Abstract:
When the climate is reconstructed from paleoevidence,
it shows that the Last Glacial Maximum (LGM, ca.
21 000 yr ago) is cold and dry compared to the present-day.
Reconstruction also shows that compared to today, the vegetation
of the LGM is less active and the distribution of vegetation
was drastically different, due to cold temperature,
dryness, and a lower level of atmospheric CO2 concentration
(185 ppm compared to a preindustrial level of 285 ppm).
In the present paper, we investigate the influence of vegetation
change on the climate of the LGM by using a coupled
atmosphere-ocean-vegetation general circulation model
(AOVGCM, the MIROC-LPJ). The MIROC-LPJ is different
from earlier studies in the introduction of a bias correction
method in individual running GCM experiments. We examined
four GCM experiments (LGM and preindustrial, with
and without vegetation feedback) and quantified the strength
of the vegetation feedback during the LGM. The result shows
that global-averaged cooling during the LGM is amplified
by +13.5% due to the introduction of vegetation feedback.
This is mainly caused by the increase of land surface albedo
due to the expansion of tundra in northern high latitudes
and the desertification in northern middle latitudes around
30 N to 60 N. We also investigated how this change in climate
affected the total terrestrial carbon storage by using offline
Lund-Potsdam-Jena dynamic global vegetation model
(LPJ-DGVM). Our result shows that the total terrestrial carbon
storage was reduced by 597 PgC during the LGM, which
corresponds to the emission of 282 ppm atmospheric CO2. In
the LGM experiments, the global carbon distribution is generally
the same whether the vegetation feedback to the atmosphere
is included or not. However, the inclusion of vegetation
feedback causes substantial terrestrial carbon storage
change, especially in explaining the lowering of atmospheric
CO2 during the LGM.
