The United Nations Intergovernmental Panel on Climate Change (IPCC) released a climate report on August 9, 2021. In this report, experts constructed five forecasting models to more vividly reflect the different results of global temperature changes under different greenhouse gas emission reduction rates.
Scenario 1 This is the most optimistic future scenario forecast. In this scenario, the world will reach net zero carbon dioxide emissions around 2050, and the global society will achieve a transition to sustainable development. The global temperature rise will therefore briefly exceed 1.5°C, reaching around 1.6°C by mid-century. But then it will fall back and stabilize at around 1.4°C by the end of the century. It is also the only projected scenario to limit global temperature rise to around 1.5°C as set by the Paris Agreement. In such a scenario, extreme weather would still become common, but the world could successfully avoid the worst hazards posed by climate change.
Scenario 2 This is a next-best scenario, where global CO2 emissions drop significantly, but not fast enough to reach net-zero global CO2 emissions after 2050. After that, the whole society also turned to sustainable economic development. As a result, the global temperature rise will reach around 1.7°C by the middle of this century and stabilize at around 1.8°C by the end of the century.
Scenario 3 In this scenario, global CO2 emissions will remain at current levels for the next 30 years, and will not begin to decline until mid-century, and global net-zero CO2 emissions will not be reached by the end of the century, and the global society fails to transition to an economic sustainable development. In this scenario, global temperature rises would reach a dangerous 2°C by mid-century and 2.7°C by the end of the century.
Scenario 4 This is a worse scenario, where global carbon dioxide emissions will continue to rise, and total emissions will roughly double by 2100. Under this scenario, the global temperature will rise by 2.1°C by the middle of this century and by 3.6°C by the end of the century.
Scenario 5 This is an extremely poor future forecast scenario, and one that we want to avoid anyway. In this scenario, global carbon dioxide emissions double by 2050, and the rapid growth of the global economy is based on the massive extraction of fossil fuels and the maintenance of energy-intensive lifestyles. Under such a scenario, the global temperature would rise by 2.4°C by the middle of this century and a terrifying 4.4°C by the end of the century.
What does global warming over 1.5°C mean? The climate report points out that with every little bit of global warming, the probability of extreme weather increases. For example, for every 0.5°C increase in global temperature, the frequency and intensity of extreme high temperature weather, extreme heavy rainfall, and drought will increase significantly. If global warming exceeds 1.5°C, extreme weather that used to be very infrequent will occur more frequently. In the past few months, many countries in Europe, Asia and Africa have been hit by floods due to extreme rainfall, and extreme heat and wildfires have also occurred frequently in many countries around the world.
