An interview with paleoecologist Normunds Stivriņš
It is very pleasing to know that Latvian scientists are researching climate issues without relying solely on the experience of other countries.
Climate issues are currently highly polarised, both politically and scientifically. Predicting the future is unrealistic, which is why I try to view and assess climate change solely from a scientific perspective, based on both my own research and that of my colleagues. How do we operate? We use the reconstruction principle, which means looking at what has happened in the past, what is happening now and how, and on that basis, we attempt to reconstruct and model various possibilities. How is the “past” climate determined, how is it reconstructed and how is it calculated how warm it was at a certain time? I have personally studied pollen deposits in Latvian lakes. A lake is a very suitable environment for such research because much of what grows around or near the lake ends up in the water and is preserved: there is pollen every year, and tree leaves as well. By knowing the climatic conditions in which plants grow today, one can attempt to determine what the climate was like when these plants were growing in the past.
Looking back historically, ice retreated from Latvian territory approximately 15,000 years ago, and since then, gyttja (also known as sapropel) began to accumulate in the lakes, formed by dead plants, algae and animals. We take an appropriate corer, row out into the lake, and usually core in the middle, where the sediments are least affected and influenced by various conditions. After extracting the contents, we take them to the laboratory and study them centimetre by centimetre, millimetre by millimetre, or at other necessary intervals. We determine the timeline using the C14 (radiocarbon) method. We also determine the pollen present in the various layers to understand which tree species were growing in a particular location at a given time. As is known, every plant has optimal conditions in which it can live and grow: moisture, warmth, etc. For instance, these parameters differ for birch, spruce and pine. By performing the described measurements layer by layer, we find out what the temperature was during the respective period. Once such an analysis (measurements) has been performed for the entire core, we can map and model scales of how the temperature has changed over time. Studies are often explained using so-called average temperature, which has a significant drawback: it is not stated that a so-called error zone exists. If the resulting average figure is one value, the error zone dictates that the real figure could be the average, but also any other number within that zone—in other words, this figure can be “nudged” one way 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 good cooperation with a Finnish colleague, I reconstructed the average air temperature for both summer and winter; it appears that the climate has become significantly warmer in winter rather than in summer, similar to what is happening now and what is predicted to happen in the future.
Why is that? If we talk about the aforementioned period 15,000 years ago, the ice age ended, “global warming” began, the air temperature rose rapidly and then gradually decreased... and we arrive at the present day, when it is rising again. 7,500–5,000 years ago, the average air temperature in Latvian territory was approximately 2.5–3.5 degrees higher than today.
Specialists in our field are comparing the relevant time periods, and, for example, in the north of Canada, the temperature has currently exceeded what it was 7,500–5,000 years ago. Therefore, we cannot keep using the excuse that it was much warmer at some point in the past. What does this mean and what will the consequences be? I must say, we do not really know, but looking at what is happening to vegetation: at the end of the ice age, the prevailing forests were of the boreal (coniferous) type, whereas during the warmest period, broad-leaved forests (elm, wych elm, oak) “reigned” here. Conversely, for the last 4,500 years, the “grand climate” has become cooler and more humid, resulting in a mixture of broad-leaved and boreal-type forests. If we look to the future, it is possible that we may see the “return” of broad-leaved forests.
Applied research is increasingly in demand, and colleagues are turning their focus towards it. Based on pollen, one can determine the wood stock per hectare for a specific period, thereby modelling the potential situation—what we should expect in the future. For example, which tree species it would be sensible to grow and plant, based on calculations from the past.
Colleagues at the forestry research institute “Silava” are also thinking very seriously about this.
Yes, and there is a debate: how to react to the information obtained! One option is to panic (which is neither practical nor sensible), the other is to use the information for the benefit of humanity and science. Of course, one of the goals of science is to research, investigate and use the results for the benefit of society. How? For example, the information obtained can be used and integrated into forest management models.
