When the Paris Agreement on climate change was finalized after two weeks of fraught negotiations and years of past failures, diplomats hugged and shed tears of joy. They had haggled over verb tenses, cut deals, and in the end, brought 196 countries into the accord. 

Five years later, governments are lagging far behind in implementing the deal, struck on Dec 12, 2015. Annual greenhouse gas emissions hit a new high last year. And climate change impacts are intensifying, from the thawing Arctic to raging wildfires in Australia and the US West.

The Paris Agreement aims to hold the rise in average global temperatures to "well below" 2 degrees Celsius above preindustrial levels, and preferably 1.5C -- a threshold beyond which climate impacts are projected to sharply intensify.

Temperatures have already risen by more than 1C since pre-industrial times, and scientists say that the world's fossil fuel-dependent economies will have to undergo wholesale transformation to bring those goals within reach.

As delegates prepare for a one-day online UN climate summit today, negotiators point to signs of progress: rapid advances in renewable energy, growing appetite for greener investments, and pledges on emissions by the European Union and China. US President-elect Joe Biden has vowed to rejoin the accord.

At the summit on Saturday, diplomats will be watching for signs that countries are preparing to ramp up climate efforts ahead of a major round of UN climate talks in Glasgow due to take place in November 2021.

Perhaps the most encouraging sign for the Paris deal is the number of countries that have begun to pledge to slash carbon emissions to net zero -- meaning they will release only as much as they remove from the air -- by 2050.

Britain and the European Union adopted the target last year, and China - the largest emitter - surprised many in September by announcing of goal of net-zero by 2060. Subsequent pledges by Japan and South Korea mean more than 50% of global emissions are now under net-zero targets, UN officials say.

Pacific island nations on the frontline of climate change yesterday demanded the world "get serious" about saving the planet ahead of today's anniversary.

Fiji Prime Minister Frank Bainimarama told a virtual summit of the Pacific Islands Forum (PIF) that progress had stalled since the Paris climate agreement was signed.

The call came ahead of rare good news: Carbon emissions fell a record seven percent in 2020 as countries imposed lockdowns and restrictions on movement during the Covid-19 pandemic.

The fall of an estimated 2.4 billion tonnes is considerably larger than previous annual record declines, such as 0.9 billion tonnes at the end of World War II or 0.5 billion tonnes in 2009 at the height of the financial crisis, the Global Carbon Project said yesterday in its annual assessment. Emissions reductions were most pronounced in the United States (down 12 percent) and the European Union (down 11 percent).