I’ll tell you the story of 1.5 degrees in Glasgow
James Hansen's Diplomatic Note
The number is famous. 1.5 degrees Celsius is, according to many speakers at the recent COP26 climate conference in Glasgow , that increase in global temperature beyond which the human race would face extinction – no small risk. However, more 1.5 ° C than what? What is the starting point for the deadly calculation?
The documentation only says "compared to the pre-industrial era", but no one says – at least authoritatively, there are many opinions – when industrialization started, or where. There are climatic studies that start the measurement from 1720. The most commonly used period for a comparison is that from 1850 to 1900. Americans – who weigh in this speech – instead use 1880, for the excellent reason that until then there was no reliable global data on climatic temperatures.
To make the matter more complicated, until the COP21 conference in Paris (2015), the increase that would have caused the end of the world had to be two degrees Celsius. The agreement reached there set the limitation of the increase in global warming at 2 ° C, but opened the door to the new limit, committing the signatories to "continue their efforts anyway" in order not to exceed the familiar 1.5 ° C today. . The motivation behind the target change was the concern of some small maritime countries to disappear underwater sooner than expected – a consideration reiterated at the time by the former President of the Maldives, Mohamed Nasheed, in a 2009 press conference held for the 'precisely in diving …
Furthermore, there was a strong need to increase the sense of urgency regarding the "climate emergency", which is not always evident to the populations. And then, admits an activist: "Two degrees seemed like a number thrown in, while 1.5 degrees, complete with a decimal fraction, is more 'scientific'". The uncertainty about where, exactly, the human survival limit would lie creates another problem: How will we know when we will be there?
Ambient temperatures are determined not only by the level of CO2 in the atmosphere, but also by transient events such as the periodic shifts in the Pacific Ocean of the El Niño and La Niña currents. As well as other events, major volcanic eruptions for example, can change atmospheric circulation around the planet and cause global temperatures to swing up or down 0.2 ° C from the trajectory of man-made warming. In fact, the World Meteorological Organization believes that there is a one in four chance that the Earth's surface temperature will exceed the 1.5 ° C increase in at least one of the years as early as 2025 – without human cause. Therefore, you will have to measure the change over an average of several years – not just one – before you know you have reached your limit. It has not yet been decided on how many years to carry out the monitoring or on how to proceed. Now, there is no question: the planet is warming. Any glacier that retreats revealing the remnants of a previous human occupation proves this. But this is in some ways a consolation: it shows that all this has already happened … Otherwise, how would our ancestors have slipped under all that ice?
This is a machine translation from Italian language of a post published on Start Magazine at the URL https://www.startmag.it/energia/vi-racconto-la-storia-di-1-5-gradi-a-glasgow/ on Sun, 28 Nov 2021 06:40:17 +0000.