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Roy Spencer on the Unsettled Science of Climate Change: A Primer

By Robert Bradley Jr. -- January 17, 2018

“Climate researchers … have a pretty good understanding of how the climate system works on average, but the reasons for small, long-term changes in climate system are still extremely uncertain.”

“The total amount of CO2 humans have added to the atmosphere in the last 100 years has upset the radiative energy budget of the Earth by only 1%. How the climate system responds to that small ‘poke’ is very uncertain. The IPCC says there will be strong warming, with cloud changes making the warming worse. I claim there will be weak warming, with cloud changes acting to reduce the influence of that 1% change.”

” … those of us who are skeptical of mankind’s influence on climate have a wide variety of views on the subject…. [I]t only takes one of us to be right for the IPCC’s anthropogenic global warming (AGW) house of cards to collapse.

– Roy Spencer, “My Global Warming Skepticism, for Dummies” (below).

The ever patient, scholarly, credentialed, and nice-guy climate scientist Roy Spencer has an excellent primer on the contentious issue of climate change. Nines year old, his 19-point summary (below) was and is excellent reading. It spells out what is the middle ground in a very contentious debate between the ultra-skeptics (CO2 as a trace gas is overwhelmed by natural climatic forces) and the ultra-alarmists (CO2 drives climate change and in very bad directions).

Spencer’s take, firmly within the global lukewarming camp, is presented below.


My Global Warming Skepticism, for Dummies

I receive many e-mails, and a recurring complaint is that many of my posts are too technical to understand. This morning’s installment arrived with the subject line, “Please Talk to Us”, and suggested I provide short, concise, easily understood summaries and explanations “for dummies”.

So, here’s a list of basic climate change questions, and brief answers based upon what I know today. I might update them as I receive suggestions and comments. I will also be adding links to other sources, and some visual aids, as appropriate.

It is important to understand at the outset that those of us who are skeptical of mankind’s influence on climate have a wide variety of views on the subject, and we can’t all be right. In fact, in this business, it is really easy to be wrong. It seems like everyone has a theory of what causes climate change. But it only takes one of us to be right for the IPCC’s anthropogenic global warming (AGW) house of cards to collapse.

As I like to say, taking measurements of the climate system is much easier than figuring out what those measurements mean in terms of cause and effect. Generally speaking, it’s not the warming that is in dispute…it’s the cause of the warming.

If you disagree with my views on something, please don’t flame me. Chances are, I’ve already heard your point of view; very seldom am I provided with new evidence I haven’t already taken into account.

1) Are Global Temperatures Rising Now? There is no way to know, because natural year-to-year variability in global temperature is so large, with warming and cooling occurring all the time. What we can say is that surface and lower atmospheric temperature have risen in the last 30 to 50 years, with most of that warming in the Northern Hemisphere. Also, the magnitude of recent warming is somewhat uncertain, due to problems in making long-term temperature measurements with thermometers without those measurements being corrupted by a variety of non-climate effects. But there is no way to know if temperatures are continuing to rise now…we only see warming (or cooling) in the rearview mirror, when we look back in time.

2) Why Do Some Scientists Say It’s Cooling, while Others Say the Warming is Even Accelerating?
Since there is so much year-to-year (and even decade-to-decade) variability in global average temperatures, whether it has warmed or cooled depends upon how far back you look in time. For instance, over the last 100 years, there was an overall warming which was stronger toward the end of the 20th Century. This is why some say “warming is accelerating”. But if we look at a shorter, more recent period of time, say since the record warm year of 1998, one could say that it has cooled in the last 10-12 years. But, as I mentioned above, neither of these can tell us anything about whether warming is happening “now”, or will happen in the future.

3) Haven’t Global Temperatures Risen Before? Yes. In the longer term, say hundreds to thousands of years, there is considerable indirect, proxy evidence (not from thermometers) of both warming and cooling. Since humankind can’t be responsible for these early events is evidence that nature can cause warming and cooling. If that is the case, it then opens up the possibility that some (or most) of the warming in the last 50 years has been natural, too. While many geologists like to point to much larger temperature changes that are believed to have occurred over millions of years, I am unconvinced that this tells us anything of use for understanding how humans might influence climate on time scales of 10 to 100 years.

