A 4°C world
A global mean temperature change of 4°C is close to the difference between the temperatures of the present day and those of the last ice age, when much of central Europe and the northern United States were covered with kilometers of ice, and the current change – human induced – is occurring at a much faster rate, over a century, not millennia.
If the currently planned actions are not fully implemented, a warming of 4°C could occur as early as the 2060s. Such a warming level by 2100 would not be the end point: a further warming to levels over 6°C would likely occur over the following centuries.
Floods, droughts, and extreme weather
The science is unequivocal that humans are the cause of global warming and unequivocal effects of greenhouse gas emissions already observed have continued to intensify, more or less unabated over the last decades. A world in which warming reaches 4°C above preindustrial levels, would be one of unprecedented heat waves, severe drought, and major floods in many regions, with serious impacts on human systems, ecosystems, and associated services.
More specifically, this level of warming could bring:
- the inundation of coastal cities;
- increasing risks for food production potentially leading to higher malnutrition rates; many dry regions becoming dryer, wet regions wetter;
- unprecedented heat waves in many regions, especially in the tropics;
- substantially exacerbated water scarcity in many regions;
- increased frequency of high-intensity tropical cyclones;
- irreversible loss of biodiversity, including coral reef systems.
Is it still possible to avoid a global temperature increase of 4°C?
With decisive action, a 4°C world can be avoided and warming can likely be held below 2°C.
Numerous studies show that there are technically and economically feasible emissions pathways to achieve this. Thus, the level of impact that developing countries and the rest of the world experience will be a result of government, private sector, and civil society decisions and choices about climate change which includes, unfortunately, inaction.
The global community has committed itself to holding warming below 2°C to prevent “dangerous” climate change, but the sum total of current policies – those already in place and those that have been pledged – will very likely lead to warming far in excess of these levels. Indeed, present emission trends put the world plausibly on a path toward 4°C warming within the century.
Brun indikerer områder der vil blive uboelige pga. oversvømmelser, tørke eller ekstremt vejr. Orange er ubeboelig ørken. Røde kystområder vil ligge under vand. Den grønne farve står for zoner med fødevareproduktion.
Foto: connectography
What if this 4°C increase is not avoided?
A world in which warming reaches 4°C above preindustrial levels, would be one of unprecedented heat waves, severe drought, and major floods in many regions, with serious impacts on human systems, ecosystems, and associated services.
A global mean temperature difference of 4°C is close to that between the temperatures of the present day and those of the last ice age, when much of central Europe and the northern United States were covered with kilometers of ice, and the current change – human induced – is occurring over a century, not millennia.
If the currently planned actions are not fully implemented, a warming of 4°C could occur as early as the 2060s. Such a warming level by 2100 would not be the end point: a further warming to levels over 6°C would likely occur over the following centuries.
The impacts are likely to hit the world’s poorest regions the hardest, since they have the least economic, institutional, scientific, and technical capacity to cope and adapt. Small Island Developing states (SIDS) and Least Developed Countries (LDCs) have identified that a global warming of 1.5°C as the level above which there would be serious threats to their own development and, in some cases, survival. Among the likely impacts are:
- Even though absolute warming will be largest in high latitudes, the warming that will occur in the tropics is larger when compared to the historical range of temperature and extremes to which human and natural ecosystems have adapted and coped. The projected emergence of unprecedented high-temperature extremes in the tropics will consequently lead to significantly larger impacts on agriculture and ecosystems.
- Sea-level rise is likely to be 15 to 20 percent larger in the tropics than the global mean.
- Increases in tropical cyclone intensity are likely to be felt disproportionately in low-latitude regions.
- Increasing aridity and drought are likely to increase substantially in many developing country regions located in tropical and subtropical areas.
Avoiding a 4°C world, a matter of commitment
Numerous studies show that there are technically and economically feasible emissions pathways that can limit the warming to 2°C.
The level of impact that the world will experience will be a result of the decisions and choices about climate change that governments, the private sector, and civil society will take. Unfortunately, this also has to include the possibility of inaction.
