The watchdog received complaints from 10 viewers about the advert, which urged viewers to "adopt a polar bear today, because we don't want to say goodbye to them forever".
Complaints centred on four areas, including challenges to whether the Arctic ice was shrinking, as the advert stated, and that it presented opinions on climate change as fact.
In a ruling published today, the ASA dismissed all the complaints and concluded that the advert was not misleading.
David Norman, director of campaigns at WWF-UK, said: "Obviously, we are pleased that the ASA council has adjudicated that our advertisement did not in any way breach ASA guidelines.
"All four challenges to our science were rejected after thorough scrutiny, and our content was rightly found to be accurate."