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A Geological Perspective of Wildfires: ‘Global biomass burning during past century has been lower than at any time in past 2000 years’

Guest essay by David Middleton


This post was inspired by Anthony Watts’ recent post about wildfires and their unwillingness to cooperate with the Gorebal Warming narrative.

If the “climate” was warming faster or sea level was rising faster “than at any time in the past 2000 years,” it would be front page material (they aren’t, see Addendum 1).  However, actual evidence that “global biomass burning during the past century has been lower than at any time in the past 2000 years” doesn’t get much notice in the mainstream media.

Analysis of charcoal records in sediments [31] and isotope-ratio records in ice cores [32] suggest that global biomass burning during the past century has been lower than at any time in the past 2000 years. Although the magnitude of the actual differences between pre-industrial and current biomass burning rates may not be as pronounced as suggested by those studies [33], modelling approaches agree with a general decrease of global fire activity at least in past centuries [34]. In spite of this, fire is often quoted as an increasing issue around the globe [11,2629].

Doerr & Santin, 2016

In spite of this, fire is often quoted as an increasing issue around the globe…

Why is fire “often quoted as an increasing issue around the globe”?

We have been told, many times, that wildfires are multiplying and will continue to increase in severity and/or frequency due to global warming.

From November 2012:

4. Wildfires are multiplying


Fires on the rise (National Research Council)

This map published in the National Research Council report shows how rising temperatures and increased evaporation will cause widespread fires in the western US. Fire damage in the northern Rocky Mountain forests, marked by region B, is expected to more than double annually for each 1.8 degree Fahrenheit increase in average global temperatures. With the same temperature increase, fire damage in the Colorado Rockies (region J) is expected to be more than seven times what it was in the second half of the 20th century.

The Atlantic

Despite no “direct relationship between climate change and fire,” they are continuing to tell us “that wildfires [will] increase due to global warming”…

Will global warming produce more frequent and more intense wildfires?

There isn’t a direct relationship between climate change and fire, but researchers have found strong correlations between warm summer temperatures and large fire years, so there is general consensus that fire occurrence will increase with climate change.

Hot, dry conditions, however, do not automatically mean fire—something needs to create the spark and actually start the fire. In some parts of the country (like Alaska), most fires are ignited by lightning. In other regions (like California), most fires are ignited by humans.

Climate models tell us that average summer temperatures will continue to increase through this century, but ignition is the wild card. What will happen in the future is a more complicated story because we don’t understand what will happen with convective storms and the lightning.


“There isn’t a direct relationship between climate change and fire, but…”  There’s always a BIG BUT…

But models and consensus say that Gorebal Warming will increase the frequency and/or severity of wildfires… But… another BIG BUT… There’s no scientific basis for the first BIG BUT.

A Geological Perspective of Wildfires

The Fire Window

Geological evidence for ancient wildfires generally consists of sedimentary charcoal deposits (inertinite).  Fossil charcoal is also a key factor in understanding the evolution of Earth’s atmosphere, particularly oxygen content.  The first clear evidence of fire is in the Late Silurian.

Fossil charcoal provides direct evidence for fire events that, in turn, have implications for the evolution of both terrestrial ecosystems and the atmosphere. Most of the charcoal record is known from terrestrial or near-shore environments and indicates the earliest occurrences of fire in the Late Silurian. However, despite the rise in available fuel through the Devonian as vascular land plants became larger and trees and forests evolved, charcoal occurrences are very sparse until the Early Mississippian where extensive charcoal suggests well established fire systems.  We present data from the latest Devonian of North America from terrestrial and marine rocks indicating that fire became more widespread and significant at this time. This may be a function of rising O2 levels and the occurrence of fire itself may have contributed to this rise through positive feedback. Recent atmospheric modelling suggests an O2 low during the Middle Devonian (around 13%), with O2 rising steadily through the Late Devonian and Early Carboniferous (Mississippian) (from 17-19%). In Devonian-Carboniferous marine black shales, fossil charcoal (inertinite) steadily increases up-section suggesting the rise of widespread fire systems. Scanning electron and reflectance microscopy of charcoal from Late Devonian sites indicate that the fires were moderately hot (around 550 °C) and burnt mainly surface vegetation dominated by zygopterid ferns and lycopsids, rather than being produced by forest crown fires.

