Guest essay by Pat Frank –
When Jim Hansen testified before the Senate Committee on Energy and Natural Resources, on June 23, 1988, he said that he was 99% sure human-caused global warming was already happening.
Ever wonder how he got so sure?
I discovered the answer while researching the validity of the global surface air temperature record.
The story is worth attention because Jim Hansen’s 1988 testimony set the low evidentiary standard subsequently adopted by consensus climatology.
The background is well-known. Senator Tim Wirth arranged to have the committee meeting on the historically hottest day of summer. And the record 98 F that day fully met his needs. Senator Wirth also ensured that the meeting-room windows were left open over-night, so that the air conditioning was ineffective. The room was sweltering. Jim Hansen was a hit. It was a fine victory of cynicism and circumstance over scruples and science.
1. The 99% Solution: The substance of Jim Hansen’s testimony that day is provided in the little Appendix at the bottom of this essay; see  for the full record. But the essence of 99% is in the next Figure, the GISS 1987+ global air temperature record, complete with ludicrously small error bars (1sigma = ±0.035 C, or ±0.025 C).
Original Caption: “Global surface air temperature change for the past century, with the zero point defined as the 1951-1980 mean. Uncertainty bars (95% confidence limits) … [are] the result of incomplete spatial coverage by measurement stations, primarily in ocean areas. The 1988 point compares the January-May temperature to the mean for the same 5 months in 1951-1980.”
This is pretty much Jim Hansen’s Figure 1 presented to the senate committee. I’ve added the green box, showing the ±0.13 C 1sigma jitter of global temperature during the 1951-1980 reference period.
The 1987 record was Figure 1 in Hansen and Lebedeff published in April 1988, about 3 months before his testimony,  and was Figure 6 of Hansen and Lebedeff, November 1987. 
In his testimony Jim Hansen implied that this 1sigma = ±0.13 C jitter was the full sum total of natural climate variability. The rise air temperature by mid-1988, nearly 0.4 C, was then 3s beyond nature. Obviously, that made the trend 99% unnatural.
That’s the whole ball of wax. Don’t believe it? Check out the quotes in the Appendix.
Somehow the 1884 and 1937 trend was overlooked by both Jim Hansen and the Senators. Right before their eyes was a 0.84 C global air temperature increase. Let’s see, that’s more than 6sigma beyond nature. In Jim Hansen world, that makes the trend more than 99.99966 % likely to be unnatural. Hmmm … what could possibly have caused that?
What about the probable ~1 C, unnaturally 7.7 sigma, increase in global air temperature between the Little Ice Age, 1650, and 1900?  Humans couldn’t have done it. Climate gremlins, maybe?
And those darn Dansgaard-Oeschger and Heinrich events, with their trends of multiple degrees Centigrade of global air temperature change per decade. Unnatural, too?
Or maybe they never happened. There’s an exciting new challenge the AGW stalwarts can take up for the cause: ‘We have to get rid of the Dansgaard-Oeschger and Heinrich periods.‘
2. Enter Physical Causality: But, testimony didn’t end there. Jim Hansen next offered his GISS Model II global warming scenarios A, B, and C to prove that the recent 99% unnatural warming was caused by CO2 emissions. After all, physics provides causality. The next Figure shows what the senators saw and what JGR published, after peer-review and all. 
The committee saw, and peer-reviewed JGR published, predictions without error bars. Pace JGR, but that makes them physically meaningless. They can not and do not signify any physical causality, at all.
If one goes ahead and imports scientific credibility by computing physically valid error bars (±8.9 C in 1988), the scenarios show themselves to be, well, physically meaningless.  Oh, well. No rescue there.
From the testimonial legend: “Annual mean global surface air temperature computed for trace gas scenarios A, B and C described in reference 1 (reference  below – P). … The shaded range is an estimate of global temperature during the peak of the current and previous interglacial periods, about 6,000 and 120,000 years before present, respectively. …”
So there you have it, Jim Hansen’s 99 % surety: for his purposes the entire 1sigma range of natural global variability in air temperature is ±0.13 C. The fact that there is no physical justification at all for his choice didn’t seem to bother anyone, including a trained Ph.D. astrophysicist. It is a very opportune statistic, though.
Jim Hansen’s physical causality? Established by reference to warming scenarios of unrevealed, unremarked, and almost certainly uncalculated accuracy, computed using a model that was (and remains) unvetted by any published critical physical analysis.
