Pushing the Great American Desert Eastward – Reality or Hype?

Guest essay by Rick Yarnell

In 1877 an explorer and scientist named John Wesley Powell conceived a dividing line in the North American continent that marked the separation of the green and humid East from the dry, desert West. That dividing line was the 100th Meridian. East of this line, conventional agriculture, which he asserted depends on at least 20 inches of rain, would succeed. West of the line, with its desert conditions, could not support conventional, non-irrigated agriculture.

Mr. Powell and the story of the 100th Meridian was recently explored in a beautifully written essay in the Wall Street Journal, by John F. Ross, (The Prophet of the Dust Bowl, § Review, June 16-17, 2018, pC4).

The essay is adapted from Mr. Ross’s book “The Promise of the Grand Canyon: John Wesley Powell’s Perilous Journey and his Vision for the American West”, Viking, 2018.

Toward the end of the essay, one conclusion Mr. Ross puts forward is that Mr. Powell, in his warnings that the arid west was not farmable, “did not consider one crucial factor, because he did not know about it: the effects of a warming atmosphere, caused by greenhouse gas emissions from the burning of fossil fuels.”

Mr. Ross tells us, “Columbia University climatologist Richard Seager and his team of researchers…looking at data collected since 1980…found that warming conditions have pushed Powell’s line 140 miles to the east.”

The 100th meridian west (solid line) has long been considered the divide between the relatively moist eastern United States, and the more arid West. Climate change may already have started shifting the divide eastward (dotted line).
CREDIT Modified from Seager et al. Earth Interactions, 2018

Now, Mr. Powell’s 100th Meridian line stretched from the Dakotas to Texas, a region with vastly different temperature extremes, so, of course, the Dry Line was not marked by primarily by temperature, but rather by rainfall. Locations west of the 100th Meridian usually received less than 20 inches of rainfall in a year, while those locations east of the 100th Meridian would get greater than 20 inches of rain.

In my home state of Kansas anyone with a passing familiarity of the state’s agriculture knows that the western third of the state is dry. Early maps of the region in fact noted the high plains through which passed the Oregon, California and Santa Fe Trails as the Great American Desert. I happen to own a small farm in the Flint Hills about an hour east of Wichita, Kansas, and I keep pretty good records of rainfall on my farm. It struck me that, if the Dry Line had moved eastward, my own records would provide a clue. But my farm wasn’t experiencing a significant decrease in rainfall. In fact, last year, 2017, was perfect growing weather that yielded a bumper crop. I wondered, to what data was Mr. Seager looking?

So, I did my own research.

An article in Earth Magazine gave more information. “Dividing Line, the Past, Present and Future of the 100th Meridian”, by Harvey Leifert, (January 22, 2018). Mr. Leifert states, “The researchers developed a standard measure called the aridity index to assess aridity across a geographic area, using observational data from the North American Land Data Assimilation System. They estimated potential evapotranspiration — the amount of water the atmosphere could potentially extract from the surface — from the land based on temperature, wind speed, solar radiation and relative humidity. The ratio of actual precipitation to potential evapotranspiration provides the aridity index.”, (emphasis mine).

Notice that this is not the same measurement used by Mr. Powell in his “Report on the Lands of the Arid Region of the United States” (Second Edition, Washington, Government Printing Office, 1879). Mr. Powell wrote in that report, “records are such as to indicate approximately the boundary between the Arid Region, where irrigation is necessary to agriculture, and the Humid Region, where the lands receive enough moisture from the clouds for the maturing of crops. Experience teaches that it is not wise to depend upon rainfall where the amount is less than 20 inches annually, if this amount is somewhat evenly distributed throughout the year.” The “mean annual rainfall line of 20 inches, as indicated on the rain chart accompanying [Mr. Powell’s] report, begins on the southern boundary of the United States, about 60 miles west of Brownsville, on the Rio Grande del Norte, [note: just south of Palmview, TX at about 98.5 degrees W] and intersects the northern boundary about 50 miles east of Pembina [note: at Maida, ND at about 98.4 degrees W]. Between these two points the line is very irregular, but in middle latitudes makes a general curve to the westward.” Mr. Powell also noted three other modifiying conditions to successful non-irrigated agriculture along this line: altitude, latitude and temperature.