4) But Didn’t the “Hockey Stick” Show Recent Warming to be Unprecedented? The “Hockey Stick” reconstructions of temperature variations over the last 1 to 2 thousand years have been a huge source of controversy. The hockey stick was previously used by the IPCC as a veritable poster child for anthropogenic warming, since it seemed to indicate there have been no substantial temperature changes over the last 1,000 to 2,000 years until humans got involved in the 20th Century. The various versions of the hockey stick were based upon limited amounts of temperature proxy evidence — primarily tree rings — and involved questionable statistical methods. In contrast, I think the bulk of the proxy evidence supports the view that it was at least as warm during the Medieval Warm Period, around 1000 AD. The very fact that recent tree ring data erroneously suggests cooling in the last 50 years, when in fact there has been warming, should be a warning flag about using tree ring data for figuring out how warm it was 1,000 years ago. But without actual thermometer data, we will never know for sure.

5) Isn’t the Melting of Arctic Sea Ice Evidence of Warming? Warming, yes…manmade warming, no. Arctic sea ice naturally melts back every summer, but that meltback was observed to reach a peak in 2007. But we have relatively accurate, satellite-based measurements of Arctic (and Antarctic) sea ice only since 1979. It is entirely possible that late summer Arctic Sea ice cover was just as low in the 1920s or 1930s, a period when Arctic thermometer data suggests it was just as warm. Unfortunately, there is no way to know, because we did not have satellites back then. Interestingly, Antarctic sea ice has been growing nearly as fast as Arctic ice has been melting over the last 30+ years.

6) What about rising sea levels? I must confess, I don’t pay much attention to the sea level issue. I will say that, to the extent that warming occurs, sea levels can be expected to also rise to some extent. The rise is partly due to thermal expansion of the water, and partly due to melting or shedding of land-locked ice (the Greenland and Antarctic ice sheets, and glaciers). But this says nothing about whether or not humans are the cause of that warming. Since there is evidence that glacier retreat and sea level rise started well before humans can be blamed, causation is — once again — a major source of uncertainty.

7) Is Increasing CO2 Even Capable of Causing Warming? There are some very intelligent people out there who claim that adding more carbon dioxide to the atmosphere can’t cause warming anyway. They claim things like, “the atmospheric CO2 absorption bands are already saturated”, or something else very technical. [And for those more technically-minded persons, yes, I agree that the effective radiating temperature of the Earth in the infrared is determined by how much sunlight is absorbed by the Earth. But that doesn’t mean the lower atmosphere cannot warm from adding more greenhouse gases, because at the same time they also cool the upper atmosphere]. While it is true that most of the CO2-caused warming in the atmosphere was there before humans ever started burning coal and driving SUVs, this is all taken into account by computerized climate models that predict global warming. Adding more “should” cause warming, with the magnitude of that warming being the real question. But I’m still open to the possibility that a major error has been made on this fundamental point. Stranger things have happened in science before.

8 ) Is Atmospheric CO2 Increasing? Yes, and most strongly in the last 50 years…which is why “most” climate researchers think the CO2 rise is the cause of the warming. Our site measurements of CO2 increase from around the world are possibly the most accurate long-term, climate-related, measurements in existence.

9) Are Humans Responsible for the CO2 Rise? While there are short-term (year-to-year) fluctuations in the atmospheric CO2 concentration due to natural causes, especially El Nino and La Nina, I currently believe that most of the long-term increase is probably due to our use of fossil fuels. But from what I can tell, the supposed “proof” of humans being the source of increasing CO2 — a change in the atmospheric concentration of the carbon isotope C13  — would also be consistent with a natural, biological source. The current atmospheric CO2 level is about 390 parts per million by volume, up from a pre-industrial level estimated to be around 270 ppm…maybe less. CO2 levels can be much higher in cities, and in buildings with people in them.

10) But Aren’t Natural CO2 Emissions About 20 Times the Human Emissions? Yes, but nature is believed to absorb CO2 at about the same rate it is produced. You can think of the reservoir of atmospheric CO2 as being like a giant container of water, with nature pumping in a steady stream into the bottom of the container (atmosphere) in some places, sucking out about the same amount in other places, and then humans causing a steady drip-drip-drip into the container. Significantly, about 50% of what we produce is sucked out of the atmosphere by nature, mostly through photosynthesis. Nature loves the stuff. CO2 is the elixir of life on Earth. Imagine the howls of protest there would be if we were destroying atmospheric CO2, rather than creating more of it.

