Climate alarmists are continually warning the world about potentially-catastrophic negative consequences of CO2-induced global warming, which they contend will wreck havoc with Earth's natural and agro-ecosystems. In this summary we review how vegetative productivity has fared throughout various countries in Asia outside of China over the past few decades, when air temperatures and atmospheric CO2 concentrations have risen to levels that climate alarmists claim are unprecedented over thousands (temperature) to millions (CO2 concentration) of years. For if these two factors are really as devastating as climate alarmists claim they are, we should surely see signs of their negative impacts on terrestrial vegetation over this crucial period of time. So what's been happening in this regard?
Starting with the southern portion of Asia near Africa, we begin with the work of Grunzweig et al. (2003), who tell the tale of the Yatir forest (a 2800-hectare stand of Aleppo and other pine trees) that had been planted some 35 years earlier at the edge of the Negev Desert in Israel. An intriguing aspect of this particular forest, which they characterize as growing in poor soil of only 0.2 to 1.0 meter's depth above chalk and limestone, is that although it is located in an arid part of Asia that receives less annual precipitation than all of the other scores of FluxNet stations in the global network of micrometeorological tower sites that use eddy covariance methods to measure exchanges of CO2, water vapor and energy between terrestrial ecosystems and the atmosphere (Baldocchi et al., 2001), the forest's annual net ecosystem CO2 exchange was just as high as that of many high-latitude boreal forests and actually higher than that of most temperate forests. But how could this possibly be?
Grunzweig et al. note that the increase in atmospheric CO2 concentration that has occurred since pre-industrial times should have improved water use efficiency (WUE) in most plants by increasing the ratio of CO2 fixed to water lost via evapotranspiration. That this hypothesis is indeed correct has been demonstrated by Leavitt et al. (2003) within the context of the long-term atmospheric CO2 enrichment experiment of Idso and Kimball (2001) on sour orange trees. It has also been confirmed in nature by Feng (1999), who obtained identical (to the study of Leavitt et al.) CO2-induced WUE responses for 23 groups of naturally-occurring trees scattered across western North America over the period 1800-1985, which response, Feng concludes, "would have caused natural trees in arid environments to grow more rapidly, acting as a carbon sink for anthropogenic CO2," which is exactly what Grunzweig et al. found to be happening in the Yatir forest on the edge of the Negev Desert. In addition, the latter researchers report that "reducing water loss in arid regions improves soil moisture conditions, decreases water stress and extends water availability," which "can indirectly increase carbon sequestration by influencing plant distribution, survival and expansion into water-limited environments."
Further eastward, Singh et al. (2011) used U.S. National Oceanic and Atmospheric Administration (NOAA) satellite-derived Advanced Very High Resolution Radiometer (AVHRR) data, together with the Global Production Efficiency Model (GloPEM) developed by Prince and Goward (1995), to calculate annual NPP over all of India for the period 1981-2000. According to the five researchers, regression analysis of the 20-year NPP database showed a significant increase in the temporal trend of NPP over India (r=0.7, p<0.001), with the mean rate of increase being 10.43 gC/m2/year, which yields a mean rate-of-increase of 34.3 TgC/year for the entire country, including its arid and semi-arid regions, its forests, and its dry-land and irrigated agricultural regions.
Moving north into Russia, in an area that extends from 72°02'N to 72°40'N and from 101°15'E to 102°06' E - a total of approximately 36,000 ha that includes the Ary-Mas forest (the northernmost forest on the planet) plus larch forests on southeastern slopes descending to the Khatanga River - Kharuk et al. (2006) analyzed remote-sensing images made by Landsat satellites in 1973 and 2000. In doing so, they found that "the most significant changes were observed in the class of normal larch stands (canopy density > 0.3): their area increased by 66%," while "the areas of open and sparse forests (0.1 < canopy density < 0.3, and canopy density < 0.1) increased by 16 and 8%, respectively, whereas the background area became 19% smaller." In addition, they report that the rates of expansion of larch onto tundra "for sparse, open, and normal stands were estimated at 3, 9, and 11 m per year, respectively." However, they remark that "since sparse stands are at the forefront of advancement to the tundra, the rate for this class (approximately 3 m per year) should be regarded as the rate of larch expansion in general," and that "the above rates reflect not only the expansion of trees into the tundra, but also an increase in the density of sparse and open stands."
With respect to the cause of the changes identified, Kharuk et al. feel that they were "induced by climatic trends," and that the continuation of this process "will result in the expansion of larch to the Arctic coast," which they describe as a "phenomenon that took place in the Holocene." Thus, it would appear that the Ary Mas forest is merely reclaiming that which had previously been lost by the progressive cooling of the planet after the Holocene Climatic Optimum, which cooling culminated in the record interglacial cold of the Little Ice Age from which the Earth and its biosphere are now making an impressive comeback.