If we look not only at temperature, but also at the pathogens and pests currently very relevant in Europe (bark beetle, oak disease, etc.), we have discovered that 1,400–1,000 years ago, there was a distinct period in Lapland, Estonia, Latvia, Russia and Poland when alder trees died off rapidly. How did we establish this? In the mentioned period, the volume of alder biomass in the forests dropped sharply. It is thought that the reason could be short-lived but rapid climate changes combined with some disease (pathogen), because the other tree species do not show such sharp and noticeable changes around that time. If it was once believed that the reason for the decrease in alder biomass was human activity, our research (in 2017 and 2019) proved a different cause. Moreover, we specifically chose those regions in Finland and Russia where there was no reason (nor possibility) to engage in agriculture: neither suitable land nor signs of human presence. This suggested that alders were affected by some other factor—a pathogen. We are observing similar things today.
I would like to emphasise that in understanding and analysing the situation, we must take into account our knowledge now, which, compared to earlier times, “gives” us more information. Therefore, it is not that “everything is bad”, but that we know and understand more! In the past, life seemed simpler and conditions less harsh.
Of course, speaking of the alders already mentioned, I can investigate today when the relevant drop in biomass began and how long it (the drop) lasted. Paleoecology views issues through the lens of the past.
Modern ecologists, including forest scientists, view and assess processes over shorter periods. We can conclude what should ultimately be considered a natural forest if we look at the natural state of the forest: a natural forest is a forest before the start of active human activity (active intervention). Here, we must speak of or return to approximately the year 1200, which we also conducted research on in the lakes. This is exactly what we wanted to find out: which time (century) should be considered the “time before active human intervention”. In the 13th century, as is historically known, active economic and political changes took place in many places, which also affected forests and the environment in general. From that time on, both forests and lakes were changed or altered. As is known, in the past, forests were very intensively logged, which was encouraged by the development of exports; this can also be said of most of the forests in the territory of what is now Latvia.
Now we have returned to a situation where forest areas are increasing again. Let’s say, in the last 80 years, although the reasons for this are very different...
My colleagues are actively involved in research on more recent times. Looking at and reading their work, I see it—forest areas are increasing. If one were to look only and exclusively at biological processes, everything should be left as it is. But we are humans; we have to survive, we have to live, we have to think about how to combine everything. So that there is both biological diversity and people can live. This requires extensive knowledge and the compilation of a wide range of information.
Another example: we recently prepared a study on forest fires in Latvia (Fires in the Vidzeme Highlands and Eastern Latvia over the last 10,000 years). We concluded that during the time the tree species characteristic of the boreal type “reigned”, there were more fires, the number decreased during the broad-leaved period, and now the number of forest fires has increased again because...
...conifers burn relatively better!
Of course! There is a certain paradox here—people often think that the reason for fires is a warmer climate, but that is not the only stimulating factor! Warmth (or warmer conditions) is one thing; another is that vegetation has also changed under the influence of warmth. A warmer climate has “brought” us broad-leaved trees, which burn worse! While conducting research in Lapland (Finland and Russia), looking at tree rings, we found that drought also increases the possibility of forest fires—in both warm and cold climatic conditions. In the relatively cool Little Ice Age, there were more fires even in places where no human activity was observed. A colleague at “Silava”, Māra Kitenberga, has research on fires in Latvian forests, and she, too, has found that drought “controls” fires.
We are currently researching the impact of fires in peatlands; the results are expected later.
Fires and nature. How to scientifically understand the occasionally debated issue: that it is necessary to burn forests in a controlled manner for scientific purposes.
People believe that a fire is a loss. We can look at the past, but we have to translate and interpret past events ourselves, because we do not know exactly what happened and how in the past. Burning experiments today can be useful for explanation, as they show exactly what is happening in nature right now and immediately after fires. There are a number of possible dynamic changes that paleoecology cannot determine, but which experimental ecological studies can.
Can one not study, for example, the site of a fire that has already occurred? In Latvia, there are plenty of forest fires in the summer alone.
