Continental climate reconstructions for mid-Holocene and Last Glacial Maximum

Pollen-based continental climate reconstructions for the mid-Holocene and the Last Glacial Maximum

Main reference: Pollen-based continental climate reconstructions at 6 and 21 ka: a global synthesis Bartlein, P. J., S. P. Harrison, S. Brewer, S. Connor, B. A. S. Davis, K. Gajewski, J. Guiot, T. I. Harrison-Prentice, A. Henderson, O. Peyron, I. C. Prentice, M. Scholze, H. Seppä, B. Shuman, S. Sugita, R. S. Thompson, A. E. Viau, J. Williams, H. Wu, 2011. , Climate Dynamics, 37, 775-802. DOI 10.1007/s00382-010-0904-1

These data are a synthesis of existing and available quantitative reconstructions of six bioclimatic variables based on fossil pollen for the mid-Holocene and the Last Glacial Maximum. The reconstructions are expressed as anomalies and associated uncertainties on a 2×2-degree grid. The data were gridded by simple averaging of the reconstructions in individual grid cells, and the uncertainties were obtained by pooling the prediction error estimates of individual reconstructions. No attempt was made to interpolate or fill in empty grid points.

Click on the pictures below to download the HIGH resolution pdf
mid- Holocene	Last Glacial Maximum

Please see the original paper for exact definitions of the time slices used here, the specific approaches used in synthesizing data from multiple sources, and recommendations for the use of the data in data-model comparisons.

The gridded reconstructions are available in two formats (binary and text), with one file per variable and per period:

binary NetCDF files: variable_delta_period_ALL_grid_2x2.nc

Note: in the NetCDF files, the grid cells where there are no data sites are masked

text (.csv) files: variable_delta_period_ALL_grid_2x2.csv

Note: the text files only list the grid cells that contain data sites

Where the variables are...

mat: Mean Annual Temperature (°C)

map: Mean Annual Precipitation (mm)

mtco: Mean Temperature of the Coldest Month (°C)

mtwa: Mean Temperature of the Warmest Month (°C)

gdd5: Growing Degree Days above 5°C (°C days)

alpha: moisture index, defined as Mean Annual Actual Evaporation/Mean Annual Potential Evaporation (no units)

... and the periods are:

06ka: mid Holocene

21ka: Last Glacial Maximum

Each file contains the following variables:

Variable	Column (.csv file)	Detail
lat	1	Latitude of grid-cell center (degrees North)
lon	2	Longitude of grid-cell center (degrees East)
variable_anm_mean	3	Grid-cell mean of reconstructed anomalies
variable_se_mean	4	Grid-cell mean of standard errors of estimates
variable_tstat	5	t-statistic = mean anomaly / mean standard error of estimate = variable_anm_mean / variable_se_mean
variable_sig	6	Significance of the t-statistic: -1, 0, 1 = sign(variable_tstat) if abs(variable_tstat) > 2 = 0 if abs(variable_tstat) < = 2
variable_sig_value	7	Value of anm_mean if the t-statistic was significant = variable_anm_mean if variable_sig <> 0 = 0 if variable_sig == 0
variable_npts	8	Number of sites in the grid cell

variable_anm_mean: grid-cell mean of reconstructed anomalies

variable_se_mean: grid-cell mean of standard errors of estimates

variable_tstat: mean anomaly / mean standard error of estimate (anm_mean/se_mean

variable_sig: = sign(t) if abs(t) > 2 (same for all variables?)

variable_sig_val: =anm_mean if sig.ne.0

variable_npts: number of sites in grid box

Click here to access the data

Extension of the Bartlein et al (2011) reconstructions

Main reference: Harrison et al?

The following files are “extended” files with additional (unpublished) speleothem data and a few sites from the Shakun et al. appendix from the Schmittner et al. (2011) Science paper. These have been used in the Harrison et al. “benchmarking” paper.

map_delta_06ka_ALL_grid_2x2_ex.csv

mat_delta_06ka_ALL_grid_2x2_ex.csv

mat_delta_21ka_ALL_grid_2x2_ex.csv

map_delta_06ka_ALL_grid_2x2_ex.nc

mat_delta_06ka_ALL_grid_2x2_ex.nc

mat_delta_21ka_ALL_grid_2x2_ex.nc

The additions consist of:

Last Glacial Maximum, Mean Annual Temperatures: 1 speleothem record and 2 terrestrial records from Shakun et al.

Mid-Holocene, Mean Annual Temperatures: 3 speleothem records

Mid-Holocene, Mean Annual Precipitation: 4 speleothem records

The organisation of the files are the same as described in section 1 above.

References:

Schmittner, A., N. M. Urban, J. D. Shakun, N. M. Mahowald, P. U. Clark, P. J. Bartlein, A. C. Mix, A. Rosell-Melé, 2011. Climate Sensitivity Estimated from Temperature Reconstructions of the Last Glacial Maximum. Science, 334, 1385-1388, DOI: 10.1126/science.1203513

Shakun, J. D., P. U. Clark, F. He, S. A. Marcott, A. C. Mix, Z. Liu, B. Otto-Bliesner, A. Schmittner and E. Bard, 2012. Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation, Nature, 484, 49-55, DOI:10.1038/nature10915

Harrison, S. P., P. J. Bartlein, S. Brewer, I. C. Prentice, M. Boyd, I. Hessler, K. Holmgren, K. Izumi, K. Willis, 2013. Climate model benchmarking with glacial and mid-Holocene climates. Climate Dynamics, DOI 10.1007/s00382-013-1922-6

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