Mr. Seager’s research team, according to Mr. Leifert, presented their findings “at the American Geophysical Union’s fall meeting in December 2016” and “at the American Meteorological Society’s meeting in January 2017. The work has been accepted for publication in the journal Earth Interactions.”

Here is the abstract of the research of Mr. Seager’s team: “The potential evapotranspiration (PET) is first computed using a suite of three NLDAS-2 land surface models and the Penman-Monteith Equation, and the aridity index (AI), defined as precipitation divided by PET, is used as the aridity metric. There is a sharp gradient in aridity along and just east of the 100th Meridian, verifying Powell’s observations. We further determined that this arid-humid boundary is primarily caused by strong spatial gradients in precipitation and humidity, which in turn are caused by the seasonal cycle in wind direction and moisture transport. Using CMIP5 climate model data, the future was projected in 20-year increments from the present through 2100. Models project that the arid-humid boundary will shift eastward by approximately 2 to 3 degrees by the end of the 21st Century, the gradient will weaken, and that the entire continental US will experience at least some degree of aridification.” (Whither the 100th Meridian: The once and future physical geography of America’s arid-humid divide; http://adsabs.harvard.edu/abs/2016agufmgc11b1136t), again, emphases mine.

Wow, America’s Breadbasket will dry up and we will all starve to death. Oh, woe.

So, really, have warming conditions pushed Mr. Powell’s line 140 miles to the east, as asserted by Mr. Ross in his Wall Street Journal essay? That’s easy enough to find out: let’s look at rainfall records for towns along the 100th Meridian, and of towns that are approximately 140 miles east of that line.

First, I looked at a map of the high plains to find village or town sites that had weather observational records. The high plains are sparsely settled, so there are not a lot of sites that sit very close to the 100th Meridian. I chose four sites in North Dakota, four in South Dakota, three in Nebraska, four in Kansas and five in Oklahoma/Texas, then looked up the average annual rainfall reported on various weather and climate websites. The annual rainfall records indicate that reporting stations near the 100th Meridian in the northern high plains are much drier than those in the southern high plains. The average annual rainfall for the four chosen sites in North Dakota was 18.22 inches. Averages proceeding southward: South Dakota: 20.65”, Nebraska: 22.67”, Kansas: 23.30”, OK/TX: 24.08”. Reported annual average rainfall for sites near the 100th Meridian ranged from a low of 16.12” in Strasburg, ND to 27.16” in Eden, TX. The seven northernmost reporting stations all had annual average rainfall of less than twenty-one inches, as did the southernmost station in Carrizo Springs, Texas. I then looked up a corresponding weather station that was approximately 140 miles east of these twenty sites, to determine average annual rainfall.

For the twenty stations that were approximately 140 miles east of the 100th Meridian, approximately between the 97th and 98th Meridians, we find as we did further west, that the northern plains are drier than the southern plains. The stations in ND/Minn. recorded average rainfall of 22.42” annually. Averages proceeding southward: South Dakota: 24.27”, Nebraska: 27.89”, Kansas: 33.20”, OK/TX: 36.35”. Reported annual average rainfall for sites about 140 miles east of the 100th Meridian ranged from a low of 21.66” in Argyle, Minnesota to 37.54” in Fort Worth, Texas.

The average annual rainfall for all twenty stations that are about 140 miles east of the 100th Meridian is greater than, or much greater than, 20”. From what I see in the average annual rainfall records, it seems that the assertion by Mr. Ross “that warming conditions have pushed Powell’s line 140 miles to the east” is untrue. But, remember, that is not what Prof. Seager’s team reported. The team wrote, “Models project that the arid-humid boundary will shift eastward by approximately 2 to 3 degrees (or the 98th and 97th Meridians West) by the end of the 21st Century.”

I questioned, next, whether the average rainfall amounts were skewed by larger numbers back further in time, and that, maybe, the most recent years are drier than earlier years. So I chose a set of eleven stations to examine the actual reported rainfall for each month in the five most recent years: 2013-2017. For this data I used www.wunderground.com/history. This website has monthly history data for only larger regional weather stations, thus, the limit to eleven stations.