How to assess what and how much has burned if we arrive at a burnt site but have no information about what was there before?! If you “give” a scientist a forest that has burned down, they lack the link to what was there before. Of course, humanly speaking, many people do not like such a scene, but people who carry out such research will know the positive side of fires best. Speaking of fires that break out without human involvement: drought (dry biomass), lightning, a spark... Natural fires occur in one place every 100–126 years. If the site is boggy but dry, fires could happen more often. Burning conditions will differ for every forest growth condition type.
Are other Latvian lakes being studied as well?
Yes, of course! Lake Trikāta, Lake Lielais Svētiņu, Lake Kurjanova, Lake Bricu, Lake Lielais Vipēdes, Lake Lilastes, Lake Ķikuru, and lakes near Talsi and Ēdole.
When studying lakes, do unexpected and ancient cultural heritages appear?
Even for Lake Āraiši, not its whole story is known—it is clear when the lake fortress was built, but at what moment people of that time entered the landscape, what happened to the landscape and what happened to the lake itself is not clear. Of course, we collaborate with archaeologists, attempting to perfect the scene of ancient events. Lake Bricu is also from the group of lake-fortress lakes; archaeologists concluded this back in the 60s and 70s. But... there is no newer research, therefore there is no information; this lake should be addressed more seriously. However, for Lake Bricu, we do have a rough idea of when humans “entered” there.
It is interesting that in Lake Āraiši, we found Icelandic volcanic ash from the 1875 eruption. Ash particles have also been discovered in the Teiču bog and Lake Trikāta. This shows that we are not at a sufficiently safe distance from volcanoes, especially if the wind is blowing in our direction.
1875 is not such an ancient time; has the volcanic eruption been described in any way in the chronicles or press of that time?
We talked to archaeologists about the possibility of studying historical data, for example, what happened in terms of mortality and disease at that time.
In 1782–1783, an eruption of another Icelandic volcano occurred, as a result of which a lot of toxic gases entered the atmosphere. Incidentally, in Europe, this also “added fuel” to the Great French Revolution, because the eruption was “followed” by many years of crop failure, famine, poverty, etc.
Can the wavy and circular motion (variability) of the climate observed in the past continue in this way?
One must definitely look further into the ancient past: what has happened over 2.58 million years. What happened between ice ages? (Interglacial period). The last interglacial period was approximately 130,000–115,000 years ago, followed by an ice age. We are currently living in an interglacial period. On average, interglacial periods last 10,000–15,000 years, and the ice age cycle repeats every 100,000 years. If it were not for humans and their activity, perhaps (perhaps!!!!) an ice age might have started by now! I allow for the possibility that we have postponed the “new” ice age by several thousand years. Whether that is good or bad will only be seen and understood “afterwards”. Humans have a specific place in this system; in our research, we see the interaction between humans and nature. The question would be: how long will nature be able to withstand the load?
The climate cannot remain just warmer all the time; there is a certain threshold beyond which changes in the opposite direction will begin. We in Latvia are very directly influenced by processes in the North Atlantic. If the Gulf Stream changes, coolness and humidity can reach us. Thus, if snow accumulates year after year without melting, in the long term, a new ice age could begin. When that will be, we do not know.
Speaking of climate, in the Teiču bog, we measured how quickly peat accumulates and forms. The results were encouraging: in the last 180 years, it has formed at about 3–4 mm per year (previously it was believed to be 1 mm per year, no more). Of course, research is needed to understand the situation in other bogs, but we also looked at how much carbon bogs accumulate. We concluded that in the last 180 years, the climate has become warmer, but more carbon has accumulated in the bogs. It would seem there should have been the opposite effect, but the vegetation period has lengthened, and photosynthesis takes place for longer. This could continue for about 200–300 years, and if the warmth continues to increase, humidity conditions may change, and a situation could arise like the one 8,000–4,500 years ago, when our current territory experienced its warmest period. Thus, step by step, study by study, we are “putting together” the picture of environmental and climatic conditions.
Photographs by Normunds Stivriņš used