Fig. 1. “Study of Cirrus Clouds”, painting by John Constable, circa 1822. Cirrus as a cloud type was first defined by Luke Howard in 1802.

2025 isn’t just the current year, or a Heritage Foundation project of conservative principles for political action for the new Republican President. In the 1990s it was also the result of an Air Force directive to “examine the concepts, capabilities, and technologies the United States will require to remain the dominant air and space force in the future“.

As a partial response to that directive, several students at the Air War College in 1996 produced a document, largely theoretical in content, entitled Weather As a Force Multiplier: Owning the Weather in 2025. That document, which was declassified in 1998, seems to have provided sufficient evidence some people needed to claim that our government has been secretly modifying the weather, altering the atmosphere, poisoning us with chemicals, or whatever else you can think of.

Now, as a general rule, I’m not against conspiracy theories. For example, it has become clear that experts knew early on that the COVID-19 virus likely did indeed come from a lab leak in Wuhan, China, and one might reasonably conclude there was a conspiracy to hide such evidence. Even the New York Times says we were misled. Conspiracies exist.

But not everything we see in the world that we perceive as a threat is the result of a conspiracy, and some people are just easily triggered by what they see. Many years ago I attended a local town hall meeting where a congressional candidate was speaking. During the Q&A period, an appropriately-attired biker dude got up and wanted to know what the candidate was going to do about all of the “chemtrails” the biker saw in the skies above him as he traveled around the country. The candidate provided a an appropriately vague and soothing response.

So, how did this “chemtrail” theory arise?

It seems to be a combination of peoples’ misunderstanding of the clouds they see in the sky combined with increasing distrust in our government, fueled by the 2025 Air Force study alluded to above. It also seems to be exacerbated by lesser standards of math and science education in recent decades, leading to a new generation of adults who can not critically examine claims made by others.

Contrail Production by Jet Aircraft is Well Understood

For those of us who know meteorology, those visible cloud streaks left behind travelling jets are “contrails” (condensation trails), produced during the combustion of jet fuel. The chemistry of jet fuel combustion is well understood, which includes the by-products of that combustion. During combustion, 1 kg of jet fuel produces about 1.3 kg of water (hydrogen in the fuel combines with oxygen from the atmosphere to produce H2O, water). That water exits the jet engine as water vapor in such high concentrations at extremely cold temperatures (around generally -30 to -50 deg. F) that there is much more water than the atmosphere can hold without condensation (cloud formation) occurring.

As a result, trails of cirrus clouds (contrails) are produced. Depending upon the relative humidity (RH) of the surrounding environmental air, those contrails can either rapidly evaporate (if RH is very low), leaving essentially no visible evidence, or can persist and even expand in coverage for many hours if the RH is high. In a high RH environment, jet-produced cirrus can actually scavenge water vapor from the surrounding atmosphere, causing continued growth of the contrails.

Fig. 2. Four-engine contrails produced by jet aircraft. Different illumination situations can change the contrail appearance, just as is the case with natural cirrus clouds (source).

The presence of wind shear (changing wind direction or speed with height) can cause distortion of the resulting clouds into myriad shapes. Often, the resulting jet-produced cirrus clouds are not easily distinguishable from natural cirrus clouds produced by weather systems; other times they are easily distinguishable. Literally as I was writing this, I took a picture out my office window showing both natural and jet-produced cirrus clouds.

Fig. 3. Natural and jet-produced cirrus clouds at sunrise, Huntsville, Alabama, 19 March 2025.

But when, and why, did the “chemtrail” conspiracy theory theory gain traction? And why does it persist today? The theory posits that the visual trails of condensed water vapor seen behind jet aircraft operating at high altitudes in reality represent the spraying of chemicals for some nefarious purpose(s). I routinely see comments on X and Facebook from people alarmed at the “chemtrails” they see. Those evil purposes of chemtrail production range from geoengineering (purposely changing the climate) to mind control and the spread of sickness that can be treated by pharmaceutical companies to increase their profits. Many weather experts have tried to debunk these ideas, for example Cliff Mass, professor of atmospheric science at the University of Washington.

Weather as a Force Multiplier: Owning the Weather in 2025

So, does the U.S. Air Force now own the weather in 2025, as predicted in the 1996 report? Of course not. Most of the theoretically possible technologies in that report for either clearing clouds, or creating clouds, in the battlefield did not exist in the 1990s. The report is full of pie-in-the-sky concepts, including cloud seeding to produce precipitation (the subject of much civilian research in recent decades), but admits “artificial weather technologies do not currently exist. But as they are developed, the importance of their potential applications rises rapidly.”

Yes, there have been experiments (mainly civilian) extending back to the 1950s involving seeding clouds to get them to precipitate. This involved dropping a chemical, such as dry ice or silver iodide crystals, to help convert super-cooled water droplets into precipitation. Project Stormfury, started in the 1960s, researched seeding hurricanes in the periphery to reduce the intensity of the central part of the cyclone, which is where most of the damaging winds and storm surge occur. But the idea was abandoned when it was realized hurricanes already convert almost all of the condensed cloud into precipitation anyway, without any help from humans.

This isn’t to say that it is impossible to seed clouds and produce precipitation, at least on a very localized basis in specific weather situations. But the research results have been mixed, and generally speaking, unless a cloud is getting ready to precipitate anyway, seeding doesn’t do much to the cloud, except make it precipitate sooner rather than later. People have a greatly exaggerated perception of what humans can do to purposely impact weather processes.

Now, I’m not privy to any weather modification technologies that DoD might have in the works. But after nearly a half-century of working in weather and climate, I can tell you there is little we can do to affect weather, either intentionally or unintentionally.

Let’s examine the AF report example of creating or clearing clouds in the battlefield. Imagine a wartime situation where the AF wants to clear a cloud (or fog) to allow precision visual identification of a target for bombing. Theoretically, this could be done with a powerful microwave directed-beam energy source (maybe from a special aircraft flying just ahead of a missile-carrying aircraft) to temporarily evaporate the cloud water. To give some idea of the energy that would be required to do that, we can compute how much energy is required to evaporate a path of fog having dimensions of 100x100x100 meters having a liquid water content of 0.1 grams water per kg of air. Assuming maybe 25% or so of the directed microwave beam energy will go into heating air and evaporating the liquid water, one can estimate the energy required of such a directed-beam device would be around 1 billion Watts (1 billion Joules of energy produced for 1 second). This is indeed in the realm of the estimated power output of DoD directed beam energy sources, at least from the ground. I have no idea whether such a large energy source could be produced by an aircraft.

But, even if the Air Force could, would they even want to? I’m pretty sure smart weapons now exist which have passive microwave technology allowing a target to be seen through relatively modest cloud cover.

So, What About Chemtrails? And Geoengineering?

