Letter from astronauts, scientists and mission control demands NASA end warming advocacy
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NASA's climate rebellion:
Letter from astronauts, scientists and mission control demands
space agency end warming advocacy
March 28, 2012
The Honorable Charles Bolden, Jr.
NASA Administrator
NASA Headquarters
Washington, D.C. 20546-0001
Dear Charlie,
We, the undersigned, respectfully request that NASA and the Goddard
Institute for Space Studies (GISS) refrain from including unproven
remarks in public releases and websites. We believe the claims by NASA
and GISS, that man-made carbon dioxide is having a catastrophic impact
on global climate change are not substantiated, especially when
considering thousands of years of empirical data. With hundreds of
well-known climate scientists and tens of thousands of other scientists
publicly declaring their disbelief in the catastrophic forecasts,
coming particularly from the GISS leadership, it is clear that the
science is NOT settled.
The unbridled advocacy of CO2 being the major cause of climate change
is unbecoming of NASA’s history of making an objective assessment of
all available scientific data prior to making decisions or public
statements.
As former NASA employees, we feel that NASA’s advocacy of an extreme
position, prior to a thorough study of the possible overwhelming impact
of natural climate drivers is inappropriate. We request that NASA
refrain from including unproven and unsupported remarks in its future
releases and websites on this subject. At risk is damage to the
exemplary reputation of NASA, NASA’s current or former scientists and
employees, and even the reputation of science itself.
For additional information regarding the science behind our concern,
we recommend that you contact Harrison Schmitt or Walter Cunningham, or
others they can recommend to you.
Thank you for considering this request.
Sincerely,
(Attached signatures)
CC: Mr. John Grunsfeld, Associate Administrator for Science
CC: Ass Mr. Chris Scolese, Director, Goddard Space Flight Center
./s/ Jack Barneburg, Jack – JSC, Space Shuttle Structures, Engineering Directorate, 34 years
/s/ Larry Bell – JSC, Mgr. Crew Systems Div., Engineering Directorate, 32 years
/s/ Dr. Donald Bogard – JSC, Principal Investigator, Science Directorate, 41 years
/s/ Jerry C. Bostick – JSC, Principal Investigator, Science Directorate, 23 years
/s/ Dr. Phillip K. Chapman – JSC, Scientist – astronaut, 5 years
/s/ Michael F. Collins, JSC, Chief, Flight Design and Dynamics Division, MOD, 41 years
/s/ Dr. Kenneth Cox – JSC, Chief Flight Dynamics Div., Engr. Directorate, 40 years
/s/ Walter Cunningham – JSC, Astronaut, Apollo 7, 8 years
/s/ Dr. Donald M. Curry – JSC, Mgr. Shuttle Leading Edge, Thermal Protection Sys., Engr. Dir., 44 years
/s/ Leroy Day – Hdq. Deputy Director, Space Shuttle Program, 19 years
/s/ Dr. Henry P. Decell, Jr. – JSC, Chief, Theory & Analysis Office, 5 years
/s/Charles F. Deiterich – JSC, Mgr., Flight Operations Integration, MOD, 30 years
/s/ Dr. Harold Doiron – JSC, Chairman, Shuttle Pogo Prevention Panel, 16 years
/s/ Charles Duke – JSC, Astronaut, Apollo 16, 10 years
/s/ Anita Gale
/s/ Grace Germany – JSC, Program Analyst, 35 years
/s/ Ed Gibson – JSC, Astronaut Skylab 4, 14 years
/s/ Richard Gordon – JSC, Astronaut, Gemini Xi, Apollo 12, 9 years
/s/ Gerald C. Griffin – JSC, Apollo Flight Director, and Director of Johnson Space Center, 22 years
/s/ Thomas M. Grubbs – JSC, Chief, Aircraft Maintenance and Engineering Branch, 31 years
/s/ Thomas J. Harmon
/s/ David W. Heath – JSC, Reentry Specialist, MOD, 30 years
/s/ Miguel A. Hernandez, Jr. – JSC, Flight crew training and operations, 3 years
/s/ James R. Roundtree – JSC Branch Chief, 26 years
/s/ Enoch Jones – JSC, Mgr. SE&I;, Shuttle Program Office, 26 years
/s/ Dr. Joseph Kerwin – JSC, Astronaut, Skylab 2, Director of Space and Life Sciences, 22 years
/s/ Jack Knight – JSC, Chief, Advanced Operations and Development Division, MOD, 40 years
/s/ Dr. Christopher C. Kraft – JSC, Apollo Flight Director and Director of Johnson Space Center, 24 years
