ALBERT

Description: One of the controlling factors of net ecosystem exchange that is highly sensitive to changes in climate is fire activity. A model study to describe these controlling factors is validated using multiple proxies to understand fire activity on a continental scale. We present results form a transient integration with the fully coupled Earth System Model (ESM) ECHAM5/MPI-OM1/JSBACH of the Max-Planck-Institute for Meteorology covering the last 6000 years. The model comprises dynamical components for atmosphere, ocean, and biosphere including an approach to simulate fire dynamics. The simulation is analyzed with a focus on land carbon and fire dynamics. A range of observational products are used to constrain the models ability to simulate fire distribution and changes in fire regimes over the course of the last 6000 years. On the global land scale, the model run shows a small decrease of the global mean temperature and a decline in annual precipitation. For the land carbon storage there is a significant decrease. Due to the changes in the orbital parameters with time, regionally the effect on precipitation and temperature is stronger, which results in a shift of the tropical rain belt combined with changes in vegetation. Striking is for example a reduction in the vegetation cover in central East Asia over the last 6000 years with a subsequent decreasing trend in land carbon. Related to climatic changes the fire activity is changing as well. We simulate a reduction of 5% in annual global burned area within the last 6000 years. Regionally, the simulation points out trends in the fire activity corresponding to the changes in vegetation shifts: e.g. there is an increase of 15% in central East Asia and a reduction of about 20% in tropical West Africa in burned area mainly a result of the redistribution of fuel abundance. Simulated changes in fire activity are compared to fire activity records reported in the global charcoal database (Power et al., 2008) and levoglucosan values out of ice cores. As the charcoal data and levoglucosan data show opposite trends, we demonstrate the sensitivity of the modeled and observed trend to the chosen grid boxes of the model domain. Whereas the charcoal sites are biased to North-America and show an opposite trend than the ice-core data from Kilimanjaro, the investigation of levoglucosan data out of remote ice cores (EPICA or NEEM) are additional used to get a global view on the trend in fire activity.

Description: One of the controlling factors of NEE that is highly sensitive to changes in climate is fire activity. Here we present results form a transient integration with the fully coupled MPI- Earth System Model (MPI-ESM) of the Max-Planck-Institute for Meteorology covering the last 6000 years. The model comprises dynamical components for atmosphere, ocean, and biosphere including an approach to simulate fire dynamics. The simulation is analyzed with a focus on land carbon and fire dynamics. A range of observational products is used to constrain the models ability to simulate fire distribution and changes in fire regimes over the course of the last 6000 years. On the global land scale, the model run shows a small decrease of the global mean temperature and a decline in annual precipitation. For the land carbon storage there is a significant decrease. On the regional scale, the effect on temperature and precipitation due to changes in the orbital parameters with time is much stronger. A shift of the tropical rain belt combined with changes in vegetation is simulated. Striking is for example a reduction in the vegetation cover in central East Asia over the last 6000 years with a subsequent decreasing trend in land carbon. Related to these climatic changes the fire activity is changing as well. We simulate a reduction of 5% in annual global burned area within the last 6000 years. Regionally, the simulation points out trends in the fire activity corresponding to the changes in vegetation shifts: e.g. there is an increase of ~ +15% in central East Asia and a reduction of about 20% in tropical West Africa in burned area mainly a result of the redistribution of fuel abundance. Simulated changes in fire activity are compared to fire activity records reported in the global charcoal database (Power et al., 2008) and levoglucosan values out of ice cores. A special focus of the analysis will lie on an assessment of correlation between fire activity and large-scale climate indexes (e.g. ENSO, NAO). Focusing on the last 100 yrs the modeled variability is checked against a reconstruction of a yearly global fire history (Mouillot et al., 2005). This comparison points out regions with a significant influence of anthropogenic disturbed fires, which are not represented in the ESM, but play a major role in the last few decades.

