter. The difference in smoothing is critically important for interpreting what the graph actually says, and the error confused me and at least one climate scientist writing in our comments.

Here is a replication of the 21-point smoothing generated from the annual values, which will allow for my effort to replicate the graph from the Independent.

So far so good. But replication of the adjusted curve is a bit tricky as changing data for any one year has implications for the shape of the curve 10 years before that year and 10 years after. Upon trying to create a exact replication of the graph from The Independent, right away I realized that there was a major problem, because adding any increment to where Thompson et al. said it should begin (in 1945) instantly raised the adjusted curve to a point above the unadjusted curve. And as you can see in the Independent graph that at no point does the adjusted curve rise above the unadjusted curve, much less by a significant amount as implied by Thompson et al..

So right away it seems clear that we are not trying to make an adjustment that actually draws on the guidance from Thompson et al. This might seem odd, since the graph is supposed to show a proposed “guess” at the implications of Thompson et al. In any event, with that constraint removed I simply tried to get the best visual fit to the Independent graph that I could. And here is what I came up with.

Now, given the complicated smoothing routine, there is certainly any number of combinations of weird adjustments that will result in a very similar looking curve. (And if anyone from CRU is reading and wants to share with us exactly what you used, and the basis for it, please do so.) The adjustments I used are as follows:

1945 0
1946 0
1947 0
1948 0.1
1949 0.25
1950 0.18
1951 0.18
1952 0.18
1953 0.18
1954 0.16
1955 0.16
1956 0
1957 0
1958 0
1959 0
1960 0

Oh yeah, the effect of these visually pleasing adjustments on the IPCC trend from 1950? Not that it actually means anything given the obvious incorrectness, but it would reduce the trend by about 15%.

[UPDATE]Real Climate did not like the figure shown below, so I responded to them with the following request, submitted as a comment on their site:

If these guys know what is “wrong” then they must have an idea about what is “right”.

Real Climate writes an entire post responding to Steve McIntyre’s recent discussions of buckets and sea surface temperatures, explaining why the issue doesn’t really matter, but for some weird reason they can’t seem to mention him by name or provide a link to what they are in fact responding to. (If the corrections don’t matter, then one wonders, why do them? Thompson et al. seemed to think that the issue matters.)

Real Climate does seem have mastered a passive voice writing style, however. Since they did have the courtesy to link here, before calling me “uninformed” (in deniable passive voice of course), I though a short response was in order.

Real Climate did not like our use of a proposed correction suggested by He Who Will Not Be Named. So Real Climate proposed another correction based on a graphic printed in The Independent. Never mind that the correction doesn’t seem to jibe with that proposed by Thompson et al., but no matter, we used the one suggested by Mr. Not-To-Be-Named so lets use Real Climate’s as well and see what difference it makes to temperature trends since 1950. Based on what Real Climate asserts (but oddly does not show with numbers), you’d think that their proposed adjustment results in absolutely no change to mid-20th century trends, and indeed anyone suggesting otherwise is an idiot or of ill-will. We’ll lets see what the numbers show.

The graph below shows a first guess at the effects of the Real Climate adjustments (based on a decreasing adjustment from 1950-60) based on the graphic in The Independent.

What difference to trends since 1950 does it make? Instead of the about 50% reduction in the 1950-2007 trend from the first rough guess from you-know-who, Real Climate’s first guess results in a reduction of the trend by about 30%. A 30% reduction in the IPCC’s estimate in temperature trends since 1950 would be just as important as a 50% reduction, and questions of its significance would seem appropriate to ask. But perhaps a 30% reduction in the trend would be viewed as being “consistent with” the original trend

Try again Real Climate. And next time, his name is STEVE MCINTYRE — and his blog is called CLIMATE AUDIT. There is a lot of science and civil discussion there, with a healthy mix of assorted experts and a range of ordinary folks. Questioning scientific conclusions is a lot healthier for science than rote defense, but we all learned that in grad school, didn’t we?