Don Healy, July 2023
In the past two decades we have witnessed a upturn in the number of acres of forest lands burned in the United States. As shown in the graph below compiled by the National Interagency Fire Center, the years from 1958 to 1998 marked a consistently lower incidence of forest fires, averaging about 4 million acres burned per year. In the years since 1998 the number of acres burned has increased with two years equaling or exceeding 10 million acres. Aside from the catastrophic loss of timber resources, homes, structures and in some cases entire towns, the resultant smoke from these fires has created very hazardous air quality issues over broad swathes of the American West. In an ominous start to the 2023 fire season, fires in Eastern Canada have been so extensive as to impact much of the Eastern U.S. with dangerous air quality. There has been much handwringing, but thus far little motivation to seriously address this problem. The time has come to act, but the first step is to identify the root of the problem. Please take a moment to study the graph below.
You will notice that during the years from 1926 to about 1956 forest fires were a much bigger issue virtually all years, showing more acres burned in all, with two years experiencing more than 5 times greater areas than the worst recent year. To put this in perspective, earlier in our history dense forests were viewed as an impediment to settlement and development in much of the west and there was little concern if vast acreages were burned so long as humans and settlements weren’t impacted. To many of our earlier citizens periods of heavy smoke commonly prevalent were viewed as “the price of progress”. It wasn’t until the mid-1930s that the recently formed U.S. Forest Service became active in suppressing forest fires.
What is the common denominator between the numbers on the right side of the chart versus those on the left side, separated by the relatively benign period between 1956 and 1998? As my forestry professor told us during Forest Protection class in 1965, the three most important factors in preventing forest fires were “fuel load, fuel load and fuel load, in that order”. Prior to the 1950s, extending back millennia, fuel loads in the western U.S. were massive. The anecdotal records from the early Spanish and British explorations of the Pacific Northwest indicate dense smoke from massive forest fires extending well out into the Pacific, and a record of Mark Twain’s visit to Tacoma Washington, in 1895 describes the city fathers apologizing to Mr. Twain for the heavy forest fire smoke that obscured the view of the surrounding mountains. The reality is that the period from the early 1950s to just a few years ago was probably a “goldilocks” event, one of the few periods when large fires and heavy smoke were not a common experience.
In conversations with many fellow citizens, it is my perception that most are quite convinced that the United States has less forested area and less wood volume currently than it did decades ago. However, the U.S. Forest Service takes a complete inventory of all United States forest resources on all ownerships on a regular basis that belie that notion.
Row 2: Thousands of Acres of Forested Land in U.S., Table 3.
Row 3: Volume of Growing Stock in U.S. in Millions of Cubic Feet; Table 20
From: Forest Resources of the United States, 2017: https://www.fs.usda.gov/research/treesearch/57903
Between 1953 and 2017 the acreage of forested land in the U.S. increased by 3.2%, while the volume of growing stock, fuel load, increased by 60%. Due to the actions of environmental groups, harvesting on federal lands essentially ceased in about 1980, resulting in the shuttering of most of our forest products industry. However, the trees continued to grow during the past 43 years and with increased competition has led to areas of stagnation and the resultant insect and disease problems that occur in a natural environment; problems that had been reduced prior to the suspension of selective harvest silvicultural programs that reduced these issues and fuel load. Not only has the fuel load increased dramatically on federally controlled forested areas, but the susceptibility to fire has also increased disproportionately, leading to the uptick in acres burned that we see on the right side of the graph in Figure 1. If we continue to do nothing to reduce fuel load it is only reasonable to conclude that on average the number of acres burned annually will on average increase until we reach the numbers shown on the left side of the graph in figure 1.
In many news reports regarding recent forest fires much of the blame is placed on global warming. Mankind’s addition of CO2 and other greenhouse gases does play a role in the fire issue, but I believe that a serious review of the empirical evidence will reveal that global warming thus far is a relatively minor player. The graph in Figure 3 is very accurate, but the proportion is out of scale to the human experience. This information comes from the NASA sponsored work Drs. Spencer and Christy, University of Huntsville, Alabama, using satellites to take millions of atmospheric soundings daily is probably the most accurate global. temperature record
available. The trend for the 43 years of this record is .13 degrees per decade, which would equate to 1-degree centigrade above today’s global temperature in the year 2100. Yes, a slight increase but nothing like the predictions generated by recent climate models upon which the IPCC relies for their predictions, many of which run 3 times hotter.
Figure 4. Data from same source as Figure 3, but displayed on scale more typical to the human experience using the highest and lowest known temperatures recorded on earth as the upper and lower bounds..
The graph in Figure 5 shows data from the USCRN. This is the best surface station record available. Unfortunately, it was not installed until 2005 and only covers the United States and shows no discernable trend.
