| Impact of uncertainty in values of two governing parameters on spread of climate and carbon
cycle response to anthropogenic and natural forcing in North Eurasia is studied employing
ensemble simulation with the A.M.Obukhov Institute of Atmospheric Physics, Russian
Academy of Sciences (IAP RAS) climate model of intermediate complexity. Individual
members within this ensemble were constructed by sampling two global parameters
conditioning the dynamics of terrestrial carbon cycle. The first parameter is the
Michaelis–Menten half saturation point for plant fertilisation by atmospheric CO2. The
second parameter controls soil respiration enhancement due to land use cultivation. The IAP
RAS model is forced by reconstructed anthropogenic and natural climate forcings for the
16–20th centuries. For the 21st century, anthropogenic emissions of greenhouse
gases (except CO2 emissions due to land use) and sulphate aerosols are prescribed
according to the Special Report on Emission Scenarios (SRES). Uncertainty ranges are
calculated by using the Bayesian averaging which allows to suppress impact of
non–realistic ensemble members on final statistics. It is obtained that, even for the small
number of sampled governing parameters employed in this study, carbon cycle
response is statistically indistinguishable between different SRES scenarios. In
particular, during the 21st century the model–simulated primary production in Eurasia
poleward of 50oN (North Eurasia thereafter) increases from 6.0 ± 0.1 PgC-yr
to 10.6 ± 0.5 PgC-yr and vegetation carbon stock in this region increases from
48 ± 1 PgC to 84 ± 4 PgC. Changes of soil carbon stock in North Eurasia are
statistically insignificant. Carbon uptake by North Eurasian ecosystems increases from
0.08 ± 0.05 PgC-yr in the late 20th century to 0.6 ± 0.2 PgC-yr in the middle of the 21st
century and then decreases reaching 0.4 ± 0.4 PgC-yr in the end of this century.
However, drastic difference in anthropogenic emissions between different SRES
scenarios leads to statistically significant difference in build up of carbon dioxide in
the atmosphere and in rise surface air temperature. In particular, carbon dioxide
atmospheric content under SRES scenario A2 (A1B, B1) in year 2100 reaches
773 ± 28 ppmv (662 ± 24 ppmv, 534 ± 16 ppmv). The corresponding annual
warming over the Eurasia poleward of 50oN in the 21st century amounts 8.3 ± 0.3 K
(6.7 ± 0.3 K, 5.4 ± 0.3 K). Respectively, precipitation in North Eurasia increases
from 535 ± 4 mm-yr to 787 ± 12 mm-yr (741 ± 11 mm-yr, 690 ± 9 mm-yr). |