Response to David Evans Opinion Piece on Climate Science

This is a point-by-point response to a David Evans op-ed that I wrote a couple years ago. It addresses some common misconceptions held by the public regarding climate science.

The debate about global warming has reached ridiculous proportions and is full of micro-thin half-truths and misunderstandings.


I am a scientist who was on the carbon gravy train, understands the evidence, was once an alarmist, but am now a skeptic.

Dr. Evans is an engineer, not a climate scientist. This is not to say that his opinion should be automatically disqualified, but based on this article it is clear that he does NOT understand the evidence.

Also, it is rather ironic that Dr. Evans is implying that it is more beneficial for a scientist to be an “alarmists” rather than a “skeptic”. I wonder which has worked out better for Dr. Evans? When he was an “alarmist” nobody had ever heard of him. Now that he is a “skeptic” he is a mini-celebrity who’s opinion is being championed by opportunistic politicians.

The whole idea that carbon dioxide is the main cause of the recent global warming is based on a guess that was proved false by empirical evidence during the 1990s. But the gravy train was too big, with too many jobs, industries, trading profits, political careers, and the possibility of world government and total control riding on the outcome. So rather than admit they were wrong, the governments, and their tame climate scientists, now outrageously maintain the fiction that carbon dioxide is a dangerous pollutant.

I would love for Dr. Evans to go to an American Geophysical Union meeting and see how climate science really works. The whole scientific process is inherently adversarial. Scientists have large egos and it is obvious that many of them take great pleasure in debating even the most insignificant claims. Not only that, but proving other people wrong is exactly how you make a name for yourself in science. The idea that scientists all over the world at thousands of different institutions are all colluding about global warming is ridiculous. There is simply way too much to be gained by being the person who could prove the consensus wrong.

The planet reacts to that extra carbon dioxide, which changes everything. Most critically, the extra warmth causes more water to evaporate from the oceans. But does the water hang around and increase the height of moist air in the atmosphere, or does it simply create more clouds and rain? Back in 1980, when the carbon dioxide theory started, no one knew. The alarmists guessed that it would increase the height of moist air around the planet, which would warm the planet even further, because the moist air is also a greenhouse gas.

First of all, the “carbon dioxide theory” did not start in 1980. Instead, the effects of CO2 increases on surface temperature have been being studied for at least 115 years:

Arrhenius, Svante, 1896, On the influence of carbonic acid in the air upon temperature of the ground 

Secondly, science specifically concerning the water vapor feedback has been accumulating for at least the last 45 years:

Manabe, Wetherald, 1966, Thermal equilibrium of the atmosphere with a given distribution of relative humidity

This is the core idea of every official climate model: For each bit of warming due to carbon dioxide, they claim it ends up causing three bits of warming due to the extra moist air. The climate models amplify the carbon dioxide warming by a factor of three — so two-thirds of their projected warming is due to extra moist air (and other factors); only one-third is due to extra carbon dioxide.

Climate models are built with a bottom up approach, element by element. This is what makes them useful for studying the climate system. It is true that climate models all enhance any initial warming from CO2 (i.e. they have positive feedbacks). It is very important to understand, however, that climate models are not specifically programmed to do this. Instead, the positive feedback is PREDICTED from all of the smaller scale parameterizations. The implication the models are simply assuming positive feedbacks is very misleading.

The alarmist case is based on this guess about moisture in the atmosphere, and there is simply no evidence for the amplification that is at the core of their alarmism.

This is just blatantly false. For a very concise and accessible summary of the work that has been done on the water vapor feedback see:

Dessler, Sherwood, 2009, A matter of humidity

This is a good overview and also points to some important references (particularly references 9, 10, 11, 12, and 14).

For a more technical but less up to date summary see:

Held, Soden, 2000, Water vapor feedback and global warming

Or you could consult some of the primary literature. For example:

Soden, B. J., R. T. Wetherald, G. L. Stenchikov, and A. Robock, 2002: Global cooling after the eruption of Mount Pinatubo: A test of climate feedback by water vapor. Science,296(5568), 727-730.

Dessler, A.E., and S. Wong, Estimates of the water vapor feedback during the El Nino Southern Oscillation,J. Climate, 22, 6404-6412, 2009.

Dessler, A.E., Zhang, Z, and Yang, P. The water-vapor climate feedback inferred from climate fluctuations, 2003-2008, Geophys. Res. Lett., 35, L20704, DOI: 10.1029/2008GL035333, 2008.

Minschwaner, K., and Dessler, A.E. Water vapor feedback in the tropical upper troposphere: Model results and observations. J. Climate 17, 1272-1282, 2004.

Chung, E-S., D. Yeomans and B.J. Soden, 2010: An assessment of climate feedback processes using satellite observations of clear-sky OLR, Geophys. Res. Lett., 37, L02702, doi:10.1029/2009GL041889.

