A + 4 °C world!

If the objective of the Paris Agreement (PA) is to maintain global warming within 2°C at the end of the century compared to the pre-industrial era, what could happen in a world at + 4°C?

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To this question answered at Cop23, British researchers of University of Exeter and the MetOffice-Hadley Center, the United Nations World Food Program and the United Nations University presented the HELIX Project (High-End cLimate Impacts and eXtremes).
The project tried to quantify the impacts of climate change at a regional level, considering different warming scenarios at the end of the century: 1.5 °C and 2 °C scenarios, as set out in the PA goals, and 4 °C as probable average scenario in case of inaction. Infact,without more ambitious mitigation measures, there is a high risk that the + 4 °C scenario at the end of the century will materialise.

But what about PA objectives? In the case of application of Intended Nationally Determined Contributions (INDCs) by each country, the best estimate is to reach the threshold of 2 °C by 2050. In the case of continuous high emission scenarios this threshold could already be reached t by 2040.

Therefore, the risks arising in the various areas of the world require adaptation actions that in some cases must be planned well in advance. In fact, it is no longer possible to act only in terms of mitigation , that is to say on the reduction of greenhouse gas emissions, since even if the emissions were drastically cut, they would only allow to avoid the worst impacts but could not avoid changes.

Impacts cover a large number of sectors, such as: the availability of fresh water, the risk of floods in coastal areas and river flooding, agriculture and food production, the forests and the environment, human health and economy.
The focus of the study was addressed in particular to the risks arising from extreme events and heat waves that, joined with the increase in humidity, have serious consequences on human health and life.

A 4 °C warming would lead to an increase of the risk of heat waves especially in tropical areas, with dramatic consequences in Africa and Southeast Asia.The same rise in temperature would result in a doubling of the frequency of flood events in river basins in many countries with high population density such as China, India and Bangladesh.

Bangladesh has been the subject of an in-depth study. Only in 2016-2017 have been observed 10 disastrous events in this country due to intense precipitation events during the monsoon season.The effect of sea rising on the coast and the increase of flood events may have dramatic consequences in the future in a country characterised by high population density and strong socio-economic vulnerabilities.

Finally, a particular attention in the study was placed on the issue of migrations as a consequence of an increase in extreme events that shows a more complex situation to be interpreted.In fact, migratory dynamics are determined by a number of, political, social, economic and demographic facts, as well as the environmental ones that climate change tends to affect. These factors contribute together but differ according to the geographic areas of the world. The erosion of the coast of an African village, as in the case described, does not necessarily induce a migration but rather a simple inward movement, thus people stay in a risky area. In fact, the choice of local people is to move with lower costs, to continue fishing in their own sea and to maintain their cultural habits!

Certainly, in a +4 °C world for many populations to access to minimal living conditions with a house, access to fresh water, food availability and basic health conditions can be more difficult. Maybe it will not be enough to move only a few kilometers away!