/s/ Paul C. Kramer – JSC, Ass.t for Planning Aeroscience and Flight Mechanics Div., Egr. Dir., 34 years
/s/ Alex (Skip) Larsen
/s/ Dr. Lubert Leger – JSC, Ass’t. Chief Materials Division, Engr. Directorate, 30 years
/s/ Dr. Humbolt C. Mandell – JSC, Mgr. Shuttle Program Control and Advance Programs, 40 years
/s/ Donald K. McCutchen – JSC, Project Engineer – Space Shuttle and ISS Program Offices, 33 years
/s/ Thomas L. (Tom) Moser – Hdq. Dep. Assoc. Admin. & Director, Space Station Program, 28 years
/s/ Dr. George Mueller – Hdq., Assoc. Adm., Office of Space Flight, 6 years
/s/ Tom Ohesorge
/s/ James Peacock – JSC, Apollo and Shuttle Program Office, 21 years
/s/ Richard McFarland – JSC, Mgr. Motion Simulators, 28 years
/s/ Joseph E. Rogers – JSC, Chief, Structures and Dynamics Branch, Engr. Directorate,40 years
/s/ Bernard J. Rosenbaum – JSC, Chief Engineer, Propulsion and Power Division, Engr. Dir., 48 years
/s/ Dr. Harrison (Jack) Schmitt – JSC, Astronaut Apollo 17, 10 years
/s/ Gerard C. Shows – JSC, Asst. Manager, Quality Assurance, 30 years
/s/ Kenneth Suit – JSC, Ass’t Mgr., Systems Integration, Space Shuttle, 37 years
/s/ Robert F. Thompson – JSC, Program Manager, Space Shuttle, 44
years/s/ Frank Van Renesselaer – Hdq., Mgr. Shuttle Solid Rocket
Boosters, 15 years
/s/ Dr. James Visentine – JSC Materials Branch, Engineering Directorate, 30 years
/s/ Manfred (Dutch) von Ehrenfried – JSC, Flight Controller; Mercury, Gemini & Apollo, MOD, 10 years
/s/ George Weisskopf – JSC, Avionics Systems Division, Engineering Dir., 40 years
/s/ Al Worden – JSC, Astronaut, Apollo 15, 9 years
/s/ Thomas (Tom) Wysmuller – JSC, Meteorologist, 5 years
http://www.cfact.org/a/2112/Astronauts-and-scientists-send-le...
Top Opinion
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Savious 2012/04/11 21:54:08
Check for yourself if you don't believe me, it's here:
http://www.ipcc.ch/ipccreport...
Chapter 7, page 202.
Yeah, right. And here is the testimony of Dr. David Deming before a U.S. Senate committee: "I had another interesting experience around the time my paper in Science was published. I received an astonishing email from a major researcher in the area of climate change. He said, "We have to get rid of the Medieval Warm Period."
And they did, with Michael Mann's phony "hockey stick" graph. You AGW alarmists are just full of scams and fraud, as the emails from the climate group proved.
It's there in the very graph you just showed me - a warm period around 1100AD, and gradual cooling towards the 19th Century, followed by rapid 20th Century warming we all know about as shown in the instrumental record.
In fact there have been three warm periods over the past 5,000 years that were as warm, or warmer, than the late 20th century, the Minoan, Roman and Medieval Warm Periods - and no "man-made CO2" to blame.
Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia - http://holocene.meteo.psu.edu...
Why would you say that the MWP has been 'minimised' when clearly that is not the case at all?
http://www.ltrr.arizona.edu/w...
This is the origin of the graph you showed in your "yeah right" comment. It appears in the IPCC's Third Assessment Report, 2001.
The second graph is Europe - a rather small proportion of the northern hemisphere - and it doesn't say where the data comes from either. The IPCC TAR says:
Medieval warmth appears, in large part, to have been restricted to areas in and neighbouring the North Atlantic. This may implicate the role of ocean circulation-related climate variability. The Bermuda rise sediment record of Keigwin (1996) suggests warm medieval conditions and cold 17th to 19th century conditions in the Sargasso Sea of the tropical North Atlantic. A sediment record just south of Newfoundland (Keigwin and Pickart, 1999), in contrast, indicates cold medieval and warm 16th to 19th century upper ocean temperatures. Keigwin and Pickart (1999) suggest that these temperature contrasts were associated with changes in ocean currents in the North Atlantic. They argue that the "Little Ice Age" and "Medieval Warm Period" in the Atlantic region may in large measure reflect century-scale changes i...
http://www.ltrr.arizona.edu/w...