11) Is Rising CO2 the Cause of Recent Warming? While this is theoretically possible, I think it is more likely that the warming is mostly natural. At the very least, we have no way of determining what proportion is natural versus human-caused.

12) Why Do Most Scientists Believe CO2 is Responsible for the Warming? Because (as they have told me) they can’t think of anything else that might have caused it. Significantly, it’s not that there is evidence nature can’t be the cause, but a lack of sufficiently accurate measurements to determine if nature is the cause. This is a hugely important distinction, and one the public and policymakers have been misled on by the IPCC.

13) If Not Humans, What could Have Caused Recent Warming? This is one of my areas of research. I believe that natural changes in the amount of sunlight being absorbed by the Earth — due to natural changes in cloud cover — are responsible for most of the warming. Whether that is the specific mechanism or not, I advance the minority view that the climate system can change all by itself. Climate change does not require an “external” source of forcing, such as a change in the sun.

14) So, What Could Cause Natural Cloud Changes? I think small, long-term changes in atmospheric and oceanic flow patterns can cause ~1% changes in how much sunlight is let in by clouds to warm the Earth. This is all that is required to cause global warming or cooling. Unfortunately, we do not have sufficiently accurate cloud measurements to determine whether this is the primary cause of warming in the last 30 to 50 years.

15) How Significant is the Climategate Release of E-Mails? While Climategate does not, by itself, invalidate the IPCC’s case that global warming has happened, or that humans are the primary cause of that warming, it DOES illustrate something I emphasized in my first book, “Climate Confusion”: climate researchers are human, and prone to bias.

16) Why Would Bias in Climate Research be Important? I thought Scientists Just Follow the Data Where It Leads Them When researchers approach a problem, their pre-conceived notions often guide them. It’s not that the IPCC’s claim that humans cause global warming is somehow untenable or impossible, it’s that political and financial pressures have resulted in the IPCC almost totally ignoring alternative explanations for that warming.

17) How Important Is “Scientific Consensus” in Climate Research? In the case of global warming, it is nearly worthless. The climate system is so complex that the vast majority of climate scientists — usually experts in a variety of specialized fields — assume there are more knowledgeable scientists, and they are just supporting the opinions of their colleagues. And among that small group of most knowledgeable experts, there is a considerable element of groupthink, herd mentality, peer pressure, political pressure, support of certain energy policies, and desire to Save the Earth — whether it needs to be saved or not.

18) How Important are Computerized Climate Models? I consider climate models as being our best way of exploring cause and effect in the climate system. It is really easy to be wrong in this business, and unless you can demonstrate causation with numbers in equations, you are stuck with scientists trying to persuade one another by waving their hands. Unfortunately, there is no guarantee that climate models will ever produce a useful prediction of the future. Nevertheless, we must use them, and we learn a lot from them. My biggest concern is that models have been used almost exclusively for supporting the claim that humans cause global warming, rather than for exploring alternative hypotheses — e.g. natural climate variations — as possible causes of that warming.

19) What Do I Predict for Global Temperature Changes in the Future? I tend to shy away from long-term predictions, because there are still so many uncertainties. When pressed, though, I tend to say that I think cooling in our future is just as real a possibility as warming. Of course, a third possibility is relatively steady temperatures, without significant long-term warming or cooling. Keep in mind that, while you will find out tomorrow whether your favorite weather forecaster is right or wrong, no one will remember 50 years from now a scientist today wrongly predicting we will all die from heat stroke by 2060.

Concluding Remarks

Climate researchers do not know nearly as much about the causes of climate change as they profess. We have a pretty good understanding of how the climate system works on average…but the reasons for small, long-term changes in climate system are still extremely uncertain.

The total amount of CO2 humans have added to the atmosphere in the last 100 years has upset the radiative energy budget of the Earth by only 1%. How the climate system responds to that small “poke” is very uncertain. The IPCC says there will be strong warming, with cloud changes making the warming worse. I claim there will be weak warming, with cloud changes acting to reduce the influence of that 1% change. The difference between these two outcomes is whether cloud feedbacks are positive (the IPCC view), or negative (the view I and a minority of others have).

So far, neither side has been able to prove their case. That uncertainty even exists on this core issue is not appreciated by many scientists!