In another forest-related study from Russia, Lapenis et al. (2005) analyzed trends in forest biomass in all 28 ecoregions of the Russian territory, based on data collected from 1953 to 2002 within 3196 sample plots comprised of about 50,000 entries, which database, in their words, "contains all available archived and published data." This work revealed that over the period 1961-1998, as they describe it, "aboveground wood, roots, and green parts increased by 4%, 21%, and 33%, respectively," such that "the total carbon density of the living biomass stock of the Russian forests increased by ~9%." They also report there was a concomitant increase of ~11% in the area of Russian forests. In addition, the team of US, Austrian and Russian scientists reported that "within the range of 50-65° of latitude [the range of 90% of Russian forests], the relationship between biomass density and the area-averaged NDVI is very close to a linear function, with a slope of ~1," citing the work of Myneni et al. (2001). Therefore, as they continue, "changes in the carbon density of live biomass in Russian forests occur at about the same rate as the increase in the satellite-based estimate in the seasonally accumulated NDVI," which observation strengthens the findings of all satellite-based NDVI studies.
Acknowledging that remote sensing data suggest that tundra vegetation in North America may be responding to recent warming via enhanced photosynthetic activity (Goetz et al., 2005; Verbyla , 2008), Forbes et al. (2010) write that "at a circumpolar scale, the highest photosynthetic activity and strongest growth trends are reported in locations characterized by erect shrub tundra (Reynolds et al., 2006)," noting that "live leaf phytomass from deciduous shrubs, shown to have increased in northern Alaska during the second half of the last century (Sturm et al., 2001; Tape et al., 2006), is believed to be a key driver of the observed trends (Jia et al., 2003; Goetz et al., 2005; Verbyla, 2008)." Against this backdrop and working with Salix lanata L. (sensu latu) -- an abundant deciduous dioecious willow with nearly circumpolar geographic distribution from the northern boreal forest of Russia to the northern limits of the Low Arctic -- Forbes et al. analyzed annual ring growth for 168 stem slices of 2- to 3-cm thickness that they collected from 40 discrete individuals spread across 15 sample sites within an area of approximately 3 x 2.3 km, which was located at about 68°40'N, 58°30'E.
The three researchers say their work revealed "a clear relationship with photosynthetic activity for upland vegetation at a regional scale for the period 1981-2005, confirming a parallel 'greening' trend reported for similarly warming North American portions of the tundra biome," and they state that "the standardized growth curve suggests a significant increase in shrub willow growth over the last six decades." Additionally, while noting that "the quality of the chronology as a climate proxy is exceptional," Forbes et al. state that their findings "are in line with field and remote sensing studies that have assigned a strong shrub component to the reported greening signal since the early 1980s," adding that the growth trend agrees with the qualitative observations of nomadic reindeer herders, which suggest there have been "recent increases in willow size in the region." In fact, they say that their analysis "provides the best proxy assessment to date that deciduous shrub phytomass has increased significantly in response to an ongoing summer warming trend."
Still in Russia, but focusing in on the arid lands of Central Asia, Lioubimtseva et al. (2005) describe a number of findings pertinent to the subject at hand that are generally not available to the international scientific community, due to their publication in the Russian language. According to the four-member team of Russian and American scientists, "there has been a general warming trend in Central Asian republics on the order of 1-2°C since the beginning of the 20th century," but they add that it is expressed most strongly in winter and that "the amplitude of this trend seems to be comparable with Holocene climate variability," suggesting that it is nothing unusual nor does it require an anthropogenic explanation. Citing the IPCC (2001), on the other hand, they report that precipitation has remained basically unchanged throughout the 20th century, stating that "there were no discernible trends in annual precipitation during 1900-95 for the region as a whole, nor in most parts of this region."
In the face of unchanging precipitation and significant warming, it might be expected that the aridity of Central Asia would have increased significantly in recent years, especially throughout the 1990s, when climate alarmists claim the world saw its most oppressive heat of both the 20th century and the past two millennia. However, Lioubimtseva et al. report that "analyses of the NOAA AVHRR temporal series since the 1980s showed a decrease in aridity from 1991-2000 compared to 1982-1990 in the northern part of the region and a southward shift of the northern boundary of the desert zone in Central Asia," citing the work of Zolotokrylin (2002). So what's the explanation for this unexpected development? Lioubimtseva et al. suggest it could well have been the historical rise in the air's CO2 content.
