* Kenya aims to become global carbon credits market leader * Govt says communities must benefit from offset projects * Some local projects criticised over methodology and claims By Chloe Farand KASIGAU, Kenya, March 30 (Thomson Reuters Foundation) - F or years, Kenyan farmer John Tembo made extra cash to buy food and pay his seven children's school fees by cutting down trees in the dryland forest near his village and then selling the charcoal he produced. But since a carbon credit project was established in the area a decade ago, Tembo no longer fells trees.