This is what the science suggests those very different realities could look like.
Year 2100: the nightmare scenario
The 21st century draws to a close without action having been taken to prevent climate change. Global temperatures have risen by over 4°C. In many countries, summer temperatures persistently stay above 40°C. Heatwaves with temperatures as high as 50°C have become common in tropical countries.
Every summer, wildfires rage across every continent except Antarctica, creating plumes of acrid smoke that make breathing outdoors unbearable, causing an annual health crisis.
Ocean temperatures have risen dramatically. After repeated bleaching events, Australia’s Great Barrier Reef has been officially declared dead.
The Great Barrier Reef Via Greenpeace Australia
Frequent and prolonged droughts torment vast swathes of the Earth’s land. The deserts of the world have expanded, displacing many millions of people. Around 3.5 billion live in areas where water demand exceeds what’s available.
Air pollution has a new major cause outside the traffic-choked cities: dust whipped up from now-barren farmland.
The Arctic is free of sea ice every summer. Average temperatures in the far north have risen by over 8°C as a result. The Greenland and Western Antarctic ice sheets have started to melt, releasing a huge amount of freshwater into the oceans.
Most mountain glaciers have completely melted. Skiing is now a predominantly indoor sport which takes place on giant artificial slopes. Most of the Himalayan plateau’s ice has disappeared, reducing the flows of the Indus, Ganges, Brahmaputra and Yamuna rivers which over 600 million people rely on for plentiful water.
Markus Spiske via Unsplash
The extra heat in the ocean has caused it to expand. Combined with water from melting ice sheets, sea levels have risen by more than one metre. Many major cities, including Hong Kong, Rio de Janeiro and Miami, are already flooded and uninhabitable. The Maldives, the Marshall Islands, Tuvalu and many other small island nations have been abandoned.
Many coastal and river areas are regularly flooded, including the Nile Delta, the Rhine valley and Thailand. Over 20% of Bangladesh is permanently under water.
Winter storms are more energetic and unleash more water, causing widespread wind damage and flooding each year.
Tropical cyclones have become stronger and affect tens of millions of people every year. Mega-cyclones, like 2013’s Typhoon Haiyan, have become more common, with sustained wind speeds of over 200 mph.