|Review for “Biome changes in Asia since the mid-Holocene – an analysis of different transient Earth system model simulations”|
This manuscript describes the vegetation changes in the Monsoon-Westerly (forest-steppe-desert) transition zone and high northern latitude (taiga-tundra) transition zone in Asia since the mid-Holocene using several different transient simulations and a slightly modified BIOME4 vegetation model. To validate the simulated vegetation changes in the two areas, the authors also try to implement model-data comparison.
The analyses applied to this study are not new (in particular vegetation changes between 0k and 6ka), and thus there are still some problems that should be resolved for data-model comparison with regard to paleo-vegetation changes. Because the paleoclimate and paleovegetation community already know the arguments about data-model comparison in this manuscript, the authors might have to propose a new approach. Anyway, the authors did a great job in analyzing so much data and in producing very nice figures.
The topic is really interesting, but I had several problems here.
L95-98. Although I understand the three research aims in this study, I am not sure that the authors use reasonable approaches for achieving the goals. Data-model comparison approach in this study is not new, and thus we might not improve our knowledge about uncertainties of simulated vegetation changes?
It seems that the authors mainly use multi-model ensemble approach for the transient vegetation change analyses (Figure 6 - 11), but the authors show the results from the several simulations including the ensemble mean for mid-Holocene vegetation changes (Figure 3 and 5). If possible, you show the results from the ensemble model mean for general trends in main text and each model result in the Appendix because you do not discuss the climate and vegetation changes and their causes among the models thoroughly.
L105. “absolute minimum temperature” for “annual minimum temperature”?
L112-113. The authors need many PFTs and thus biomes for describing the diverse taxa found in Asia. On the other hand, the authors grouped the BIOME4 28 biomes into 12 mega-biomes for the analysis. It sounds that your argument and your approach is inconsistent here. Moreover, the authors discuss the vegetation margin analysis using only “desert”, “steppe”, “forest” and “tundra” later. If you use these limited biomes, you can use other process-based vegetation models such as LPJ-GUESS. Your target areas for the vegetation changes in Asia are limited (only transition zones), and the target biomes are also limited.
L120-123. Although I checked the Table 1 for bioclimatic limits for the model, I do not understand how the authors used the altitude information from ETOPO5. If possible, you should describe how to use the information? Moreover, do we need to change the surface air pressure for running BIOME4 at high altitude grid points?
L134-135. What is 0k and 6k here? You need to define these words before this sentence or here. Otherwise, you can delete the texts after “(Fig. A2)”.
L138-141. In the previous studies with BIOME4 for simulating paleovegetation, they used CLIMATE2.2 climate data. Why do use CRU TS3.10, not CLIMATE2.2 in this study? If you need higher-resolution of modern climatology as reference data, why do not you use CRU CL2.0 (New et al., 2002)? The data includes the necessary climate variables for BIOME4 and elevation information.
L 144-145. To simplify/ignore the impact atmospheric CO2 concentration on vegetation, the authors might use 280 ppm for 0k simulation. If so, you can delete this sentence and the related figure because you do not need to discuss the atmospheric CO2 effect to vegetation in this study.
L 151-152. I do not understand what “the main biome distribution” is. Do you mean that the model sufficiently simulates the large-scale (or continental scale) biome distribution in Asia.
L156-168. These sentences describe results and your arguments. Thus you should not put these sentences here.
L179. Remove “of the year”? This absolute minimum temperature is based on an annual data or climatology (e.g. 1960-2000)?
L225. “CRU TS3.10” for “CRUTS3.10”
L229. “(Harrison et al., 1998)” for “(Harrison, 1998)”
L230-231.According to Harrison et al. (1998), the anomaly approach has two advantages; 1) reducing the effects of systematic model biases and 2) capturing some of the locale-scale spatial pattern because of terrestrial geography. The authors already describe these advantages in this part, and I understand them. But I do not understand the sentence “We are however aware of… meso- and large scale” Do you need this sentence and the next sentence in this section? I mean, you can describe the methodology here.
L243-244. For comparison, the authors choose one high quality pollen record at each key transition area. But the model output is based on 500-year interval data. Thus, if possible, the authors should use relatively low temporal resolution pollen data. I think one data at each zone is very small number, they might not validate your results well.
L260-272. As mentioned earlier, the authors can describe results from only ensemble model mean because “the vegetation change is small and similar for all models”. You can move the other models output into the Appendix. Moreover, You can combine two figures (Figure 2 and Figure 3) into one because you do not need to show “CRU TS3.1 0k” twice.
L282. Delete “East”? Your target area is the entire Asia, not East Asia right?
L283-289. This paragraph (except the first sentence) describes a method for a sensitivity study, not results. Thus, you should move this content to the “Methods” section.
L288. “CRU TS3.10” for “CRUTS3.10”
L288. “absolute minimum temperature” for “absolute annual minimum temperature”
L290-298. This result is really interesting for me, and it is easy to know the causes of vegetation changes over each transition during the mid-Holocene. Do you make the map from ENSMEAN for Fig.5? Moreover, this information is directly concerned with vegetation changes between 0k and 6k, and thus you can put this information into 3.1.
L291. Your sensitivity experiment cannot deduce “the prolongation of the warmer season” because these climate variables does not have temporal concept probably. We might deduce warmer during the growing season in the northern latitudes (from the table 1: tundra vs. boreal forest and Fig. 5).
L301. “46%” in the text, but “45%” in the table.
L313-. Although “geographical distances are given in degrees of latitude or longitude in the following, for simplification, only ° is used”, the authors use “100 km” here. Should you use the unit ° here? The same issues are on L507, L520, and L521.
L375. Is it possible to compare between affinity scores (reconstruction) and fractional area cover (%) of biomes. I hope you understand the concept of biomization.
Discussin. The authors focus on the two point of discussion. I think you have several arguments in the methods and results sections. Moreover, to support your argument/discussion, you should use other references effectively.
L398. I do not know whether your approach is correct or not. At least, using several transient climate model output, you run the BIOME4, and then you get the simulated biome over the last 6000 years. But, I do not think this small number of output does not show a range of possible biome changes in Asia.
L398-435. I do not understand your discussion (4.1) well. Does your discussion directly have a concoction with your result (which ones)?
L442-445. I understand your argument here, but you need a limited number of biomes in this study. Moreover, Basil Davis (Université de Lausanne) has a funded project, HORNET (Holocene pollen based climate reconstruction for the Northern Hemisphere extra-tropics) and he makes biomised biome data over the Holocene, so far as I know. Thus, your argument will be solved soon, and you might use his database probably.
Table 4, 5, and 6. Do you need to show the all model results here? If you describe the general/common/robust pattern, you can show only 0k and 6k (minimum, ENMEAN, maximum) values without model names.
Figure captions. “CRU TS3.10” for “CRUTS3.10” and “BIOME4” for “Biome4”
Figure 11. Please put (a), (b), and unit of model output on the figure.