The sharp growth, as governments expanded existing areas and declared new ones, was needed to help slow a loss of animal and plant species and to conserve eco-systems which serve vital functions such as purifying water and storing greenhouse gases, it said.

"These rich natural areas are very important for people, who rely on them for food and clean water, climate regulation and reducing the impacts of natural disasters," said Julia Marton-Lefevre, head of the International Union for Conservation of Nature (IUCN).

The IUCN report, issued during a meeting of the organization in South Korea, said the areas protected had risen to 12.7 percent of the world's terrestrial area in 2010, or 17 million sq km (6.6 million sq miles), from 8.8 percent in 1990.

The United Nations has set a goal of protected areas reaching 17 percent of land area by 2020 - that would mean adding at least 6 million sq km (2.3 million sq miles) or an area about twice the size of Argentina or India, it said.

The area of the sea protected within national jurisdictions has risen more than four-fold to 4 percent, from 0.9 percent in 1990, but is also far short of a U.N. goal of 10 percent by 2020. Reaching the target would require adding marine areas the size of Australia.

Protected areas also vary widely in their effectiveness, according to the study by IUCN, which includes governments, scientists and activists.

"Some of the world's protected areas are properly managed but many, many of them aren't," Trevor Sandwith, director of the IUCN's Global Protected Areas Programme, told Reuters.

One possible option to meet the U.N. target would be to recognize more of the land that is under the control of indigenous peoples as protected, he said. Indigenous peoples were often better at conserving territory than governments.

Sandwith said U.N. climate negotiations had failed to agree a financial reward for governments which protect rainforests, putting a brake on conservation efforts.

Trees soak up carbon as they grow and release it when they burn or rot. Deforestation, from the Amazon Basin to the Congo, may account for 17 percent of all greenhouse gases from human activities, according to some government estimates.

Talks on a new global deal to fight climate change, which may include forest carbon, are making slow progress. The United Nations' goal is to strike an agreement by 2015 which will come into effect in 2020.

(Reporting By Alister Doyle; Editing by Pravin Char)

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