Volume 13, Number 20: 19 May 2010
In the introduction to their report on the response of High Arctic tundra vegetation to the warming experienced in that part of the world over the past quarter-century, Hudson and Henry (2009) note that the Arctic has warmed by about 1.6°C over the past four decades, citing the analysis of McBean et al. (2005); and they state that this temperature increase has "led the Arctic Climate Impact Assessment (ACIA) and Intergovernmental Panel on Climate Change (IPCC) to predict that tundra ecosystems will be particularly threatened by climate change [i.e., warming] over the next century." Thus, their work represents what could be called a "biospheric referendum" on the validity of the ACIA's and IPCC's predictions, as the plants of the High Arctic tundra have been casting their votes on the issue - year after year - by either doing or not doing what the ACIA and the IPPC have predicted, which is growing less vigorously and less abundantly.
So what did the two researchers do?
At an 8-km2 coastal lowland adjacent to Alexandra Fiord on the east-central coast of Ellesmere Island, Nunavut, Canada, they measured biomass and composition changes in a heath community dominated by several vascular plants and bryophytes. This they did over a period of 13 years (1995-2007), using a point-intercept method in permanent plots, and over a period of 27 years (1981-2008) using a biomass harvest comparison.
And what did they find?
"Results from both methods," in the words of the Canadian scientists, "indicate that the community became more productive over time," that "bryophyte and evergreen shrub abundances increased," while "deciduous shrub, forb, graminoid, and lichen cover did not change," so that "species diversity also remained unchanged [italics added]," all of which changes - and non-changes - are a far cry from the "particularly threatening" view of the ACIA and IPCC.
In further support of their "contrary" findings, Hudson and Henry additionally report that "satellite-based remote sensing models, such as green trends derived from the normalized difference vegetation index (NDVI; e.g., Myneni et al., 1997; Zhou et al., 2001; Stow et al., 2004; Verbyla, 2008), and global vegetation and ecosystem process simulations of the terrestrial carbon cycle (e.g., Kimball et al., 2006; Zhang et al., 2008), indicate increasing trends in vegetation photosynthetic activity and net primary production in the Arctic over the past several decades."
So what drove this welcome transformation of the tundra?
Hudson and Henry say "it is likely that warming directly increased plant growth and reproduction and indirectly increased resource supply," while noting that "increased temperatures also lengthened the growing season, increased soil temperature, deepened the active [soil] layer, and consequently may have influenced nutrient uptake in the plant community."
All in all, therefore, it would appear that the "threatening" future predicted for Arctic tundra by the ACIA and IPPC to accompany warming in that part of the world is more a work of fiction than a work of science.
Sherwood, Keith and Craig Idso
References
Hudson, J.M.G. and Henry, G.H.R. 2009. Increased plant biomass in a High Arctic heath community from 1981 to 2008. Ecology 90: 2657-2663.
Kimball, J.S., Zhao, M., Mcguire, A.D., Heinsch, F.A., Clein, J., Calef, M.P., Jolly, W.M., Kang, S., Euskirchen, S.E., McDonald, K.C. and Running, S.W. 2006. Recent climate-driven increases in vegetation productivity for the Western Arctic: evidence for an acceleration of the northern terrestrial carbon cycle. Earth Interactions 11: 1-23.
McBean, G., Alekseev, G., Chen, D., Forland, E., Fyfe, J., Groisman, P.Y., King, R., Melling, H., Vose, R. and Whitfield, P.H. 2005. Arctic climate: past and present. In: Arctic Climate Impact Assessment: Scientific Report. Cambridge University Press, Cambridge, UK, p. 21-60.
Myneni, R.B., Keeling, C.D., Tucker, C.J., Asrar, G. and Nemani, R.R. 1997. Increased plant growth in the northern high latitudes from 1981 to 1991. Nature 386: 698-702.
Stow, D.A. et al. 2004. Remote sensing of vegetation and land-cover change in Arctic tundra ecosystems. Remote Sensing of Environment 89: 281-308.
Verbyla, D. 2008. The greening and browning of Alaska based on 1982-2003 satellite data. Global Ecology and Biogeography 17: 547-555.
Zhang, K., Kimball, J.S., Hogg, E.H., Zhao, M.S., Oechel, W.C., Cassano, J.J. and Running, S.W. 2008. Satellite-based model detection of recent climate-driven changes in northern high-latitude vegetation productivity. Journal of Geophysical Research-Biogeosciences 113: G03033.
Zhou, L.M., Tucker, C.J., Kaufmann, R.K., Slayback, D., Shabanov, N.V. and Myneni, R.B. 2001. Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981 to 1999. Journal of Geophysical Research 106: 20,069-20,083.