This is the origin of the graph you showed in your "yeah right" comment. It appears in the IPCC's Third Assessment Report, 2001.
The second graph is Europe - a rather small proportion of the northern hemisphere - and it doesn't say where the data comes from either. The IPCC TAR says:
http://www.grida.no/climate/i...
So the two different graphs in your figure, even if the second one is valid, don't necessarily contradict each other at all. It's perfectly possible that Europe saw greater extremes than other areas of the northern hemisphere or the world as a whole. It's worth reading more of that chapter of the TAR - it deals with exactly this kind of thing.
That "assumption" has been proven to be incorrect by a number of papers published since the turn of the 21st century. There have been at least three papers, and I believe another one recently, that have concluded that the MWP was world-wide.
Anyway, none of this contradicts AGW in any way. If the world did warm and cool by several tenths of a degree from what I gather were rather small solar and volcanic forcings, all that proves is that our now-larger influence is going to have a big impact on the climate.
"Medieval warmth appears, in large part, to have been restricted to areas in and neighbouring the North Atlantic."
Greenland, then, is exactly the kind of place that you would expect to reflect Mediaeval warmth even if that warmth was not global. Your Carter 2007 graph doesn't represent global or even hemispheric temperature as far as I can tell. Spencer and Loehle have each had their own stab at quantifying global temperature over the last few hundred years -
Both show the same kind of temperature evolution over the last millennium as Mann 2008 -
i.e. indicating that we have now very likely exceeded Mediaeval warmth. I do take your point about 'Little Ice Age' temperatures not being conducive to human well-being, but there's no danger of us going back to that any time soon. Now it's excessive warmth we have to worry about.
I wonder why, with all of the major volcanic eruptions over the ages, the earth hasn't burned up already, assuming you are correct about the positive feedback loop? The answer is that the assumption of positive feedback is wrong.
"How strongly climate was affected by CO2 variations of the past can be estimated from data using correlation analysis. This has been done for the Vostok ice core data for variations over an ice age cycle. Of course, CO2 is not the primary cause of an ice age, but it provides a feedback in this case. One needs to be very careful to account for all factors, including the presence of large continental ice sheets, methane variations, and atmospheric dust variations. Those data can be obtained from the ice core. The French scientists of the Vostok team that drilled the core performed such a correlation analysis and arrived at 3–4°C for climate sensitivity.17 That is an estimate made solely on the basis of data."
Stefan Rahmstorf, "Anthropogenic Climate Change"
http://www.pik-potsdam.de/~st...
Do you understand that? If there was a very small, zero or even net negative feedback then it would be very hard to explain the large (~5°C) global warming of the last deglaciation from the very small (~0.25W/m²) solar forcing. Of course, if you argue that 0.25W/m² of forcing can produce a warming of 5°C even with net negative feedbacks then you're arguing for an absolutely h...
"How strongly climate was affected by CO2 variations of the past can be estimated from data using correlation analysis. This has been done for the Vostok ice core data for variations over an ice age cycle. Of course, CO2 is not the primary cause of an ice age, but it provides a feedback in this case. One needs to be very careful to account for all factors, including the presence of large continental ice sheets, methane variations, and atmospheric dust variations. Those data can be obtained from the ice core. The French scientists of the Vostok team that drilled the core performed such a correlation analysis and arrived at 3–4°C for climate sensitivity.17 That is an estimate made solely on the basis of data."
Stefan Rahmstorf, "Anthropogenic Climate Change"
http://www.pik-potsdam.de/~st...
Do you understand that? If there was a very small, zero or even net negative feedback then it would be very hard to explain the large (~5°C) global warming of the last deglaciation from the very small (~0.25W/m²) solar forcing. Of course, if you argue that 0.25W/m² of forcing can produce a warming of 5°C even with net negative feedbacks then you're arguing for an absolutely huge climate sensitivity of 20°C/W/m², which would mean that the 1.6W/m² of anthropogenic forcing to date would be expected to produce 32°C of global warming and leave most of the planet uninhabitable for anything except micro-organisms. I don't know of anyone who thinks that's going to happen.