Graph created by the United States Climate Research Network (USCRN). This information is obtained from state-of-the-art weather stations in the United States. The sites are excellently situated to avoid urban heat island effects and other undo influences with instruments that provide triple redundancy. This network was created in 2005 after much criticism about the prior U.S. Historical Climate Network which had all manner of deficiencies with only about 11% to its stations meeting NOAA standards.
We do know empirically that increasing CO2 levels will raise temperature modestly. In lab experiments a doubling of CO2 levels from 280 ppm to 560 ppm will raise temperate about 1-degree Centigrade. The next doubling would raise temperature even less as the absorption spectra quickly becomes saturated. So the actual temperature increase due to greenhouse gases is proving to be relatively minimal. A far more important effect, especially from the aspect of the fuel load situation in our nation’s forests is that of the CO2 fertilization effect (CFE) on all vegetative growth, plants, crops and certainly trees. We shall delve more deeply into this aspect shortly, but a little historical perspective is necessary first. When coniferous trees evolved about 360 million years ago, CO2 levels were about 4000 ppm (parts per million), 9 times today’s levels. When deciduous trees, broadleaves evolved about 160 million years ago CO2 levels were about 2200 ppm. The thousands of botanical experiments to study the effect of elevated CO2 on crops, trees, grasses, and other vegetative forms indicate that 800 to 1000 ppm CO2 is the optimum level for most species.
Not only does CO2 fertilization produce more growth, but it also increases the drought resistance of most plants. Additionally, since the stomata, the pores on the leaves through which the CO2 enters the leaf to allow photosynthesis to take place do not need to remain open as long to allow CO2 to enter, less transpiration of water takes place and the plants become more drought resistant. Thus, plants grow more rapidly and require less soil moisture for the same unit of growth. These two issues, CO2 fertilization and increased drought resistance are two important factors in accelerating the increase in fuel load that have yet to receive much media coverage.
When dealing with critical issues such as the appropriate response to our nation’s forest fire issue we need to be totally pragmatic about the thought process that goes into formulating a rational response. We can continue to put the blame on the global warming issue, but the harsh reality is that the U.S. has already done a great deal to reduce our carbon emissions. However, China, India and many lesser developed countries are going in the opposite direction. Both China and India are continuing to build new coal-fired power plants and have no plans to stop this expansion until mid-century at the earliest. CO2 levels in the atmosphere will continue to rise at current rates for the foreseeable future. However, our nation can take immediate action to reduce the fuel load problem, but we need to get started. It will take a multi-pronged approach to work involving:
- Education of the public in the necessity of reducing our fuel loads and the ways in which we can do this in an environmentally friendly fashion. The public needs to be made aware of:
- Clear cutting is no longer necessary or desirable on most sites. The alternative is selective harvesting where forests are thinned, focusing on species diversification, size distribution, removal of trees with insect or disease issues and wildlife issues as well as the reduction in the fire hazard.
- Thinning is a very expensive operation and we have millions of acres that need attention. To raise the funds necessary to address the full scope of the issue we will need to harvest some merchantable timber to reduce the cost per acre.
- To have a competitive market for the merchantable wood component of the proposed thinning operations, we need to reestablish a modest forest products industry. Much of our fuel load issue is a result of the elimination of most of our wood products industry in the 1980s. Now we currently import about $20 billion dollars-worth of wood products annually. With farm goods the mantra is to buy locally; should not the same philosophy apply to forest products?
- The public needs to be made aware of the scope of the fuel load problem. Most of our citizens are quite convinced that both forested acreage and net growing stock have been in a dramatic decline over the past seven decades, when the reality is forested acreage is up slightly, and net growing stock has increased by 60%. The reality is dramatically different from the public’s perception; something that needs to be addressed to accomplish a solution.
- A major factor that also needs to be addressed is the interference created by our legal system, where anyone or any group can stop a harvesting project on federal land for the small price of filing a lawsuit. This problem is what created this problem in the first place, commencing in the 1970s and 1980s. The health issues that we will face if we continue on our current path make something like a war powers act designated by Congress necessary so a rational plan can be created and implemented without continued delay and interference. The alternative is to repeat the fire conditions we experienced prior to the 1950s and for much of our prior history.
Between 1953 and 2017 (volume at the last USFS inventory) the total growing stock on all ownerships has increased by 369,354 million cubic feet. Now, let’s examine the fuel load issue going forward. Since 1953 our timber base has been growing at 1.56% per year, adding 5,771 million cubic feet each year. If our forests were to simply keep growing at that rate in another 64 years our total net growing stock would reach 1,354,592 million cubic feet. At these levels, we would be potentially facing the average burned area shown on the left side of Figure 1, and 5 times greater than anything seen recently.
