The US, the world’s largest emitter of greenhouse gases has refused to ratify the agreement, leading some climate scientists to say the agreement is “toothless” and virtually obsolete without US support.

It has no enforcement mechanism. Many nations— including those developing nations that are fast becoming the leading emitters of greenhouse gases—are excused from any significant responsibilities under the agreement.

It is not global in nature; rather, it imposes obligations only on a few countries. Many countries that have committed to meeting modest greenhouse gas emission limitation targets have now found that accomplishing even those initial goals is a task easier said than done.