We can also derive feedbacks from modern observations. From 1900 to 2010, CO₂ rose from about 290 to 380ppm. The 'no-feedback' warming would therefore be calculated as follows:
ΔF = 5.35 * ln(C/C₀)
= 5.35 * ln(380/290)
= 1.44W/m²
ΔT = ΔF * 0.27 (because as everyone agrees, the 'no feedback' warming from CO₂ is about 1°C from a doubling of CO₂, and a doubling of CO₂ is a forcing of about 3.7W/m², and hence the no-feedback climate sensitivity would be 1/3.7 = 0.27°C/W/m²).
Therefore ΔT in this scenario is 1.44 * 0.27 = 0.39°C at equilibrium. Climate inertia means that we would expect to see about 60% of that in 2010, i.e. about 0.23°C.
As everyone knows, we have seen much more warming in the period than that - about 0.7°C, or 3 times as much. Numerous studies show that net natural temperature change over this period would have been roughly zero in the absence of anthropogenic forcings, and we know that the net anthropogenic forcing is about equivalent to the CO₂ forcing, so this 0.7°C of warming can be attributed to the anthropogenic increase in atmospheric CO₂.
Clearly, the contention that natural feedbacks are small, zero or even negative is very much contradicted by this data. In fact, a factor of 3 (i.e. 0.27/0.23=3.04) is precisely what climate scientists are citing as the best estimate for fast feedback climate sensitivity, meaning that we can expect a great deal of global warming from the already very large anthropogenic forcings. Even taking the lower limit of the 90% confidence range for the aerosol forcing, -0.5W/m², still makes derived climate sensitivity 1.2 / 2.3 = 0.52°C/W/m², or 1.9°C for a doubling of CO₂.
So basically all the evidence we have, whether it's from palaeoclimate data or modern instrumental data, rules out a low value for climate sensitivity.
Wasn't it a judge in the U.K. who ordered that before Gore's propaganda epic "An Inconvenient Truth" be shown to British school children there had to be a disclaimer pointing out 8 or 9 lies in the piece of crap?
"...not substantiated, especially when considering thousands of years of empirical data"
"declaring their disbelief..."
"...advocacy of an extreme position, prior to a thorough study of the possible overwhelming impact of natural climate drivers..."
Do you see what I mean? It's all just vague wishy-washy handwaving. There isn't even an *attempt* to say what exactly it is they object to, let alone provide supporting arguments or evidence for their case. It's almost as if they simply put their names to a fact-free propaganda piece written by the architects of the AGW denial scam... which is probably exactly what did happen.
Does this look 'relatively stable' to you? Our CO₂ forcing *alone* is already nearly 7 times larger than this Milankovitch forcing (1.7W/m² vs 0.25W/m²). The 'thousands of years of empirical data' categorically rule out a low value for climate feedbacks.
Yes, it does look stable, notice that it varies around a norm and hasn't encountered a runaway condition in the past. You can continue to blow smoke with your "forcing" equations, but CO2 does not drive the earth's climate, and most certainly the miniscule amount that mankind contributes, 5 gigtons per annum out of a total of ~ 155 gigatons (3.22%) isn't causing catastrophic global warming, any more than humans were responsible tor the last phony climate scare in the late 1970s, when the very same climate scientists were claiming we were in for a new ice age.
How about the 'Maunder Minimum' in solar irradiance which exacerbated the Little Ice Age around 1750AD? That was a drop in solar irradiance of around 0.2%, according to the solar physicists. You can confirm this in plenty of places. It's interesting to work out how much cooling that would cause if it happened again, and how it compares to anthropogenic forcings.
Solar irradiance S at Earth's orbit is about 1366W/m².
Surface area of the Earth is 4πr².
The area which intercepts solar radiation is πr² (the area of a circle of the Earth's diameter - look this up if the reasoning isn't clear) so solar irradiance averaged over the Earth's surface is 1366 / 4 = 341W/m².
Some of that radiation is reflected by clouds and the surface, such that the albedo (α, the proportion of radiation reflected) is around 0.298 and therefore the incident solar irradiance (that proportion which is actually absorbed by the planet) is (1-α)S/4 = 239.54W/m². Work it out yourself to confirm that I'm right.