However, we are living in a much different climatic situation today, one that could make the fire situation even more dire. Yes, we do get modestly higher temperatures with increased greenhouse gases, but with higher CO2 levels there comes an effect termed CO2 fertilization. From your high school botany or biology class we have the formula for photosynthesis:
At 430 ppm CO2 in the atmosphere currently most terrestrial plants are just starting to get in their happy zone. As mentioned above, the optimum CO2 levels for most plant species is between 800 and 1000 ppm.
While these two issues appear to be a piling on of negative factors, we need to realize that this only applies to fuel load; a situation that can easily be controlled with selective timber harvesting practices. On the positive side we need to realize that both the CO2 fertilization effect and the increase in drought resistance are both a major boon to crop production upon which the survival of the human population is dependent.
We had heard very little about the CO2 fertilization effect (CFE); just how big a factor is it? It turns out that it is very important and very likely has been a salvation for the human species in recent decades as the human population continues to climb toward the 9 billion mark.
How do we know CFE is a factor in plant growth? We now have several lines of evidence that validate this:
1. There is the formula in Fig. 6 that supports this when combined with German scientist Justus von Liebig’s Law of the Minimum which states: ”that the yield achievable is dictated by the nutrient that is most limiting.’
There are 16 essential elements that are supplied in mineral form from the soil and CO2 which is absorbed from the atmosphere. In comparing today’s CO2 levels to the optimum levels stated earlier, we are assured that if all the other essential elements are available plants will grow more rapidly.
2. Global satellite surveys have confirmed a global greening of the planet with one study published April 26, 2016 from NASA titled, “Carbon Dioxide Fertilization Greening Earth, Study Finds”. The first two paragraphs read:
. “From a quarter to half of Earth’s vegetated lands have shown significant greening over the last 35 years largely due to rising levels of atmospheric carbon dioxide”, according to a new study published in the journal Nature Climate Change on April 25.
An international team of 32 authors from 24 institutions in eight countries led the effort, which involved using satellite data from NASA’s Moderate Resolution Imaging Spectrometer and the National Oceanic and Atmospheric Administration’s Advanced Very High Resolution Radiometer instruments to help determine the leaf area index, or amount of leaf cover, over the planet’s vegetated regions. The greening represents an increase in leaves on plants and trees equivalent in area to two times the continental United States.”
The full article available here: https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth
The United States comprises about 6.27% of the terrestrial area of our planet, So the numbers in this paper indicate a greening equal to 13.8 % over the 35 years of the study, 3.9% per decade.
3. Thousands of laboratory and FACE (Free Air CO2 Enrichment) studies have been conducted to observe the results of growing numerous plant species at higher than ambient levels of CO2. A great repository of the data from many of these experiments can be found at: co2 science.org. Virtually all of these species show results ranging from modest to surprisingly large increases. In the table below please find a list for some major forest and crop species grown at CO2 levels 300 ppm above current atmospheric levels.
Percentage Increase in Dry Weight with 300 ppm CO2 Increase above ambient level.
4. Two recent papers have been published also document the effects of CFE.
A. “Higher than expected CO2 fertilization inferred from leaf to global observations.” Vanessa Haverd et al, Global Change Biology 2020:26:2390-2402. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7154678/
This paper covers the increase in photosynthetic activity between 1910 and 2010 and attempts to isolate the CO2 fertilization effect for other factors. The abstract from this paper reads:
“Several lines of evidence point to an increase in the activity of the terrestrial biosphere over recent decades, impacting the global net land carbon sink (NLS) and its control on the growth of atmospheric carbon dioxide (ca). Global terrestrial gross primary production (GPP)—the rate of carbon fixation by photosynthesis—is estimated to have risen by (31 ± 5)% since 1900, but the relative contributions of different putative drivers to this increase are not well known. Here we identify the rising atmospheric CO2 concentration as the dominant driver. We reconcile leaf‐level and global atmospheric constraints on trends in modeled biospheric activity to reveal a global CO2 fertilization effect on photosynthesis of 30% since 1900, or 47% for a doubling of ca above the pre‐industrial level. Our historic value is nearly twice as high as current estimates (17 ± 4)% that do not use the full range of available constraints. Consequently, under a future low‐emission scenario, we project a land carbon sink (174 PgC, 2006–2099) that is 57 PgC larger than if a lower CO2 fertilization effect comparable with current estimates is assumed. These findings suggest a larger beneficial role of the land carbon sink in modulating future excess anthropogenic CO2 consistent with the target of the Paris Agreement to stay below 2°C warming, and underscore the importance of preserving terrestrial carbon sinks.”
From 1900 to 2010 atmospheric CO2 levels have increased from 291 to 390.1 ppm, an increase on 99.1 ppm, which equates to an increase in photosynthetic activity of .302% per increase per I ppm of CO2. With CO2 increasing at 2.37 ppm per year this converts to a 7.157% increase in photosynthesis per decade.