As far as I can tell, the AF report cited above does not mention technologies that would disperse chemicals through jet exhaust (or other aircraft orifices). Besides, if such chemtrails exist, they are spreading their “chemicals” over everyone, including the families of the people conspiring to cause chemtrails.

Why would anyone do that?

Isolated photos do exist of jets dumping fuel, which comes out of different special wing ports, away from the engines. Sometimes this is cited as evidence of chemicals being spread for nefarious purposes. But this “fuel jettisoning” is a rare occurrence, usually in emergency situations, and is estimated to occur less than once per 100,000 commercial flights.

But there has been lots of research into whether jet contrails inadvertently affect climate, which would be a case of accidental geoengineering. Contrails reduce the amount of sunlight reaching the surface (a cooling effect), but that is more than offset by their reduction in the infrared (IR) cooling of the climate system, leading to a net heating. The best estimates are that global jet traffic produces less than 0.1 Watt per sq. meter of net radiative heating of the climate system, which is in the noise level (by comparison, natural solar heating and infrared cooling of the global-average climate system is ~240 Watts per sq. meter). Locally, where there is lots of air traffic, that value goes up to possibly 0.5 Watts per sq. meter, which is probably still not detectable in the presence of natural variations in temperature. An early study of the temperature effects of a jet traffic shutdown after 9/11 were later debunked by a subsequent study.

Now, what IS being discussed is the possibility of carrying large quantities of sulfur into the upper atmosphere (the stratosphere) to produce sulfur dioxide aerosols in an attempt to slightly reduce incoming sunlight and so partially offset global warming. This is an example of what “geoengineering” usually refers to. This would require huge amounts of sulfur compounds and many jet flights to even come close to the natural cooling effects of a major volcanic eruption, the most recent example of which was the 1991 eruption of Mt. Pinatubo in the Philippines. That eruption injected an estimated 15-20 million tons of SO2 into the stratosphere, which resulted in cool-ish summers over Northern Hemisphere land areas in 1992. Personally, I don’t ever see this happening because there would be too much public resistance to the idea.

But no one bats an eye when Mother Nature does it.

And the few news reports you see where supposed experiments involving the ground-level release of a few kg of sulfur compounds to test the idea of altering clouds are laughable. The EPA estimates that in 2023, 1.7 million tons of SO2 were released in the U.S. from anthropogenic sources. That is over 9 million pounds per day. Compare that to the “experimental” release of a few pounds by some headline-grabbing “researchers”. As I said… laughable.

A Major Reason for the Hysteria: Jet Contrails are Visible

Chemtrail hysteria would not exist if not for the fact that jet contrails are visible. Cars and trucks also produce huge amounts of water vapor, which is sometimes seen as condensed water in cold or high-RH conditions. The reason they don’t persist is that at the temperatures and air pressures present at ground level, the air can hold orders of magnitude more water vapor without cloud formation than jet-altitude air can hold.

But no one accuses car drivers (or car manufacturers) of purposely poisoning our air with chemicals, do they?

Yes, cars produce some chemicals as a by-product of combustion (all invisible), and through EPA regulations some of those chemicals have been greatly reduced with new fuel formulations, engine design changes, and catalytic converters. But cars are never blamed for producing chemtrails because, generally speaking, we never see those emissions (including the water vapor emissions). But we DO see jet contrails.

Finally, one part of the problem is that our public education system has produced too many science-illiterate adults. They are susceptible to crazy ideas spread by attention- (and money-) seeking charlatans, some of whom might be convinced that a chemtrail conspiracy exists. Too many people today seem to be incapable of independent, critical thought.

After all, who would doubt evidence such as this?:

Some Background

I will admit that the legal profession mystifies me. Every time I say anything related to environmental law, one or more lawyers will correct me. But I suppose “turnabout is fair play”, since I will usually correct any lawyers about their details describing climate change science.

Lawyers aren’t like us normal people. Their brains work differently. I first suspected this when one of my daughters took the LSAT and gave me examples of questions, most of which my brain was not wired to answer correctly. I became further convinced of this when she went to law school, and told me about the questions they deal with, how lawyers can impress judges just by being novel in their arguments, etc.

I know I could never be a lawyer (even after staying at a Holiday Inn Express), and I never even played one on TV. But I did co-author a paper in Energy Law Journal (relating to the Daubert Standard) on my view that science cannot demonstrate causation in any rigorous way in the theory of human-caused climate change.

Regulating CO2: Is the EPA Really Trying to Help Us?

The regulation of CO2 emissions (and some other chemicals) by the EPA has also mystified me. However many of the EPA’s ~185 lawyers worked on the 2009 Endangerment Finding, they must have known that regulating CO2 emissions from U.S. cars and light-duty trucks would have no measurable impact on global climate, including sea level rise (which was a major argument in Massachusetts v. EPA).

None.

But apparently actually trying to “fix” the climate “problem” is not the EPA’s concern.

Their reason for existence is to regulate pollutants (and it doesn’t matter if Nature produces far more of a “pollutant” than people produce). And once they start regulating it, they won’t stop with certain thresholds. They will keep lowering the threshold. This keeps everyone in jobs.

I know this is the case. I once attended a meeting of the Carolinas Air Pollution Control Association (CAPCA), and the keynote speaker (from the EPA) stated, “we can’t stop making things cleaner and cleaner”. There was a collective look of astonishment in the audience, which was primarily industry representatives who try to keep their companies in compliance with state and federal environmental regulations. I assumed their real-world experience told them it is impossible to make everything 100% clean (what would it cost to keep your home 100% clean?).

And we wouldn’t want to anyway because (as Ed Calabrese has explained in many published papers), it is necessary for resilience in biological systems to be exposed to stressors. I almost never get sick, which I attribute to a pretty filthy childhood of playing in heavily bacteria-contaminated waters, not washing my hands, etc. I was sick a lot then. But not later in life. This is why the EPA’s reliance on the “linear no threshold” assumption (simply put, if a gallon of something can kill you, then one molecule is also dangerous) has little to do with our real-world experience and common sense. Kind of like the legal profession.

So, is the EPA really trying to help us? I increasingly believe they are not. They are trying to keep their jobs (and grow even more jobs; coming from NASA, I know how that works). The law (and regulations) are tools to accomplish that. Yes, the EPA has accomplished needed pollution controls through the Clean Air Act. I’m old enough to remember driving through Gary, Indiana in the 1960s, trash lining the highways everywhere, waterways choked with pollution and even catching fire.

But at what point does the Government say, “OK, we fixed the problem. Good enough. Let’s not throw the baby out with the bathwater with damaging over-regulation.” No, that doesn’t happen. Because of the perverse way in which environmental regulations are written.

So, EPA, What About Regulating Water Vapor Emissions?

The EPA regulating CO2 emissions has a few problems, which seem to have not stopped the legal profession from doing what they do best. As I mentioned above, U.S. CO2 emissions from cars and light-duty trucks will have no measurable impact on global temperatures or sea level rise.. You could get rid of them completely. No measurable effect, Yet, here we are… regulating.