So a 'Maunder Minimum' 0.2% reduction in incident solar irradiance is 239.54 * 0.002 = 0.48W/m² - a fraction of our CO₂ forcing of 1.7W/m². The...
How about the 'Maunder Minimum' in solar irradiance which exacerbated the Little Ice Age around 1750AD? That was a drop in solar irradiance of around 0.2%, according to the solar physicists. You can confirm this in plenty of places. It's interesting to work out how much cooling that would cause if it happened again, and how it compares to anthropogenic forcings.
Solar irradiance S at Earth's orbit is about 1366W/m².
Surface area of the Earth is 4πr².
The area which intercepts solar radiation is πr² (the area of a circle of the Earth's diameter - look this up if the reasoning isn't clear) so solar irradiance averaged over the Earth's surface is 1366 / 4 = 341W/m².
Some of that radiation is reflected by clouds and the surface, such that the albedo (α, the proportion of radiation reflected) is around 0.298 and therefore the incident solar irradiance (that proportion which is actually absorbed by the planet) is (1-α)S/4 = 239.54W/m². Work it out yourself to confirm that I'm right.
So a 'Maunder Minimum' 0.2% reduction in incident solar irradiance is 239.54 * 0.002 = 0.48W/m² - a fraction of our CO₂ forcing of 1.7W/m². The 'no feedback' effect on temperature for 0.48W/m² is 0.12°C. If climate sensitivity is around 3°C (or 0.75°C/W/m²) then a new Maunder Minimum would cause just 0.36°C of global cooling - i.e. at the current rate of global warming of around 0.18°C per decade, it would delay AGW by just 20 years.
Just goes to show that our influence on the climate is already several times larger than the largest variations in solar irradiance in the historical record, and can therefore be expected to produce more warming than any of the natural climate changes of recent centuries.
Forty internationally-known experts on forecasting methods and 123 expert reviewers codified evidence from research on forecasting into 140 principles. The empirically-validated principles are available in the Principles of Forecasting handbook and at forecastingprinciples.com.
These principles were designed to be applicable to making forecasts about diverse physical, social and economic phenomena, from weather to consumer sales, from the spread of nonnative species to investment strategy, and from decisions in war to egg-hatching rates. They ...
Forty internationally-known experts on forecasting methods and 123 expert reviewers codified evidence from research on forecasting into 140 principles. The empirically-validated principles are available in the Principles of Forecasting handbook and at forecastingprinciples.com.
These principles were designed to be applicable to making forecasts about diverse physical, social and economic phenomena, from weather to consumer sales, from the spread of nonnative species to investment strategy, and from decisions in war to egg-hatching rates. They were applied to predicting the 2004 U.S. presidential election outcome and provided the most accurate forecast of the two-party vote split of any published forecast, and did so well ahead of election day (see polyvote.com).
The authors of this study used these forecasting principles to audit the IPCC report. They found that:
Out of the 140 forecasting principles, 127 principles are relevant to the procedures used to arrive at the climate projections in the IPCC report. Of these 127, the methods described in the report violated 60 principles. An additional 12 principles appear to be violated, and there is insufficient information in the report to assess the use of another 38. (Note: That leaves only 17 of the applicable 127 principles of forecasting that the IPCC “scientists” definitely followed!)
As a result of these violations of forecasting principles, the forecasts in the IPCC report are invalid. The IPCC also ignored historic data regarding the Roman and Medieval Warm Periods and used a fraudulent “hockey stick” temperature graph to claim that the 20th century was the warmest in two millennia.
The forcing associated with an increase in atmospheric CO₂ is calculated by:
ΔF = 5.35 * ln(C/C₀)
... where C₀ is the initial atmospheric concentration of CO₂, C is the final concentration, and ΔF is the climate forcing associated with that increase in W/m². 'ln' just means the natural logarithm (you can use the Excel function to calculate this - it's really easy, you'll have no trouble doing it). An increase from 280 to 390 works out as a forcing of 1.7W/m². The formula is derived from calculations of the spectroscopic properties of CO₂. You can read about it here:
http://folk.uio.no/gunnarmy/p...
Myhre et al 1998
It's really interesting - you'd be able to understand as much of it as I can. If you plug in the values of 280 and 560 (i.e. a doubling of CO₂ from its pre-industrial concentration) then you get 3.7W/m², which everyone agrees on, including 'skeptics' like Spencer and Lindzen. They ev...