Rimmer et al., 2015

The evolution of vascular land plants from the Late Silurian through the Mississippian (Lower Carboniferous) provided both the fuel and the oxygen required for widespread fire systems.

Fire is an exothermic oxidation reaction dependent on the rapid combination of fuel and oxygen in the presence of heat11. Charcoal is a by-product of wildfire and is first documented in the latest Silurian12,13, and has subsequently been recorded in all geological periods from a range of sedimentary settings14. Calculation of fuel flammability at varying oxygen concentrations enables past pO2 to be constrained within the range 15-35% (`fire window’) whenever charcoal is recovered from the fossil record11,15,16.

Glasspool & Scott, 2010

The “fire window” is defined as an atmospheric oxygen content range of 13-15% to 35%.  Below 13-15% fire will not ignite and above 35% fire cannot be extinguished (which would really suck!).

Under modern atmospheric O2 conditions (Present Atmospheric Level (PAL) = 21%), a low plant-moisture content is necessary for fire to spread (Wildman et al., 2004) as is a sufficient fuel build-up and an ignition source (usually lightning) (Pyne et al., 1996). Atmospheric O2 levels are crucial: below 13% fires will not ignite and spread (Chaloner, 1989) whereas at high O2 levels (above 35%) plants may burn irrespective of fuel moisture, resulting in an upper limit for atmospheric O2 concentration as above this level no fire could be extinguished (Watson et al., 1978; Lenton and Watson, 2000; Lenton, 2001). This has led to the concept of the fire window (Jones and Chaloner, 1991).

Rimmer et al., 2015

Inertinite abundance provides estimates of past fire systems and atmospheric oxygen content.  As vascular land plants became more abundant, atmospheric oxygen levels rose.  The increasing abundance of vascular land plants and higher atmospheric oxygen levels led to an increase in the prevalence of fire.


Figure 1.  Inertinite abundance (top) and pO from internite (lower) over past 400 Myr (modified after Glasspool & Scott 2010).

As can be seen in Figure 1, wildfires were far more common during the Late Paleozoic and Mesozoic than they have been in the Cenozoic.  While the various methods of estimating Phanerozoic atmospheric O2 yield somewhat different results (Berner 1999, 2006, 2009), they generally depict a rapid rise from about 15% to 25-30% during the Carboniferous, an Early Permian peak of 30-35%, about 25% from the Triassic through mid-Cretaceous, punctuated by drops to 15-20% associated with anoxic events.


Figure 2. Phanerozoic oxygen levels modeled from carbon and sulfur cycles (modified after Berner, 1999).

The atmospheric oxygen level has been slowly declining over time.  O2/N2 ratios from Greenland and Antarctic ice cores indicate that atmospheric oxygen has declined by 0.7% over the past 800,000 years (Stolper et al., 2018).


Figure 3. Decline in atmospheric oxygen over past 800,000 years (Stolper et al., 2018).

The modern decline in atmospheric oxygen is also reflected in recent instrumental records.


Figure 4. Decline in atmospheric oxygen 1989-2018 measured at La Jolla, California (Scripps)

While the atmosphere is still well-within the “fire window,” the trend in atmospheric oxygen content has been steadily moving in the opposite direction of increased fire risk since the Late Cretaceous.

So, atmospheric oxygen has not been playing ball with the Gorebal Warming narative… Unless the Gorebal Warming narative asserts that oxygen levels will decline as wildfires increase… Which would be one of the most fracking moronic things a Gorebot could assert.

What Does Fire Need Apart From Oxygen?


Wood and other biomass.  Dry wood and other dry biomass, to be more precise.  The U.S. Forest Service Wildland Fire Assessment System bases fire risk on a number of factors revolving around humidity, atmospheric stability, lighting potential, winds, humidity and moisture.

