-One of the reasons for the development of electric mobility is to avoir major climate changes. Thus, we can wonder what climate change is and if it is a really serious matter. This video deals with these two issues. When solar radiations reach the surface of the Earth and oceans, they are largely reflected by this surface in the form of infra-red light which is captured by a greenhouse gas layer in the atmosphere. This is fortunate because thanks to this layer, the temperature of the Earth's surface is an average of 15°C instead of -18°C. This is how life as we know it can exist so it is really advisable to have these greenhouse gases. The problem is that since the industrial revolution, humanity has increased the concentration of these greenhouse gases through its emissions. We notice that it led to a 1-degree increase in temperature since the pre-industrial era. When we look at this curve, we can notice two facts. First, there is a rather strong natural variability of climate systems. There have always been warm winters and cold winters, cool and less cool summers. However, beyond this natural variability, the average temperature on the surface of the Earth tends to increase. The temperature is increasing faster and faster when we get closer to our period. This increase is concomitant with the increase in greenhouse gas emissions. Beyond this link, is there an obvious causal relationship between two phenomena? Scientists are trying to answer this question. They try to understand which climate system evolution elements are linked to natural factors, changes in the Earth's orbit, changes in solar activities, and which elements are linked to human factors, these infamous greenhouse gas emissions. The problem is that the climate system is complex with many interactions. Today, we are unable to fully understand and represent it. We can represent parts of it thanks to fluid mechanics or atmospheric chemistry. Other parts can only be represented thanks to hypotheses on how connections are made between the explanatory factors and the factors we are seeking to explain. This is the reason why there are several climate models which tell different stories about how the climate evolves and works. But these different models are being discussed in a setting organized by the World Meteorological Organization under the supervision of the UN within the IPCC. IPCC stands for Intergovernmental Panel on Climate Change. This panel does not produce information on the climate. It summarizes what science has to say about climate. It reports elements on which science agrees, things we have perfectly understood, but also controversies, elements on which different scientific works do not agree. Thus, there can be scientific works that wonder about the very causality between greenhouse gas concentration and the evolution of the climate system. But if these works are undertaken by scientists using the right scientific protocols, they will be reused by the IPCC. The IPCC is a gathering of several hundred authors, scientists from the 5 continents, to produce this state of the art. It is extremely interesting for us because it gives us a picture of everything science has to say, where it coincides or differs regarding the climate change issue. During the rest of this video, I will mainly use the IPCC's works to illustrate my words. First, I will talk about greenhouse gases. The Kyoto Protocol had retained six of them. Among them, there are two main gases: carbon dioxide, CO2, and methane, CH4. CO2 comes from two sources. First, the combustion of fossil fuels. It represents 65% of greenhouse gas emissions. The second source is the changes is land use: when cultivating a surface that was not cultivated, the land is plowed and the CO2 contained in the ground is released. It is even worse when the cultivated surface was a forest since we also release the CO2 contained in the wood. Second main greenhouse gas, methane which comes from three sources: agriculture, for instance rice cultivation generates methane, livestock farming since livestock digestion also generates methane, and finally waste that generates methane when left to decompose in the open air. In order to compare methane and CO2, we use what we call the global warming potential. It tells us how a tonne of greenhouse gas changes radiative forcing during a century. In order to say that methane represents 16% of greenhouse gas emissions, I use its global warming potential which equals 28. It means that one tonne of methane will have a warming potential 28 times higher than CO2 over a century. But this warming potential is actually condensed on the first years of the methane lifetime which is shorter than that of CO2. If I consider this phenomenon, today I can observe that for the moment, methane is rather responsible for 40% of radiative forcing linked to human emissions. Now, if I want to know where the source of these emissions is, what can I notice? Of course, developed countries have higher emissions per inhabitant than developing countries. However, it does not mean that developing countries have low emissions since China has become the first greenhouse gas emitter since 2007. Now, if I consider each dollar of wealth created, developed countries are not the largest emitters. It is quite the opposite. They are more efficient in wealth creation. It is quite natural since the wealth they create partly corresponds to services, which are less C02 intensive than manufactured goods produced in developing countries. Historically, developed countries were almost the only emitters during the century that followed the industrial revolution. But starting from the second part of the 20th century, developing countries also increasingly produced emissions. Thus, since 2007, developing countries have become the main greenhouse gas emission producers. Today they represent about 55% of the global emissions. Thus, it is mandatory for these countries to eventually also control and reduce their greenhouse gas emissions. If I compare emissions per inhabitant in France and China, it is surprising since their emission levels are almost identical: 5.5 tonnes. But these are the emissions produced on the French and Chinese territories divided by the number of inhabitants in France and China. But a certain amount of emissions produced in China are connected to manufactured products that China exports to France. If I consider the emissions produced by the products used by French people, I see that the emissions in France are over 8 tonnes per inhabitant per year whereas emissions in China are around 2.5 tonnes per inhabitant per year. Even though I could think that the emission levels were identical, actually