Here is the average annual rainfall for the years 2013-2017 for weather stations near the 100th Meridian, and the corresponding overall average annual rainfall from www.usclimatedata.com:

2013-17 overall

North Dakota*

Winner, SD 17.39 23.93

Ainsworth, NE 20.56 23.29

Dodge City, KS 22.39 21.49

Canadian, TX 18.88 21.72

Abilene, TX 26.62 24.83

* Note: none of the towns along the 100th Meridian in North Dakota have reliable history data on wunderground.com (Rugby, Harvey, Steele, Strasburg).

Here is the average annual rainfall for the years 2013-2017 for weather stations about 140 miles east of the 100th Meridian, and the corresponding overall average annual rainfall from www.usclimatedata.com:

2013-17 overall

Grand Forks, ND 21.59 20.73

Sioux Falls, SD 28.98 26.35

Wayne, NE 21.28 27.39

Wichita, KS 38.47 34.33

Oklahoma City, OK 39.04 36.46

Fort Worth, TX 33.44 37.54

There is no noticeable pattern of decreased rainfall in any of the above records. Of the five locations near the 100th Meridian, two have more average annual rainfall in the last five years than their usual average, and three have less. Of the six locations east of the 100th Meridian, four have more average annual rainfall in the last five years than their usual average, and two have less.


John Wesley Powell made his conception of the Dry Line using his observations of plant and animal life and especially rainfall. When we use that same rainfall methodology today, we confirm that the Dry Line is, today, still near the 100th Meridian. No modeling needed.

Supporting data:

ICT DDG rainfall 13-18 (Excel)


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Phillip Bratby

Excellent article with good research – well done Rick Yarnell.

When they use models, you know the answer – GIGO. Measurements always Trump models.

Models are the tools of alarmists.


“Models are the tools of alarmists.”

Should that read ‘muddles’ ???


Muggles are people who can’t use magic.
Alarmists use magic every day to create data from thin air.

Raymond Williamson

Latitude is important to consider as ND (as a former resident) has no trouble growing crops at a lower precip/evap rate.

Jeff Alberts

Without irrigation? Seems like pretty much any farm uses supplemental irrigation.


North Dakota is the most vulnerable to attacks of dry, frosty air from the north. I suppose that the growing season in this American state will be shortened.
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Curious George

That’s why agricultural production keeps rising.


Anti science alarmists. US precipitation is increasing and not looking bipolar. Midwest has gotten wetter too. 1910 to 1911 had the most change. But I guess its the skeptics who are the deniers?


Looking at that CHART it seems to be INCREASING RAINFALL to me.
While there would be INCREASING EVAPORATION it has a lot more
water to evaporate. Once the grass or crop grew it would be transpiration
but evaporation would surely decline because the soil would be protected
(shaded ) from the sun and wind surely !?
Once the water penetrates the sub-soil it tends to linger , and a series of
wet winters would achieve that……and the rainfall chart seems to show that !

Percy Jackson

The author here is confusing two different measures the aridity index and the annual rainfall. If the rate of evaporation increases while the annual rainfall stays constant then the amount of water available for plant growth will decrease and this is measured by the aridity index. The paper discusses the aridity index rather than just the annual rainfall which is a more crude measure.

There are two papers by Seager. One establishes that Powell’s dividing line is real. The other presents a model suggesting that it may be moving eastward. There are no measurements, observations or data demonstrating that it has shifted.


It has actually shifted westward.

Robert B

“found that warming conditions have pushed Powell’s line 140 miles to the east.”
That’s the point. Its not pushing any line east. Its a completely new, and convoluted, indicator. No need to refer to Powell’s line except to give modelling more of an appearance of a historical measure. Putting lipstick on a gigo.

yes, but in order to show changes in the aridity index, you have to assume changes in the temperature. And in potential evaotranspirative plant life.

That is essentially what the IPCCs mandate is: to ASSUME climate change, and project its effects.

However there are two bad assumptions made.

The first is that CO2 is in fact driving global warming. Remove that assumption and the whole case for this paper collapses.

The second is that rising CO2 IS DEFINITELY impacting on plant growth in arid regions.

It’s allowing plants to grow with less water.

So the REAL net effect is contrary to this paper the aridity boundary should be pushing west whilst rainfall remains broadly constant.

Alarmist assumptions, Alarmist conclusions.

Alan Tomalty

“If the rate of evaporation increases while the annual rainfall stays constant”


Where do you think the INCREASED evaporated water will go? OUTER SPACE? The incompetence of alarmists is mind boggling.