Fire Potential / Danger

  • Fire Danger Rating
  • Haines Index
  • Dry Lightning
  • Potential Lightning Ignition
  • Lightning Efficiency
  • NDFD Fire Danger Forecasts


  • Fire Weather

Moisture / Drought

  • Dead Fuel Moisture
  • Growing Season Index
  • Keetch-Byram Index
  • Palmer Index
  • National Fuel Moisture Database

The National Park Service also has a very informative web page on the assessment of fire danger, which includes the following:

Ignition Component (IC)

The Ignition Component is a number that relates the probability that a fire will result if a firebrand is introduced into a fine fuel complex. The ignition component can range from 0 when conditions are cool and damp, to 100 on days when the weather is dry and windy. Theoretically, on a day when the ignition component registers a 60 approximately 60% of all firebrands that come into contact with wildland fuels will require suppression action.

  • A firebrand must come into contact with the dead fuel,
  • the fuel particle must be dry, and
  • the temperature of the fuel particle must be raised to the kindling point which is about 380 degrees centigrade.

Living material in the fine fuel complex reduces the efficiency of ignition. Therefore, an adjustment to the ignition component is made based on the percentage of live fuel (herbaceous vegetation) in the fine fuel complex.

The moisture content of the dead component of the fine fuel (1-hr. timelag fuel moisture) is determined by the state of the weather (sunny or cloudy), air temperature, and relative humidity at the time of the 2 p.m. fire weather observation.

The condition of the herbaceous (live) vegetation and the 1-hour time lag fuel moisture are then integrated in the calculation the fine fuel moisture (FFM) which expresses the effective moisture content of the fine fuels.

The closer the initial temperature of the fuel is to the ignition temperature, the more likely a fire will result when a firebrand is introduced into the fine fuel complex, since not a much energy is required to raise the fuel particle to its ignition temperature.

It’s little wonder that wildfires don’t correlate very well with the rise in average surface temperatures over the past 500 years.  15.0 °C isn’t significantly closer to 380 °C, than 14.2 °C is.

Referring back to Rimmer et al., 2015:

Under modern atmospheric O2 conditions (Present Atmospheric Level (PAL) = 21%), a low plant-moisture content is necessary for fire to spread (Wildman et al., 2004) as is a sufficient fuel build-up and an ignition source (usually lightning) (Pyne et al., 1996).

From a climatological perspective, fuel moisture is the key factor in fire risk and the second most important factor from a geological perspective, right behind atmospheric O2conditions.

Fuel moisture is closely related to drought conditions.  If the soil is wet, the fuel is probably wet, and the “global” soil has actually been getting wetter since 1950.

An overall increasing trend in global soil moisture, driven by increasing precipitation, underlies the whole analysis, which is reflected most obviously over the western hemisphere and especially in North America.

Sheffield & Wood, 2008

And there has been no statistically meaningful change in global drought conditions since 1950.

Here we show that the previously reported increase in global drought is overestimated because the PDSI uses a simplified model of potential evaporation7 that responds only to changes in temperature and thus responds incorrectlyto global warming in recent decades. More realistic calculations, based on the underlying physical principles8 that take into account changes in available energy, humidity and wind speed, suggest that there has been little change in drought over the past 60 years.

Sheffield, Wood & Roderick, 2012


Here we show that the previously reported increase in global drought is overestimated because the PDSI uses a simplified model of potential evaporation that responds only to changes in temperature and thus responds incorrectlyto global warming in recent decades.

PDSI *overestimates* drought conditions?  Too fracking funny!


Figure 5. Palmer Drought Severity Index, Contiguous United States, 1895-2018, 13-month rolling average (NOAA NCDC).

Does anyone need an explanation of Figure 5?

So… Why Are We Experiencing So Many “Megafires”?

Modern Megafires Are Truly Unusual

By Live Science Staff May 16, 2012

The gigantic wildfires that blow through the southwestern United States today are unprecedented in the long-term historical record, new research suggests, and are due to modern human activities.

“The U.S. would not be experiencing massive large-canopy-killing crown fires today if human activities had not begun to suppress the low-severity surface fires that were so common more than a century ago,” study researcher Christopher Roos, of Southern Methodist University, said in a statement.


Ancient Fires


They discovered that this time period, the Medieval Warm Period, was no different from the Little Ice Age in terms of what drives frequent low-severity surface fires: year-to-year drought patterns.

“It’s true that global warming is increasing the magnitude of the droughts we’re facing, but droughts were even more severe during the Medieval Warm Period,” Roos said. “It turns out that what’s driving the frequency of surface fires is having a couple wet years that allow grasses to grow continuously across the forest floor and then a dry year in which they can burn. We found a really strong statistical relationship between two or more wet years followed by a dry year, which produced lots of fires.”

