Dr. William Gray and Dr. Kevin Trenberth Debate Global Warming — Part 1

The following, which took place before ClimateGate, is a written debate between Dr. Kevin Trenberth — head of the Climate Analysis Section at the National Center for Atmospheric Research in Boulder — and Dr. William Gray, Professor Emeritus of Atmospheric Science at Colorado State University. This debate originally appeared in the Fort Collins Forum and was later reposted on my quondam website:

Editor’s note: While the issue of anthropogenic global warming is much more than a local issue, we are fortunate to have two leading authorities on climate science in Northern Colorado. Each has a different view of the issue and agreed to this in-paper debate. The Forum believes this type of direct debate is all too rare on this topic and thank doctors Gray and Trenberth for their efforts. The Forum also wants to thank author Ray Harvey for bringing them together for this debate — John Kirsch, Publisher of the Fort Collins Forum:

Dr. William Gray

We Are Not In Climate Crisis

by Dr. Bill Gray
Professor Emeritus of Atmospheric Science at Colorado State University

Ask ten people on the street if mankind’s activities are causing global warming, and at least eight will say yes. This is because nearly 20 years of gross exaggeration on the part of scientists, environmentalists, politicians, and media; most of whom wish to profit in some way from the public’s lack of knowledge on the topic-have distorted the subject of human-induced global warming out of all sensible proportion. Many have been lead to believe that Al Gore’s movie and book An Inconvenient Truth provides incontrovertible evidence that human-induced global warming is a real threat. Yet, contrary to what is heard from warming advocates, there is considerable evidence that the global warming we have experienced over the last 30 years and over the last 100 years is largely natural. It is impossible to objectively determine the small amount of human-induced warming in comparison to the large natural changes which are occurring.

Many thousands of scientists from the US and around the globe do not accept the human-induced global warming hypothesis as it has been presented by the Intergovernmental Panel on Climate Change (IPCC) reports over the last 15 years. The media has, in general, uncritically accepted the results of the IPCC and over-hyped the human aspects of the warming threat. This makes for better press than saying that the climate changes we have experienced are mostly natural. The contrary views of the many warming skeptics have been largely ignored and their motives denigrated. The alleged “scientific consensus” on this topic is bogus. As more research on the human impact on global temperature change comes forth, more flaws are being found in the hypothesis.

It must be pointed out that most climate research is supported by the federal government. All federally sponsored researchers need positive peer-reviews on their published papers and grant proposals. This can be difficult for many of the “closet” warming skeptics who receive federal grant support. Many are reluctant to give full expression of their views, primarily because of worries over continuing grant support. It is difficult to receive federal grant support if one’s views differ from the majority of their peers who receive support to find evidence of the warming threat. The normal scientific process of objectively studying both sides of the question has not yet occurred. Such open discussion has been largely discouraged by warming advocates.

Implementation of the proposed international treaties restricting future greenhouse gas emissions by as much as 20 to 80 percent of current emissions would lead to a large slowdown in the world’s economic development and, at the same time, have no significant impact on the globe’s future temperature.

Many of the Global Climate Model (GCMs) simulations by large US and foreign government laboratories and universities, on which so much of these warming scenarios are based, have some very basic flaws. These global models are not able to correctly model the globe’s small-scale precipitation processes. They have incorrectly parameterized the rain processes in their models to give an unrealistically enhanced warming influence to CO2. This is the so-called positive water-vapor feedback. The observations I have been analyzing for many years show that the globe’s net upper-level water vapor does not increase but slightly decreases with warming. These GCMs also do not yet accurately model the globe’s deep ocean circulation which appears to be the primary driving mechanism for most of the global temperature increases that have occurred over the last 30 and last 100 years. GCMs should not be relied upon to give global temperature information 50 to 100 years into the future. GCM modelers do not dare make public short-period global temperature forecasts for next season, next year, or a few years hence. This is because they know they do not have shorter range climate forecasting skill. They would lose credibility if they issued shorter-range yearly forecasts that could be objectively verified. Climate modelers live mostly in a “virtual world” of their own making. This virtual world is isolated from the real world of weather and climate. Few of the GCM modelers have any substantial weather or short-range climate forecasting experience. It is impossible to make skillful initial-value numerical predictions beyond a few weeks. Although numerical weather prediction has shown steady and impressive improvement since its inception in 1955, these forecast improvements have been primarily made through advancements in the measurement (i.e. satellite) of the wind and pressure fields and the advection/extrapolation of these fields forward in time 10-15 days. For skillful numerical prediction beyond a few weeks, it is necessary to forecast changes in the globe’s complicated energy and moisture fields. This entails forecasting processes such as amounts of cloudiness, condensation heating, evaporation cooling, cloud-free radiation, air-sea moisture- temperature flux, etc. It is impossible to accurately code all these complicated energy moisture processes, and integrate these processes forward for hundreds of thousands of time-steps and expect to obtain anything close to meaningful results. Realistic climate forecasting by numerical processes is not possible now, and, because of the complex nature of the earth’s climate system, they may never be possible.

