Martin Wagner, "The Environmental Kuznets Curve, Cointegration and 
Nonlinearity", Journal of Applied Econometrics, Vol. 30, No. 6, 2015, 
pp. 948-967.

The data are provided in three text files, one for each variable:

Log per capita (real) GDP 
Log per capita CO2 emissions
Log per capita SO2 emissions

The files are ASCII files in DOS format. They are zipped in the file
mw-data.zip. Unix/Linux users should use "unzip -a".

The emissions data are measured in [kg] (prior to taking the logarithm); 

The data range is 1870-2000, annual data. For New Zealand the CO2
emissions data only start in 1878. Note that the GDP and SO2 data are
in fact available until 2001 in these files. In the files the first
row indicates the year, and in the first column the country names are
indicated (in alphabetical order). 

The GDP data have been downloaded from the homepage of Angus Maddison
(http://www.ggdc.net/maddison)

Note that by now, August 2014, there is an updated dataset available
from the Maddison project, which implies slightly different GDP values
available up to 2010. 

The CO2 emissions data were downloaded from the homepage of the Carbon
Dioxide Information Analysis Center (http://cdiac.ornl.gov), and the
SO2 emissions data are from Stern (2006).