Rick Yarnell

Mr. Jackson,
Actually, I took pains to point out that Prof. Seager used a different method of measurement than did Mr. Powell, and that is the point. Prof. Seager uses a new, made-up ‘aridity index’ to model his projections that the Dry Line will move eastward by 140 miles in 80 years. But Mr. Powell, not having access to satellite data back in the 1890s, used rainfall. Using Mr. Powell’s admittedly cruder method – but being consistent with it – we can see that the Dry Line has not moved.

[Moderator Note: Should anyone get offended or perturbed by the fact that their comment has been placed in moderation, please note that this comment by the author of the head posting was also, hilariously, put into moderation by WordPress. -mod]

A great example of an all too frequent occurrence: Model projections being reported as actual observations.

william Johnston

In other words “Well, it looked good on paper”.

It always does… LOL!


Yes – and showing the opposite of observation. The arid line has moved westward, not eastward.


If the facts do not support the theory, then we should just ignore the facts (as inconvenient truths!) This is more evidence of the emergence of a post-rational society.


we have a similar thing in Aus
the Goyder line
across the lower part of aus sth aus especially
problem was?
when Goyder rode through n made the line it had been a wet season or two(or more) as land returned to the dry pattern the poor buggers that bought n tried to grow crops went bust fairly soon;-(
and hell 20 inches min? to farm?
what utter luxury;-)

John Garrett

NPR Regurgitation (7/30/18):
“Changing Climate Pushes Arid West Eastward, Impacting Farming”

Joe Wertz of StateImpact Oklahoma brings us this story. It’s the latest in our series on the impacts of a warming climate.

“When in fear or in doubt,
run in circles,
scream and shout.”


The ‘greening’ of the planet map shows some decreases and some increases of the east of the line but a lot of increase on the west.

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Wim Röst

The drier part of the US profits most of the extra CO2, while CO2 makes that vegetation closes some of her H2O exhaling leaf mouths because they can inhale easier the needed CO2. Plants are losing water by open leaf mouths. Less open leaf mouths result in less water needed per plant and even with the same rainfall, more plants can grow.

The same pattern is visible in for example West Australia and the Sahel and other drier parts in Africa.

Bruce Cobb

Alarmologists move lines as easily as they move goalposts.

Alexander Vissers

Yet another conclusion: if you want to sell a book better make it a juicy story.

Johann Wundersamer

OT – but recently discussed –

Google-Search algorithms :

“The essay is adapted from Mr. Ross’s book “The Promise of the Grand Canyon: John Wesley Powell’s Perilous Journey and his Vision for the American West”, Viking, 2018.”


Google search “perilous” FIRST yields

 Perilous – Google-Search



And that’s OK with me – we gain from using Google Search

and Google lives on ADVERTISING.

Jeff Alberts

“OT – but…”

Then don’t post it.


The similar Canadian arid area is called Palliser’s Triangle after John Palliser who declared the region as unfit for agriculture around 1860. It does suffer from droughts but otherwise it is very productive.

Does anyone know what Lewis and Clark had to say about America’s arid regions? Did it have any effect on settlement? I’m guessing the answer is about the same as in Palliser’s case.


Jim Bridger to Brigham Young in 1847: “I’d give $1,000 for a bushel of corn raised in the basin.” http://www.slcdocs.com/utilities/NewsEvents/news2010/news8202010.htm

Rich Lambert

My limited observation from North Central Oklahoma. In the past few years I’ve seen upland unirrigated corn grown that I’ve never seen before in 50+ years. Perhaps the Dry Line is moving west.

Greg Woods

or perhaps more drought resistant strains of corn are being planted…


Or perhaps higher CO2 levels are allowing plants to use water more efficiently.

Bill Murphy

“Perhaps the Dry Line is moving west.”
“or perhaps more drought resistant strains of corn are being planted…”
“Or perhaps higher CO2 levels are allowing plants to use water more efficiently.”

The evidence suggests a combination of all three of those. I live almost exactly on the 100W line in SD and have family anecdotal and photographic evidence going back 80 years that both the crops and the native prairie grasses are doing better now. But then, how could a bunch of sod bustin’ hay seed farmers possibly know something that a super computer model doesn’t?