The forcing associated with an increase in atmospheric CO₂ is calculated by:
ΔF = 5.35 * ln(C/C₀)
... where C₀ is the initial atmospheric concentration of CO₂, C is the final concentration, and ΔF is the climate forcing associated with that increase in W/m². 'ln' just means the natural logarithm (you can use the Excel function to calculate this - it's really easy, you'll have no trouble doing it). An increase from 280 to 390 works out as a forcing of 1.7W/m². The formula is derived from calculations of the spectroscopic properties of CO₂. You can read about it here:
http://folk.uio.no/gunnarmy/p...
Myhre et al 1998
It's really interesting - you'd be able to understand as much of it as I can. If you plug in the values of 280 and 560 (i.e. a doubling of CO₂ from its pre-industrial concentration) then you get 3.7W/m², which everyone agrees on, including 'skeptics' like Spencer and Lindzen. They even agree that this forcing will, by itself (with no feedbacks) warm the planet by around 1°C. Here's the formula to calculate that:
R = σTr^4
... where R is the radiative flux emitted by the planet, σ is the Stefan-Boltzmann constant (5.67×10^−8 Wm^−2 K^−4) and Tr is the radiating temperature of the planet, i.e. the effective temperature at the mean radiating level of the atmosphere. So if Tr is 255K, the radiative flux is 239.74 and if Tr is 256K, the radiative flux is 243.52 - A difference of 3.78W/m², confirming that if you double atmospheric CO₂, which is a forcing of around 3.7W/m², then the planet has to warm up around 1K (i.e. 1°C) to radiate 3.7W/m² more and thereby restore equilibrium. No-one disputes this. Look:
Dr. Roy Spencer says:
"We calculated, as others have, a direct (no feedback) surface warming of about 1 deg. C as a result of doubling CO2 (“2XCO2”)."
http://www.drroyspencer.com/2...
Dr. Richard Lindzen says:
"A doubling of CO2 should lead (if the major greenhouse substances, water vapour and clouds remain fixed), on the basis of straightforward physics, to a globally averaged warming of about 1C."
http://www.publications.parli...
Honestly, you can work this stuff out yourself, just get a spreadsheet and start plugging in the numbers. You're easily smart enough to do that. The forcings really aren't in dispute - it's only the feedbacks which people have any legitimate debate about.
They may agree that a doubling of the CO2 concentration, without feedback, would result in an increase of 1 degree C., but from what I've read they also believe that there would be negative feedback, not positive. Do the calculations, what would the CO2 forcing have been back when the concentration of CO2 was 7,000 ppmv?
(I know what a natural logarithm is, log to the base e -- I took science courses in college back when we used slide rules that operated with a logarithmic scale.)
The forcing between 280ppm and 7,000ppm would be 17W/m². By comparison, the sun has been warming up for billions of years as it gradually turns hydrogen into helium -
On this basis the sun has warmed up by about 0.5% over the last 65 million years, and given that incident solar irradiance is only about 240W/m², that's a climate forcing of only 1.2W/m². So you can see that the CO₂ forcing is much more significant than the solar forcing, which explains why the Earth cooled so much over the last 65 million years while the sun has been warming -
The gradual decline in CO₂ over this period gave a cooling forcing which was around ten times larger than the warming influence from the sun. The thing is though, if feedbacks were negative then you'd expect only about 2°C of cooling, or less, instead of 8°C. Same goes for the modern instrumental record - it shows that feedbacks *must* be significantly positive, otherwise the climate would change much less than it has done.
The forcing between 280ppm and 7,000ppm would be 17W/m². By comparison, the sun has been warming up for billions of years as it gradually turns hydrogen into helium -
On this basis the sun has warmed up by about 0.5% over the last 65 million years, and given that incident solar irradiance is only about 240W/m², that's a climate forcing of only 1.2W/m². So you can see that the CO₂ forcing is much more significant than the solar forcing, which explains why the Earth cooled so much over the last 65 million years while the sun has been warming -
The gradual decline in CO₂ over this period gave a cooling forcing which was around ten times larger than the warming influence from the sun. The thing is though, if feedbacks were negative then you'd expect only about 2°C of cooling, or less, instead of 8°C. Same goes for the modern instrumental record - it shows that feedbacks *must* be significantly positive, otherwise the climate would change much less than it has done.