Since these are “global” problems, it has long been known that the EPA (and maybe even the Supreme Court’s Massachusetts v. EPA decision) could be on shaky ground, and maybe these are matters better left to legislation by the U.S. Congress.

But what about water vapor emissions from such vehicles? Now, there is a real possibility! Burning of any fuel (especially if we have hydrogen-powered vehicles) produces water vapor. And on a local basis (in your town or city) this extra water vapor will increase the heat index in the summer. And, and as everyone knows, “it’s not the heat, it’s the humidity”.

That’s a local problem caused by local sources of pollution, and seems to be much better suited for regulation by the EPA, which is a U.S. agency, dealing with U.S. pollution concerns.

The climate scientists who publish papers about the supposed dangers of greenhouse gas emissions make sure to exclude water vapor from their concerns, claiming CO2 is the thermostat that controls climate. I have commented extensively on the sleight of hand before. The vast majority of climate scientists believe CO2 controls temperature, and then temperature controls water vapor. CO2 is the forcing, water vapor is the feedback. But this argument (as I have addressed for many years) is just circular reasoning. The amount of water vapor in the atmosphere (did I forget to mention it’s our main greenhouse gas?) is partially controlled by precipitation processes we don’t even understand yet. The climate modelers simply tune their models to remove water vapor (through precipitation processes) in an arbitrary and controlled way that has no basis in the underlying physics, which are not yet well understood. Often, these simplifying assumptions translate into assuming relative humidity always remains constant.

But I digress. What I’m talking about here isn’t regulating water vapor emissions for global climate concerns… it’s to reduce their impact on summertime heat, especially in cities.

But why stop at vehicle emissions? Humans exhale lots of water vapor (joggers even more!). Maybe we should limit jogging and the sale of bottled water? Not a big enough problem, you say? Or maybe that’s an FDA thing? I don’t know… I’m just a simple country climate scientist.

As attorney Jonathan Adler commented in response to my recent blog post on the Endangerment Finding,

The problem is, the concerns you raise are not relevant in making an endangerment finding under the Clean Air Act. The textual standard is precautionary and does not allow for any cost-benefit balancing or consideration of other trade offs. All that is required is that the EPA administrator can reasonably anticipate some threats from warming to health or welfare, the latter of which is defined quite broadly.

So, we are back to the regulatory fact that if a “pollutant” (whatever that means) causes any level of threat, discomfort, worry, anxiety, then the EPA is compelled to regulate it. How convenient. Well, I would argue water vapor emissions, especially in the summer in cities, are better suited to regulation under the Clean Air Act than CO2 emissions are.

So Why Hasn’t Water Vapor Been Regulated?

Clearly it’s not because water vapor is “necessary” to the functioning of the Earth system, since CO2 is necessary for life on Earth to exist. Which brings me back to my question, is the EPA really trying to help us when it comes to climate-related regulation?

I’m increasingly convinced that science has been hijacked in an effort to (among other motives) shake down the energy industry. This has been planned since the 1980s. It makes no difference that human flourishing depends upon energy sources which are abundant and affordable. It doesn’t matter how many people are killed in the process of Saving the Earth. The law demands regulation, and that’s all that matters.

I have evidence. In the early 1990s I was at the White House visiting Al Gore’s environmental advisor, Bob Watson, a ex-NASA stratospheric chemist who was just coming off the successful establishment of the Montreal Protocol on Substances that Deplete the Ozone Layer. He told me (as close as I can recall), “We succeeded in regulating ozone-depleting chemicals, and carbon dioxide is next“.

Keep in mind this was in the early days of the IPCC, which was tasked to determine whether humans were changing the climate with greenhouse gas emissions. Their work was just getting started, including the scientists who would assist the process. But the regulatory goal had (wink, wink, nod, nod) already been established.

So, I don’t believe the EPA is actually trying to help Americans when it comes to climate regulation. I’m sure many of their programs (waste cleanup, helping with the Flint, MI water problem, and some others) are laudable and defensible.

But when it comes to regulation related to global climate (or even local climate, as the government tries to pack even more people into small spaces, e.g. with “15 minute cities“), my experience increasingly tells me no one in the political, policy, regulatory, legal, or environmental advocacy, side of this business really cares about the global climate. Otherwise, they would admit their regulation (unlike, say, regulating the precursors to ground-level ozone pollution in cities) will have no measurable impact. They wouldn’t be trying to pack people into urban environments which we know are 5-10 deg. F hotter than their rural surroundings.

It’s all just an excuse for more power and vested interests.

The Version 6.1 global average lower tropospheric temperature (LT) anomaly for February, 2025 was +0.50 deg. C departure from the 1991-2020 mean, up a little from the January, 2025 anomaly of +0.45 deg. C.

The Version 6.1 global area-averaged linear temperature trend (January 1979 through February 2025) remains at +0.15 deg/ C/decade (+0.22 C/decade over land, +0.13 C/decade over oceans).

The following table lists various regional Version 6.1 LT departures from the 30-year (1991-2020) average for the last 14 months (record highs are in red).

YEAR	MO	GLOBE	NHEM.	SHEM.	TROPIC	USA48	ARCTIC	AUST
2024	Jan	+0.80	+1.02	+0.58	+1.20	-0.19	+0.40	+1.12
2024	Feb	+0.88	+0.95	+0.81	+1.17	+1.31	+0.86	+1.16
2024	Mar	+0.88	+0.96	+0.80	+1.26	+0.22	+1.05	+1.34
2024	Apr	+0.94	+1.12	+0.77	+1.15	+0.86	+0.88	+0.54
2024	May	+0.78	+0.77	+0.78	+1.20	+0.05	+0.20	+0.53
2024	June	+0.69	+0.78	+0.60	+0.85	+1.37	+0.64	+0.91
2024	July	+0.74	+0.86	+0.61	+0.97	+0.44	+0.56	-0.07
2024	Aug	+0.76	+0.82	+0.70	+0.75	+0.41	+0.88	+1.75
2024	Sep	+0.81	+1.04	+0.58	+0.82	+1.31	+1.48	+0.98
2024	Oct	+0.75	+0.89	+0.61	+0.64	+1.90	+0.81	+1.09
2024	Nov	+0.64	+0.88	+0.41	+0.53	+1.12	+0.79	+1.00
2024	Dec	+0.62	+0.76	+0.48	+0.52	+1.42	+1.12	+1.54
2025	Jan	+0.45	+0.70	+0.21	+0.24	-1.06	+0.74	+0.48
2025	Feb	+0.50	+0.55	+0.45	+0.26	+1.04	+2.10	+0.87

The full UAH Global Temperature Report, along with the LT global gridpoint anomaly image for February, 2025, and a more detailed analysis by John Christy, should be available within the next several days here.

