US presidential envoy on climate and former secretary of state John Kerry said the IPCC report, which warned the world is on course to reach 1.5C of warming around 2030, showed "the climate crisis is not only here, it is growing increasingly severe".

Current US Secretary of State Anthony Blinken said in a statement that world leaders, the private sector and individuals must "act together with urgency and do everything it takes to protect our planet".

Frans Timmermans, the European Union's deputy climate chief, said the 3,500-page report proved "it's not too late to stem the tide and prevent runaway climate change". 

Britain's Boris Johnson, whose government is hosting a crucial UN climate summit in November, said the assessment "makes for sobering reading".

"I hope today's IPCC report will be a wake-up call for the world to take action now, before we meet in Glasgow in November for the critical COP26 summit," he said.

Read also: Climate science report 'critical for success' of COP26: UN

French President Emmanuel Macron called for the November climate conference to fully recognize the gravity of the situation, saying on Twitter: "The time for outrage is behind us... In Glasgow, let's seal a deal that matches the urgency."

Former Maldives president Mohamed Nasheed said the document confirmed that climate-vulnerable nations such as his were "on the edge of extinction".

'Suicidal'

Saleemul Huq, director of Dhaka-based environmental think tank ICCCAD, said the IPCC report was "the final warning that bubble of empty promises is about to burst".

He said it showed G20 countries needed to accelerate emissions cuts to ensure their economies are in line with the 1.5C target. 

"It's suicidal, and economically irrational to keep procrastinating," Huq said.

The Indian government called the report a "clarion call for the developed countries to undertake immediate, deep emission cuts and decarbonisation of their economies".

India is the world's third-biggest emitter of greenhouse gases but its emissions per head are low owing to its large population of 1.3 billion.

The report "vindicates India’s position that historical cumulative emissions are the source of the climate crisis that the world faces today," the environment ministry said in a statement.

Dorothy Guerrero, head of policy at Global Justice Now, said the report was a "terrifying warning of our future unless drastic action is taken."

"There is no denying the science of the climate crisis," she said. 

"But policymakers refuse to face up to the fact that it is rooted in economics and a history of colonial exploitation."

Action

Many interpreted the IPCC's assessment as a clarion call to overhaul the fossil fuel-powered global economy.

"Where can we start? Almost everywhere," said Katherine Hayhoe, chief scientist for The Nature Conservancy. 

"Accelerating the transition to clean energy; reforming our most environmentally damaging activities; and recalibrating financial flows to accelerate the economic transition."

Read also: Greta Thunberg's generation most likely to believe climate change is a crisis: Poll

Climate wunderkind Greta Thunberg said the report was a "solid (but cautious) summary" of the state of the planet. 

"It doesn't tell us what to do," she said on Twitter. 

"It is up to us to be brave and take decisions based on the scientific evidence provided in these reports. We can still avoid the worst consequences, but not if we continue like today, and not without treating the crisis like a crisis."

Ugandan climate justice activist Vanessa Nakate tweeted: "Scientists warn time running out on the 1.5C target! World leaders must get serious about climate change!"

Fossil fall guys

UN Secretary-General Antonio Guterres said Monday's report "must sound a death knell" for coal, oil and gas and warned that fossil fuels were destroying the planet.

Greenpeace was even more direct. 

"Dear fossil fuel industry," the charity said on Twitter. "We'll see you in court."