Climate researchers Wilhelm May and Paul Miller at the Centre for Environmental and Climate Research (CEC) at Lund University present a new report, co-authored with Benjamin Smith from the Department of Physical Geography and Ecosystem Science, which focuses on land issues and has been used as input to the Swedish government’s strategy on how Sweden should achieve negative greenhouse gas emissions. The report highlights the relevance of both the biophysical effects and biogeochemical effects of land-use and land-cover changes on regional climate and terrestrial ecosystem change in Sweden. Today, the biogeochemical effects associated with the carbon cycle are the main consideration when assessing the effects of climate mitigation measures.
Land-based mitigation solutions highlighted
To fulfill the goals set in the Swedish national climate policy from 2018, the government has recognized that mitigation solutions, including land-based interventions, are required. The national climate policy emphasizes forests and forestry as key to reducing greenhouse gas emissions.
“It is apparent from our synthesis that forests and the forestry sector in Sweden will come to play a very important role for mitigating climate change by reducing the net carbon emissions and, thus, contribute to fulfilling the Swedish goal of net-zero emissions of greenhouse gases in 2045 and negative emissions thereafter”, Wilhelm May says.
However, Wilhelm May and his co-authors argue that focusing primarily on the carbon budget, i.e. carbon sequestration in terrestrial ecosystems such as vegetation and soils and avoiding carbon emissions from fossil fuels, may not be sufficient to evaluate the overall effects of efforts to mitigate climate change. This is because the biophysical effects of the associated changes in land use and land cover as well as other biogeochemical effects, for example the effects of aerosols and biogenic volatile organic compounds, have significant impacts on local climate as well.
“At the moment there are no specific land-use and land-cover scenarios available for Sweden, that comply with the goals of the Swedish national climate policy, which we can use for assessing the biophysical effects of these changes”, Wilhelm May says.
Complex effects of forests depend on climate change
In contrast to what is often thought to be an exclusively positive action, the research shows that planting trees on open land will have both negative and positive effects on near-surface temperature. Although the balance of the effects is uncertain, the report concludes that the reduced surface reflection of solar radiation leads to a warming, while increased mean wind speed near the ground and increased evaporation and plant transpiration from the land surface to the atmosphere, especially in late spring and summer, result in a cooling of near-surface temperatures.
The efficacy of re- and afforestation, as well as forest management practices, as a mitigation measure will also be affected by the long-term climatic changes in Sweden, according to the research. Warmer near-surface temperatures, in particular in winter, and reduced precipitation during summers would counteract the cooling effects of afforestation.
Socio-economic factors needed in future climate models
The researchers conclude that dynamic, interactive socio-economic components, for example the impacts of climate change on specific sectors, which affect greenhouse gas emissions or land use and land cover changes, need to be included in future climate models.
“There is a clear need for models that take into account interactive, coupled biogeochemical, biophysical and socio-economic aspects in climate projections, not least to be able to understand the true climate (and sustainable development) effects of policies and behavior as they relate to land use and management. Much progress has been made, but there is more to do”, Paul Miller says.
The researchers explain that human decision-making is generally not incorporated in climate models since this is quite a demanding task.
“Including human decision-making would markedly increase the amount of computing resources and model complexity. Such an approach would, however, result in more representative climate projections by fully incorporating human responses to climate change”, Wilhelm May concludes.