The monthly anomalies for various regions for the four deep layers we monitor from satellites will be available in the next several days at the following locations:

Lower Troposphere

Mid-Troposphere

Tropopause

Lower Stratosphere

Today, the Washington Post is reporting the EPA Administrator is considering recommending to the White House that the EPA’s 2009 CO2 Endangerment Finding be rescinded. Let’s look at a few of the reasons why this might be a good thing to consider.

The Science

The science of human-caused climate change is much more uncertain that you have been led to believe. The globally-averaged surface temperature of Earth seems to have warmed by 1 deg. C or so in the last century. The magnitude of the warming remains uncertain with a 30% range in different thermometer-based datasets, and considerably weaker warming in global “reanalysis” datasets using all available data types. But whatever the level of warming, it might well be mostly human-caused.

But we don’t really know.

As I keep pointing out, the global energy imbalance caused by increasing human-caused CO2 emissions (yes, I believe we are the cause) is smaller than the accuracy with which we know natural energy flows in the climate system. This means recent warming could be mostly natural and we would never know it.

I’m not claiming that is the case, only that there are uncertainties in climate science that are seldom if ever discussed. The climate models that are the basis for future projections of climate change are adjusted (fudged?) so that increasing CO2 is the only cause of warming. The models themselves do not have all of the necessary physics (mostly due to cloud process uncertainties) to determine whether our climate system was in a state of equilibrium before CO2 was increasing. (And, no, I don’t believe the warming caused the oceans to outgas more CO2 — that effect is very small compared to the size of the human source).

As most readers here are aware, for many years I’ve been saying the science of “climate change” has been corrupted by big government science budgets, ideological worldview biases, and group-think. Even my career has depended upon Congress being convinced the issue is worthy of big budgets.

It is almost impossible for new science to be published in the peer-reviewed literature that in any way runs counter to the current narrative which states that humans are causing a “climate crisis” from our CO2 emissions, a natural consequence of fossil fuel burning. That “peer review” is now in the hands of climate scientists whose research careers depend upon continuing government funding. If the “problem” of global warming were to be much less than previously believed, funding for that research could dry up.

The most alarmist science papers are the ones that get all of the press, which then get exaggerated and misrepresented by the news media. As a result, the public has a very skewed perception of what scientists really know.

As Roger Pielke, Jr. has been pointing out for many years, even the IPCC’s official reports do not claim that our greenhouse gas emissions have caused changes in severe weather. Every severe weather event in the news is now dutifully tied in some inferential way to human causation, but with public opinion of mainstream news outlets at an all-time low, fewer and fewer people take those news reports seriously. Severe weather has always existed, and always will. Storm damages have increased only because of increasing infrastructure and everyone wanting to live on the coast.

And about the only, clear, long-term change I’m aware of is a 50% decline in strong to violent tornadoes since the 1950s.

But you would never know of any good climate news if your main source of information is Al Gore’s books, your favorite environmental think tank (that you contribute to so you can get their yearly calendar), or the mainstream media.

Costs vs. Benefits

If there was no cost to replacing fossil fuels with renewable sources of energy, I might be a little more supportive of regulations which choose winners and losers, rather than letting the marketplace decide. But everything humans do requires energy, and so human flourishing depends upon abundant and affordable energy. We in the developed world might have excess wealth to spend on pricey new forms of energy (although our rapidly increasing national debt argues we don’t have excess wealth to squander), but most of the world’s poor continue to struggle to pay for energy we have in relative abundance… if they even have access to it.

The 2009 Endangerment Finding

The Supreme Court has ruled that CO2 falls under the EPA’s Clean Air Act, and so EPA would need to regulate it if it was considered a threat to human health and welfare. Which it did in 2009.

But this “threat to human health and welfare” business cuts both ways.

For example, I could argue that most premature human deaths are caused, indirectly, by what we eat (or don’t eat). The incidence of obesity and related illnesses continues to rise. So, given the threat of food to human and welfare, why not just outlaw food? Food is a threat to human health and welfare, too.

Clearly we don’t do that because food is necessary for life. But so is CO2.

CO2 is required for photosynthesis, which in turn is required for the food chain on land and in the oceans. NASA-based satellite measurements since the 1980s have documented global greening from increasing CO2. It has been estimated global agricultural productivity has increased by trillions of dollars from crops growing better, with more drought resistance, in a CO2-enriched atmosphere.

I’ve read the technical support document for the 2009 EF. It is full of gloom and doom. Any benefits to more CO2 are downplayed while costs are trumpeted. Its authorship appears to have been heavily influenced by environmental activists, most of whom have their own agendas. Much of the science in it now sounds more like Al Gore’s original alarmist book Earth In The Balance (which referenced me, but couldn’t get my science contributions right) than a balanced assessment of the science of climate change.

Fifteen years since the 2009 Endangerment Finding, we now know much more. None of the scary scenarios originally predicted have actually come to pass, or at a minimum they were greatly exaggerated. Ten-year deadlines to “do something” about the “climate crisis” have come and gone since this mess started in the 1980s… a few times over. Even the IPCC (which only allows alarmist-leaning scientists to participate) has admitted it is unlikely we will experience significant changes in severe weather by the year 2100 that can be tied to increasing CO2.

It makes sense to now reconsider the Endangerment Finding. Let the free market (including consumer preferences) decide which forms of energy we use.

The Version 6.1 global average lower tropospheric temperature (LT) anomaly for January, 2025 was +0.46 deg. C departure from the 1991-2020 mean, down substantially from the December, 2024 anomaly of +0.62 deg. Most of this cooling was over the global oceans.

The Version 6.1 global area-averaged temperature trend (January 1979 through January 2025) remains at +0.15 deg/ C/decade (+0.22 C/decade over land, +0.13 C/decade over oceans).

The following table lists various regional Version 6.1 LT departures from the 30-year (1991-2020) average for the last 13 months (record highs are in red).

YEAR	MO	GLOBE	NHEM.	SHEM.	TROPIC	USA48	ARCTIC	AUST
2024	Jan	+0.80	+1.02	+0.58	+1.20	-0.19	+0.40	+1.12
2024	Feb	+0.88	+0.95	+0.81	+1.17	+1.31	+0.86	+1.16
2024	Mar	+0.88	+0.96	+0.80	+1.26	+0.22	+1.05	+1.34
2024	Apr	+0.94	+1.12	+0.77	+1.15	+0.86	+0.88	+0.54
2024	May	+0.78	+0.77	+0.78	+1.20	+0.05	+0.20	+0.53
2024	June	+0.69	+0.78	+0.60	+0.85	+1.37	+0.64	+0.91
2024	July	+0.74	+0.86	+0.61	+0.97	+0.44	+0.56	-0.07
2024	Aug	+0.76	+0.82	+0.70	+0.75	+0.41	+0.88	+1.75
2024	Sep	+0.81	+1.04	+0.58	+0.82	+1.31	+1.48	+0.98
2024	Oct	+0.75	+0.89	+0.61	+0.64	+1.90	+0.81	+1.09
2024	Nov	+0.64	+0.88	+0.41	+0.53	+1.12	+0.79	+1.00
2024	Dec	+0.62	+0.76	+0.48	+0.53	+1.42	+1.12	+1.54
2025	Jan	+0.46	+0.70	+0.21	+0.24	-1.06	+0.74	+0.48

The full UAH Global Temperature Report, along with the LT global gridpoint anomaly image for January, 2025, and a more detailed analysis by John Christy, should be available within the next several days here.

