New research says most of br carbon emissions caused by humans br could be fixed by global planting projects. Worldwide, the report says there is br 1.7 billion hectares of land where trees could be grown. This accounts for just over br one-tenth of all land on earth. All urban spots and areas where crops br are grown were br not included. The report's lead researcher, Professor Tom Crowther, says tree restoration is far more powerful br than previously thought. He adds that it would br take up to a century to be br fully effective in removing br carbon dioxide. Even though it doesn't detail a planting program, Crowther says br it is the cheapest way to br combat climate change. He adds anyone can get involved by br donating to restoration groupsbr or planting on their own.