James Hansen has published an online letter entitled

A Light On Upstairs? The letter concludes by saying:

My apologies if the quick response that I sent to

Andy Revkin and several other journalists, including the

suggestion that it was a tempest inside somebody’s

teapot dome, and that perhaps a light was not on

upstairs, was immoderate. It was not ad hominem, though.

I haven’t seen the original letter and don’t know who the

comment was about. However, it certainly sounds like an ad

hominem remark and one that is highly inappropriate for a

federal civil servant. I have a number of comments about

other aspects of the letter.

Hansen says:

Recently it was realized that the monthly

more-or-less-automatic updates of our global temperature

analysis (http://pubs.giss.nasa.gov/abstracts/2001/Hansen_etal.html)

had a flaw in the U.S. data. In that (2001) update of

the analysis method (originally published in our 1981

Science paper – http://pubs.giss.nasa.gov/abstracts/1981/Hansen_etal.html)

we included improvements that NOAA had made in station

records in the U.S., their corrections being based

mainly on station-by-station information about station

movement, change of time-of-day at which max-min are

recorded, etc.

Unfortunately, we didn’t realize that these

corrections would not continue to be readily available

in the near-real-time data streams. The same stations

are in the GHCN (Global Historical Climatology Network)

data stream, however, and thus what our analysis picked

up in subsequent years was station data without the NOAA

correction. Obviously, combining the uncorrected GHCN

with the NOAA-corrected records for earlier years caused

jumps in 2001 in the records at those stations, some up,

some down (over U.S. only).

The first sentence “it was realized” certainly makes it

sound like they identified the problem themselves (a

position not taken in the webpage itself.) Moving on, Hansen

says that the USHCN “corrections would not continue to be

readily available in the near-real-time data streams”. If

GISS is using USHCN adjusted data (as appears to be case

from the description in Hansen et al 2001 and the website),

this claim is incorrect. Readers in doubt of this may go to

the USHCN website ftp://ftp.ncdc.noaa.gov/pub/data/ushcn/ ;

the file hcn_doe_mean_data.Z contains three versions of

USHCN data, included the version that Hansen says is

unavailable. This file was most recently updated on March 1,

2007 and, for the majority of sites, contains adjusted USHCN

data up to Oct 2006. At present, GISS has only updated USHCN

records to March 2006. Thus, not only are the adjusted USHCN

versions available, they are available more recently than

presently incorporated into the GISS temperature

calculations.

Data from the other major station archive (GHCN) can be

downloaded from ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/v2 .

The GHCN raw data set and v2.mean.Z and the adjusted data

set v2.mean_adj.Z are both updated all the time, most

recently Aug 11, 2007. In the version that I downloaded in

June, the USHCN record only went to March 2006, the period

of the GISS record. However, readers can confirm that both

the GHCN raw and GHCN adjusted versions have been archived

concurrently and that the switch from one version to another

was not required because of version unavailability.

In this context, the form of the present layer of GISS

corrections seems extremely rushed and inappropriate. If

GISS wishes to start with GHCN adjusted data, then it’s easy

to do so. Just use it. There’s no need to estimate the

required correction to undo the effect of switching data

sets. Just stick with the data set that they started with.

Far simpler and cleaner than throwing another “correction”

into the mix – a correction which has required overwriting

their entire input data for all 1221 USHCN stations prior to

2000.

1998

Hansen goes on to say:

Also our prior analysis had 1934 as the warmest

year in the U.S. (see the 2001 paper above), and it

continues to be the warmest year, both before and after

the correction to post 2000 temperatures. However, as we

note in that paper, the 1934 and 1998 temperature are

practically the same, the difference being much smaller

than the uncertainty.

Unfortunately, this statement is again untrue. The data

online at GISS http://data.giss.nasa.gov/gistemp/graphs/Fig.D.txt

immediately prior to the changes showed 1998 as the warmest

year (admittedly by a negligible margin of 0.01 deg C), but

still the warmest, contrary to the claim made here. GISS has

overwritten this data file and did not preserve an online

version of the uncorrected data that they had previously

shown. However, by chance, I happened to have had the data

in my R-session when GISS made the changes and I assure

readers that the GISS data

shown here

purported to show that 1998 was the “warmest”. Hansen may

have been for 1934 before he was against it. But now that

he’s for 1934 once again, he can’t say that he was for it

all along.

In the

NASA press release in 1999 , Hansen was very strongly

for 1934. He said then:

The U.S. has warmed during the past century, but

the warming hardly exceeds year-to-year

variability.Indeed, in the U.S. the warmest decade was

the 1930s and the warmest year was 1934.

This was illustrated with the following depiction of US

temperature history, showing that 1934 was almost 0.6 deg C

warmer than 1998.

From a Hansen 1999 News Release:

http://www.giss.nasa.gov/research/briefs/hansen_07/fig1x.gif

However within only two years, this relationship had

changed dramatically. In

Hansen et al 2001 (referred to in the Lights On letter),

1934 and 1998 were in a virtual dead heat with 1934 in a

slight lead. Hansen et al 2001 said

The U.S. annual (January-December) mean temperature

is slightly warmer in 1934 than in 1998 in the GISS

analysis (Plate 6)… the difference between 1934 and 1998

mean temperatures is a few hundredths of a degree.

From Hansen et al 2001 Plate 2. Note the change in

relationship between 1934 and 1998.

Between 2001 and 2007, for some reason, as noted above,

the ranks changed slightly with 1998 creeping into a slight

lead.

The main reason for the changes were the incorporation of

an additional layer of USHCN adjustments by Karl et al

overlaying the time-of-observation adjustments already

incorporated into Hansen et al 1999. Indeed, the validity

and statistical justification of these USHCN adjustments is

an important outstanding issue.

Arctic Changes

Changes in the relationship of the 1930s to recent values

have not merely been made in the United States. In the

Arctic, there has also been a progressive change in the

relationship of temperatures in the 1930s to recent

temperatures, a point previously discussed at

CA here .

Hansen and Lebedeff 1987 showed very warm 1930s in the

Arctic, as shown in the excerpted figure showing the 64-90N

temperature history.

Excerpt from Hansen and Lebedeff 1987, showing 64-90N

temperature. The horizontal plot is from 1880 to 1985 (as

seen in the full Figure 7 of the original article shown

here )

The graphic below compares the most recent version of the

same graph (plotted from online data at GISS), marking two

bold points for 1937 and 1938 obtained from the printed

information in Hansen and Lebedeff 1987 (which prints out

the data now shown online). For both 1937 and 1938, the GISS

estimates have been reduced by approximately 0.4 deg C.

Despite recent warming, 2005 was the first year in which

64-90N values exceeded the former 1938 value – see dotted

line – (indeed, 2003 was the first year that exceeded the

“adjusted” 1938 value). While there are undoubtedly “good”

reasons for these adjustments (and I am not here arguing the

point one way or the other), the net effect of the

adjustments has been to consistently lower temperatures in

the 1930s relative to more recent values. Whether these

adjustments prove justified or not, modifications to the

temperature record of this magnitude surely warrant the most

careful scrutiny before turning the “lights out upstairs.”

64-90N from Hansen 64-90N zone downloaded today. Thick – 5

year running mean (often used by Hansen). Points are

selected values from Hansen and Lebedeff 1987. Dotted line

compares 1938 value from Hansen and Lebedeff 1987 to other

values.