The monthly anomalies for various regions for the four deep layers we monitor from satellites will be available in the next several days at the following locations:

Lower Troposphere

Mid-Troposphere

Tropopause

Lower Stratosphere†

2024 Sets New Record for Warmest Year In Satellite Era (Since 1979)

The Version 6.1 global average lower tropospheric temperature (LT) anomaly for December, 2024 was +0.62 deg. C departure from the 1991-2020 mean, down slightly from the November, 2024 anomaly of +0.64 deg.

The Version 6.1 global area-averaged temperature trend (January 1979 through December 2024) remains at +0.15 deg/ C/decade (+0.22 C/decade over land, +0.13 C/decade over oceans).

As seen in the following ranking of the years from warmest to coolest, 2024 was by far the warmest in the 46-year satellite record averaging 0.77 deg. C above the 30-year mean, while the 2nd warmest year (2023) was +0.43 deg. C above the 30-year mean. [Note: These yearly average anomalies weight the individual monthly anomalies by the number of days in each month.]

The following table lists various regional Version 6.1 LT departures from the 30-year (1991-2020) average for the last 24 months (record highs are in red).

YEAR	MO	GLOBE	NHEM.	SHEM.	TROPIC	USA48	ARCTIC	AUST
2023	Jan	-0.06	+0.07	-0.19	-0.41	+0.14	-0.10	-0.45
2023	Feb	+0.07	+0.13	+0.01	-0.13	+0.64	-0.26	+0.11
2023	Mar	+0.18	+0.22	+0.14	-0.17	-1.36	+0.15	+0.58
2023	Apr	+0.12	+0.04	+0.20	-0.09	-0.40	+0.47	+0.41
2023	May	+0.28	+0.16	+0.41	+0.32	+0.37	+0.52	+0.10
2023	June	+0.30	+0.33	+0.28	+0.51	-0.55	+0.29	+0.20
2023	July	+0.56	+0.59	+0.54	+0.83	+0.28	+0.79	+1.42
2023	Aug	+0.61	+0.77	+0.45	+0.78	+0.71	+1.49	+1.30
2023	Sep	+0.80	+0.84	+0.76	+0.82	+0.25	+1.11	+1.17
2023	Oct	+0.79	+0.85	+0.72	+0.85	+0.83	+0.81	+0.57
2023	Nov	+0.77	+0.87	+0.67	+0.87	+0.50	+1.08	+0.29
2023	Dec	+0.75	+0.92	+0.57	+1.01	+1.22	+0.31	+0.70
2024	Jan	+0.80	+1.02	+0.58	+1.20	-0.19	+0.40	+1.12
2024	Feb	+0.88	+0.95	+0.81	+1.17	+1.31	+0.86	+1.16
2024	Mar	+0.88	+0.96	+0.80	+1.26	+0.22	+1.05	+1.34
2024	Apr	+0.94	+1.12	+0.77	+1.15	+0.86	+0.88	+0.54
2024	May	+0.78	+0.77	+0.78	+1.20	+0.05	+0.22	+0.53
2024	June	+0.69	+0.78	+0.60	+0.85	+1.37	+0.64	+0.91
2024	July	+0.74	+0.86	+0.62	+0.97	+0.44	+0.56	-0.06
2024	Aug	+0.76	+0.82	+0.70	+0.75	+0.41	+0.88	+1.75
2024	Sep	+0.81	+1.04	+0.58	+0.82	+1.32	+1.48	+0.98
2024	Oct	+0.75	+0.89	+0.61	+0.64	+1.90	+0.81	+1.09
2024	Nov	+0.64	+0.88	+0.41	+0.53	+1.12	+0.79	+1.00
2024	Dec	+0.62	+0.76	+0.48	+0.53	+1.42	+1.12	+1.54

The full UAH Global Temperature Report, along with the LT global gridpoint anomaly image for December, 2024, and a more detailed analysis by John Christy, should be available within the next several days here.

The monthly anomalies for various regions for the four deep layers we monitor from satellites will be available in the next several days at the following locations:

Lower Troposphere

Mid-Troposphere

Tropopause

Lower Stratosphere

AP photo/ Ty O’Neil.

Summary

• Previous research has shown the temperatures recorded at Death Valley National Park (DVNP) have curious warm biases on very hot days, possibly due to instrument deficiencies or proximity to mounting structure apparatus and other manmade structures.
• Here it is shown from 21 years of summertime (June, July, August) data that DVNP has many more days when temperatures are much higher than those at the nearby Stovepipe Wells station, than when Stovepipe Wells has hotter days than DVNP station.
• These lines of evidence suggest that the hot summer daytime temperatures reported at Death Valley National Park have potentially large biases, and should only be used for their entertainment value.

In our continuing examination of the world record hottest temperature of 134 deg. F recorded at Greenland Ranch (now Death Valley National Park station) on 10 July 1913, we are finding some curious behavior in recent summertime temperatures there. (The Bulletin of the American Meteorological Society [BAMS] has accepted my proposal for a BAMS article showing the evidence that the 134 deg. F world record was 8 to 10 deg. F higher than what actually existed on that date [10 July 1913]).

Previous Work on Excessively Hot Death Valley Temperatures

Climatologist, weather observer, and storm chaser Bill Reid has blogged extensively over the years on the evidence against the 134 deg. F world record. A good place to start is his most recent post (Part 6) that deals with the Greenland Ranch foreman who made the excessively hot temperature measurements in the first half of July 1913. Bill has agreed to co-author the BAMS paper with John Christy and me.

There was also an experiment carried out with a variety of temperature instrumentation placed next to the DVNP weather station during 2021 and 2022. This revealed that on the near-record hot day of 9 July 2021 (130 deg. F), the “official” DVNP sensor produced temperatures a few degrees hotter than the other instruments (AMS conference poster here). The photo in Fig. 1 shows that the older-style DVNP instrument (which is not aspirated) is mounted next to a lot of metal structure and a small solar panel.

Fig. 1 Death Valley National Park weather station, with additional instrumentation added by Dirk Baker (Campbell Scientific, Inc.) and co-investigators to compare to the ‘official’ temperature readings in 2021 and 2022. (Figure adapted from this AMS conference presentation).