Tom Abbott

It is definitely wetter in Oklahoma for July. We don’t normally get much rain in July and August but this year we are getting good rain, even in western Oklahoma.

My lawn has gone from dead to bright green over the last few days with all the rain we have had. Rain in Oklahoma in summer is always a blessing.

The temperatures for Oklahoma for this July are probably going to be below average, too.

tim maguire

Why would they even bother? If the dividing line is between land that needs irrigation and land that doesn’t , then look to irrigation practices–are they moving East? Or are they not?


The cool fronts of the northwest are in fact bringing an increase in rainfall in the mountainous regions of the Midwest.

Russell Mitchell

Is Mr. Ross perhaps some terribly provincial Coastie who’s missed the factthat millions of people actually live on that line and would have noticed if the place were turning into a desert under their feet?


Considering the fact that climate has been warming generally for thousands of years since the interglacial began, what has this got to do with the co2 hypothesis of climate change? I see no correlation between what man does and the aridity of the “great American desert” or any hypothesized dividing line. Whatever is happening is naturally occurring.

Now on the other hand, if you plow up grasses that have not been disturbed for thousands of years over a large portion of semiarid land to plant wheat, we have proven that one can, along with nature’s assist with less precipitation, cause a dust bowl. CO2 having nothing to do with it.

The hubris of man is virtually unlimited. We are in reality like ants crawling around on a giant rock 70% covered by water saying “Oh, look what we have done!”.


The problem is that Prairie grass, a drought resistant plant, was ploughed up by, Mr John Deere, in the early 19th century. Only his steel could make mince meat of this grass.

Prairie grass is very versatile –

“During the Great Drought, the shortgrass of Nebraska and Kansas spread hundreds of miles to the east into the mixed grass region, while the mixed grass spread hundreds of miles into the tallgrass”


Prairie grass can withstand 30 years of drought and illustrates what kind of climate the US is used to.


Having just driven through Texas, I can attest that the green line is still approximately at the 100th meridian. It is a very abrupt change. It is around Abilene on Highway 20, and Just west of San Antonio if you are driving a more southerly route. Texas bluebells still seem pretty happy east of 100.

DeLoss McKnight

Am I missing something? The Ross essay quotes the Seager study that the arid/humid line has already moved east by 140 miles. But when I looked at the abstract for the Seager study, it said this: “There is a sharp gradient in aridity along and just east of the 100th Meridian, verifying Powell’s observations.” (describing current conditions). The study then ran projections in 20 year increments, which indicated that the line would move 2 to 3 degrees by 2100. So it appears that Ross was misquoting the study by saying the change had already occurred. Am I misreading this? Because it seems like an important distinction. Furthermore, as Leo Smith earlier observed, no mention is made of plant life making do with less water, so if the line *does* move by 140 miles, will that necessarily mean that yields will decrease?

D. J. Hawkins

It appears that Ross has taken Seager’s predictions and moved them to the present. In addition, it seems Seager himself does the same in his interview with NPR. It’s a terrible muddle

Rick Yarnell

Yes, Mr. Hawkins, that is exactly what Mr. Ross did. It is a bit of sleight-of-hand journalism. Dare I call it “Fake News”?.


Delightful read.

Having — from 1962 thru 1980 — been routinely ‘carted’ from California to Missouri by my Dad … to spend each summer on a farm, overalls clad, sockless, teeshirted, brown-as-a-nut (sunscreen? what’s that?), I can say with remarkably good memory, that COLORADO, WYOMING, MONTANA, are not deserts.

Not in the slightest. They’re verdant, lovely endless grasslands.



Evaporation is notoriously difficult to model since it depends on a large number of factors. Temperature (including annual and diurnal variation), humidity (relative and absolute), wind, the nature of the surface (flat/rough/vegetated/unvegetated /permeable etc).


Pull the dry land farming stats from USDA for counties along the 100th Meridian.

I drive West Texas all the time and other than drought years, I see healthy fields. And I know my family is doing well out there.

Jim Clarke

Rick Yarnall has produced a bit of climate science. He used the scientific method of testing a hypothesis with science and observation, then made a conclusion based on that method. He did so in response to an article and a paper that are not climate science. They are the equivalent of a vintage Saturday Night Live skit asking “What if Napoleon had a B-52 at Waterloo?”

