UN Secretary-General Ban Ki-moon has said the world needs to press ahead in the struggle against climate change.In his final press conference as Secretary-General, Ban on Friday said the UN must maintain the impetus that resulted in the signing of the Paris Agreement on climate change, Xinhua news agency reported."Climate action means jobs, growth, cleaner air and better health. Leaders from across the globe and on every front understand this -- from Fortune 500 CEOs to governors and mayors," he said."The Paris Agreement on climate change is a precious achievement that we must support and nurture," Ban said. "There is no turning back."The accord, which was signed by 194 nations and came into effect last month, is considered one of the most important achievements of Ban's tenure, which officially ends on December 31, when Antonio Guterres will take over the post.However, the election of Donald Trump as US president has cast a shadow of uncertainty over the pact's implementation.In recent days, Trump said he was considering whether to pull out of the Paris Agreement, which he suggested could make the US economy less competitive with rivals such as China, even though Beijing is also a signatory to the pact.Four years ago, Trump described climate change as a "hoax invented by China" to harm the US.