UPDATE 1-S.Korea says to set 2020 emissions target

* South Korea says to opt for "mild" 2020 emissions goal

* Each target to cost between 0.3 and 0.5 percent of GDP

* More use of renewable energy, nuclear, efficient lighting (Adds details throughout)

SEOUL, Aug 4 (Reuters) - South Korea, Asia's fourth largest economy, has pledged to set one of three targets for carbon emissions by 2020, voluntarily joining Kyoto signatories in moving toward a firm commitment to roll back climate change.

The government said on Tuesday it would choose a 2020 gas emission target this year from three options: an 8 percent increase from 2005 levels by 2020, unchanged from 2005, or 4 percent below 2005 levels.

The country is one of Asia's richest nations and an industrial powerhouse. Emissions doubled between 1990 and 2005 and per-capita emissions of planet-warming carbon dioxide based on 2005 levels were 11.1 tonnes, the same as some European nations and the 17th largest among OECD members.

"Compared with developed countries, the targets may look mild," said Sang-hyup Kim, Secretary to the President for National Future and Vision at the Presidential Office.

"But these are utmost, sincere efforts, reflecting Korea's capabilities."

The government estimated each target to cost between 0.3 and 0.5 percent of GDP and will curb emissions by increased use of hybrid cars, renewable and nuclear energy consumption, energy efficiency with light-emitting diodes and smart grids.