Again I will emphasize, some very smart people who consider themselves skeptics will disagree with some of my views stated above, particularly when it involves explanations for what has caused warming, and what has caused atmospheric CO2 to increase.

Unlike the global marching army of climate researchers the IPCC has enlisted, we do not walk in lockstep. We are willing to admit, “we don’t really know”, rather than mislead people with phrases like, “the warming we see is consistent with an increase in CO2”, and then have the public think that means, “we have determined, through our extensive research into all the possibilities, that the warming cannot be due to anything but CO2”.

Skeptics advancing alternative explanations (hypotheses) for climate variability represent the way the researcher community used to operate, before politics, policy outcomes, and billions of dollars got involved.


  1. Ed Reid  

    Thank you, Dr. Spencer, for a rare display of humility and candor from a leading climate scientist.

    Please stay well away from your office windows for the foreseeable future. 😉


  2. John W. Garrett  

    Thank you for this clear, concise statement.

    Science is all about evidence. Thus far, there is precious little to support the CAGW conjecture.


  3. Mark  

    “Antarctic sea ice has been growing nearly as fast as Arctic ice has been melting over the last 30+ years.”

    A new global warming fear mongering technique: At this rate, the World will soon become bottom heavy and stop rotating.


  4. Roger Guevremont, retired scientist (chemistry)  

    This clever fellow left out one important question. What are the consequences of being WRONG?
    (A) if human-caused increase of CO2 really does nothing to the climate – result of being wrong: waste of money
    (B) if humans and our CO2 is the cause of rapid clime warming. – result of being wrong: if we do nothing then we (and our children) will suffer.

    Conclusion: doing nothing about our CO2 production does not seem very wise! Do something FIRST, and argue about causes and mechanisms and 1000yr drifts etc. etc. later.


  5. Robert  

    I read lately the earth rotation has slowed a bit. Would that not add to warmer climate as every inch of earth’s surface being slightly slower to move would the absorb more sunlight and more heat. That would definetly be beyond human cause.


  6. Energy & Environmental Newsletter: February 19, 2018 - Master Resource  

    […] Roy Spencer on the Unsettled Science of Climate Change: A Primer […]


  7. Tom Hayward  

    Do you believe the thesis that temperature increases well before evidence of CO2 emission increase, the opposite of the CAGW thesis?


    • Aert Driessen  

      As I see it, the proposition that temperature moves before CO2 levels in the atmosphere is confirmed by evidence from ice cores. This makes eminent sense in that CO2 is more soluble in cold water than warm water. Hence any warming of oceans, from whatever causes (sea floor volcanism, solar radiation, distributed by currents) releases CO2 to the atmosphere. Furthermore, oceans contain about seventy times more CO2 than the atmosphere so that I see them as a mayor player — a huge sink keeping us on an even keel.


  8. Denis Ables  

    I think you’ are being overly prudent about the MWP.

    The alarmists DENY (ironic?) that the Medieval Warming Period was a global event, and likely warmer then now. (Mann’s hockey-stick graph comes to mind). The likely reason for their DENIAL is that they cannot explain a global MWP because rising co2 is the only significant force related to human activity incorporated into the computer models. But co2 did not begin rising until the 1800s, which is long after the MWP. This lack of co2 increase during the MWP, also implies there would have been no water vapor feedback. (Water vapor feedback is ASSUMED, in the alarmist computer models, to be the actual culprit, causing 2 to 3 times the increase in temperature as brought on by an increasing co2 level.)

    The alarmists, to support their DENIAL, would have to first perform nothing less than temperature investigations around the globe. But wait …. that has been done by others, but apparently ignored by alarmists.

    A meta study demonstrating that the MWP was global and at least as warm as current temperatures follows:

    There are 6,000 boreholes around the globe The borehole temperature data show conclusively that the MWP trend was global. An enlightening discussion of the borehole data can be found at Joanne Nova’s website. Her spouse, Dr David Evans, is well acquainted with climate models.

    Google the Greenland Temperature study (gisp2). That study demonstrates, among other things, that Greenland was warmer during the MWP than it is now.

    The Mendenhall glacier in Alaska recently receded sufficiently to expose a shattered 1,000 year-old forest still standing in its original position. No trees have grown at that latitude anywhere near that site since then. Alaska and Greenland are remote from each other and remote from Europe (the locale where MWP is acknowledged by all).

