Hydrological system modification - Ocean current modification

Methane is a highly potent greenhouse gas and its reduction is given ever greater priority in international emission reduction policies. Given the increasing, and potentially catastrophic rate of methane release from the thawing Arctic and Northern permafrost, these regions are crucial in this endeavor. Apart from the methane release from microbial activity in thawing permafrost on land, methane also escapes in the form of hydrates which have been formed under sediments beneath the sea.

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.

Methane is a highly potent greenhouse gas and its reduction is given ever greater priority in international emission reduction policies. Given the increasing, and potentially catastrophic rate of methane release from the thawing Arctic and Northern permafrost, these regions are crucial in this endeavor. Apart from the methane release from microbial activity in thawing permafrost on land, methane also escapes in the form of hydrates which have been formed under sediments beneath the sea.

In many Arctic and Northern regions, domesticated or semi-domesticated reindeer (Rangifer tarandus) are the only large herbivores (Uboni et al. 2016). Reindeer play a crucial role in these ecosystems and in the livelihoods and traditions of multiple local and indigenous populations. In light of the major impact of climate change in the Arctic, the capacity of large herbivores to mitigate some of these effects is being explored. Herbivores can have different climate positive effects as they can reduce shrubification and slow ecosystem responses to climate change (Olofsson and Post 2018; Happonen et al. 2021), modify summer and winter surface albedo (te Beest et al. 2016), trample winter snow to thicken permafrost (Beer et al. 2020; Windirsch et al. 2022), and increase biomass and soil carbon sequestration (Ylänne et al. 2018; Ylänne et al. 2021; see also soil management).

Fisheries contribute to global CO2 emissions by the extraction of fish, disturbance of coastal and oceanic blue carbon ecosystems, and the use of fossil fuels as their main energy source. Fishing vessels are moreover a major source of short-lived climate forcers like black carbon (McKuin and Campbell 2016), which can have a major effect in Arctic and Northern regions (see Black carbon reduction).

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.

Large areas of the Northern and Arctic regions consist of permafrost, almost permanently frozen soil. As global temperatures rise, these permafrost areas are thawing at an ever faster rate. This thawing leads to massive amounts of GHGs being released into the atmosphere, either as CO2 or CH4 in generally dry or wet areas. Because methane is a very potent GHG, the thawing of the permafrost is considered a major tipping point in the climatic system. Permafrost preservation is of the utmost importance because Arctic terrestrial regions alone hold up to 1500 Pg C (Schuur et al. 2015), and although there is large uncertainty about the total amount of emissions from permafrost (Miner et al. 2022), especially when it comes to nonlinear abrupt thawing (Turetsky et al. 2020), significant amounts of carbon release is to be expected as the Northern regions warm.

Large areas of the Northern and Arctic regions consist of permafrost, almost permanently frozen soil. As global temperatures rise, these permafrost areas are thawing at an ever faster rate. This thawing leads to massive amounts of GHGs being released into the atmosphere, as carbon stored in the permafrost is converted into methane by bacteria. Because methane is a very potent GHG, the thawing of the permafrost is considered a major tipping point in the climatic system. Permafrost preservation is of the utmost importance because Arctic terrestrial regions alone hold up to 1500 Pg C (Schuur et al. 2015), and although there is large uncertainty about the total amount of emissions from permafrost (Miner et al. 2022), especially when it comes to nonlinear abrupt thawing (Turetsky et al. 2020), significant amounts of carbon release is to be expected as the Northern regions warm.