Description: Two model studies based on the Earth System Model (ESM) ECHAM5/MPI-OM1/JSBACH of the Max-Planck-Institute for Meteorology will be presented showing the vegetation response to orbital forcing. A 6000 years transient simulation of the Holocene and a time-slice model experiment for the Eemian are investigated. The model comprises dynamical components for atmosphere, ocean, and biosphere including an approach to simulate vegetation disturbance by fire dynamics and wind. The model results show reasonable patterns for temperature and precipitation changes (compared to present day climate). For the Holocene the annual mean global temperature is slightly decreasing (approximately 0.1 K), but the regional and seasonal changes are much larger. For example, Arctic temperatures are in winter up to 5 K higher (for the Holocene) and differences of up to -3 K are simulated for tropical west Africa, but only minor changes in the precipitation patterns related to changes within the tropical rain belt are simulated by MPI-ESM. At the same time shifts in the fractional vegetation cover are computed. Striking is for example the shift of the boreal tree line and the greening of West Africa during the early Holocene. The patterns derived from the Eemian snap-shot simulation feature similar, but more pronounced changes. All these vegetation changes are also reflected in the carbon storage on land. The amount of carbon stored in biomass decreases during the transient 6000 years from the Holocene to present day, as the fraction of forest covered area decreases with time and is replaced by grass and shrubs.

Description: One of the controlling factors of net ecosystem exchange that is highly sensitive to changes in climate is fire activity. A model study to describe these controlling factors is validated using multiple proxies to understand fire activity on a continental scale. We present results form a transient integration with the fully coupled Earth System Model (ESM) ECHAM5/MPI-OM1/JSBACH of the Max-Planck-Institute for Meteorology covering the last 6000 years. The model comprises dynamical components for atmosphere, ocean, and biosphere including an approach to simulate fire dynamics. The simulation is analyzed with a focus on land carbon and fire dynamics. A range of observational products are used to constrain the models ability to simulate fire distribution and changes in fire regimes over the course of the last 6000 years. On the global land scale, the model run shows a small decrease of the global mean temperature and a decline in annual precipitation. For the land carbon storage there is a significant decrease. Due to the changes in the orbital parameters with time, regionally the effect on precipitation and temperature is stronger, which results in a shift of the tropical rain belt combined with changes in vegetation. Striking is for example a reduction in the vegetation cover in central East Asia over the last 6000 years with a subsequent decreasing trend in land carbon. Related to climatic changes the fire activity is changing as well. We simulate a reduction of 5% in annual global burned area within the last 6000 years. Regionally, the simulation points out trends in the fire activity corresponding to the changes in vegetation shifts: e.g. there is an increase of 15% in central East Asia and a reduction of about 20% in tropical West Africa in burned area mainly a result of the redistribution of fuel abundance. Simulated changes in fire activity are compared to fire activity records reported in the global charcoal database (Power et al., 2008) and levoglucosan values out of ice cores. As the charcoal data and levoglucosan data show opposite trends, we demonstrate the sensitivity of the modeled and observed trend to the chosen grid boxes of the model domain. Whereas the charcoal sites are biased to North-America and show an opposite trend than the ice-core data from Kilimanjaro, the investigation of levoglucosan data out of remote ice cores (EPICA or NEEM) are additional used to get a global view on the trend in fire activity.

Description: The large variety of atmospheric circulation systems affecting the eastern Asian climate is reflected by the complex Asian vegetation distribution. Particularly in the transition zones of these circulation systems, vegetation is supposed to be very sensitive to climate change. Since proxy records are scarce, hitherto a mechanistic understanding of the past spatio-temporal climate–vegetation relationship is lacking. To assess the Holocene vegetation change and to obtain an ensemble of potential mid-Holocene biome distributions for eastern Asia, we forced the diagnostic biome model BIOME4 with climate anomalies of different transient Holocene climate simulations performed in coupled atmosphere–ocean(–vegetation) models. The simulated biome changes are compared with pollen-based biome records for different key regions. In all simulations, substantial biome shifts during the last 6000 years are confined to the high northern latitudes and the monsoon–westerly wind transition zone, but the temporal evolution and amplitude of change strongly depend on the climate forcing. Large parts of the southern tundra are replaced by taiga during the mid-Holocene due to a warmer growing season and the boreal treeline in northern Asia is shifted northward by approx. 4° in the ensemble mean, ranging from 1.5 to 6° in the individual simulations, respectively. This simulated treeline shift is in agreement with pollen-based reconstructions from northern Siberia. The desert fraction in the transition zone is reduced by 21 % during the mid-Holocene compared to pre-industrial due to enhanced precipitation. The desert–steppe margin is shifted westward by 5° (1–9° in the individual simulations). The forest biomes are expanded north-westward by 2°, ranging from 0 to 4° in the single simulations. These results corroborate pollen-based reconstructions indicating an extended forest area in north-central China during the mid-Holocene. According to the model, the forest-to-non-forest and steppe-to-desert changes in the climate transition zones are spatially not uniform and not linear since the mid-Holocene.