London(CNN) Just months ago, consensus was growing that COP26 would be a once-in-a-lifetime opportunity to hit the reset button on the climate crisis, bringing world leaders together to make new commitments to save the planet.
While the summit in Glasgow, Scotland, is still of vital importance in the battle against climate change, there is now a question mark on whether it will adequately put flesh on the bones of the 2015 Paris Agreement, which is its main purpose.
During a summer of extreme weather and new science showing that climate change is happening faster than we previously understood, there was a real sense that COP26 would be a huge moment for the global community to come together and lay out clear, real-world actions to halve emissions over this decade with the aim of keeping global warming to 1.5 degrees Celsius. But less than a week out, things are looking shaky.
British government officials shared with CNN their concerns that some of the most important nations in the G20 have yet to disclose their updated Nationally Determined Contributions (NDCs) on cutting emissions with just days to go until the summit kicks off.
There are also worries over the symbolic absence of several key leaders. Chinese President Xi Jinping, leader of the world's largest emitter, is unlikely to attend, having not left the country since the start of the Covid-19 pandemic.
British officials had hoped that the UK's successful vaccine rollout and the broader global response to the pandemic would mean the summit would go ahead as close to normal as possible. However, in recent weeks, the UK's infection rate has soared and last week the country saw its deadliest day since March. The consequences of lifting almost all Covid restrictions before summer and returning life to normal have become impossible to ignore.
Ministers are now facing calls to impose further restrictions, and Health Secretary Sajid Javid has floated the possibility of introducing vaccine passports and other measures for those most vulnerable to the virus.
Questions are now being raised over how this all might affect COP26, which 25,000 people are expected to attend amid planned mass protests, as well as potential rail and bus strikes.
The pandemic is part of the reason some world leaders say they won't attend. Russian President Vladimir Putin and Brazilian President Jair Bolsonaro have confirmed they aren't coming, while yet to confirm are Mexico's Andres Manuel Lopez Obrador, South Africa's Cyril Ramaphosa and Japanese Prime Minister Fumio Kishida -- all G20 leaders who are significant in the climate discourse because of their countries' emissions, fossil fuel production, or both.
"If a world leader chooses not to attend for whatever reason, it sends a very clear signal that climate simply isn't at the top of their priority list and depletes the momentum going into the summit," says Mark Lynas, author of the book "Our Final Warning: Six Degrees of Climate Emergency."
"It cannot be entirely coincidental that many of those reluctant to attend COP in person happen to lead countries that are high emitters or producers of fossil fuels," Lynas says.
Underscoring the importance of COP26, Lynas says that Glasgow's gathering "won't just be a shindig where people can pose for photos," but our "last real chance of setting out measures to meet the commitments made in Paris" of limiting warming to 1.5C and halving emissions by 2030.
UK government officials have played down the significance of any specific no-shows, stating that what really matters are commitments on emissions and spending that accompany any national delegation. They are awake to the fact, however, that Glasgow needs real-world commitments to match the rhetoric of Paris, and anything resembling a lack of seriousness from some of the most powerful or big-emitting countries sets the tone for an unsuccessful summit.
But even by that metric, the picture is bleak. Saudi Arabia made a pledge to achieve net zero on Sunday, but only by 2060, which scientists say is 10 years too late. And as China unveiled its climate road map the same day, it failed to mention any actual increase in its ambitions on slashing greenhouse gas emissions, despite vowing to cut fossil fuel use to 20% by 2060.
Lynas reasons that as the scientific consensus on climate change is now even more comprehensive than in 2015, the only reason anyone might be reluctant to make the necessary commitments is "short-term financial considerations."
Lynas isn't alone in his belief of how serious this moment is.
"This COP must be very honest about how little time we actually have," says Mary Robinson, a former UN High Representative on human rights, and campaigner for climate justice.
"It's not just a step along the way, but the moment we need to come good on Paris and commit to even more ambitious goals. We need hard commitments from India, Saudi Arabia, China, South Africa, Brazil on switching to clean energy and helping poorer countries make the switch. There is no wriggle room left."
At this late stage ahead of COP26, it's not just Covid putting the summit at risk.
The global energy crisis has served as a reminder that there are very few ready-to-use alternatives to gas and coal, while data shows that without serious government intervention, humans are not ready to stop burning fossils any time soon.
A report backed by the UN and published earlier this year revealed that, despite commitments made in Paris and a reduction due to the global pandemic, "emissions are rapidly recovering" and are "nowhere close to reduction targets." Meanwhile, "greenhouse gas concentrations in the atmosphere continue at record levels, committing the planet to dangerous future warming."
That's why COP26 is so important. As UN Secretary-General António Guterres puts it, unless something happens in this "critical year for climate action," then "limiting warming to 1.5°C will be impossible, with catastrophic consequences for people and the planet on which we depend."
There has been much focus on to what extent the summit in Glasgow will be a success for Boris Johnson, given he is hosting this critical meeting. However, British government officials pointed out to CNN, not unreasonably, that Glasgow is about proving whether the commitments made in Paris are possible. Ambition is one thing; real-world action -- like cutting coal, scrapping cars, planting trees and putting money on the table -- is what matters now. If Glasgow fails, then Paris also failed.
For all the optimism surrounding COP26 earlier this year, as the event gets nearer, the mood music isn't great. Multiple sources have told CNN that fossil fuel producing countries have been fighting against any firm language committing to the 1.5C target, and China has publicly accused the US and UK of moving goalposts from the original top end of 2C in Paris.
Reports have emerged in British media that some of the world's biggest coal producing nations are trying to water down the Intergovernmental Panel on Climate Change's (IPCC) forthcoming report of findings that threaten their national economic interest. Some of those nations -- Australia, Brazil, Saudi Arabia and Japan -- happen to be the same ones that either failed to update their emissions-cutting pledges or have done so without any meaningful increase in their pledges.
That's hardly a sign of global unity on climate.
COP26 comes as the world reaches a point of no return. If the commitments in the Paris Agreement are not met, then, the vast majority of the science suggests, it will be too late to curb the long-term impact of global warming.
What must be exasperating for Johnson is that as he gets ready to host this summit of huge importance, the solution to the greatest threat humanity faces is well known and perfectly achievable. It just relies on his fellow global leaders caring enough. And somehow, in 2021, that is not something that can be banked on.