In 2020, despite past pledges, the international support for the Paris Agreement starts to wane. In the years that follow, CO2 emissions are reduced at the local and national level but efforts are limited and not always successful. Radiative forcing increases and, due to chance, the most extreme events tend to happen in less populated regions and thus do not increase global concerns. Nonetheless, there are more frequent heatwaves in several cities and less snow in mountain resorts in the Alps, Rockies and Andes. Global warming of 1.5°C is reached by 2030 but no major changes in policies occur. Starting with an intense El Niño–La Niña phase in the 2030s, several catastrophic years occur while global warming starts to approach 2°C. There are major heatwaves on all continents, with deadly consequences in tropical regions and Asian megacities, especially for those ill-equipped for protecting themselves and their communities from the effects of extreme temperatures. Droughts occur in regions bordering the Mediterranean Sea, central North America, the Amazon region and southern Australia, some of which are due to natural variability and others to enhanced greenhouse gas forcing. Intense flooding occurs in high latitude and tropical regions, in particular in Asia, following increases in heavy precipitation events. Major ecosystems (coral reefs, wetlands, forests) are destroyed over that period, with massive disruption to local livelihoods. An unprecedented drought leads to large impacts on the Amazon rainforest, which is also affected by deforestation. A hurricane with intense rainfall and associated with high storm surges destroys a large part of Miami. A two-year drought in the Great Plains in the USA and a concomitant drought in eastern Europe and Russia decrease global crop production, resulting in major increases in food prices and eroding food security. Poverty levels increase to a very large scale, and the risk and incidence of starvation increase considerably as food stores dwindle in most countries; human health suffers. There are high levels of public unrest and political destabilization due to the increasing climatic pressures, resulting in some countries becoming dysfunctional. The main countries responsible for the CO2 emissions design rapidly conceived mitigation plans and try to install plants for carbon capture and storage, in some cases without sufficient prior testing. Massive investments in renewable energy often happen too late and are uncoordinated; energy prices soar as a result of the high demand and lack of infrastructure. In some cases, demand cannot be met, leading to further delays. Some countries propose to consider sulphate-aerosol based Solar Radiation Modification (SRM); however, intensive international negotiations on the topic take substantial time and are inconclusive because of overwhelming concerns about potential impacts on monsoon rainfall and risks in case of termination. Global and regional temperatures continue to increase strongly while mitigation solutions are being developed and implemented. Global mean warming reaches 3°C by 2100 but is not yet stabilized despite major decreases in yearly CO2 emissions, as a net zero CO2 emissions budget could not yet be achieved and because of the long lifetime of CO2 concentrations. The world as it was in 2020 is no longer recognizable, with decreasing life expectancy, reduced outdoor labour productivity, and lower quality of life in many regions because of too frequent heatwaves and other climate extremes. Droughts and stress on water resources renders agriculture economically unviable in some regions and contributes to increases in poverty. Progress on the sustainable development goals is largely undone and poverty rates reach new highs. Major conflicts take place. Almost all ecosystems experience irreversible impacts, species extinction rates are high in all regions, forest fires escalate, and biodiversity strongly decreases, resulting in extensive losses to ecosystem services. These losses exacerbate poverty and reduce quality of life. Life for many indigenous and rural groups becomes untenable in their ancestral lands. The retreat of the West Antarctic ice sheet accelerates, leading to more rapid sea level rise. Several small island states give up hope of survival in their locations and look to an increasingly fragmented global community for refuge. Aggregate economic damages are substantial, owing to the combined effects of climate changes, political instability, and losses of ecosystem services. The general health and wellbeing of people is substantially reduced compared to the conditions in 2020 and continues to worsen over the following decades.
Scenario 3 [one possible storyline among worst-case scenarios]
IPCC special report, Global Warming of 1.5°C, 2018