Effects of climate change

• 1. Introduction

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  Effects of climate change are already documented across Earth's natural environment and human societies, yet the full scale of what is coming remains the defining question of our time. Global surface temperatures have risen by 1.1 degrees Celsius. That figure carries within it a cascade of consequences: forests burning with greater ferocity, ancient ice sheets retreating, coastlines swallowing land that people have lived on for generations. And the story is not static. Scientists studying tree rings, ice cores, corals, and ocean sediments have found that recent temperatures have surpassed anything in the last 2,000 years. How much further will they rise? What happens to the ecosystems and communities in the path of those changes? And at what point do certain shifts become impossible to reverse? Those are the questions this documentary will pursue.

• 2. A Warming Atmosphere

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  The lower and middle atmosphere, where nearly all weather occurs, is heating because of the greenhouse effect. Water vapour increases as temperatures rise, and since water vapour is itself a greenhouse gas, that creates a self-reinforcing loop. The excess moisture gets pulled into storms, making them more intense, larger, and potentially longer-lasting.

  Heatwaves over land have become more frequent and more intense in almost all world regions since the 1950s. A heatwave that would have occurred once every ten years before global warming began now occurs 2.8 times as often. Marine heatwaves are twice as likely as they were in 1980. The wet-bulb temperature, which measures both heat and humidity combined, is a hard biological ceiling. Humans cannot survive a wet-bulb temperature above 35 degrees Celsius. If warming exceeds 1.5 to 2 degrees, deadly heat and humidity may become unavoidable in parts of the tropics.

  For every degree Celsius that air warms, it can hold 7% more water vapour. That additional moisture intensifies rainfall events while also increasing evaporation, which deepens droughts. Climate change is producing longer hot dry spells broken by more violent bursts of rain. Without mitigation, around one third of land areas are likely to experience moderate or more severe drought by 2100.

  Storms are also tracking toward the poles. Some regions will see large changes in maximum wind speeds as tropical cyclones and storm tracks shift poleward. Scientists expect fewer tropical cyclones overall, but expect the ones that do form to be stronger. There has probably been an increase in the number of tropical cyclones that intensify rapidly.

• 3. Ice, Oceans, and Rising Seas

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  Sea ice in the Arctic has declined more than 50% since the first satellite records, at a rate of 4.7% per decade. The mechanism driving further loss is self-reinforcing: sea ice reflects 50% to 70% of incoming solar radiation, while the open ocean reflects only 6%. As ice disappears, the ocean absorbs more heat, which melts more ice. The Arctic is expected to become ice-free at the end of some summers before 2050.

  Glaciers separate from the polar ice sheets lost around 8% of their mass between 1971 and 2019. In the Andes and the Himalayas, that retreat could directly threaten water supplies for large populations and trigger landslides or glacial lake outburst floods.

  The Greenland and West Antarctic ice sheets present longer-term concerns. The complete loss of the West Antarctic ice sheet would cause over 5 metres of sea level rise. A partial collapse would still be irreversible for decades and possibly millennia. The complete loss of the Greenland ice sheet would contribute 7 metres to sea levels globally. Sustaining warming between 1 and 4 degrees Celsius could trigger that process over millennia through the elevation-surface mass balance feedback: when ice melts on top of the sheet, the surface drops to a lower and warmer altitude, which accelerates further melting.

  Permafrost, the frozen ground underlying vast areas of the Arctic, warmed by about 0.3 degrees between 2007 and 2016. As it thaws, it releases methane from decomposing microbes. Scientists estimate carbon storage in permafrost globally at approximately 1,600 gigatons, roughly twice the amount currently in the atmosphere. The thaw can also seriously damage railways, settlements, and pipelines built on what was once stable frozen ground.

  The ocean is also acidifying as it absorbs carbon dioxide from the atmosphere, threatening shell-forming organisms like oysters. Between 70% and 90% of today's warm-water coral reefs will disappear even if warming is kept to 1.5 degrees Celsius. Coral reefs provide habitat for thousands of species and offer coastal protection. Estimates of people at risk from coastal flooding due to sea level rise range from 190 million to 300 million, and could reach 640 million in a worst-case scenario tied to Antarctic ice sheet instability.

• 4. Tipping Points

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  At 1 degree Celsius above pre-industrial temperatures, there is already a moderate risk of global tipping points. At 2.5 degrees, that risk becomes high. Tipping points occur when parts of the natural environment shift into a new state from which they cannot easily return. The West Antarctic and Greenland ice sheets, the Amazon rainforest, and warm-water coral reefs are all cited as potential candidates.