The final paragraph in the paper reads: By reconciling multiple global‐scale observational constraints, we identified a CO2 fertilization effect on historical global GPP that is significantly higher than current estimates. Independent regional studies using amplitude of seasonal cycle data (Northern Hemisphere extra‐tropics; Wenzel et al., 2016) and catchment water balance (tropical forests; Yang et al., 2016) have also inferred larger CO2 fertilization effects than predicted by TBM ensembles. The causes of such model‐data discrepancies are poorly known, but biases associated with the representation of nutrient limitations on GPP have been invoked as one possible cause (Wenzel et al., 2016; Yang et al., 2016). Our results, that account for nitrogen‐cycle effects on ecosystem productivity, suggest that underprediction of GPP trends and CO2 responses is associated with a failure by current TBMs to account for plant coordination of photosynthesis. This finding is important for the future role of land carbon sinks, suggesting an underestimate by current models of potential CO2 removal under low‐emission scenarios consistent with the Paris Agreement targets.”
B. “CO2 fertilization of terrestrial photosynthesis inferred from site to global scales.” Chi Chen et al. PNAS 2022 Vol. 119 No. 10 e2115627119. https://www.pnas.org/doi/10.1073/pnas.2115627119
The abstract in this paper states: “Global photosynthesis is increasing with elevated atmospheric CO2 concentrations, a response known as the CO2 fertilization effect (CFE), but the key processes of CFE are not constrained and therefore remain uncertain. Here, we quantify CFE by combining observations from a globally distributed network of eddy covariance measurements with an analytical framework based on three well-established photosynthetic optimization theories. We report a strong enhancement of photosynthesis across the observational network (9.1 gC m−2 year−2) and show that the CFE is responsible for 44% of the gross primary production (GPP) enhancement since the 2000s, with additional contributions primarily from warming (28%). Soil moisture and specific humidity are the two largest contributors to GPP interannual variation through their influences on plant hydraulics. Applying our framework to satellite observations and meteorological reanalysis data, we diagnose a global CO2-induced GPP trend of 4.4 gC m−2 year−2, which is at least one-third stronger than the median trends of 13 dynamic global vegetation models and eight satellite-derived GPP products, mainly because of their differences in the magnitude of CFE in evergreen broadleaf forests. These results highlight the critical role that CFE has played in the global carbon cycle in recent decades.”
The conclusion this paper identifies the “CO2 caused Gross Primary Production trend is comparable to the EC-inferred counterpart and translates this CO2 fertilization effect to a global increase in photosynthesis of 4.1% decade since the 2000s…”
5. For crop species, we have another empirical test that can be applied to see if CFE is real. The U. S. Department of Agriculture has records going back into the late 1800s concerning crop production, including yields per acre, for our species most critical for the survival of humanity. In the chart below the period of comparison has been pared down to compare the average of the yields from the decade of 1950 to 1959 to the most recent decade ending in the year 2022. The reason for starting this comparison in 1950 was to reduce the influence of the dramatic increase in the use of the nitrogen-based fertilizers that we began to use heavily prior to 1950, created using the Haber-Bosch process (H-B). Before the H-B process crop rotation and other methods were used to replenish the nitrogen content of farm soils, but nowhere as efficiently as the H-B process.
Yields Per Acre: Comparison of Decade of 1950s to Most Recent Decade.
The average increase in yield for all crop species of 254%, or about 36% per decade. This is an amazing increase, and very likely the reason that the Malthusians have been proven wrong. The predictions in Dr. Paul Ehrlich’s book “The Population Bomb”, published in 1968 appear to have been erroneous because he did not consider the impact of nitrogen rich fertilizers produced with the H-B process, nor the beneficial effects of the increase in CO2 in both the growth rate and the drought resistance of plant species. Had we not implemented the artificial fertilization methods while the natural CFE benefit was taking hold, Dr. Ehrlich’s dire predictions of global famine may have occurred.
We now have data from 4 different approaches to determining the CFE. They include the two model-based studies dealing with the photosynthetic Gross Primary Production estimates that generated estimates of 7.1% and 4.1% increase per decade, the 2016 NASA study, numerous laboratory, and FACE CO2 fertilization studies on numerous species under controlled conditions, and the analysis of U.S.D.A data on crop production from 1950 to the present. All show that the CFE is both real and substantial. While it is a major boon to mankind due to its effect on crop production, its impact on our forest resources is perhaps too much of a good thing and requires that we immediately take steps to control and utilize the bounty, so we do not have to continually endure smoke-filled skies and very hazardous air quality.
Conclusion: The CO2 fertilization effect is both real and substantial in both beneficial and harmful ways. The United States can do very little to reduce CO2 emissions in the short term. However, if we move promptly we can do a great deal to contain the future impact that CFE will have on our forest’s fuel load, and if done properly can also create jobs and provide needed forest products and greatly reduce the negative effects of rampant forest fires.