This morning when I woke up, I instintively checked the meteo forecast on my mobile phone. Having regular and accurate news about the weather is, for us now, as normal as we, probably underestimate the importance of measuring temperature, pressure, and so on.
In fact, after a lot of attempts, only in 1641 a sealed thermometer was constructed by the Grand Duke of Tuscany, Ferdinand II. The Duke stated also the regular measurement of temperature. During the following two centuries, as the instruments were more accurate and were able to record other parameters, such pressure and humidity, measurement of climate parameters became widly diffused all over the world. But for regular and official measurement it takes to wait the XIX century, when have been also the first attempts to predict weather (for military and commercial purposes, mainly).
Weather is not climate...
...but climate derives from combining weather's conditions in a given time and space. So measuring climatic parameters and recording type and intensity of precipitations is foundamental to describe the climate; those observations have, also, to be taken for an enough long time frame, to appreciate the changes of climate patterns. In fact changes happen not suddenly, normally, and you've got to analyse a great amount of data to establish correlations and appreciate the evolutionary trends.
It's clear that, almost, complete informations are available only for the last two centuries, and so what about for all the time humans lived without thermometers, barometers...and mobile phone apps?
A hole in the ice
The earth is naturally able to record changes occurred during its history. The geological deposits are, for example, important archives of the evolution of lithosphere during the millenia. More difficult is the analysis of changes occurred in the atmosphere, but not impossible. In fact, another type of deposit helps scholars to determine the global climate of the past: ICE.
Icecores drilled mainly in Antartica, record climate for a time frame of millennia: ice, in fact, during the solidification, freeze in it all the components of the atmosphere in the same time of its formation. In this way, each icecore shows a succession of layers, different in thickness and chemical composition. Each layer corresponds to a climate stage, with peculiar characteristics of temperature and balance of gases in the air.
From global to local
Antartica is a giant and almost complete archive of the climate of the past; but it's a GLOBAL archive.
We learned at school that climate is linked to latitude, altitude and proximity to the sea. And so every point on the surface of the planet has a peculiar local climate. If you want to study the relationship between the history of local communities, environment and climate, you can't only take in account the global climatological data.
Moving from a GLOBAL TO A LOCAL SCALE is not so easy, as it's not easy modelling the climate for a given region and for times instrumental measures are not available. At local scale several parameters and archives can be take in account: lake sediments, pollen analysis are able to provide important information about the environment in the past and, in consequence, about the local climate; but, considering the human impact in the landscape, they also record the anthropic modification of the landscape itself. Related to the presence of human communities are the alluvial deposits, dated by archaeological remains and witnessing the effects of climate patterns, but also the use of the soil of the communities themselves.
Giving a light in this almost deep dark scenario scholars can take in account the written sources, various in types and information provided. They are NOT QUANTITATIVE sources, but are important to relate natural phenomena and their effects in the landscape.
That's it: modelling the local climate of the past is not so easy as you can imagine. I'll need a lot of information, but also I'll must to record and relate data very different in type and origin.
And the scheme became more and more complex.
Nessun commento:
Posta un commento