Global temperatures have always fluctuated and will continue to do so regardless of how much anthropogenic greenhouse gases are put into the atmosphere.

The globe has many serious environmental problems. Most of these problems are regional or local in nature, not global. Forced global reductions in human-produced greenhouse gases will not offer much benefit for the globe’s serious regional and local environmental problems. We should, of course, make all reasonable reductions in greenhouse gases to the extent that we do not pay too high an economic price. We need a prosperous economy to have sufficient resources to further adapt and expand energy production.

Even if CO2 is causing very small global temperature increases there is hardly anything we can do about it. China, India, and Third World countries will not limit their growing greenhouse gas emissions. Many experts believe that there may be net positive benefits to humankind through a small amount of global warming. It is known that vegetation and crops tend to benefit from higher amounts of atmospheric CO2, particularly vegetation which is under temperature or moisture stress.

I believe that in the next few years the globe is going to enter a modest cooling period similar to what was experienced in the 30 years between the mid-1940s and the mid-1970s. This will be primarily a result of changes in the globe’s deep-ocean circulation. I am convinced that in 15-20 years we will look back on this period of global warming hysteria as we now look back on other popular and trendy scientific ideas that have not stood the test of time.


Dr. Kevin Trenberth

Response by Dr. Kevin Trenberth

Global Warming: Coming Ready Or Not

by Kevin E Trenberth
Head of the Climate Analysis Section at the National Center for Atmospheric Research

Bill Gray suggests that we are not in a climate crisis. He should speak for himself. Maybe there is not a crisis in the sense that the world’s weather is falling apart now. But there is a major crisis in the failure to act to prevent potentially catastrophic changes in the future, in the times of our grandchildren, and their children. Changes in the climate are already evident. The Intergovernmental Panel on Climate Change has spoken:

“Warming of the climate system is unequivocal” and it is “very likely” due to human activities. Those were the key conclusions approved by 113 nations in Working Group I, which studies the science of climate change and the role of humans in affecting climate. The full report that is the basis for the summary was drafted by 154 lead authors and more than 450 contributing authors and runs to over 1,000 pages. Two other IPCC working groups deal with impacts of climate change, vulnerability, and options for adaptation to such changes, and options for mitigating and slowing the climate change, including possible policy options. In recognition of the stalwart work over 20 years, the 2007 Nobel Peace Prize was awarded to the IPCC and Al Gore.

Global mean temperatures have increased since the 19th century, and especially since the mid-1970s. Temperatures have increased nearly everywhere over land, and sea temperatures have also increased, reinforcing the evidence from land. However, global warming does not mean that temperatures increase steadily or uniformly because the atmospheric circulation also changes. As Gray suggests, natural variability has always been around and will continue. But we can now clearly demonstrate with climate models (and replicate this in many different countries and groups) that since about 1970 observed climate change is well outside the realm of natural variability. Some changes arising from global warming may be benign or even beneficial, such as a longer growing season.

But warming means increased heat waves and drying that increases risk of drought and reduces snowpack and water resources, a major concern in the West. It also increases water vapor in the atmosphere leading to more intense storms, heavier rains and greater risk of flooding, something observed to be happening in the US and elsewhere. Moreover, as noted by IPCC, there is clear evidence that upper level water vapor is increasing. The scientific understanding of climate change is now sufficiently clear to show that specific global and regional changes resulting from global warming are already upon us. The future projections are for much more warming, but with rates of change perhaps a hundred times as fast as those experienced in nature over the past 10,000 years. Just how fast depends on how humans as a whole respond to these warnings. There are uncertainties (although these cut both ways). However, the inertia of the climate system and the long life of carbon dioxide in the atmosphere mean that we are already committed to a significant level of climate change.

Bill Gray suggests that there has been a gross exaggeration and major distortion on climate change. IPCC scientists come from all parts of the political spectrum and dozens of countries; climate “skeptics” can and do participate, some as authors, and their goal is to produce the best scientific statements possible. Yet Gray implies that these scientists somehow no longer act independently, as scientists are wont to do, but instead conspire to mislead the public on climate change for their own selfish reasons. I don’t know anyone who has so profited. Gray’s comments about peer review fail to recognize that scientists are naturally very skeptical. However, it is not “views” that matter but rather evidence and reasoning, the very basis of science. Open discussion based on sound science is widely encouraged.

