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The State of Earth's Terrestrial Biosphere:
How is it Responding to Rising Atmospheric CO2 and Warmer Temperatures?

Continental-Scale Analyses of Terrestrial Productivity: Asia (China - Country-wide)

In examining how vegetative productivity has fared throughout all of China over the past few decades, we begin with the modeling work of Liu et al. (2004), who derived detailed estimates of the economic impact of predicted climate change on agriculture in China. This was accomplished using county-level agricultural, climate, social, economic and edaphic data for 1275 agriculture-dominated counties for the period 1985-1991, together with the outputs of three general circulation models of the atmosphere that were based on five different scenarios of anthropogenic CO2-induced climate change that yielded a mean countrywide temperature increase of 3.0°C and a mean precipitation increase of 3.9% for the 50-year period ending in AD 2050. In doing so, they determined that "all of China [italics added] would benefit [italics added] from climate change in most scenarios." In addition, they state that "the effects of CO2 fertilization should [also] be included, for some studies indicate that this may produce a significant increase in yield," an increase, it should be noted, that is extremely well established.

The great significance of these findings is readily grasped when it is realized, in Liu et al.'s words, that "China's agriculture has to feed more than one-fifth of the world's population, and, historically, China has been famine prone." As one example of this fact, they report that "as recently as the late 1950s and early 1960s a great famine claimed about thirty million lives (Ashton et al., 1984; Cambridge History of China, 1987)." Acting together, therefore, it is clear that the increases in China's agricultural production estimated to result from the direct effects of increased anthropogenic CO2 emissions plus the increases due to the changes in temperature and precipitation typically predicted to result from these emissions as well, could easily prove the deciding factor in determining whether China's population will or will not be able to adequately feed itself at the midpoint of the current century.

Fang et al. (2003) also looked at the whole of China, finding that its terrestrial NPP increased by 18.7% between 1982 and 1999. Referring to this result as "an unexpected aspect of biosphere dynamics," they say that this increase "is much greater than would be expected to result from the fertilization effect of elevated CO2, and also greater than expected from climate, based on broad geographic patterns." But it may not be, considering that from 1982 to 1999, the atmosphere's CO2 concentration rose by approximately 27.4 ppm, which increase could be expected to have increased the NPP of the conglomerate of forest types found in China by about 7.3% (see for an explanation of this calculation). But this increase is only a part of the total NPP increase one could expect, for Fang et al. note that "much of the trend in NPP appeared to reflect a change towards an earlier growing season," which was driven by the 1.1°C increase in temperature they found to have occurred in their region of study between 1982 and 1999.

Following this lead, it should be noted from the study of White et al. (1999), which utilized 88 years of data (1900-1987) that were obtained from 12 different locations within the eastern U.S. deciduous forest that stretches from Charleston, SC (32.8°N latitude) to Burlington, VT (44.5°N latitude), that a 1°C increase in mean annual air temperature increases the length of the forest's growing season by approximately five days. In addition, White et al. determined that a one-day extension in growing season length increased the mean forest NPP of the 12 sites they studied by an average of 1.6%. Hence, there could easily be an additional NPP increase due to the warming-induced growing season expansion experienced in China from 1982 to 1999 of 1.6%/day x 5 days = 8.0%, which brings the total CO2-induced plus warming-induced increase in NPP to 15.3%.

Last of all, as noted previously in our report, there is a well-documented positive synergism between increasing air temperature and CO2 concentration (Idso and Idso, 1994), such that the 1°C increase in temperature experienced in China between 1982 and 1999 could easily boost the initial CO2-induced 7.3% NPP enhancement to the 10.7% enhancement that when combined with the 8.0% enhancement caused by the warming-induced increase in growing season length would produce the 18.7% increase in NPP detected in the satellite data. And in view of these observations, the findings of Fang et al. are seen to be right in line with what would be expected to result from the increases in air temperature and atmospheric CO2 concentration that occurred between 1982 and 1999 in China: a dramatically stimulated terrestrial biosphere that is growing ever more productive with each passing year.

In a similar study, Piao et al. (2005a) say their results suggest that "terrestrial NPP in China increased at a rate of 0.015 Pg C yr-1 over the period 1982-1999, corresponding to a total increase of 18.5%, or 1.03% annually." They also found that "during the past 2 decades the amplitude of the seasonal curve of NPP has increased and the annual peak NPP has advanced," which they say "may indirectly explain the enhanced amplitude and advanced timing of the seasonal cycle of atmospheric CO2 concentration (Keeling et al., 1996)," the former of which phenomena they further suggest "was probably due to the rise in atmospheric CO2 concentration, elevated temperature, and increased atmospheric N and P deposition," while the latter phenomenon they attribute to "advanced spring onset and extended autumn growth owing to climate warming."

Citing a total of 20 scientific papers at various places in the following quote from their research report, Piao et al. conclude that "results from observed atmospheric CO2 and O2 concentrations, inventory data, remote sensing data, and carbon process models have all suggested that terrestrial vegetation NPP of the Northern Hemisphere has increased over the past 2 decades and, as a result, the northern terrestrial ecosystems have become important sinks for atmospheric CO2."