Chung, E-S. and B.J. Soden, 2009: A satellite-based assessment of upper tropospheric water vapor measurements during AFWEX, J. Appl. Meteor. Clim., 11, 2284-2294.

Buehler, S.A., M. Kuvatov, V.O. John, M. Milz, B.J. Soden, and D.L. Jackson, 2008: An upper tropospheric humidity data set from operational satellite microwave data. Journal of Geophysical Research , 113, D14110, doi:10.1029/2007JD009314.

John, V.O. and B.J. Soden, 2007: Temperature and humidity biases in global climate models and their impacts on climate feedbacks. Geophysical Research Letters, 34, L18605, doi:10.1029/2007GL030736.

Soden, B.J., 2007: Water Vapor. Our Changing Planet: The View from Space, Cambridge, UK: Cambridge University Press, 26-29.

Soden, B. J., D. D. Turner, B. M. Lesht, and L. M. Miloshevich, 2004: An analysis of satellite, radiosonde, and lidar observations of upper tropospheric water vapor from the Atmospheric Radiation Measurement Program. Journal of Geophysical Research, 109, D04105, doi:10.1029/2003JD003828.

The point is that the water vapor feedback has been studied extensively, from many different angles and it is not based on a “guess”. Furthermore, this literature gives very strong evidence that the water vapor feedback is both positive and strong.

Weather balloons had been measuring the atmosphere since the 1960s, many thousands of them every year. The climate models all predict that as the planet warms, a hot spot of moist air will develop over the tropics about 10 kilometres up, as the layer of moist air expands upwards into the cool dry air above. During the warming of the late 1970s, ’80s and ’90s, the weather balloons found no hot spot. None at all. Not even a small one. This evidence proves that the climate models are fundamentally flawed, that they greatly overestimate the temperature increases due to carbon dioxide.

First of all, the upper tropospheric hot spot has nothing to do with warming specifically related to CO2. Instead, it is a fundamental prediction for any surface warming (due to the moist adiabatic lapse rate).

See this post for more details:

Secondly, more recent observations have indeed shown evidence for an upper tropospheric hot spot:

Also, as the IPCC notes, upper tropospheric trends in moisture are observed to be positive, which corroborates a positive water vapor feedback:


There are now several independent pieces of evidence showing that the earth responds to the warming due to extra carbon dioxide by dampening the warming.

Any study that claims that the climate system is dominated by negative feedbacks is an extreme outlier. One of the key reasons for this is that many climate changes of the past cannot be explained unless the climate system contains significant positive feedbacks. For a summary, see:

Knutti, Gabriele, 2008, The equilibrium sensitivity of the Earth’s temperature to radiation changes. 

Every long-lived natural system behaves this way, counteracting any disturbance. Otherwise the system would be unstable. The climate system is no exception.

A positive feedback does not automatically imply a runaway feedback. Even with positive feedbacks, the system will reach a new equilibrium. This claim shows that Dr. Evans lacks a fundamental understanding of how feedbacks work in the climate system.

It is no surprise that their predictions of planetary temperature made in 1988 to the U.S. Congress, and again in 1990, 1995, and 2001, have all proved much higher than reality.

Previous predictions of future climate change have actually done pretty well:

The official thermometers are often located in the warm exhaust of air conditioning outlets, over hot tarmac at airports where they get blasts of hot air from jet engines, at waste-water plants where they get warmth from decomposing sewage, or in hot cities choked with cars and buildings. Global warming is measured in 10ths of a degree, so any extra heating nudge is important. In the United States, nearly 90% of official thermometers surveyed by volunteers violate official siting requirements that they not be too close to an artificial heating source.

Urban heat island/micro site influences have been known about for decades and all global temperature reconstructions go to great lengths to remove any bias that they may cause. For instance, in the NASA gistemp analysis, they use night light intensity maps to identify urban vs rural stations in a given area:


The long-term trends of urban stations are then adjusted to agree with long-term trends of nearby rural stations. (

Also, the trends for poorly sited US stations have been compared to the trends from well sited US stations and it has been found that poorly sited stations actually introduce a cool bias rather than a warm bias:


Furthermore, satellite data, which is not subject to these potential biases, confirms the warming trend seen in other reconstructions (see below).

Global temperature is also measured by satellites, which measure nearly the whole planet 24/7 without bias. The satellites say the hottest recent year was 1998, and that since 2001 the global temperature has levelled off. Why does official science track only the surface thermometer results and not mention the satellite results?

Scientists do care about the satellite temperature data. The problem with this claim is that the satellite data AGREES with the thermometer based data:


Notice how misleading the claim is that temperatures have leveled off since 2001.

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