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The oceans are the largest carbon sink for atmospheric carbon, and have taken up over 30% of anthropogenic emissions. Carbon uptake occurs abiotically through processes like ocean-atmosphere interaction and weathering processes, and biotically, mainly through carbon consuming photosynthesising organisms.

The potential of carbon sequestration by marine based plants such as mangroves, seagrass and algae, often referred to as blue carbon, and the importance of better understanding it, has clearly been recognised (Mcleod et al. 2011). The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (2019) concluded blue carbon can play an important role in both climate regulation and adaptation. The term algae groups together several kinds of marine photosynthetic organisms. These are often subdivided into very small microalgae like phytoplankton, and larger macroalgae like kelp and seaweed. Although there is still large uncertainty about the total amount of carbon sequestered by these marine organisms, a recent estimate by Duarte et al. (2022) indicated that all macroalgae took in as much CO2 as the Amazon rainforest.

Sea water has a low albedo of around 0.1 and therefore absorbs most of the incoming solar energy. Since water covers over two thirds of the Earth’s surface, changes to this albedo can potentially cause significant changes in global temperatures.

Ocean bioproductivity through photosynthesis stops beyond the photic layer as no more energy from the sun can penetrate beyond that point.

The oceans are the largest carbon sink for atmospheric carbon and have taken up over 30% of anthropogenic emissions. Carbon uptake occurs abiotically through processes such as ocean-atmosphere interaction and weathering processes. Biotic processes play an important role in oceanic carbon uptake too, with most attention going  to carbon-consuming photosynthesising organisms.

Oceans play an important role in global heat transfer and carbon storage processes. As global temperatures and atmospheric carbon levels rise, some have suggested artificially modifying the vertical movement of water to enhance these processes.

Oceans play an important role in global heat transfer and carbon storage processes. As global temperatures and atmospheric carbon levels rise, some have suggested artificially modifying the vertical movement of water to enhance these processes.

The deep waters in the Baltic are severely deoxygenated. Although the causes of the current state are complex, this is mainly a result of increased eutrophication from sewage and agricultural runoff from surrounding lands, which leads to extreme bioproductivity (Rolff et al. 2022). Some species manage to survive in the upper water layers, but many organisms living on the seafloor are severely impacted by the hypoxia, thereby influencing the health of a wide network of ecosystems and biochemical processes. There are attempts to reduce nutrient runoff into the Baltic (see for example: https://helcom.fi/baltic-sea-action-plan/). However, some argue these will be insufficient and argue for engineering solutions to the issue.

The oceans are the largest carbon sink for atmospheric carbon, and have taken up over 30% of anthropogenic emissions. Carbon uptake mainly occurs directly through ocean-atmosphere interaction or through weathering processes. Due to this uptake of carbon the oceans turn more acidic overtime, and since the start of the industrial revolution oceans have become 30% more acidic. This has all sorts of effects, as it for example impacts marine biochemistry, and prevents certain organisms from successfully growing.

The pH of water is lowered when it takes up atmospheric carbon. Given that the Earth’s oceans serve as a major carbon sink, there is increasing interest in the possibility to artificially increase the alkalinity of water to restore pH to previous levels, and/or increase carbon uptake potential.

Fire is important to the healthy functioning of boreal ecosystems. However, as wildfires increase, they release greater amounts of GHGs into the atmosphere, contributing to climate change. While boreal fires typically contribute 10% of global CO2 emissions, in 2021, an extreme fire year, they accounted for 23% of global emissions (Zheng et al. 2023). Particulate matter in wildfire smoke (soot or black carbon, see also Black carbon mitigation) can also reduce albedo on sea ice and glaciers, enhancing ice melt (e.g., Aubry-Wake et al. 2022). Wildfires are projected to increase in both frequency and intensity over the coming decades (UNEP 2022). By 2050, wildfires in North American boreal forests alone could contribute close to 12 Gt CO2, almost 3% of the remaining global CO2 emissions to keep temperatures to below 1.5oC (Phillips et al. 2022a).

Although the rate of deforestation has slowed over the last few decades, the world is still losing forest cover (FAO 2020). Adequate management, protection, and restoration of existing forests, and the planting of unforested areas, play a crucial role in climate mitigation scenarios (IPCC AR6 WG3), and many countries now include forests in their climate mitigation targets (NDCs).The Northern and Arctic regions are essential in this endeavor since they are home to large swaths of boreal forests that make up 27% of total global forest area (FAO 2020).