Table 2.

Unit root test

Variables	ADF		PP		Order of cointegration
	Level	First difference	Level	First difference
CO2	−2.28218	−9.979*	−2.434	−19.523*	I(1)
	0.1785	0.000	0.133	0.000
NC	−1.02597	−14.215*	−1.366	−19.177*	I(1)
	0.7447	0.000	0.599	0.000
ND	−1.31653	−13.303*	−2.554	−49.982*	I(1)
	0.6226	0.000	0.104	0.000
LD	−1.71519	−7.668*	−1.724	−17.378*	I(1)
	0.4226	0.000	0.418	0.000

*, **, and *** represent 1%, 5%, and 10% level of significance, respectively