In my view, the analysis is horridly incompetent. But it set the standard of consensus climatology that has remained in force right up to the present.
Jim Hansen’s oral proof testimony to the committee: “[The] global temperature … is the highest of the period of record (then about 100 years). The rate of warming over the past 25 years … is the highest on record. 1988 will be the warmest year on the record.
“Causal association requires first that the warming be larger than natural climate variability and, second, that the magnitude and naturel of the warming be consistent with the greenhouse mechanism.
“The warming is almost 0.4 degrees Centigrade by 1987 relative to climatology, which is defined as the 30 year mean, 1950 to 1980 and, in fact, the warming is more than 0.4 degrees Centigrade in 1988. The probability of a chance warming of that magnitude is about 1 percent. So, with 99 percent confidence we can state that the warming during this time period is a real warming trend.
“The main point to be made here is that the expected global warming [Jim Hansen’s Model II Scenarios A, B, and C – P] is of the same magnitude as the observed warming. Since there is only a 1 percent chance of an accidental warming of this magnitude, the agreement with the expected greenhouse effect is of considerable significance.” 
Jim Hansen’s written proof testimony to the committee: “The present observed global warming is close to 0.4 oC, relative to … the thirty year (1951-1980) mean. A warming of 0.4 oC is three times larger than the standard deviation of annual mean temperature in the 30-year climatology. The standard deviation of 0.13 oC is a typical amount by which the global temperature fluctuates annually about its 30 year mean; the probability of a chance warming of three standard deviation is about 1%. Thus we can state with about 99% confidence that current temperatures represent a real warming trend rather than a chance fluctuation of the 30 year period.” 
And, just to lock it in, here’s what the GRL authoritatively peer-reviewed Hansen and Lebedeff say about the trend: “What is the significance of recent global warming? The standard deviation of annual-mean global-mean temperature about the 30-year mean is 0.13 oC for the period 1951-1980. Thus the 1987 global temperature of 0.33 oC, relative to the 1951-1980 climatology, is a warming of between 2s and 3s. If a warming of 3s is reached, it will represent a trend significant at the 99% confidence level. However, causal connection of the warming with the greenhouse effect requires examination of the expected climate system response to a slowly evolving climate forcing, a subject beyond the scope of this paper.” 
The “expected climate response” was Hansen’s Model II A, B, and C scenarios, both published,  and presented before the committee,  without any error bars.
From the testimony scenario Figure legend: “[Scenario A assumes continued growth rates of trace gas emission rates typical of the past 20 years, i.e., about 1.5 % yr-1 emission growth; scenario B has emission rates approximately fixed at current rate; scenario C drastically reduces trace gas emissions between 1990 and 2000].”
[1s, (2s, 3s, etc) changed to 1sigma for clarity. ]
1. Hansen, J. Statement of Dr. James Hansen, Director, NASA Goddard Institute for Space Studies. 1988 [Last accessed: 11 August 2014; Testimony before the US Senate Committee on Energy and Natural Resources: The Greenhouse Effect: Impacts on Current Global Temperature and Regional Heat Waves]. Available from: http://image.guardian.co.uk/sys-files/Environment/documents/2008/06/23/ClimateChangeHearing1988.pdf.
2. Hansen, J. and S. Lebedeff, Global Surface Air Temperatures: Update through 1987. Geophys. Res. Lett., 1988. 15(4): p. 323-326.
3. Hansen, J. and S. Lebedeff, Global Trends of Measured Surface Air Temperature. J. Geophys. Res., 1987. 92(D11): p. 13345-13372.
4. Keigwin, L. Bermuda Rise Box Core Data. IGBP PAGES/World Data Center-A for Paleoclimatology Data Contribution Series # 96-030. 1996 [Last accessed: 14 September 2007; Available from: ftp://ftp.ncdc.noaa.gov/pub/data/paleo/paleocean/by_contributor/keigwin1996/.
5. Hansen, J., et al., Global Climate Changes as Forecast by Goddard Institute for Space Studies Three‐Dimensional Model. J. Geophys. Res., 1988. 93(D8): p. 9341-9364.
6. Frank, P., Propagation of Error and the Reliability of Global Air Temperature Projections; Invited Poster, in American Geophysical Union Fall Meeting. 2013: San Francisco, CA; Available from: http://meteo.lcd.lu/globalwarming/Frank/propagation_of_error_poster_AGU2013.pdf (2.9 MB pdf).