The Earth as an extrasolar planet: the vegetation spectral signature today and during the last Quaternary climatic extrema

The so-called vegetation red-edge (VRE), a sharp increase in the reflectance around 700 nm, is a characteristic of vegetation spectra, and can therefore be used as a biomarker if it call be detected in all unresolved extrasolar Earth-like planet integrated reflectance spectrum, Here, we investigate the potential for the detection of vegetation spectra during the last Quaternary climatic extrema, the Last Glacial Maximum (LGM) and the Holocene optimum, for which past climatic simulations have been made. By testing the VRE detectability during these extrema, when Earth's climate and biomes maps were different from today, we are able to test the vegetation detectability on a terrestrial planet different from our modern Earth. Data from the Biome3.5 model have been associated to visible Global Ozone Monitoring Experiment (GOME) spectra for each biome and cloud cover to derive Earth's integrated spectra for given Earth phases and observer positions. The VRE is then measured. Results show that the vegetation remains detectable during the last climatic extrema. Compared to the Current Earth, the Holocene Optimum, with a greener Sahara, slightly increases the mean VRE on one hand, while on the other hand, the large ice cap over the northern hemisphere during the LGM decreases vegetation delectability. We finally discuss the detectability of the VRE in the context of recently proposed space missions.