May 29, 2020

# Mathematical data of climate change | Science

Although most scientists (in fact, 97%) believe there is strong evidence of climate change caused by human beings, there is no total agreement on its importance or its impact in the future. Mathematics can help us deal with certain crucial points of the debate, and the first step is to carefully analyze the available data. There are many indisputable statistical data, referring to various phenomena, which show that the current climate is changing. For example, you may have noticed that the number of extreme weather events has increased, such as the recent wind and rain storms that have hit southeast Spain causing five deaths. Are these phenomena evidence of climate change? The answer is, almost certainly, yes. To understand why we need to understand a few statistical concepts.

We know that the last three decades have been the warmest and that the average recorded temperature of the Earth has increased by one degree Celsius, since the records began (with the creation of the United Kingdom Meteorological Office in 1850). This may not seem like much, since in a single day the variation in temperatures is much greater. However, this change in the average temperature significantly increases the likelihood of extreme temperatures and related weather events, such as higher rains (since a warmer atmosphere can retain more water). To see this, it is convenient to take a look at the graph below.

This graph shows the typical statistical distribution of temperatures, which follows a bell curve with the center in the average value. The portion on the far right is the distribution queue and the area under the tail shows the probability of a hot temperature. The curve on the right represents what happens if the average temperature increases: the entire curve moves to the right. That small displacement significantly increases the height of the curve in the right tail. That is, they increase the chances of a hot and extreme climate, which in turn dramatically increases the possibility of extreme weather events. The increase in extreme temperature events and the frequency of tropical storms observed is consistent with this prediction.

Another direct consequence of global warming, and one of the clearest indications of its impact, has been the thaw of the Arctic. There is clear evidence of this thanks to the satellite of the National Snow and Ice Data Center of NASA, which monitors the extent of sea ice in the Arctic summer since 1979. In 36 years, approximately 2.5 million square kilometers have been lost Of surface. If this rate continues, all Arctic sea ice will have disappeared in 100 years. A long-term consequence of this is that the Earth will darken. One of the functions of the ice sheets is that they reflect a large amount of energy from the Sun and, as a result, keep the planet colder. Therefore, as ice disappears, warming increases.

But … what do mathematics say about the causes of global warming? He Intergovernmental Panel for Climate Change (IPCC), considers, based on gigantic computational models, that one of the main reasons is the increase in carbon dioxide. Of course, we know – it is possible to precisely control the amount of CO2 in the atmosphere— that the level of carbon dioxide has increased rapidly. Specifically, in the last fifty years the average amount has increased from 320 ppm to the current value of 406 ppm. This fact is undeniable and, most likely, is due to the burning of fossil fuels such as oil, coal and gas.

However, the relationship between the variation in the level of carbon dioxide and the changes in Earth's temperature is what generates a lot of controversy, and it is also the basis of the IPCC recommendations on the need for a "low economy in carbon". The key question is whether the increase in CO2 leads to an increase in temperature (due to the greenhouse effect) or, conversely, if it is an increase in temperature (due, for example, to natural causes), which has led to an increase in the levels of carbon dioxide carbon. If it were first, then we must (and can) do something to stop the climate disaster. In the second case, we are victims of natural climatic variations, and we cannot do anything about it. Say what some politicians say, the mathematical models of climate change (which we will talk about in the next Coffee and theorems) are consistent with the first point of view and not with the second.

Chris Budd is gresham professor of Geometry at the University of Bath (United Kingdom) and has been one of the speakers of the session “Climate crisis: facts and actions”Which took place on September 24 at the 7th Heidelberg Laureate Forum.

Translation: Agate Timón García-Longoria

Coffee and theoremsIt is a section dedicated to mathematics and the environment in which they are created, coordinated by the Institute of Mathematical Sciences (ICMAT), in which researchers and members of the center describe the latest advances in this discipline, share meeting points between mathematics and other social and cultural expressions and remember those who marked their development and knew how to transform coffee into theorems. The name evokes the definition of the Hungarian mathematician Alfred Rényi: "A mathematician is a machine that transforms coffee into theorems."

Editing and coordination: Agate Timon (ICMAT).