"The worst is yet to come, and it will affect the lives of our children and grandchildren far more than our own," points out the interim report of the Intergovernmental Panel of Experts on Climate Change (IPCC), quoted by the news agency France-Presse (AFP).
According to the document, global warming above the 1.5°C (degrees centigrade) threshold set by the Paris agreement would have "irreversible impacts for human and ecological systems", with experts stressing that the survival of humanity could be threatened.
"Life on Earth can recover from major climate change by evolving into new species and creating new ecosystems. Humanity cannot," the report's 137-page technical summary of four thousand underlines.
With average temperatures rising by 1.1°C since the mid-19th century, the effects on the planet are already serious and will become increasingly violent, even if carbon dioxide (CO2) emissions are reduced, warn the experts.
Water shortages, famine, fires and mass exodus are some of the dangers highlighted by UN experts.
At least 420 million people will face "extreme heat waves" if global warming reaches another 2°C instead of another 1.5°C, IPCC climate experts warn.
In addition, 80 million more people worldwide could be threatened by hunger and 130 million could fall into extreme poverty within a decade, they add.
For some animals and plant species it may already be too late.
"Even at +1.5 °C, living conditions will change beyond the ability of some organisms to adapt," the draft report reads, citing coral reefs, on which half a billion people depend.
Global warming is also expected to lead to worsening diseases and epidemics. By 2050, half of the planet's inhabitants could be exposed to diseases such as dengue fever, yellow fever or the Zika virus.
Diseases linked to ozone levels in the atmosphere, due to heat waves, will also "increase substantially", they say.
The IPCC experts therefore anticipate pressures on health systems similar to those caused by the pandemic of the new coronavirus.
The global warming impacts assessment report, created to support policy decisions, is much more alarming than its predecessor, released in 2018.
The document is due to be published in February 2022, after approval by all 195 UN member states and after the COP26 climate conference, scheduled for November in Glasgow, Scotland.
Originally scheduled for November 2020, the 26th UN Climate Change Conference (COP26), with leaders from 196 countries, businesses and experts, was postponed due to the pandemic.
By signing the Paris Agreement in 2015, world leaders pledged to limit warming to +2 °C compared to values in the pre-industrial era, if possible to +1.5 °C.
However, according to the IPCC draft report, exceeding +1.5 °C could already lead to progressively severe, "sometimes irreversible" consequences.
According to the World Meteorological Organisation, the probability of the +1.5 °C threshold being exceeded as early as 2025 is 40 percent.
Despite the alarming conclusions, the report also offers a note of hope.
According to the UN experts, humanity can still secure a better future, but this will require taking drastic measures to halt climate change already today.
"We need a radical transformation of processes and behaviours at all levels. We need to redefine the way we live and consume," say the experts.