[!tag=VB | lemma=trim] [tag=JJ] | [lemma=greatest | □]
[!tag=VB | lemma=trim] [tag=JJ] | [lemma=greatest | □=□]
[!tag=VB | lemma=trim] [tag=JJ] | [lemma=greatest | □ & □]
Nevertheless , writing about the future can be one of the most dangerous undertakings , because the future is essentially unknown and uncertain . Falling yields , linked to poor extension and farming practices and to relatively higher costs of inputs , have encouraged farmers to expand production through extension , often into forests and woodlands . For many applications these technologies are now mature , and recent cost reductions have brought them into the competitive range . Access to energy is essential for development , but energy generated by the combustion of fossil fuels and biomass often results in air pollution , with negative impacts on human and ecosystem health . Where there are threats of serious or irreversible damage , lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation .