Almost every country on the planet signed up to the 2015 Paris Agreement, which calls for capping global warming at "well below" two degrees Celsius compared to pre-industrial levels, and 1.5C if possible.

The first raft of so-called "nationally determined contributions" (NDCs) would -- if fulfilled -- still see Earth become 3C hotter, but nations pledged to intensify their emissions cuts, with revised plans due every five years.

As the December 31, 2020, deadline approached, several large emitters said they would achieve net-zero output this century, but many nations allowed the year end to pass without publishing details of their renewed short-term targets.

Most NDC pledges run to 2030, with a few -- including that of the U.S. -- ending in 2025.

As of January 1, only around 70 out of nearly 200 nations had filed updated commitments, according to the United Nations, with some countries blaming delays on the Covid-19 pandemic.

Climate advocates are particularly eager to see the latest plans from China, the world's largest emitter.

President Xi Jinping last year outlined new ambitions to achieve carbon neutrality by 2060. But the country has yet to formally submit proposals.

Another notable omission is the world's second largest emitter, the United States, which was yanked out of the Paris Agreement by Donald Trump.

Incoming President-elect Joe Biden has however pledged carbon neutrality by 2050 and a return to Paris commitments.

'Critical test'

The UN has estimated that emissions need to be cut by 7.6 percent a year in the ten years to 2030 if there is to be a hope of limiting heating to 1.5C.

Earth's surface has already warmed nearly 1.2C on average, intensifying extreme weather and making it more deadly.

In his new year's message, UN Secretary General Antonio Guterres said building a global coalition for net zero emissions by mid century would be the "central ambition" of the world body in 2021.

"Every government, city, business and individual can play a part in achieving this vision," he said.

According to the most recent appraisal by Climate Action Tracker, the 49 states that had submitted their new proposals by mid-December -- which included the then 27-nation European Union -- only represented 23.7 percent of global greenhouse gas emissions.

Since that assessment, a further 20 states have filed their plans, including large economies such as South Korea and Argentina.

But revised commitments are not necessarily increased commitments.

According to Climate Action Tracker, Brazil, Japan, Russia, New Zealand, Switzerland and Vietnam have submitted updated plans that are no more ambitious than their initial commitments.

Even among the nations that have improved upon earlier pledges, experts have warned of a paucity of ambition.

The EU bolstered its target to cut greenhouse gas emissions at least 55 percent by 2030 -- up from 40 percent.

But this still will not be sufficient to meet the Paris climate goals, according to CAT.

The NDCs that were submitted on time will come under the scrutiny of the UN Convention on Climate Change, which will assess progress on February 21.

The picture may become clearer only later in the year, at a major UN climate meeting in Glasgow that has been postponed to November.

David Waskow, International Climate Director at the World Resources Institute, said there had been some "important headway" made on climate action in recent weeks, particularly with upgraded 2030 targets from Britain and the EU.

But much more would need to be done in 2021.

"A number of major emitters still need to come forward with greater ambition, especially to follow-through on their net-zero commitments with 2030 targets that match their long-term vision. This year will be a critical test."