Model: MPI Earth System Model for paleo studies including atmosphere (ECHAM), ocean (LSG), ocean biogeochemistry (HAMOCC), and terrestrial biosphere (LPJ).
Fig. 1: Spatial variations in the annual mean solar forcing (left) and temporal variations in the global mean solar forcing (right). (high resolution):
2. Climate change and CO2
The increase in summer insolation over the mid- and high latitudes of the northern hemisphere causes a positive temperature anomaly for 128 - 123 ky B.P. (fig. 2). From 121 ky B.P. onwards, a negative anomaly occurs here. Winter temperatures north of 60oN follow the summer temperature patterns, between 122 and 113 ky B.P. a positive anomaly occurs in the tropics.
Fig. 2: Zonal mean temperature anomalies (K) for summer (JJA) and winter (DJF). Shown are 1000 year running means. (high resolution):
Fig. 3: Fig. 4. CO2 concentration for the insolation experiment and the control run. Shown are 1000 year running means. (high resolution):
Taiga-tundra feedback in the high latitudes
The feedback between temperature and forest presence enhances the temperature increase due to insolation changes. Whereas the accelerated experiment with a prescribed land surface reaches a temperature amplitude of 2.5 K (fig. 4c), the experiment with an interactive land surface shows a clear change in albedo (fig. 5b) and has a temperature amplitude of 5 K. The change in albedo is mainly caused by changes in snow albedo with forest presence, but the difference between forest and grass albedo plays a dominant role during summer.
Fig. 4: (a) forest fraction, (b) surface albedo, and (c) surface air temperature for the land surface 60o-90oN, excluding ice sheets. Shown are 0.8 ky running means. (high resolution):
Fig. 5: Summer (JJA) average winds at 850 hPa (vectors, m s-1) and integrated water content of the atmosphere (colours, kg m-2) for 126 ky B.P. (high resolution):
Total terrstrial carbon storage
During the experiment, carbon storage in the terrestrial biosphere decreases, from 200 Pg C above the control run value for 125 ky B.P. to 150 Pg C below the control run value for 116 ky B.P. (fig. 6). The emitted carbon is taken up by the ocean and the atmosphere, thereby increasing the atmospheric CO2 concentration (fig. 4).
Fig. 6: Terrestrial carbon storage anomaly for the insolation experiment and the control run. Shown are 1000 year running means. (high resolution):
Experiments using only part of the climate data from the coupled experiment as forcing were used to explain the zonal distribution of carbon (fig. 7). For the warm phase in the beginning of the model, carbon storage increases in the latitudes north of 60oN, due to an expansion of the boreal forests caused by temperature increase. It decreases between 30oN and 60oN due to increased respiration, caused by temperature increase, despite a positive effect of increased radiation in these latitudes. An increase is seen between the equator and 30oN, caused by the enhanced monsoon. The experiment with only CO2 concentration as forcing did show only minor effects, which are counteracting the global trend in carbon storage (fig. 7).
Fig. 7: Zonal anomalies of terrestrial carbon storage (Pg C per degree latitude), for the fully coupled experiment and the experiments with only temperature, hydrology, radiation, or CO2 concentration as forcing. (high resolution):
Due to insolation changes, major shifts in vegetation occur in the high latitudes and the subtropical monsoon regions. - Positive feedbacks between land surface and atmosphere enhance this orbitally induced climate change, and thereby stimulate the vegetation shifts. Carbon storage in the terrestrial biosphere decreases during the Eemian, and causes thereby an increase of the atmospheric CO2 concentration. Carbon storage in the ocean increases as well. Largest effects on carbon storage are caused by changes in temperature: positive effects due to forest expansion and increased photosynthesis, negative effects due to increased. However, the net effect of temperature is varying, and changes in the hydrology and the radiation are important to explain the increase in atmospheric CO2 concentration.
This research was funded by the German Climate Research Program (DEKLIM) of the Federal Ministry of Ecucation and Research (BMBF).
Matthias Gröger (email@example.com)
Last modified: May 18 2006.