Gray is correct that global climate models are flawed and are just that, a model of the real world. By design, the resolution of the models can not deal with small-scale (less than about 100 miles) phenomena well. But they are by far the best tool we have for examining the enormously complex weather and climate system, and to replace model results by someone’s belief that has no physical basis does not cut it. The models continue to improve, especially as computers get faster and enable finer structure to be resolved, and many of the observed changes are simulated in climate models run for the past 100 years, adding confidence to understanding of the relationship with the agents that alter the climate and human-induced changes in atmospheric composition, and adding confidence to future projections. It may be impossible to model climate, as Gray suggests, but we are doing it anyway.

I have found that the only scientists who disagree with the IPCC report are those who have not read it and are poorly informed. The IPCC is a body of scientists from around the world convened by the United Nations jointly under the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) and initiated in 1988. Its mandate is to provide policy makers with an objective assessment of the scientific and technical information available about climate change, its environmental and socio-economic impacts, and possible response options. The IPCC reports on the science of global climate and the effects of human activities on climate in particular. Major assessments were made in 1990, 1995, 2001, and now 2007. Each new IPCC report reviews and assesses the state of knowledge, while trying to reconcile disparate claims and resolve discrepancies, and document uncertainties. The IPCC process is very open.

Two major reviews were carried out in producing each IPCC report. Every one of the thousands of comments submitted, including those by skeptics, are answered and the action taken is documented (in a huge Excel spread sheet that is publicly available), in a process overseen by independent review editors. Of course, many comments received are in conflict and many are demonstrably wrong. To get the IPCC authors to make changes, there has to be documented evidence and a reason. Opinion alone, such as Gray’s, does not make the grade. Many of the skeptics accept the IPCC report, and their arguments have changed from it is not happening to it is happening but it will be good for us!

The strength of the IPCC report is that it is a consensus report. Far from being a “gross exaggeration” as claimed by Gray, the IPCC report is really solid and conservative. It is not the latest “trendy scientific idea,” Rather it has been widely criticized for underestimating the recent observed changes in the Arctic (record low Arctic sea ice in 2007), and many scientists believe that sea level rise (from melting glaciers) will be much greater than projected by IPCC.

Since 1992 when a new satellite was launched that can provide true global measurements, sea level has risen at a rate of one foot per century, confirming the reality of global warming.

Gray goes on to claim, out of the blue, “restricting future greenhouse gas emissions by as much as 20 to 80 percent of current emissions would lead to a large slowdown in the world’s economic development …” On the contrary, saving energy and doing things more efficiently helps the economy substantially while reducing future climate change. It also helps preserve a non-renewable resource, and improves security by cutting dependence on foreign oil.

Gray then goes on to suggest that even if global warming is happening, there is nothing we can do about it because developing countries will continue growth and increase carbon dioxide emissions. Indeed this is a major concern and our government over the past eight years has failed us badly by not negotiating with these countries to protect our global atmosphere through international treaties such as the Kyoto Protocol.

The atmosphere is a global commons. The “Tragedy of the Commons” occurs when it is in everyone’s interest to use and exploit the commons but at the expense of the commons itself. Unfortunately, this is what is happening. In 2007 it is estimated that China will be the largest emitter of carbon dioxide into the atmosphere. As Americans, we should be outraged that the Chinese are dumping huge amounts of carbon dioxide into the atmosphere, sharing their emissions with everyone else and changing every one else’s climate! And we should be outraged that our politicians have not represented us well in that way. By the same token, the Chinese ought to be just as outraged that Americans are putting about as much carbon dioxide into the atmosphere. Since it is the accumulated amount that matters most, the United States more than any other nation, is responsible for the climate change underway. The United States emissions per capita are two and a half times those in Europe, and emissions per capita in Texas are three times what they are in California, highlighting the scope for major progress. Sixteen US states are keen to follow California into reducing carbon dioxide emissions from vehicles but are [and were] prevented from doing so by the EPA and the Bush Administration.

There is much that can be done, and America should lead. If done in the right way, benefits to the climate through reduced emissions save energy and promote the economy, while increasing sustainability.

[End of Part 1]

The debate rages on: read Part 2 here


  • Beefcake

    January 30, 2010

    “Only those that are not informed, do not believe in global warming”. Sounds like the discussion is over, we should admit to our stupidity and surrender to the superior intellect of those true believers!

