As the countdown clock to the Glasgow climate conference ticked past the 100-day mark late last month, several deadly natural disasters, from floods to heat domes, provided stark reminders of the risk climate change is posing to humanity.

In a recent address, John Kerry, who is America’s Special Presidential Envoy for Climate, spelt out what this threat could look like in vivid detail.

Speaking at the Royal Botanic Gardens, in the UK, Kerry emphasised that these disasters were the consequences of 1.2 °C warming and that a consistent failure to meet climate commitments meant that temperatures could rise by upwards of 2.5 °C or 3 °C by the end of the century.

Such a trajectory is not what was agreed in Paris in 2015, when commitments were made to limit temperature increases to below 2 °C by the end of the century and to pursue a 1.5 °C cap – a target that has since been adopted by the UK COP presidency as the main goal for the Glasgow negotiations.

Limiting warming to 1.5 °C will not be enough to avoid more deadly disasters, but allowing temperatures to rise even higher would be to invite catastrophe.

Already, as Kerry related, hurricanes and typhoons are more frequent and powerful, intense rainfall this year has caused deadly floods in highly developed Germany, Holland and Belgium, not to mention far less developed countries like Nigeria and Uganda.

“Fiery conflagrations” have rampaged across Australia, the American west, the Russian tundra and the rainforests of the Amazon, while record heat waves have caused deaths and illness, roads to buckle and schools to close.

In some parts, crops can no longer grow where they did before and millions of people are being forced to leave increasingly uninhabitable homelands.

More horrifying is what Kerry says the world will look like unless there is a change of course: “A world where major cities — Jakarta, Mumbai, Shanghai, Venice, Bangkok, New Orleans, and many more – will need trillions of dollars in infrastructure just to survive repeated flooding and high tides.

“A world in which the ocean is more acidic and starved for oxygen. An ocean that is increasingly hostile for marine life; devoid of most tropical coral reefs, and with that the loss of protection from storms and food security for millions.

“A world in which the Arctic may not have any ice in the summer.

“A world in which over one-third of the population will face longer-lasting heat waves with unprecedented regularity.

“A world in which farmers and construction workers cannot work outside without risking heat-stroke.

“Where a month’s worth of rain falling in an hour may become commonplace. Where droughts last months longer and occur more frequently – and hundreds of millions of people suffer from freshwater scarcity.

“A world in which the crops families have grown for generations are no longer viable. Where conditions for malaria transmission and other chronic illnesses skyrocket and pandemics, like the one we continue to battle today, become more prevalent.”