Covering the same time period of examination (1982-1999), Zhu et al. (2007) analyzed 18 years of climatic data and satellite observations of Normalized Difference Vegetation Index (NDVI) throughout all of China, calculating terrestrial vegetative net primary productivity (NPP) using the revised light-use efficiency model of Zhu et al. (2006) and Zhu et al. (2007).

In describing their results, Zhu et al. say they indicate that "climatic changes in China have eased some critical climatic constraints on plant growth." They note, for example, that "water availability most strongly limits vegetation growth over 28% of the whole country surface, whereas temperature limits growth over 43% and radiation over 29%," but they report that "from 1982 to 1999, modeled NPP increased by 1.42% per year in water-limited regions of Northwest China, 1.46% per year in temperature-limited regions of Northeast China and Tibet Plateau, and 0.99% per year in radiation-limited regions of South China and East China." Summed over the entire 18-year period, total Chinese terrestrial vegetation NPP increased by 24.2%. Last of all, they report that "interannual variations of NPP in Chinese terrestrial vegetation are positively correlated with global increases in atmospheric CO2 growth rate, indicating that NPP in Chinese terrestrial vegetation will increase with the global increases in atmospheric CO2 growth rate."

Writing as background for their work, Peng et al. (2011) report that "using satellite-derived normalized difference vegetation index (NDVI) datasets, previous studies have found that vegetation growth significantly increased in most areas of China during the period 1982-99 and that the increased vegetation growth was significantly correlated with increased temperature (e.g., Zhou et al., 2001; Piao et al., 2003)." In addition, they report that "the increased temperature boosted vegetation growth through an increase in growing season length and enhanced photosynthesis (e.g., Zhou et al., 2001; Slayback et al., 2003; Piao et al., 2006b)."

Against this backdrop, Peng et al. used NOAA/AVHRR NDVI composites at a spatial resolution of 0.083° and 15-day intervals that were produced by the Global Inventory Modeling and Mapping Studies (GIMMS) program, as described by Tucker et al. (2005), to explore vegetation activity over the whole of China for the period 1982-2010, noting that "the GIMMS NDVI datasets have been corrected to minimize the effects of volcanic eruptions, solar angle and sensor errors and shifts," as described by Zhou et al. (2001) and Slayback et al. (2003), and citing the fact that these datasets have also proved to be "one of the best products to depict the temporal change of vegetation growth," as demonstrated by Beck et al. (2011). At the national scale, the results of their analysis revealed that for the average growing season (April-October), a linear regression model predicts a significant increasing NDVI trend of 0.0007/year from 1982 to 2010, with an R2 value of 0.40 and P < 0.001 (see Figure 8). And they say that they also found increasing trends for all three sub-sets of the growing season: April-May, June-August and September-October.

Figure 8. Inter-annual variations in growing season (April-October) NDVI for China over the period 1982-2010. The linear trend in the data, as mentioned in the text, is also shown. Adapted from Peng et al. (2011).

Expanding the temporal domain of analysis back in time was Mao et al. (2009), who used a modified version of the Sheffield Dynamic Global Vegetation Model described by Woodward and Lomas (2004) to study changes in the structure, composition and carbon storage of vegetation and soils throughout all of China in response to changes in climate and atmospheric CO2 concentration that occurred between 1901 and 2000. According to the researchers who conducted this study, their modeling exercise suggested that "during the past 100 years a combination of increasing CO2 with historical temperature and precipitation variability in continental China have caused the total vegetation carbon storage to increase by 2.04 Pg C, with 2.07 Pg C gained in the vegetation biomass but 0.03 Pg C lost from the organic soil carbon matter." They also found that "the increasing CO2 concentration in the 20th century is primarily responsible for the increase of the total potential vegetation carbon." However, because the biological effects of temperature and precipitation were negative, the historical increase in the air's CO2 content was actually totally responsible for the net storage of carbon in China's terrestrial vegetation and soil over the 20th century, since without the aerial fertilization effect of CO2, there would have been a net loss of carbon that exceeded in absolute value the net gain that ultimately prevailed.

Lastly, with one eye on the past and the other looking toward the future, Mu et al. (2008) used "a well-documented daily ecosystem process model Biome-BGC (Running and Hunt, 1993; White et al., 2000; Thornton et al., 2002) to differentiate the effects of changing climate and increasing CO2 on the carbon cycle for terrestrial China for two time periods, 1961-2000 (present conditions), and future (2071-2110) conditions with projected climate change under doubled CO2." In doing so the five researchers found that "during 1961-2000 at the national scale, changes in climate reduced carbon storage in China's ecosystems, but increasing CO2 compensated for these adverse effects of climate change, resulting in an overall increase in the carbon storage of China's ecosystems," while "under the future scenario (2071-2110), with a doubling [of] CO2, China will experience higher precipitation and temperature," but once again "the concomitant doubling of CO2 will continue to counteract the negative effects of climate change on carbon uptake in the future, leading to an increase in carbon storage relative to current levels."

Given each of the findings presented above, it would appear that rather than devastating the landscape, the historical increases in atmosphere's CO2 concentration and temperature have actually fostered a significant greening of China, observed throughout the length and breadth of the country.

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