    Only one problem: I have yet to see a single shred of scientific evidnce that clearly demonstrates man made “Global Warming”. I keep an open mind and have read everything that comes my way. Universally the believers in man made global warming claim that I am stupid for not believing, and claim they are superior and the only ones who have the answer.


    I have waited for years, always looking for such evidence. I guess I will just have to wait some more.

  • goodspkr

    January 30, 2010


    They do have scientific evidence. If the AGW theory is correct there is a hotspot in the troposphere in the tropics.. All you have to do is to check….what’s that? It isn’t there? Nevermind.

  • goodspkr

    January 30, 2010

    Alarmist should never get into a debate on AGW. Their position is extremist (in order to get people to do something).

    Trenberth says:
    “Maybe there is not a crisis in the sense that the world’s weather is falling apart now. But there is a major crisis in the failure to act to prevent potentially catastrophic changes in the future.”

    Everytime one of these alarmist starts this I think of Professor Harold Hill, the con man in the Music Man. “Yes, we’ve got trouble…Right here on Planet Earth. Yes we’ve got trouble. The starts with T and that rhymes with C and that stands for C….O2.”

    The easy way to defeat an Alarmist in a debate is to talk about the actual science. It all comes down to feedback. The highly positive feedback of the alarmist should result in that hotspot in the troposphere. Where is it? Let them talk about substituting wind speed for actual temperature readings–not very convincing. Tell them about the skeptics belief that the feedback at worst is only slightly positive and at best is negative. Low level cloud reflect sunlight back into space. The ERBE satellite system has shown that when the ocean heats up (more vapor–more low level clouds) the earth does reflect more solar radiation back into space. It seems earth has a way of cooling itself off. (That’s a very powerful metaphor)

    Go on to discuss the Hockey Stick and how it was used by the IPCC to support it’s notion that the global warming we are seeing is man made. Then talk about the scandal of funny data and all of it coming down to one tree in Siberia. Without that tree, the 20th Century temperature rise is nothing out of the ordinary and in the recent past (before the big increase in CO2) we had temperatures higher than today (MWP).

    Talk about the fit of the AGW theory. CO2 has been increasing rapidly for the past 65 years and you have 25 years of global temperature rise. That means 62% of the time we should be seeing warming, we haven’t. This puts them on the defensive as they try to explain why although global warming should be happening it isn’t or didn’t.

    Focus on why the temperature hasn’t increased in the past 10 years despite their models showing that the temperature should have increased (this is the equivalent of the skeptics saying warming was happening. It allowed the alarmist to get the upper hand.)

    Sea levels are going about it a rate of about 1 foot per century. Ask how the IPCC gets as much as three feet and Al Gore talks about 20 feet? As they explain this they will show they aren’t sure and there is a range of levels that could happen.

    Alarmists tend to quote authority (IPCC) and present anecdotal evidence. I would simple ask is IPCC a scientific organization or is it a political organization? It is a political organization.

    The anecdotal evidence such as the minimum of ice in the Arctic in 2007 is the canary in the coal mine analogy. But the ice is coming back and there is now the biggest increase in two year ice ever seen (since 1979 when we started looking via satellite). Fight anecdotes with anecdotes.

  • HankHenry

    February 1, 2010

    Dr. Trenberth – “But warming means increased heat waves and drying that increases risk of drought and reduces snowpack and water resources, a major concern in the West. It also increases water vapor in the atmosphere leading to more intense storms, heavier rains and greater risk of flooding, something observed to be happening in the US and elsewhere.”

    So am I correct in reading this as both “increased drying” AND “heavier rains”? Both together are not an impossibility but why shouldn’t I dismiss this as speculative imaginings of a tenuous nature attempting to come up with dire consequences of any sort? A common refrain in this debate is that mere weather is not climate, but this statement strikes me as an attempt to turn climate into bad weather. As a person involved in farming I can play this game of imagination too. What if current global warming helps guarantee our crops against fluky killer frosts of some future time when volcanic aerosols bring a temporary precipitous cooling.

    To me the one good indication of global warming is sea level rise, which I do believe is happening (based on my reading). It’s another question how reliably we know the length, rate and variability of this trend, and what part is natural and what part is induced by human activity.

    I was surprised that Dr. Trenberth openly referred to president George W Bush in his argument. That kind of political thought must surely introduce a bias into his scientific meditations on Climate. It’s very well understood that when scientists begin to think about the way the world ought to be it infects their perception of what the world is really like. If one appreciates the importance of double blind studies in medical research one has to appreciate how subtly bias can work. Grant availability for studies demonstrating global warming effects also has to be a large source of bias. My questions for any researcher I wish to take seriously is: What do you do to fight your personal biases? And, does the political climate of this debate inhibit you from publicly expressing doubts and reservations about the proportions of a climate crisis?