Most of what passes as climate science these days is actually speculative fiction; as amusing and scientifically important as the old Saturday Night Live skit. The journals are full of speculative fiction masquerading as climate science. The proper scientific response to the question “What if the atmosphere warms 3 to 5 degrees C with a doubling of the atmospheric CO2 concentration?” is simply “Is that happening?” Climate science should only be concerned with the ladder question, but the answer (as pointed out in the above article) is “No. There is no evidence of that!”

Jeff Alberts

“What if Napoleon had a B-52 at Waterloo?”

Without fuel, pilots, bombs, runways, what good would it be?

Walter Sobchak

Will the dividing line between arid regions and well watered regions move east? Not unless they move the Gulf of Mexico and Mississippi River basin. Stopping the Coriolis would also help.


Thanks Rick. Well done.

I feel like there must be a joke in here somewhere about climate gerrymandering, but I just can’t seem to nail it down.


John F. Hultquist

Using CMIP5 climate model data, the future was projected . . .

Often such modeling involves multiple runs of a computer program(s) using the Representative Concentration Pathways (RCPs) — four CO2 concentrations adopted by the IPCC.
Headlines and other reporting frequently focus on model output using RCP 8.5.
Perhaps this was done in this study.
I don’t have time to investigate. [Likewise with the recent report of projected 3 feet of rise in Puget Sound.]


admittedly just hearsay evidence.. I moved to a little piece of land in north central Texas, located on the 7.5 minute grid quadrangle 31 45’N to 31 62′ 30″N; 99 07′ 30″ -99 15′ ( no little degree symbol on this keyboard) so pretty much on the magic 100th meridian. Been keeping rainfall records for the past 6 years or so. First few years the total was into the 20 inch range–low 23, high 28, then had a good year–nearly 40 inches. that would be in 2016. 2017 started out well also with about 14 inches by June, and then the rain stopped. 2017 total was less than 20 inches (18.6), and this year is looking bleak–9 inches through the end of July. Odd thing is that 20 miles west of here the fields are green, and there is water in the tanks, and the same to the SE about 50 miles. Haven’t driven North, but radar has shown a lot of rain in the direction. It’s real ly frustrating to watch those rain clouds circle around with nary a drop here. Suspect the ranch will be the bullseye again someday–just hoping it will be soon.

Point is in this part of the world, the weather variations can be rather extreme from year to year, and month to month. But the average is right where Powell would have it. Unfortunately, there isn’t a regional aquifer in this area, so the only wells are shallow and spotty, and in my case rather dry now. Water bill is way up there just trying to keep some fruit and pecan trees alive. But tomorrow always comes, and the weather always changes, so hopes for the future.

Jeff Alberts

“admittedly just hearsay evidence”

I think that would be anecdotal, not hearsay.

Jeff Alberts

Again, these so-called scientists expect the climate to be static, never changing. And that ANY change is bad and caused by humans. How is that in any way scientific?



Send all believers in the desert spreading eastward to live a few decades in East Texas. Tell them they have to prove movement eastward by the millimeter.

NW Sage

Given the scarcity of rainfall data because cities/towns are widely spaced – it might be useful to note that businesses like Davis Instruments have sold automatic weather stations for years and many farmers make good use of the data for their particular location. Many of these stations are connected together into networks. If it is possible to tap into the data in these networks much greater precision in the data might be obtained. Davis Instruments might be able to point out how to access this data.

John L Kelly

I haven’t had a chance to read the replies, so this may be redundant. When Mr. Powell traveled across the country we were pretty much as today, climate wise. However, that is about to change drastically as we enter the Grand Solar Minimum, in just a year or so. This means the climate will be cooler/colder than present. And as we all should know, a cooler climate is a dryer climate. When we enter this Grand Solar Minimum, expect the line to shift further eastward. Common Sense 101.

An examination of the Palmer Hydrological Drought Index (PHDI) for climate divisions within the 100 to 98 meridian shift zone highlighted by USA Today shows the opposite of what they claim. See: http://appinsys.com/GlobalWarming/The100thMeridian.htm


But the Press does not report facts like that.
This is how the climastrologers got away with “adjusting” all those records in 2015 from cooling trends to warming trends. Only WUWT and fellow travellers ever knew about it.