Effects of global warming at 4 degrees Celsius
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Global Warming at 4 Degrees Celsius: Key Impacts
Extreme Temperature and Precipitation Events
A 4°C rise in global temperatures would lead to much more frequent and intense heatwaves, with cold extremes becoming rare or disappearing altogether. Warm extremes, especially daily minimum temperatures, would increase significantly, particularly in low-latitude and northern high-latitude regions. Heavy precipitation events would become more intense and frequent, especially in high latitudes, while drought-prone regions would get drier, increasing the risk of extreme dry events in the extratropics. These changes would be much more severe than those expected at 1.5°C or 2°C of warming, posing greater threats to both natural and human systems Wang2018Tsai2022Adams2014.
Impacts on Agriculture, Water, and Ecosystems
At 4°C warming, the challenges for agriculture, water resources, and ecosystems would be much larger than at lower warming levels. Crop yields are expected to decline, water resources would become more stressed, and ecosystem services would be disrupted. In some regions, such as sub-Saharan Africa, farming systems could collapse or require complete transformation. Forests, pastures, and croplands would increasingly shift into arid climates, especially in South America, Africa, and the Northern Hemisphere, threatening food security and livelihoods New2011Adams2014Spinoni2021.
Expansion of Arid Areas and Population Exposure
Global warming of 4°C could cause about 6.8 million km² (4.5% of global land) to become arid, an area comparable to the seventh largest country in the world. In the worst-case scenario, up to 500 million people could be living in regions shifting toward arid climates, with significant impacts on forests, pastures, and croplands. This expansion of drylands would be particularly strong in South America and southern Europe .
Economic Damages and Global Inequality
The economic consequences of 4°C warming are severe. Global aggregate damages could reach 3.67% of GDP by 2100, with the net present value of damages estimated at $591.7 trillion for the period 2008–2200. This is far higher than the damages expected at 1.5°C or 2°C of warming. Per capita economic output could decline by more than 30% by 2100, with poorer countries suffering the most. The social cost of carbon would also rise dramatically, making mitigation efforts much more cost-effective compared to the damages avoided Warren2021Burke2018.
Social Vulnerability and Development Challenges
The impacts of 4°C warming would hit the poor, elderly, and children hardest, increasing social vulnerability. The risks to food, water, and energy security would make it extremely difficult to achieve development goals, reduce poverty, or promote global prosperity. In a 4°C world, many of the development gains of recent decades could be reversed, and global inequality would likely worsen Adams2014Burke2018.
Conclusion
A 4°C increase in global temperatures would bring unprecedented changes, with more extreme weather, widespread ecosystem disruption, large-scale expansion of arid areas, and severe economic and social damages. The impacts would be much greater than at lower warming levels, highlighting the urgent need for strong mitigation and adaptation efforts to avoid the most dangerous consequences of climate change New2011Wang2018Tsai2022+4 MORE.
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Most relevant research papers on this topic
Four degrees and beyond: the potential for a global temperature increase of four degrees and its implications
A global temperature increase of 4°C or more could result in larger impacts and adaptation challenges than 2°C, highlighting the need for renewed efforts to reduce emissions and research adaptation strategies.
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Extreme temperature and precipitation changes associated with four degree of global warming above pre‐industrial levels
A 4°C global warming scenario would lead to more violent temperature and precipitation extremes, posing more threats to natural and human systems compared to a 1.5°C warming scenario.
Turn Down the Heat : Confronting the New Climate Normal
Climate change impacts are already causing damage and instability, and if warming rises to 4°C, severe consequences for development, agriculture, water resources, and coastal vulnerability could be unavoidable.
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Global and regional aggregate damages associated with global warming of 1.5 to 4 °C above pre-industrial levels
Limiting global warming to 1.5°C or less results in significantly lower global aggregate damages and a significantly lower net present value of global damages compared to 4°C warming.
Large potential reduction in economic damages under UN mitigation targets
Limiting warming to 1.5°C has a more than 75% chance of reducing economic damages and reducing global inequality, while failing to meet the 2°C target may increase economic damages substantially.
Global Warming: Are We Entering the Greenhouse Century?
Human activities may be causing global warming, potentially raising temperatures by 5 degrees Celsius in less than a century, with serious consequences for agriculture, sea levels, public health, and social upheaval.
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