Bangladesh, Nov. 20 -- The U.N.'s climate chief says deadlines set by some of the world's top polluters to end greenhouse gas emissions, along with U.S. President-elect Joe Biden's pledge to take Washington back into the Paris accord, have boosted hopes of meeting the pact's ambitious goals.

The agreement signed in the French capital five years ago aims to keep global warming well below 2 degrees Celsius (3.6 Fahrenheit) - ideally no more than 1.5 C (2.7 Fahrenheit) - compared to pre-industrial times by the end of the century. Experts say the world is far off track and that, with average temperatures already up by about 1 C (2 Fahrenheit), drastic action is needed in the next 30 years.

But the recent announcement by China, the world's t...