Changing Climate

The researchers found that even when ancient climates varied from each other — one hotter and drier and the other cooler and wetter — the frequencies of year-to-year weather patterns that drive fire activity were similar.


In ancient forests, frequent small fires swept the forest floor. These “fires cleaned up the understory, kept it very open, and made it resilient to climate changes because even if there was a really severe drought, there weren’t the big explosive fires that burn through the canopy because there were no fuels to take it up there,” Roos said. “The trees had adapted to frequent surface fires, and adult trees didn’t die from massive fire events because the fires burned on the surface and not in the canopy.”

“If anything, what climate change reminds us is that it’s pretty urgent that we deal with the structural problems in the forests,” Roos said. “The forests may be equipped to handle the climate change, but not in the condition that they’re currently in. They haven’t been in that condition before.”

One answer to today’s megafires might be changes in fire management, the researchers said.

The findings were published today in the March issue of the journal The Holocene.

Live Science

Roos & Swetnam, 2011

Key points:

  • ‘The Medieval Warm Period, was no different from the Little Ice Age in terms of what drives frequent low-severity surface fires: year-to-year drought patterns.”
  • “Droughts were even more severe during the Medieval Warm Period,” than the modern era.
  •  “For at least 200 years prior to Euroamerican settlement, extensive fires occurred frequently in these forests (e.g. every 3–15 years), consuming fine surface fuels and maintaining an open, park-like structure of mixed age forests.”
  • “Frequent low-severity surface fires” cleared for forests of fuel.  These types of fires are rare in the modern era due to fire prevention methods and firefighting activities… Hence megafires.

Couple all of that with the fact that atmospheric oxygen levels are declining and soil moisture is increasing and you can schist-can the notion that Gorebal Warming is increasing the frequency and/or severity of wildfires.  Although, human activities clearly are increasing the risk of “megafires.”

So… That pretty much settles it… Gorebal Warming does not cause an increase in forest fires… And… Only you can prevent forest fires.


Citation: Unknown. 1989. “Only You .” Special Collections, USDA National Agricultural Library. Accessed July 31, 2018,

A Geologist’s Personal Perspective of Wildfires, the “Park Service,” Firefighting and Fire in General

Smokey Bear… NOT Smokey *the* Bear

Some people get annoyed at those who think Jethro Tull was a flute player in a rock band.

I couldn’t care less… I was never much of a Jethro Tull fan, the flute player or the literary figure.

But (and this is a BIG BUT), I do get annoyed at people who call Smokey, Smokey *the* Bear.  His fracking name was Smokey Bear!

The Orphan Cub

One spring day in 1950, in the Capitan Mountains of New Mexico, an operator in one of the fire towers spotted smoke and called the location in to the nearest ranger station. The first crew discovered a major wildfire sweeping along the ground between the trees, driven by a strong wind. Word spread rapidly, and more crews reported to help. Forest rangers, local crews from New Mexico and Texas, and the New Mexico State Game Department set out to gain control of the raging wildfire.

As the crew battled to contain the blaze, they received a report of a lone bear cub seen wandering near the fire line. They hoped that the mother bear would return for him. Soon, about 30 of the firefighters were caught directly in the path of the fire storm. They survived by lying face down on a rockslide for over an hour as the fire burned past them.

Nearby, the little cub had not fared as well. He took refuge in a tree that became completely charred, escaping with his life but also badly burned paws and hind legs. The crew removed the cub from the tree, and a rancher among the crew agreed to take him home. A New Mexico Department of Game and Fish ranger heard about the cub when he returned to the fire camp. He drove to the rancher’s home to help get the cub on a plane to Santa Fe, where his burns were treated and bandaged.


News about the little bear spread swiftly throughout New Mexico. Soon, the United Press and Associated Press broadcast his story nationwide, and many people wrote and called, asking about the cub’s recovery. The state game warden wrote to the chief of the Forest Service, offering to present the cub to the agency as long as the cub would be dedicated to a conservation and wildfire prevention publicity program. The cub was soon on his way to the National Zoo in Washington, D.C., becoming the living symbol of Smokey Bear.

