Ms Robinson said that leaders showed a lack of ambition at COP26
Former president Mary Robinson has said people under the age of 60 are likely to face a world that is "less liveable", with terrible floods, fires and droughts.
Ms Robinson said millions of people will be forced to leave their homes because of climate change.
She said “we didn’t quite succeed” at COP26 but said she felt that the world was “in crisis mode” at the conference.
"The climate action tracker announced during the COP was that we were heading for a 2.4 degree world and that's when I had my emotional moment,” she told RTÉ’s Morning Ireland.
"It means that anybody under 60 in our world is likely to have a world that is less liveable in that is facing terrible fires, terrible floods, terrible droughts, and millions of people having to leave their homes.
"And anyone under 30 is sure to live in that world.
“The fact that we haven't got that mindset in the leaders is the key to why we didn't have a good COP.”
She said the most disappointing part of the global agreement is that a commitment to "phase out" the use of coal was reduced to a promise to "phase down" the fuel, following interventions by China and India.
However, the deal, backed by nearly 200 countries, for the first time explicitly targeted fossil fuels, the biggest driver of man-made global warming.
Governments have been asked to accelerate emissions cuts and promised more money for poor countries struggling with climate change.
Ms Robinson – former UN High Commission for Human Rights and Chair of The Elders – said this explicit target at fossil fuels is significant.
However, she said a lack of ambition from the biggest emitters – including Australia, Brazil, China, Mexico and Russia – was disappointing.
"We didn’t quite succeed at COP26 so we go onto the African COP next year in Egypt, COP27.
“But, I think the world is in more crisis mode, that was felt.
"What was significant is that we did get language about phasing out fossil fuel in the text, we’ve never gotten that before.”
Following the conference, British Prime Minister Boris Johnson said most of Western Europe and North America have been persuaded to pull the plug on financial support for all overseas fossil fuel projects by this time next year.
Ms Robinson explained that there are two different subsidies related to fossil fuels.
“There is the production subsidies to fossil fuel companies which are tax exemptions,” she said.
"The other type of subsidies are subsidies on consumption and you have to be careful removing those subsidies because you could put people into energy poverty or into real poverty so that one has to be done really sensitively and with real thought.”
She said Ireland, along with other countries, will need to invest to “go green in an affordable way”.
The COP26 agreement included a commitment to cap global warming at 1.5C above pre-industrial levels.