  • Redmond

    February 1, 2010

    Great comment HankHenry

    I chuckled when I read that bit as well. I think that Is how cagw proponents justify the claim that plenty of snow is due to global warming as well.

    As long as the climate is changing, we are responsible… Just look at the hockey stick – 1000 years of stasis, until we started burning oil.. I can’t think of anything else that could cause that, so it must be co2

  • Dave Cochrane

    February 1, 2010

    AGW is the biggest pile of bullshit to be inflicted upon us in a long long time. Climategate revealed the extent to which IPCC data is manipulated (or “fudged”), how dissenting or merely questioning voices and papers are suppressed, and how data is cherry-picked from temperature stations that show the desired warming, whilst those showing cooling (or no warming) are routinely discarded. We also now hear how much of the IPCC’s ‘findings’ come not from scientific analysis, but from Green activist groups, and Big ‘N Bouncy magazine.

    So next time Kevin E Trenberth tells you that we are in crisis because the IPCC says so, and because 2500 000 000 000 000 scientists are of one mind and agree absolutely with the hallowed UNIPCC, and anyone who disagrees is a nincompoop, the most appropriate thing you can do is to tell him to go stick Mann’s hockey stick up his arse (the wrong way first). He wouldn’t listen to logic.

  • Dale

    February 1, 2010

    Dave, you may be right, and AGW is certainly an enormous pile, but consider the lies on lies of Obama, Reid, Pelosi et al. The AGW hoax is/was designed to tax us back to the Stone Age, but the Obama agenda is doing that now. So, while AGW is a pile, it is still [somewhat] behind the floodgates; meanwhile the Obama anti-capitalist agenda is in full swing. My question to you is: which is the bigger pile, the actuality of Obamanomics or the AGW hoax?

  • Dave Cochrane

    February 3, 2010

    Hi Dale – I would say they’re both part and parcel of the same bigger picture (he says, mixing his metaphores). Due to the fact that the Socialists (Communists) currently enjoy control of the two biggest powers of influence on Earth (namely the USA and the UN) in addition to the EU, they are attacking Capitalism and freedom on all fronts. Their strength is in their numbers and in their multiple positions of power. Their weakness is in the fact that their philosophy and economics don’t stand up to any scrutiny and are based on deception and downright lies.


    January 13, 2015

    The Royal Society presided over by Isaac Newton had a motto: “Nullius in Verba.” This means: “On the word of no one,” meaning that you should never take anyones word for anything if you can look at the data yourself and draw your own conclusions. I have looked at the “raw data” of the ice cores and the recorded global temperature since the introduction of thermometers around 1850. There is absolutely no correlation between atmospheric CO2 preceding higher global temperatures—period. Consider this. NOAA states that atmospheric CO2 was at 285 parts per million (ppm) before the industrial revolution, and it is currently 385 ppm. Now, without anything more than arithmetic you can see that 400 ppm is the same thing as 4 parts per 10,000. And so, OUT OF EVERY 10,000 MOLECULES IN THE ATMOSPHERE, THERE ARE ONLY 4 MOLECULES OF CO2, at this time. There are many things we must decide without absolute certainty, but I simply do not believe that this trivial factor dominates the climate that also depends on solar irradiance (certainly the major source of heat on our planet), the vertical upwelling and horizontal currents in the vast oceans, and the immense amount of geothermal heat beneath the earth’s mantle. I believe that the current 16 year pause in global warming is a sure sign that the IPCC and its minions have been up the wrong tree, and the sky is not falling.

  • Ray

    January 13, 2015

    Thank you for your comment, Dr. McCully.

    And thank you for dropping by.

  • Sirius_TheStarDog

    April 26, 2015

    Trenberth’s response comes across as arrogant and condescending.

  • Ray

    April 26, 2015

    I completely agree. And not only that: Trenberth’s half-assed argument is totally unpersuasive.

    This might interest you: I conducted an informal poll after this piece was originally published, and readers resoundingly responded that the winner of the debate was Bill Gray.

    Thank you for dropping by.

  • Stewart Lovell

    April 28, 2015

    Hooray to all on responses to Trenberth’s tome, which was a massive appeal to authority – as in WE say it’s true so it must be. Nice try Mr. “Travesty that we can’t” explain the “pause”. Pack sand, and the stick!

  • Ray

    May 4, 2015

    Ipse Dixit.

    I agree with you completely.

    Thank you for dropping by, Stewart Lovell.

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