Smokey received numerous gifts of honey and so many letters he had to have his own zip code. He remained at the zoo until his death in 1976, when he was returned to his home to be buried at the Smokey Bear Historical Park in Capitan, New Mexico, where he continues to be a wildfire prevention legend.

In 1952, Steve Nelson and Jack Rollins wrote the popular anthem that would launch a continuous debate about Smokey’s name. To maintain the rhythm of the song, they added “the” between “Smokey” and “Bear.” Due to the song’s popularity, Smokey Bear has been called “Smokey the Bear” by many adoring fans, but, in actuality, his name never changed. He’s still Smokey Bear.


Smokey cub sitting on a Piper PA-12 Super Cruiser

Smokey was nursed back to health by Dr. Ed Smith, who founded Smith Veterinary Hospital in Santa Fe, New Mexico.

Our History

Dr. Ed Smith opened the original Smith Veterinary Hospital on January 1st, 1946, in its original location on Pen Road, about 3/4 of a mile northwest of the current location. At the time, it was on the very outskirts of Santa Fe; today, it’s in the middle of the St. Francis Drive and Cerrillos Road intersection- one of the busiest in the city!

Dr. Smith practiced on both large and small animals and covered a large area that included Taos, Las Vegas, Estancia, and Chama.

Dr. Ed Smith served as the state vet at Santa Fe Downs for eight years and was secretary of the State Veterinary Examining Board for ten years. During that time, he helped establish the numbered license system in New Mexico.

Dr. Smith treated the pets of several famous clients, including silver chow dogs belonging to Georgia O’Keeffe, but it was a bear cub that became his most famous patient. Smokey Bear was brought to Dr. Smith in May 1950 with burns on his feet and abdomen from a forest fire. Dr. Smith nursed him back to health and later cared for Goldie, another black bear, who would later be Smokey’s mate.



Smith Veterinary Hospital

Now… You may ask yourself, “Why would a climate-denying petroleum geologist know anything or even care about Smokey Bear?”  Because I met Smokey back in 1980.


I’m the blond-haired guy in the middle… And, no, I was not handing out menus.  I think they were Smokey Bear posters… And, yes, I was wearing a badge and a Connecticut Department of Environmental Protection uniform.

My summer job in 1979 and 1980 was as a State Park Patrolman at Squantz Pond State Park in Connecticut.  As such, I went through five days of rigorous (/SARC) police training, was sworn in and issued a badge.  Among the many cool things I got to do, was to drive a patrol truck…


Can you believe I used to have hair?

And I got to hang out with other “Park Rangers” and fire trucks…


I’m on the far right side of the photo… And most everything else.  The man to my left, with the Smokey Bear hat, was the park Conservation Officer, the equivalent of a State Trooper.  He was authorized to carry a weapon, but never did… back then.  The man to his left, in the green pants, was a good friend of mine from high school and the New Fairfield Volunteer Fire Department.  His nickname was “Ranger Rick.”  My nickname was, for some reason, “Woodsie Owl.”  Rick was the unit manager.

One busy summer day, Ranger Rick and I were executing a foot patrol of the picnic area (AKA walking around).  Something in my periferal vision caught my attention.  It appeared to be a burning picnic table.  So, I said, “Rick… I think a picnic table is on fire.”  Rick replied, “Yep.  Woodsie, that’s a burning picnic table.  We should probably investigate.”

Well, as we approached the buring picnic table, we were confronted by a park patron who was complaining about the fact that her picnic table had spontaneously burst into flames.  At that point, I used all of my scientific education to figure out what had happened.  Back in the 1970’s, most charcoal grills looked like this:


The patron had removed the grill from the stand, placed it on the wooden picnic table, filled it with charcoal, ignited it, and proceeded to cook her family’s picnic lunch… And was surprised when the picnic table burst into flames.

The Thin Red Line

From 1975-1980 I was a member of the New Fairfield Volunteer Fire Department, Company A.   I decided to join the NFVFD as a junior member when I was 16, for the altruistic reason that being a volunteer fireman afforded a lot of opportunities for 16 and 17 year olds to drink beer.  That said, it also provided me with some experience hiking into the woods to fight brush fires with an Indian Tank on my back.  On one occasion, I was squirting water at a brush fire, when a nearby tree burst into flames.  That was a discomforting experience.  And Indian Tanks, full of water, were heavy!

