The longstanding target for providing climate finance to the developing world will be met within two years, according to a report ahead of the UN Cop26 climate summit.

But experts said it was “shameful” that developed countries were not doing more to help the poorest in the world, who were struggling with a climate crisis not of their making.

Rich countries agreed in 2009 that at least $100bn a year would be provided annually from public and private sector sources to the developing world by 2020, in order to help poor countries cut greenhouse gas emissions and cope with the impacts of the climate crisis.

That target has so far gone unmet, endangering the trust that developing countries have in the 2015 Paris climate agreement and jeopardising progress at the Cop26 talks, which open in Glasgow this Sunday.

The climate finance delivery plan published on Monday found that a shortfall remained between the finance likely to be provided this year and next year and the $100bn (£73bn) target, but that it would be closed by 2023 when new contributions that had already been pledged came into effect. By 2025, according to the plan, the amount flowing to developing countries should reach $117bn.

Alok Sharma, the UK cabinet minister who will preside over Cop26, said: “The delivery plan sets out how developed countries will deliver the $100bn goal that has long been promised to developing nations. Scaling up climate finance has been one of my top priorities as Cop president. This plan recognises progress, based on strong new climate finance commitments. There is still further to go, but this plan provides clarity, transparency and accountability. It is a step towards rebuilding trust and gives developing countries more assurance of predictable support.”

No new money is likely to be forthcoming immediately under the delivery plan, though there are expectations of some new pledges by the end of this year.

More significantly for the poorest countries, at Cop26 there is likely to be a refocus of existing pledges to help them cope with the impacts of extreme weather. Much of the climate finance provided to date has gone to middle-income countries to help them cut emissions, through projects such as windfarms or solar panels that are already easy to fund as they produce a profit, so a focus on poorer countries will be a welcome departure for many at the Cop26 talks.

The Climate Finance Delivery Plan, compiled by the German and Canadian governments at the request of the UK as host of Cop26, found that more than $100bn would be provided from 2023 to 2025.

Ed Miliband, the shadow business secretary, pointed to the UK’s decision to cut overseas aid while urging other countries to increase their commitment to climate finance. “Despite Alok Sharma’s best efforts, he has been undermined by the rest of the government. Cutting our aid budget has sent precisely the wrong signal to others and made it much harder for us to deliver on this vital commitment,” he said.

In Glasgow countries will be expected to come forward with targets on cutting greenhouse gas emissions in line with holding global temperature rises to 1.5C above pre-industrial levels. But the targets – known as nationally determined contributions (NDCs) – submitted so far have fallen short of the 45% cut in carbon required by 2030 to meet the goal.

On Monday, the UN published its final report on NDCs ahead of the Cop26 conference, showing that current contributions would result in an emissions rise of 16% by 2030, underlining the need for countries to do more.

The UN report also emphasised the importance of finance, because some developing countries have submitted carbon targets that are conditional on receiving financial help. If this finance is provided, current NDCs would result in emissions falling by 2030 – not enough to bridge the gap, but a substantial improvement.

Mohamed Adow, the director of the Power Shift Africa thinktank in Nairobi, criticised the plan: “The $100bn of climate finance is not only a lifeline to poor and vulnerable communities on the frontline of a climate crisis they did not cause, it’s also the bare minimum that rich countries need to do to hold up their end of the bargain at Cop26. For more than 10 years they have been promising this climate funding would be provided and every year they delay and drag their feet.”

He pointed out that $100bn was less than the UK is spending on its HS2 rail link. “It’s utterly shameful and the deal announced today is still short despite the UK government trying to spin it as ‘mission accomplished’. Poor nations will not be conned and the leaders of the developed world need to pull their finger out and get this money on the table if Cop26 is going to be a success,” he said.

David Levai, a researcher at the IDDRI thinktank in Paris, said: “This plan, which was an opportunity to reassure developing countries that their concerns were to be address addressed, fails to do that. In a year when they face compounding crises – health, climate and debt – support is more crucial than ever. Developed countries need to answer calls to deliver what was promised, to increase funding for adaptation and to improve access. If not addressed urgently by the UK presidency, this issue risks toxifying the Cop when it opens next week.”