  A collapse of the Atlantic meridional overturning circulation would likely halve rainfall in India and cause severe drops in temperature in Northern Europe. Some studies found that this circulation has already weakened by about 15% since 1950. In high emissions scenarios, it could collapse entirely, cooling parts of Europe by up to 30 degrees while warming the southern hemisphere.

  A 2019 study concluded that the Amazon could begin a 50-year-long collapse to a savanna around 2021. Rainfall in the Amazon is partly recycled when it evaporates back into the atmosphere rather than running off. Deforestation is reducing that recycling capacity, and more frequent droughts are compounding the stress. After a tipping point is crossed, the study found, it becomes increasingly and disproportionally more difficult to prevent or reverse the shift.

  A 2018 study found that 45% of environmental problems, including those caused by climate change, are interconnected. That raises the possibility of a domino effect, where triggering one tipping point sets off others. The warming of the deep ocean and ocean acidification are set to continue even after global surface temperatures stop rising. In biological systems, species extinction would be irreversible by any human timescale. Some scientists note that unique cultures, and even endangered languages, could be lost as a consequence of these cascading changes.

• 5. Human Costs

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  Humans have a climate niche: a range of mean annual temperatures below 29 degrees Celsius in which they thrive. As of May 2023-60 million people already lived outside that niche. With every additional 0.1 degree of warming, 140 million more people are pushed out of it.

  The Internal Displacement Monitoring Centre reported that extreme weather events displaced approximately 30 million people in 2020, while violence and wars displaced approximately 10 million in the same period. The World Bank estimated in 2018 that climate change will cause internal migration of between 31 and 143 million people by 2050, as populations escape crop failures, water scarcity, and rising seas. That estimate covered only Sub-Saharan Africa, South Asia, and Latin America.

  Between 1.5 and 2.5 billion people currently live in areas with regular water security issues. If global warming reaches 4 degrees, water insecurity would affect roughly twice as many people. In 2025, annual losses in food production from extreme weather were estimated at 123 billion US dollars, equivalent to 5% of global agricultural gross domestic product.

  Climate change does not affect everyone equally. The ten countries of the Association of Southeast Asian Nations are among the most vulnerable in the world. A 2020 World Bank paper estimated that between 32 million and 132 million additional people will be pushed into extreme poverty by 2030. Children under 14 are 44% more likely to die from environmental factors, according to a Lancet review. Industrialised countries, which have emitted the vast majority of carbon dioxide, have far more resources to adapt than developing nations do.

  Entire populations face the loss of their homelands. The nations of Kiribati, the Maldives, the Marshall Islands, and Tuvalu could see their populations entirely displaced by sea level rise, raising questions of statelessness without precedent in modern international law.

• 6. Economic Reckoning

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  A 2024 study drawing on 120 years of data found that climate change has already reduced welfare by 29%, and that further temperature rise will raise that figure to 47%. The temperature rise during the years 1960 to 2019 alone has cut current GDP per capita by 18%. A single degree of warming reduces global GDP by 12%. The study placed the correct social cost of carbon at 1,065 dollars per tonne of carbon dioxide.

  A 2026 study published in Nature estimated that, from 1990 through 2020, carbon dioxide emissions in the United States caused 10.2 trillion dollars in cumulative damages. Damages from China were estimated at 8.7 trillion dollars, and from the European Union, 6.42 trillion dollars. The researchers noted that future damages from past emissions are at least an order of magnitude larger than historical damages from those same emissions.

  One study found that total damages at 1.5 degrees of warming were 90% less than at 3.66 degrees, the level that would result from no effort to cut emissions. Another found that a temperature rise of 2 degrees by 2050 would reduce global GDP by 2.5% to 7.5%, with temperatures potentially reaching 4 degrees by 2100 and cutting global GDP by 30% in the worst case. Excluding tipping points from economic models likely underestimates the true global economic impact by a factor of two to eight.

  Insurance is already responding to these pressures. In 2019, Munich Re said climate change could make home insurance unaffordable for households at or below average incomes. Lack of rainfall possibly linked to climate change reduced the number of ships passing through the Panama Canal from 36 to 22 per day, with further drops expected into 2024. The German Physical Society and the German Meteorological Society published a joint statement in September 2025 warning that, if current trends continue, global temperature could rise to 3 degrees above pre-industrial levels by 2050 and to 5 degrees by 2100.