Indian Tank

The tank weighed 10-11 pounds, 5 gallons of water weighs about 42 pounds.

I enjoyed my time as a volunteer fireman and not just because of the beer.  Once a week, we would have a drill, where we practiced firefighting and rescue methods.  One of the coolest things was when we would go up to the town dump and practice cutting open junk cars with a K12 saw and prying doors open with the Jaws of Life.

I also had the distinct honor to serve with Chris Blackwell.  Chris was a fellow junior member.  As such, we weren’t supposed to drive any vehicles or enter any burning structures.  However, on two occasions, Chris and I were the only two members to respond to ambulance calls.  On both occasions, I drove (it was a Ghostbusters style Cadillac ambulance, like this one) and Chris assumed the EMT (AKA paramedic role).  After high school, Chris joined the Air Force, where he became a highly regarded heavy rescue expert.  He went on to become a highly decorated member of FDNY’s Rescue 3.  Chris and seven other members of Rescue 3 were among the 343 New York City firefighters who sacrificed their lives saving thousands on 9/11/2001.  Firefighters are our Thin Red Line.

Firefighting is dangerous work and firefighters routinely risk their lives to protect us and our property and, all too often, they sacrifice their lives protecting us.  At least four firefighters have died fighting the Carr and Ferguson fires in California, including Brian Hughes of the elite Arrowhead Hotshots team.  Hotshots teams are literally the best of the best.  The movie, Only the Brave, is a heartbreaking story about the Granite Mountain Hotshots team.  19 of 20 Granite Mountain Hotshots died fighting the Yarnell fire.  It was the single greatest loss of US firefighters since 9/11.


Two years after the first meeting of the Yarnell Hill Memorial Site Board, and thanks to a generous donation from the Arizona Public Service Foundation, the park is open to the public. “The families and the communities of Prescott and Yarnell have worked hand-in-hand with the state to develop Granite Mountain Hotshots Memorial State Park,” said Sue Black, executive director of Arizona State Parks. “We truly want the memorial to be a place for healing and to honor the lives and legacy of 19 hotshots.” Granite Mountain Hotshots Memorial State Park

Fire Hits Home

One spring day in 1997, I arrived home from work to find several fire trucks and police cars in front of my house.  It took what seemed like a very long time for me to realize that they were fighting a fire in my house.   Suddenly being homeless, without even a change of clothes is bad.  Realizing that three pets, two cats and a dog, had perished was worse.  Amazingly two dogs had survived.  Thanks to the Red Cross, we had a place to stay that night and were able to slowly begin the process of recovery.  But… It was a really bad experience.


  • There is absolutely no scientific basis to assert that Gorebal Warming has made, is making, or will make wildfires more frequent and/or severe.
  • Climate change and/or natural variability will always alter the patterns of wildfire frequency and severity.  It has always done this and it always will.
  • Forests, wildlands, grasslands and other fire-prone terrain must be maintained in such a manner to minimize the availability of fuel.
  • People need to be far more careful with potential ignition sources.
  • Arsonists should be prosecuted to the fullest extent of the law.
  • Firefighters and park rangers deserve our utmost admiration and respect.
  • Victims of fire deserve our sympathy and support.
  • Charlatans who fraudulently try to link the horrors and tragedies of wildfires to climate change deserve nothing but scorn and contempt.

Addendum 1: There is no scientific basis to claim that the recent rate of warming is unprecedented.

Q: Is the rate of global temperature rise over the last 100 years faster than at any time during the past 11,300 years?

A: Our study did not directly address this question because the paleotemperature records used in our study have a temporal resolution of ~120 years on average, which precludes us from examining variations in rates of change occurring within a century. Other factors also contribute to smoothing the proxy temperature signals contained in many of the records we used, such as organisms burrowing through deep-sea mud, and chronological uncertainties in the proxy records that tend to smooth the signals when compositing them into a globally averaged reconstruction. We showed that no temperature variability is preserved in our reconstruction at cycles shorter than 300 years, 50% is preserved at 1000-year time scales, and nearly all is preserved at 2000-year periods and longer. Our Monte-Carlo analysis accounts for these sources of uncertainty to yield a robust (albeit smoothed) global record. Any small “upticks” or “downticks” in temperature that last less than several hundred years in our compilation of paleoclimate data are probably not robust, as stated in the paper.