the emissions of a French inhabitant are almost 4 times as high than that of a Chinese inhabitant. Now, we will see why it is important to deal with climate change. We could believe, especially in temperate countries, that having one or two more degrees is not that dramatic. But you must understand that climate change is not about temperature rise. It is a complete change in climate systems that will have a certain number of impacts. We can already see some. It is impossible to say that such storm, such flood or such drought is due to climate change because there have always been such climate events. However, it is clear that the increased frequency of these extreme events is the symptom of a changing climate system. Other elements can already be seen. For instance, the sea level is rising by over 3 mm per year whereas this rise was limited to 1 mm at the beginning of the 20th century. This rise of the sea level is connected to the dilatation of the oceans when they get warmer and to the melting of ice caps at the poles. We start seeing a few consequences of climate change. But the vast majority of these consequences will happen during the second part of the 21st century. What will be these changes about? First, they will impact biodiversity. Why? Because most species will not be able to survive these climate system changes in which they will evolve. Thus, some species will simply disappear because they will not be able to withstand the temperatures or the water stress to which they will be subjected. The issue is that biodiversity is not only about the number of species. It is also about the interactions between these species. There are multiple interactions which are hard to understand. Today, scientists strive to evaluate the impact on species that are not directly threatened by climate change but by the extinction of the first species. Will they manage to adapt to the extinction of these species or will they also disappear as a consequence of the extinction of the first species? Today, we believe that about 25% of the species are threatened by climate change if we do not change our current emission levels. The second impact is related to water resources. Today, water is already distributed in a rather uneven way on Earth's surface and climate change will increase these inequalities. The Mediterranean basin is already experiencing water stress which will increase even more over the 21st century. A certain number of conflicts can be indirectly related to climate change and water access issues such as the conflict in Mali for instance. A drought and poor harvests have clearly resulted in a conflict. We see that this water resource access issue is central because it will clearly create conflicts among populations and massive population movements. In some countries, agricultural systems will experience difficulties adapting to climate change. The distribution is also very uneven between temperate and Southern countries. Temperate countries are globally able, both on technical and economic levels, to adapt their agricultural systems. Thus, they will not really suffer from climate change and benefit from the effect on productivity linked to the increase of CO2 in the atmosphere. Globally, in developed countries that will be able to adapt, the impact will be rather positive on agricultural productivity. On the other hand, developing countries do not have the technical or economic ability to adapt and they will suffer from more important climate changes compared to temperate countries which leads to a very important deterioration of agricultural productivity. This has two main consequences. First, malnutrition increases. Today, malnutrition is mainly located in these countries. Second, in many of these countries, agriculture still represents the main part of wealth production. Thus, the poverty of these people will increase when they suffer from climate change. We see that on a global scale the full impact of climate change on agricultural productivity is relatively small if we are able to change the agricultural systems in Northern countries. Besides, climate change also impacts public health. It is mainly due to the fact that the vectors of certain tropical diseases will be able to go north and bring over in temperate countries nice diseases that Northern countries do not experience yet. Finally, climate change has an impact that is already visible today: the consequences of extreme events on infrastructures that already cost insurances tens or hundred billion dollars per year in terms of indemnification when extreme events occur. Besides, the seas rising will lead to massive population movements, originating from Pacific islands that will disappear for instance, but also urban populations originating from coastal cities that will not be able to adapt in terms of infrastructures. This increase in sea levels will be about 60 cm to 1 m according to the IPCC's scenarios. To conclude, I will say that greenhouse effect is a natural phenomenon that is useful to life on Earth. But it is amplified by human actions. There are still scientific controversy issues regarding climate change but many works agree on the role played by humans in greenhouse gas emissions and on the potential impact of climate change on physical systems and human societies. Thus, acting is mandatory. Of course, Northern countries are historically responsible since they were almost the only emitters for over a century. But today's emission distribution leads to the fact that Southern countries must also implement strategies to start monitoring their emissions in order to avoid a high increase before reducing these emissions. If we consider our current emission levels, we have 20 years left if we want to remain under the 2 degrees that have been set during the COP 21 in Paris. After 20 years, our emissions will have to become negative, meaning that we do not emit anymore and that we can capture and store part of the emissions that have been emitted so far. If we reduce our emissions, we can reach this cancelation point around 2070. But during the 21st century, we need to be able to globally reach zero emission in every country. Finally, as you have seen it, considering the consequences of climate change, trying to fight climate change by mitigating our emissions and adapting to climate changes that we will be subject to no matter what, is a way to fight for peace because climate change can lead to issues regarding access to resources that are fundamental for life and extremely massive population movements. You can imagine the potential consequences as we can already see it happening with a few unfortunate examples featured in the news.
