The world is heading for an “irrecoverable overshoot” of global temperature thresholds that will plunge billions of people into disastrous climate impacts because governments have stalled for so long to cut planet-heating emissions, analysis has found.

Under current policies, the planet will heat up by 2.7C on average by the end of the century compared with preindustrial times, the report by Climate Action Tracker (CAT) found. This is up slightly from a prediction of 2.6C in the group’s analysis conducted last year.

This level of warming smashes the 1.5C threshold that was agreed by countries a decade ago but is set to be breached in just a few years. Scientists have warned that beyond this point already harmful storms, droughts, heatwaves, flooding and other impacts will become intolerable for parts of the world and potentially trigger runaway climate change that won’t be contained.

View image in fullscreenSpanish firefighters trying to extinguish a wildfire in Zamora, Spain, in July. Photograph: Ümit Bektaş/Reuters

Countries, minus the US, are gathered in the Turkish city of Antalya for UN climate talks that have centred on the looming “overshoot” of the temperature target. This reality should compel governments to act quickly to phase out use of the fossil fuels that are causing the climate crisis, the UN secretary general, António Guterres, said on Tuesday.

If countries did act decisively to slash emissions then the future temperature projections would become less daunting, the CAT report states. However, in even the most optimistic scenario – where all pledges, targets and other long-term promises made by countries were fulfilled – the world would still heat up by 1.9C by the end of the century.

Such targets have been routinely flouted by the countries that have made them, however. This means leaders face a crunch moment, experts say.

“The stark choice for governments is to either continue to support the fossil fuel industry, which would consign humanity to insurmountable economic damages, rising mortality from heat and climate-driven diseases and disasters that they are unable to adapt to – or pivot to the solutions which are available and cheaper than ever,” says Bill Hare, chief executive of CAT partner organisation Climate Analytics.