Real Climate explains Marcott

The same principle holds true for sea level rise and most other pre-industrial climate approximations.

Addendum 2: Palmer Drought Severity Index (PDSI)

The Palmer Drought Severity Index (PDSI) uses readily available temperature and precipitation data to estimate relative dryness. It is a standardized index that spans -10 (dry) to +10 (wet). It has been reasonably successful at quantifying long-term drought. As it uses temperature data and a physical water balance model, it can capture the basic effect of global warming on drought through changes in potential evapotranspiration. Monthly PDSI values do not capture droughts on time scales less than about 12 months; more pros and cons are discussed in the Expert Guidance.


  • Effective in determining long-term drought, especially over low and middle latitudes
  • By using surface air temperature and a physical water balance model, the PDSI takes into account the basic effect of global warming through potential evapotranspiration
  • Takes precedent (prior month) conditions into account


  • Not as comparable across regions as the Standardized Precipitation Index (SPI), but this can be alleviated by using the self-calibrating PDSI
  • Lacks multi-timescale features of indices like the SPI, making it difficult to correlate with specific water resources like runoff, snowpack, resevoir storage, etc.
  • Does not account for snow or ice (delayed runoff); assumes precipitation is immediately available


Addendum 3: What about the west?


U.S. Climate Regions, NOAA

What about it?


PDSI NOAA western regions, NOAA NCDC.

Addendum 4: My Writing Style

I routinely pepper my posts with sarcastic remarks, pop culture references (often videos) and geologically derived euphemisms for common cuss words.  If you don’t like my style, don’t watch the videos and pretend I’m using the words “schist” and “fracking” to describe metamorphic rocks and common well completion procedures.  If you find the phrase “Gorebal Warming” to be offensive, childish, or some other -ive or -ish… Tough schist.  I think it’s fracking hilarious.


Berner, Robert A.  Atmospheric oxygen over Phanerozoic time.  Proceedings of the National Academy of Sciences Sep 1999, 96 (20) 10955-10957; DOI: 10.1073/pnas.96.20.10955

Dai, Aiguo & National Center for Atmospheric Research Staff (Eds). Last modified 12 Jul 2017. The Climate Data Guide: Palmer Drought Severity Index (PDSI).” Retrieved from

Doerr, Stefan H., Cristina Santín.  Global trends in wildfire and its impacts: perceptions versus realities in a changing world.  Phil. Trans. R. Soc. B 2016 371 20150345; DOI: 10.1098/rstb.2015.0345. Published 23 May 2016

Glasspool, Ian & Scott, Andrew. (2010). Phanerozoic atmospheric oxygen concentrations reconstructed from sedimentary charcoal. Nature Geoscience. 3. 10.1038/ngeo923.

Rimmer, S. M., Hawkins, S. J., Scott, A. C., & Cressler, W. L. (2015). The rise of fire: Fossil charcoal in late Devonian marine shales as an indicator of expanding terrestrial ecosystems, fire, and atmospheric change. American Journal of Science, 315(8), 713-733.

Roos, Christopher I., Thomas W. Swetnam.  A 1416-year reconstruction of annual, multidecadal, and centennial variability in area burned for ponderosa pine forests of the southern Colorado Plateau region, Southwest USA.   The Holocene  Vol 22, Issue 3, pp. 281 – 290.  First Published November 24, 2011.

Sheffield, J. & Wood, E. F. Global trends and variability in soil moisture and drought characteristics, 1950–2000, from observation-driven simulations of the terrestrial hydrologic cycle. J. Clim. 21, 432–458 (2008).

Sheffield, J., Wood, E. F. & Roderick, M. L. Little change in global drought over the past 60 years. Nature 491, 435–438 (2012).

Stolper D, Bender M, Dreyfus G, Yan Y, Higgins J. A Pleistocene ice core record of atmospheric O2 concentrations. Science. 2016;353:1427–1430. doi: 10.1126/science.aaf5445.