The experimental setup in Fig. 1 used several temperature sensors, some with aspirated shields, others with no aspiration. The data shown in their AMS conference presentation suggests to me that the near-record 130 deg. F reading on 9 July 2021 was 2-3 deg. F too hot partly because of the non-aspirated design of the sensor. There was some additional warm bias that could have been due to all of the mounting structure seen in Fig. 1, including a small solar panel next to the DVNP station sensor.

More Evidence: DVNP vs. Stovepipe Wells Temperatures

For the last 21 years there have been two stations in Death Valley: the DVNP station next to the Furnace Creek Visitors Center, and a climate reference network (CRN) station at Stovepipe Wells, 29 km northwest of the DVNP station.

Fig. 2 shows a comparison of the daily maximum temperatures (Tmax) recorded at these two stations for every day in June, July, and August in all years from 2004 through 2024.

Fig. 2. Comparison between daily high temperatures (Tmax) recorded at Stovepipe Wells and Death Valley National Park, for all days in June, July, and August for the years 2004 through 2024. The dashed red line represents the median difference between the 2 stations (2 deg. F, DVNP warmer than Stovepipe Wells). Gray lines connect the days in chronological order.

The median of the Tmax differences between these 2 stations is 2 deg. F (DVNP warmer, represented by the dashed red line), while the average difference is 2.3 deg. F. The expected difference based upon elevation alone is 1.3 deg. F (DVNP station is 278 ft lower in elevation than Stovepipe Wells).

Note in Fig. 2 that there seem to be more outliers to the left of the dashed red line than to the right. That is, there are more days where DVNP is much warmer than Stovepipe Wells than there are days when Stovepipe Wells is much warmer than DVNP station.

This can be better seen if we look at a frequency distribution of these station differences, adjusted for the 2 deg. F median difference between stations (Fig. 3).

Fig. 3. Frequency distributions of how many days where one Death Valley station is hotter than the other. This is after shifting of the distributions to account for a 2 deg. F difference in their median difference.

As shown in Fig. 3, DVNP station has many more days where it is hotter than Stovepipe Wells, than Stovepipe Wells has days that are hotter than DVNP station. For the 3-4 deg. F hotter category, the difference is 2X, for the 5 to 9 deg. F hotter category the difference is 3x, and for 10 deg. F or greater the difference is 7.8X.

This suggests there is something wrong with the Death Valley National Park instrumentation itself or the immediate environment around the temperature sensor that causes some days to be biased too hot. Bill Reid, who has researched this issue extensively, suspects that days with low wind have excessive heat build-up at the DVNP thermometer site, both in the general area around the instrumentation, and due to the non-aspirated design of the temperature sensor used there.

The difference in exposure at DVNP station and Stovepipe Wells is shown in Fig. 4.

Fig. 4. Google Earth imagery of Stovepipe Wells station (top) and Death Valley N.P. station (bottom), stations circled in red. The inset photo at top is of the Stovepipe Wells Climate Reference Network station, courtesy of William T. Reid. The E-W distance across these images is just over 0.5 km.

As can be seen in Fig. 4, the Death Valley N.P station has quite a bit of development surrounding the station, with parking lots, a paved campground, the Visitors Center, solar panels (black) and trees just to the south. The Stovepipe Wells site has almost no development and no vegetation. It is possible that during the prevailing southerly wind flow during the summer, the structures and trees to the south of the DVNP station lead to stagnation of air flow around the temperature sensor.

Conclusions

The evidence presented here, along with evidence presented previously by Bill Reid, Dirk Baker, and others, suggests that Death Valley National Park temperatures should not be relied upon for accurate daytime readings, and that near-record temperatures there are biased too high. The reasons for the biases are not obvious, but the evidence suggests poor sensor ventilation during the daytime when various structures in the vicinity heat up: whether the shield of the sensor itself, its supporting structure, or various manmade objects around the station site. It is also possible that the trees and other structures to the south of the station restrict air flow, further reducing effective convective heat transport away from the solar heated desert surface.

It is my opinion that “official” Death Valley temperatures should use the Stovepipe Wells site data, which come from state-of-the-art Climate Reference Network instrumentation. The traditional site near the Death Valley National Park Visitors Center should only be used for entertainment purposes.

Maybe the National Park Service should investigate adding a CRN station; a good location would be about 1.6 km southwest of the current station, well away from the Furnace Creek tourist area.

Metop-C Satellite Added to Our Processing

With this update, we have added Metop-C to our processing, so along with Metop-B we are back to having two satellites in the processing stream. The Metop-C data record begins in July of 2019. Like Metop-B, Metop-C was designed to use fuel to maintain its orbital altitude and inclination, so (until fuel reserves are depleted) there is no diurnal drift adjustment needed. Metop-B is beginning to show some drift in the last year or so, but it’s too little at this point to worry about any diurnal drift correction.

The Version 6.1 global average lower tropospheric temperature (LT) anomaly for November, 2024 was +0.64 deg. C departure from the 1991-2020 mean, down from the October, 2024 anomaly of +0.75 deg. C.

The Version 6.1 global area-averaged temperature trend (January 1979 through November 2024) remains at +0.15 deg/ C/decade (+0.21 C/decade over land, +0.13 C/decade over oceans).

The following table lists various regional Version 6.1 LT departures from the 30-year (1991-2020) average for the last 23 months (record highs are in red). Note the tropics have cooled by 0.72 deg. C in the last 8 months, consistent with the onset of La Nina conditions.

YEAR	MO	GLOBE	NHEM.	SHEM.	TROPIC	USA48	ARCTIC	AUST
2023	Jan	-0.06	+0.07	-0.19	-0.41	+0.14	-0.10	-0.45
2023	Feb	+0.07	+0.13	+0.01	-0.13	+0.64	-0.26	+0.11
2023	Mar	+0.18	+0.22	+0.14	-0.17	-1.36	+0.15	+0.58
2023	Apr	+0.12	+0.04	+0.20	-0.09	-0.40	+0.47	+0.41
2023	May	+0.28	+0.16	+0.41	+0.32	+0.37	+0.52	+0.10
2023	June	+0.30	+0.33	+0.28	+0.51	-0.55	+0.29	+0.20
2023	July	+0.56	+0.59	+0.54	+0.83	+0.28	+0.79	+1.42
2023	Aug	+0.61	+0.77	+0.45	+0.78	+0.71	+1.49	+1.30
2023	Sep	+0.80	+0.84	+0.76	+0.82	+0.25	+1.11	+1.17
2023	Oct	+0.79	+0.85	+0.72	+0.85	+0.83	+0.81	+0.57
2023	Nov	+0.77	+0.87	+0.67	+0.87	+0.50	+1.08	+0.29
2023	Dec	+0.75	+0.92	+0.57	+1.01	+1.22	+0.31	+0.70
2024	Jan	+0.80	+1.02	+0.58	+1.20	-0.19	+0.40	+1.12
2024	Feb	+0.88	+0.95	+0.81	+1.17	+1.31	+0.86	+1.16
2024	Mar	+0.88	+0.96	+0.80	+1.26	+0.22	+1.05	+1.34
2024	Apr	+0.94	+1.12	+0.77	+1.15	+0.86	+0.88	+0.54
2024	May	+0.78	+0.77	+0.78	+1.20	+0.05	+0.22	+0.53
2024	June	+0.69	+0.78	+0.60	+0.85	+1.37	+0.64	+0.91
2024	July	+0.74	+0.86	+0.62	+0.97	+0.44	+0.56	-0.06
2024	Aug	+0.76	+0.82	+0.70	+0.75	+0.41	+0.88	+1.75
2024	Sep	+0.81	+1.04	+0.58	+0.82	+1.32	+1.48	+0.98
2024	Oct	+0.75	+0.89	+0.61	+0.64	+1.90	+0.81	+1.09
2024	Nov	+0.64	+0.88	+0.41	+0.54	+1.12	+0.79	+1.00

