Global impacts of the 1980s regime shift

Despite evidence from a number of Earth systems that abrupt temporal changes known as regime shifts are important, their nature, scale and mechanisms remain poorly documented and understood. Applying principal component analysis, change-point analysis and a sequential t-test analysis of regime shifts to 72 time series, we confirm that the 1980s regime shift represented a major change in the Earth's biophysical systems from the upper atmosphere to the depths of the ocean and from the Arctic to the Antarctic, and occurred at slightly different times around the world. Using historical climate model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) and statistical modelling of historical temperatures, we then demonstrate that this event was triggered by rapid global warming from anthropogenic plus natural forcing, the latter associated with the recovery from the El Chichón volcanic eruption. The shift in temperature that occurred at this time is hypothesized as the main forcing for a cascade of abrupt environmental changes. Within the context of the last century or more, the 1980s event was unique in terms of its global scope and scale; our observed consequences imply that if unavoidable natural events such as major volcanic eruptions interact with anthropogenic warming unforeseen multiplier effects may occur

Stochastic modeling of radiation regime in discontinuous vegetation canopies

International audienc

Investigation of a model inversion technique to estimate canopy biophysical variables from spectral and directional reflectance data

International audienc

Comment On "drought-induced Reduction In Global Terrestrial Net Primary Production From 2000 Through 2009"

Zhao and Running (Reports, 20 August 2010, p. 940) reported a reduction in global terrestrial net primary production (NPP) from 2000 through 2009. We argue that the small trends, regional patterns, and interannual variations that they describe are artifacts of their NPP model. Satellite observations of vegetation activity show no statistically significant changes in more than 85% of the vegetated lands south of 70° N during the same 2000 to 2009 period.3336046Zhao, M.S., Running, S.W., (2010) Science, 329, p. 940Nunes, E.L., (2008), www.biosfera.dea.ufv.br/phtm/teses/pdf/DS_EdsonNunes.pdf, thesis, Federal University of Vicosa available atCosta, M.H., Nunes, E.L., Senna, M.C.A., Imbuzeiro, H.M.A., (2009) Brazilian J. Meteorol., 24, p. 179Turner, D.P., (2006) Remote Sens. Environ., 102, p. 282Vieira, S., (2004) Oecologia, 140, p. 468Aragão, L.E.O.C., (2009) Biogeosciences Discuss., 6, p. 2441Zhao, M.S., Heinsch, F.A., Nemani, R.R., Running, S.W., (2005) Remote Sens. Environ., 95, p. 164Samanta, A., (2010) Geophys. Res. Lett., 37, pp. L05401Phillips, O.L., (2009) Science, 323, p. 1344Llovel, W., Becker, M., Cazenave, A., Cretaux, J.F., Ramillien, G., (2010) C. R. Geosci., 342, p. 179Myneni, R.B., Hall, F.G., Sellers, P.J., Marshak, A.L., (1995) IEEE Trans. Geosci. Rem. Sens., 33, p. 481Tucker, C.J., Fung, I.Y., Keeling, C.D., Gammon, R.H., (1986) Nature, 319, p. 195Myneni, R.B., Keeling, C.D., Tucker, C.J., Asrar, G., Nemani, R.R., (1997) Nature, 386, p. 698Nemani, R.R., (2003) Science, 300, p. 1560Ciais, P., (2005) Nature, 437, p. 52

Three-dimensional mapping of light transmittance and foliage distribution using lidar

The horizontal and vertical distributions of light transmittance were evaluated as a function of foliage distribution using lidar (light detection and ranging) observations for a sugar maple (Acer saccharum) stand in the Turkey Lakes Watershed. Along the vertical profile of vegetation, horizontal slices of probability of light transmittance were derived from an Optech ALTM 1225 instrument's return pulses (two discrete, 15-cm diameter returns) using indicator kriging. These predictions were compared with (i) below canopy (1-cm spatial resolution) transect measurements of the fraction of photosynthetically active radiation (FPAR) and (ii) measurements of tree height. A first-order trend was initially removed from the lidar returns. The vertical distribution of vegetation height was then sliced into nine percentiles and indicator variograms were fitted to them. Variogram parameters were found to vary as a function of foliage height above ground. In this paper, we show that the relationship between ground measurements of FPAR and kriged estimates of vegetation cover becomes stronger and tighter at coarser spatial resolutions. Three-dimensional maps of foliage distribution were computed as stacks of the percentile probability surfaces. These probability surfaces showed correspondence with individual tree-based observations and provided a much more detailed characterization of quasi-continuous foliage distribution. These results suggest that discrete-return lidar provides a promising technology to capture variations of foliage characteristics in forests to support the development of functional linkages between biophysical and ecological studies