The scientists begin their elucidation of this hypothesis by noting that "an increased atmospheric CO2 concentration has direct and relatively immediate effects on two important physiological processes in plants: it increases the photosynthetic rate, but decreases stomatal opening and therefore the rate at which plants lose water," so that "the combination of these two factors, increased photosynthesis and decreased water loss, implies a significant increase of water [use] efficiency (the ratio of carbon gain per unit water loss) and ... a reduction in the sensitivity to drought stress in desert vegetation as a result of elevated atmospheric CO2," citing the work of Smith et al. (2000) in support of this concept. As a result, they note that these effects could "increase productivity and biomass of natural desert vegetation," which would, of course, make the land appear (and effectively be) less arid.
Buttressing this reasoning with experimental evidence obtained from the region itself, Lioubimtseva et al. report that "CO2-enrichment experiments (both chamber and free-air) conducted in the Kara Kum (Voznesensky, 1997) and Kyzyl Kum (Voznesensky, 1997; Zelensky, 1977) deserts showed a 2-4 times increase in the photosynthetic rate under the saturating CO2 concentrations," and that "three Kara Kum species (Eminium lehmanii, Rhemum turkestanuikum and Ephedra stobilacea) responded with a six-fold increase in photosynthetic rate (Nechaeva, 1984)." In addition, they report that "the CO2 fertilization effects included not only higher vegetation but also microphytic communities including mosses, lichens, fungi, algae, and cyanobacteria," which communities, in their words, "form biogenic crusts on the soil surface varying from a few millimeters to several centimeters in thickness and play a significant role in the desert ecosystems controlling such processes as water retention and carbon and nitrogen fixation in soils."
In examining a larger area of Asia, Zhou et al. (2001) analyzed satellite-derived Normalized Difference Vegetation Index (NDVI) data from July 1981 to December 1999, between 40 and 70° N latitude. In doing so they found a persistent increase in growing season vegetative productivity in excess of 12% over this broad contiguous swath of Asia stretching from Europe through Siberia to the Aldan plateau, where almost 58% of the land is forested. And in a companion study, Bogaert et al. (2002) determined that this productivity increase occurred at a time when this vast Asian region showed an overall warming trend "with negligible occurrence of cooling."
In another study encompassing all of Asia, Ichii et al. (2005) simulated and analyzed carbon fluxes over the period 1982-1999 "using the Biome-BGC prognostic carbon cycle model driven by National Centers for Environmental Prediction reanalysis daily climate data," after which they "calculated trends in gross primary productivity (GPP) and net primary productivity (NPP)." In doing so, solar radiation variability was found to be the primary factor responsible for interannual variations in GPP, followed by temperature and precipitation variability. In terms of GPP trends, the authors report that "recent changes in atmospheric CO2 and climate promoted terrestrial GPP increases with a significant linear trend in all three tropical regions." More specifically, they report the rate of GPP increase for Asia to have been about 0.3 PgC year-1 per decade. As for the major cause of the increased growth, Ichii et al. favored carbon dioxide, reporting that "CO2 fertilization effects strongly increased recent NPP trends in regional totals."
In one final study designed to examine a large portion of the Northern Hemisphere (East Asia, including China, Japan, Korea and Mongolia), the eleven researchers of Piao et al. (2011) used three process-based ecosystem models -- the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM) described by Sitch et al. (2003), the ORganizing Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) model described by Krinner et al. (2005), and the Sheffield model described by Woodward and Lomas (2004) -- to investigate East Asia's net primary productivity (NPP) response to the climatic change and rising atmospheric CO2 concentration of the past century, which they did by running each of the three models from 1901 to 2002, using observed values of monthly climatology and annual global atmospheric CO2 concentrations.
Results indicated that between 1901 and 2002, modeled NPP "significantly increased by 5.5-8.5 Tg C per year (15-20% growth)," and the authors say that this increase in NPP "caused an increased cumulated terrestrial carbon storage of about 5-11 Pg C," about 50-70% of which "is located in vegetation biomass." And they add that "40-60% of the accumulated carbon uptake of the 20th century is credited to the period of 1980-2002," which latter interval, according to climate alarmists, was the warmest two-decade-interval of that century-long period. Thus, it is readily evident that as the air's CO2 concentration and temperature rose to their highest values of the past century -- or millennium (purportedly) -- they only served to enhance the terrestrial vegetative productivity of East Asia.
In light of the many observations described above, plant productivity across Asia is not fairing anywhere near as badly as climate models suggest it should. In fact, rising atmospheric CO2 concentrations and temperatures have actually been a great blessing for this portion of Earth's biosphere, especially for its water-stressed deserts and arid regions that appear to be thriving.
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