The full UAH Global Temperature Report, along with the LT global gridpoint anomaly image for November, 2024, and a more detailed analysis by John Christy, should be available within the next several days here.

The monthly anomalies for various regions for the four deep layers we monitor from satellites will be available in the next several days at the following locations:

Lower Troposphere

Mid-Troposphere

Tropopause

Lower Stratosphere

Update (11/12/2024): New annotated version of Fig. 1 added. Corrected who the Greenland Ranch foreman was and associated correspondence. Will fix Fig. 2 (2021/2022) problem Wednesday morning.

Update (11/13/2024): Fixed Fig. 2

In Part 1 I claimed that using stations surrounding Death Valley is a good way to “fact check” warm season high temperatures (Tmax) at the Death Valley station, using a correction for elevation since all surrounding stations are at higher (and thus cooler) elevations. In July of each year, a large tropospheric ridge of high pressure makes the air mass in this region spatially uniform in temperature (at any given pressure altitude), and daily convective heating of the troposphere leads to a fairly predictable temperature lapse rate (the rate at which temperature falls off with height). This makes it possible to estimate Death Valley daytime temperatures from surrounding (cooler) stations even though those stations are thousands of feet higher in elevation than Greenland Ranch, which was 168 ft. below sea level.

Lapse Rates Computed from Stations Surrounding Death Valley

If I use all available GHCN daily stations within 100 miles of Greenland Ranch (aka Furnace Creek, aka Death Valley N.P.) in each July from 1911 to 2024 to compute the month-average lapse rate (excluding the Death Valley stations[s]), I get the results in Fig. 1.

Fig. 1. Lower tropospheric temperature lapse rate estimated from all stations within 100 miles of Greenland Ranch, Death Valley, CA. The number of available stations for these calculations range from several in the early years to 25 or more in the later years. Here I will assume a constant lapse rate of -0.004 during the 20th Century. The 4th order polynomial fit to the data would be another way to assume how the lapse rate changes over time.

The computed lapse rates mostly fall between the dry adiabatic value and the U.S. standard atmosphere value (except in the early years). Given the few stations available in the early years, I will base the calculations that follow on an assumed lapse rate of -0.004 deg F per ft. for the first half of the record, and will assume that the observed steepening of the lapse rate after the 1980s is real, with a value of -0.0048 deg. F per ft. in the early 2020s. In Part 1, I used the actual values in Fig. 1 in each year to estimate Death Valley temperatures. This time I’m using average lapse rate values over many years, keeping in mind the early decades had few stations and so their values in Fig. 1 are more uncertain.

Daily Estimated July Tmax at Death Valley: 2021-2024

How accurately can we estimate daily Tmax temperatures in Death Valley from surrounding high-elevation stations? The following plot (Fig. 2) shows how the July daily observed Tmax temperatures in Death Valley (2021, 2022, 2023, 2024, orange for Death Valley N.P.) compare to estimates made based upon surrounding, high-elevations stations (blue), assuming a lapse rate of -0.0048 deg. F per ft (see Fig. 1).

Fig. 2. Daily estimated July Tmax temperatures for Death Valley N.P. from surrounding stations (blue) compared to those observed (orange, 194 ft. below sea level) for 2021, 2022, 2023 and 2024.

In each year the daily estimates from surrounding stations (blue) are reasonably close (within a couple of degrees) to the observed values at both Death Valley N. P. (orange) and at the nearby station Stovepipe Wells. For example, on July 7, 2024 the observed “near record” value of 129 deg. F degrees agrees well with the lapse-rate estimated value of 128 deg. F. Note there were many (27 of 28) stations within 100 miles of Death Valley available to make these estimates during these years.

Daily Estimated July Tmax at Death Valley: 1935-1938

Next, let’s travel back to the 1930s, when there were fewer stations to do these estimates (Fig. 3).

Fig. 3. Daily estimated Tmax temperatures for Death Valley during 1935, 1936, 1937, 1938 from surrounding stations (blue) compared to those observed at Greenland Ranch (orange, 168 ft. below sea level) and Cow Creek (grey, 151 t. below sea level).

Despite only having 7 or 8 stations from which to estimate Death Valley temperatures, the agreement is still reasonably good in 1935, with no bias between observed and estimated, but 1-3 deg. F bias at Greenland Ranch vs. estimated in the following 3 years. There are also a few low temperature outliers in 1937-38 at Greenland Ranch and Cow Creek; I don’t know the reason for these.

Daily Estimated July Tmax at Death Valley: 1912-1915

Finally we examine the period in question, when the 134 deg. F world record temperature was recorded on July 10, 1913 (Fig. 4).

Fig. 4. Daily estimated Tmax temperatures for Death Valley during 1912, 1913, 1914, 1915 from surrounding stations (blue) compared to those observed at Greenland Ranch (orange, 168 ft. below sea level).

During these years there were only 3 to 7 stations from which to compute Death Valley Tmax. In 1912, despite only 3 stations, the reported temperatures averaged only 3 deg. F above those estimated from surrounding stations. But in 1913 (the year of the record) the observations averaged an astounding 9 deg. F warmer than the surrounding 5 stations would have suggested. On July 10, the excess was 15 deg. F!

That second week of July 1913 was indeed unusually hot, and it was during this time that the ranch foreman (Oscar Denton) responsible for making the temperature readings from an official instrument shelter provided by the U.S. Weather Bureau in 1911 might have replaced the official values with values that more accorded with the heat he and his supervisor (Fred Corkill) were feeling on his veranda, away from the USWB instrument shelter which was sited next to an irrigated field. Bill Reid covers the details of correspondence between Corkill and a USWB official in San Francisco regarding the shelter temperatures and how much cooler they were compared to what was measured by a second thermometer farther away from the irrigated field. Reid believes (and I agree) that the shelter temperatures were, at least for a time while Denton was responsible for tabulating the daily measurements, replaced with measurements from a separate thermometer having uncertain quality and siting away from hot surfaces exposed to the sun.

