UPM- UNESCO-UNEP International Environmental Education Programme , 1987
Buku Teks
Mohd. Hafsah, author
Perpustakaan Negara Malaysia, 1997
Buku Referensi
Artikel Jurnal
edited by John E. Hay, Wimala Ponniah and Mahesh Pradhan
United Nations Enviromnet Programme, 1995
Buku Teks
Rohan Gunaratna, Stefanie Kam.
Imperial College Press, 2016
Buku Teks