We don’t know enough about forests: Carbon Sinks+ project investigates the global impact of forests on the climate

Trees serve as important carbon sinks that cool the climate. At the same time, forests and other ecosystems benefit the climate in other ways. This explains demand for the Carbon Sinks+ project, and why this research area is promoted under the direction of Professor of Aerosol and Environmental Physics Markku Kulmala.

In the spring, birds chirp and the fresh scent of plants wafts through the air, picked up by hikers. It is a smell so familiar to many that you can almost sense it reading this article.

This scent of the forest originates as a byproduct of photosynthesis, in which all the plants in the forest, from large trees to grasses, dwarf shrubs and other undergrowth, take part. To be precise, the scent comes from hydrocarbons generated during the process.

In addition to a pleasant scent, hydrocarbons have an important task, which is currently being investigated in the Carbon Sinks+ research project of Academician of Science Markku Kulmala at the University of Helsinki.

The plus in the project name refers to Kulmala’s notion that the activity of forests in the prevention of global warming is not limited to the carbon sinks in the focus so far. While those do have a significant impact on cooling the climate, the measurements and other research carried out in the project are aimed at identifying the overall climate impact of forests.

In other words, Kulmala points out, a great deal more happens in the forest besides the carbon binding activity of trees.

— For example, the hydrocarbons that end up in the air as a result of photosynthesis form non-volatile compounds through atmospheric chemical reactions, which are able to further form fine particles. These particles reflect solar radiation back into space.

In addition, these fine particles are essential to the water cycle. 

Growing large enough, they form the cloud condensation nuclei of cloud droplets, subsequently forming, under appropriate conditions, into cloud droplets and clouds. Clouds, in turn, cool the climate, as they ward off, as it were, solar radiation.

Fine particles also increase the share of scattered radiation in overall radiation. According to Kulmala, this allows the radiation deeper into the forest, down to the undergrowth, boosting photosynthesis.

All these activities together increase the benefits for the climate.

— This is exactly why we’ve taken to calling the research topic ‘carbon sink plus’.

In spring 2024, Kulmala received a donation of €400,000 from UPM for the Carbon Sinks+ project. 

— We are committed to managing our forests in a climate-positive manner and safeguarding biodiversity. We wish to promote top-level research on the impact of forests on climate change, as our business is based on forests and their wellbeing. Commercial forests have a key role in the fight against climate change, and we want to invest in understanding these effects and offer renewable alternatives to fossil fuels, says Director of Stakeholder Relations Sami Oksa of UPM Forest and UPM Timber.

Decades of measurements as the foundation

In all, Kulmala’s project measures thousands of variables. The primary measuring site is the SMEAR II station at the University of Helsinki’s Hyytiälä Forestry Field Station, where Kulmala has taken measurements for his research for a total of 30 years next year. 

Information on the overall climate effects of forests is needed because there is not enough of it at the moment. In other words, it is not currently known what kind of forest or ecosystem cools the atmosphere most effectively and by which mechanisms. 

— We have far too little information on forests and other ecosystems. Since climate change must be curbed by all possible means, we should know what forests, the soil and, for example, field ecosystems are doing in addition to being carbon sinks.

Only then can the concrete level of climate neutrality be calculated, for example, for Finland, and the offsetting of emissions considered.

Climate change is not a matter of opinion

Kulmala came up with Carbon Sinks+ in cooperation with the mathematician and forest ecologist Pertti Hari. Kulmala is one of the most internationally cited scholars in his field, and world-class research in atmospheric science is conducted at the University of Helsinki. Why is this?

According to Kulmala, Finland is small enough. Kulmala himself studied theoretical and experimental physics. In contrast, many other atmospheric scientists are, for example, chemists, meteorologists and biologists. 

— As we specialists in physics and theoretical physics have collided with forest researchers, we have been productive in creating something new and crossing interdisciplinary boundaries. 

It’s important for everyone to understand that climate change is not a matter of opinion, Kulmala emphasises.

— The climate is changing, whether we like it or not.