    There are also ancient vineyards which have been found at latitudes where grapes cannot be grown today. Ancient burial sites have been found beneath the perma-frost. This evidence also indicates that it was warmer during the MWP than now. Glacier recession in the Alps has also exposed a similar shattered 4,000 year-old forest, so there were likely similar earlier warming periods, and each had to be the result of natural climate variation.


    Finally, there are also hundreds of peer-reviewed MWP studies, performed by researchers and scientific organizations around the globe. A subset of these studies specifically address temperature rather than such subjects as rainfall or droughts. Most MWP studies have been cataloged by co2science.org and information on those studies is also accessible by region. A good exercise for the reader is to select half a dozen regions (don’t forget the southern hemisphere) and choose in each region a temperature-based study (if one exists). You will find that each selected study shows the investigated site(s) to have been at least as warm, likely warmer, than it is now. This confirms the borehole trend and various other evidence, and vice versa.

    This meta-study, provides straight-forward evidence, all of which conflicts with the alarmists’ DENIAL. While ongoing MWP studies confirming the earlier studies continue to arrive, keep in mind that a number of these studies had been performed decades ago, before there was any controversy, and during that period IPCC acknowledged that the MWP was global and warmer than now. For some strange reason there was little alarmist interest in resolving this conflict when Mann produced his dubious “hockey stick” graph. Phil Jones, an alarmist player back in the day, stated publicly that if the MWP was global, then that’s a whole new ballgame. (Why didn’t Phil and other alarmists check it out?)

    While a global MWP does not prove that our current warming (such as it is) is principally caused by human activity (related to increasing co2 level) , the overwhelming evidence clearly introduces the possibility that this warming may have also been due to natural climate variation. Certainly this meta-study conclusively shows there is no justification for alarmist scientists’ DENIAL, and that McIntyre’s debunking of Mann’s claims, based on dubious statistics and strange weighting of tree proxy data.


  9. Energy And Environmental Newsletter – February 19th 2018 | PA Pundits - International  

    […] Roy Spencer on the Unsettled Science of Climate Change: A Primer […]


  10. DC  

    Roy writes: “But that doesn’t mean the lower atmosphere cannot warm from adding more greenhouse gases, because at the same time they also cool the upper atmosphere.”

    Well, that means adding GH gas (including water vapor) supposedly makes the lapse rate greater in the troposphere, warmer at the base as Roy says, and cooler at the top.

    The trouble is, Roy, that adding more of the greenhouse gas water vapor REDUCES the lapse rate.


  11. David Overton  

    I wonder if Dr Spencer has updated his views? His own data now shows clear warming (http://www.drroyspencer.com/2018/04/uah-global-temperature-updated-for-march-2018-0-24-deg-c/).

    As of March 2018 he reports a trend line of .13 C warming per decade, which is consistent with other, longer term data sets. Dr Spencer’s own data supports the scientific consensus.


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  13. Todd Mark  

    Nearly everything here has been shown to be error-ridden.

    One only need run Hansen’s old GCM to show how robust even that model is when accounting for positive and negative forcings.

    EdGCM(which runs the old GISS core) is downloadable from Columbia.edu. Even though the model may be a bit high in CS, it models the global climate to date with high accuracy. It’s particularly eye-opening in that it treats the ocean as a flat body and still yields skillful results.

    I ran it a while ago for fun, and while the mapping resolution isn’t great – it was designed to run on 1980s paralleled computers – it runs well on even a moderately powerful current laptop.

    This article should not be taken down, but should be amended as it may be mistaken for illustrating the real issues with modern climate science, when it certainly does not.

    If the site owner wants me to issue a point-by-point refutation, he/she knows how to reach me.


    • rbradley  

      Todd: Dismissing Spencer’s post almost in its entirety (‘Nearly everything here has been shown to be error-ridden”) based on Hansen’s model seems unjustified.

      Models can be ‘right’ for the wrong reasons, and ‘wrong’ for the wrong reasons. Intuition and toy models complete against formal models too.

      What is your own climate sensitivity estimate?


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  16. basket random  

    The overall trend is a statistically significant decrease in winter snowfall of about 25% from the 1870s to the present. However, the 10-year running mean indicates that the low point was in the late 1980s and that decadally-averaged snowfall totals have increased by about 50% since then (to a level currently that is slightly more than the average over the entire period).


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