Historically, the ice retreated from the territory of Latvia approximately 15,000 years ago, and since then, gyttja (also known as sapropel) began to accumulate in lakes, formed by dead plants, algae and animals. We take a special drill, go out onto the lake and usually drill in the middle, where the deposits least affected and influenced by various conditions can be found. Once we extract the contents, we take them to the laboratory and study them centimetre by centimetre, millimetre by millimetre, or at any other necessary interval. We determine the timescale using the C14 (radiocarbon) method. We also determine the pollen present in the various layers to understand which tree species grew in a particular place at a given time. As is well known, every plant has optimal conditions in which it is able to live and grow: humidity, warmth, etc. For instance, for birch, spruce and pine, these indicators are different. By performing these measurements layer by layer, we find out what the temperature was during the respective period. Once such an analysis (measurements) has been carried out for the entire cross-section, we can plot and model scales of how the temperature has changed over time. Studies are often explained using so-called average temperatures, which have a significant drawback: they do not state that a so-called error margin exists. If the average figure obtained is one, the error margin determines that the real figure could be the average, but also any other number within this zone—in other words, this figure can be 'shifted' to one side or the other.
The latest studies, the results of which have not yet been published, were carried out at Lake Āraiši, in the Vidzeme Highlands. Thanks to a good collaboration with a Finnish colleague, I reconstructed the average air temperature for both summer and winter; it appears that the climate has become significantly warmer specifically in winter rather than in summer, similar to what is happening at present and what is predicted to happen in the future.