So, How Much Hot Bias Exists in the 134 deg. F “World Record”?

We will never know exactly how much warm bias exists in the world record value. But from comparison to the biases in 1912 and 1914, I would say 9 to 12 deg. F is a reasonable estimate.

Of course, this might be adjusted somewhat if one assumes a slightly different lapse rate than the -0.004 deg. F per ft. I have assumed here (see Fig. 1). For instance, what if the air mass on July 10, 1913 had an exceptionally steep lapse rate, such that an even greater adjustment for elevation needed to be made to estimate the hot temperature in Death Valley? If I use use the lapse rate estimated from the 5 surrounding stations on July 10, 1913 (see Fig. 5), that lapse rate value is indeed “steeper”, at -0.0053 deg. F per ft. But if we use that value to estimate the Death Valley temperature, it is still 10 deg. cooler than the 134 deg. F recorded value. This is still within the 9 to 12 degree bias range I mentioned above.

Fig. 5. The world record value of 134 deg. F (red) is 10 deg. F warmer than that suggested by the surrounding higher-elevations stations’ temperature variations with elevation on July 10, 1913.

Conclusion

The 134 deg. F world record hottest temperature from Death Valley is likely around 10 deg. F too high, compared to elevation-adjusted temperatures from surrounding stations. The most likely cause is that the ranch foreman’s reported measurements were (shall we say) unacademically recorded. I find it rather remarkable that the world record hottest temperature from Death Valley was not revised many years ago, since the methods for “fact checking” the record are fairly simple, and based upon meteorological principles known for well over 50 years.

NOTE: Since he has done extensive investigation into some implausibly hot temperatures reported in Death Valley, I asked Bill Reid to comment on my previous blog post where I maintain that the world record 134 deg. F highest recorded air temperature was likely biased warm by about 10 deg., and should not be accepted as a world record. What follows are Bill’s initial thoughts on the subject. Also, based upon his comments, I will likely update the charts found in my previous blog post with more realistic temperature lapse rate values in the early 20th Century when insufficient stations were available to determine accurate lapse rates.

by William T. Reid

A big thank you to Dr. Spencer for investigating the current (very dubious) world high-temperature record and for bringing attention to my Death Valley climate research. There are a handful of ways, both climatologically and meteorologically, to show that Greenland Ranch’s reported maximum of 134F on July 10, 1913, is likely not valid.

Dr. Spencer’s methodology here (comparing the Death Valley maximums to those the closest surrounding stations, with adjustments for station elevation) is indeed a devastating blow to the authenticity of the suspect observations. What it basically demonstrates is that the lower troposphere was not hot enough to support temperatures much above 125F in July, 1913. I have compared regional maximums for all of the hottest summertime events since 1911. In practically all instances (in which the Greenland Ranch and Death Valley reports appear reasonable), ALL of the maximums at the closest surrounding stations lend support to the maximums for Death Valley.

From July 7 to 14 of 1913, when eight consecutive afternoons had reported maximums of 127, 128, 129, 134, 129, 130, 131 and 127F in Death Valley, NONE of the maximums from the closest surrounding stations supported the Greenland Ranch maximums! The departures from average for maximums for the hottest five-day stretch were about +4 to +8 at the closest stations, while maximums at Greenland Ranch were nearly 15 degrees F above the average for July. (see table)

Annual maximums at Greenland Ranch from 1911 to 1960 ranged from 120F to 127F, except for the 134F in 1913. If the reported maximums at Greenland Ranch in July, 1913, were authentic, then the maximums at the closest surrounding stations in that month would have been much higher than reported. In addition, numerous regional heat waves have been hotter than the one during the first half of July, 1913. Why have Death Valley maximums failed to exceed 130F in the interim when three days in July 1913 purportedly reached 134, 130 and 131F?

In his “bias” chart, Dr. Spencer notes the “substantial warm biases in the temperatures reported at Greenland Ranch in the first 10-15 years.” And, he mentions that the observer(s) may have been relying to some extent on thermometers other than the official instrumentation. I do think that the observer was comparing “household thermometer” readings with the official equipment on occasion from spring to summer of 1913. Higher readings off of the poorly-exposed thermometers near the ranch house and under the veranda were probably (and inappropriately) entered onto the official climate form. But, I have not uncovered much evidence of this particular type of deviation from standard observational procedures outside of 1913.

I would contend that the generally higher “bias” numbers from the early years comparably are due primarily to changes at the closest area weather stations which promoted cooler maximums early on and warmer maximums later. For example, two of the closest stations to Greenland Ranch in 1913 were Independence and Lone Pine, in Owens Valley. In 1913, Owens River water was diverted to Los Angeles, and the Owens Valley gradually dried up. Summer maximums increased as Owens Lake evaporated, irrigation was not possible and farmland was abandoned, and desert-like conditions developed. (Roy’s note: The early years had very few stations within 100 miles of Death Valley, and the temperature lapse rates I computed from those few stations appear to be biased as a result. I will correct this in a future blog post, and will provide what should be better estimates of average July daily maximum Death Valley temperatures.)

Also, in the early decades of the 20th century, thermometer shelters were (almost invariably) sited above grass. This resulted in very conservative (i.e., coolish) maximums at desert stations. Low humidities promoted cooling due to evapotranspiration effects. In the early decades of the 20th century, desert weather stations were generally in towns, amidst shade trees and lawns. The resulting maximum temperature reports were very conservative. By mid-century and thereafter, the town weather stations were more likely to be at the airport or at a municipal utility site, fire station or equipment yard. Grass cover and shade trees were usually absent at these locales. Today, desert weather stations in towns and cities are (almost invariably!) above bare ground.

You can imagine the difference in maximums between desert stations above oft-irrigated grass and those above bare ground. (Roy’s note: In my experience, unless the vegetation area is rather large, and there is almost no wind, a weather station’s daily maximum temperature will still be largely determined by air flowing from the larger-scale desert surroundings. But note… this is different from, say a poorly sited thermometer next to a brick wall or heat pump where hot air from an isolated source can elevate the daily maximum temperature recorded).

The Greenland Ranch station was originally sited above a patch of alfalfa grass, immediately adjacent to forty acres of cultivated and irrigated land.

It is my belief that the new observer in 1913 (Oscar Denton) was rather disillusioned with the conservative maximums from the official station above grass and next to the evaporatively-cooled farmland. I think he felt compelled to fudge the maximums upwards in 1913. Photographs of the Greenland Ranch weather station show that it was above bare ground by about 1920 (see example photo at top of post).