Global figures representing 46 countries and 1,500 civil society organisations have urged rich nations and particularly the UK to ramp up global vaccine distribution or risk delaying critical climate progress.
Unequal access to COVID-19 vaccines is a threat to this year's critical climate change negotiations at COP26 as well as to climate action in general, a chorus of voices around the world has warned.
Sonam Phuntsho Wangdi is the current chair of the Least Developed Countries (LDC) group, which represents 46 poor nations extremely vulnerable to climate change at the UN's annual international climate talks known as COP.
He said he appreciated the UK government's offer to vaccinate delegates at this year's climate talks, COP26, hosted in Glasgow in November.
But even if all delegates could get vaccinated in time to get to COP26 in person, "the broader inequalities in vaccine access is a concern", he told Sky News.
So far less than 4% of the total population of LDCs have been vaccinated. "We are concerned about how this will affect the inclusivity of negotiations at COP26," said Mr Wangdi.
"If those most affected by climate change are not included in discussions, we risk decisions that are weak or unfair, and that set us back in our global efforts to address the climate crisis."
The worry was echoed by Climate Action Network (CAN) International, which convenes and coordinates civil society at the UN climate talks, comprising more than 1,500 organisations in over 130 countries.
It's executive director, Tasneem Essop, said it was "extremely morally challenging" for those who want to participate in the COP to have to decide whether to "take part in potential queue-jumping ahead of people and vulnerable populations in their own country".
Global anti-poverty campaign group ONE warned unequal access to the vaccine undermined the trust on which the talks are predicated.
Romilly Greenhill, UK director of ONE, said: "Ultimately these negotiations that are all about trust and about every country bringing something to the table and believing that others will do the same.
"[The poorest countries are] saying, well, why should we make these strong commitments on climate change? If you as the rich world... you're not playing ball on vaccines?
"Particularly given that as the poorest countries, we've done the least to actually cause climate change."
The organisations say their comments stand in spite of a G7 July pledge to donate 1bn vaccine doses to poorer countries by next summer. "That pledge is just too little and it's far too slow," said Ms Greenhill.
The World Health Organisation has said 11 billion doses are needed to end the pandemic.
The leaders also stressed a lack of vaccine access would hinder climate action in general, beyond the international talks at COP26, because countries cannot overcome the coronavirus and climate crises at the same time.
The LDC's Sonam Phuntsho Wangdi said the COVID-19 and climate crises are "interrelated, both hitting our vulnerable populations the hardest [and] exacerbating existing challenges". Yet dealing with the immediate shocks of the pandemic had "diverted capacity in those countries away from climate efforts", he said.
"We urgently need to get both the pandemic and the climate crisis under control and broader vaccine access will be key to this," he said. "The support of the international community will be needed in getting our populations vaccinated."
Ms Greenhill said there was particular onus on the UK as hosts of COP26 to get this right and if it doesn't there was a "real risk these talks fail".
"This was our moment to shine on the world stage," she said.
"And we have shot ourselves in the foot by not being ambitious enough on how fast we share doses."
A Foreign, Commonwealth & Development Office (FCDO) spokesperson said the government had made "ambitious commitments" and encouraged its international partners to "improve global vaccine access". And as COP26 hosts, they had ensured "that the most vulnerable to the impacts of climate change have the vital access to finance they need".
But Ms Greenhill claimed the UK government's decision to slash foreign aid had risked countries' willingness to engage.
The first thing the UK should do is reverse cuts to foreign aid, she said, "because actually, if you don't reverse the cuts, it's hard to do any of these other things".
CAN's Ms Essop also called out the UK for so far opposing a plan to waive intellectual property protections on the COVID-19 vaccine - known as the TRIPS waiver - to allow broader manufacturing and distribution.
"Certainly that would have been an important signal for trust building between rich and poor nations, and that was a missed opportunity," said Ms Essop.
The UK government is continuing to discuss the proposed TRIPS waiver with other World Trade Organisation members. It has also promoted the partnership of AstraZeneca and the Serum Institute of India as a good example of what works when it comes to ensuring equitable vaccine access.