Climate and forests are intrinsically linked. As a result of climate change, forests are stressed by higher mean annual temperatures, altered precipitation patterns, and more frequent and extreme weather events. At the same time, forests mitigate climate change through uptake of carbon, and the loss of forests through land-use conversion and forest degradation causes carbon dioxide emissions that contribute to climate change (IPCC 2014).
Climate Change Mitigation
Forests remove carbon from the atmosphere (carbon sequestration) and store it as trees grow (Figure 8). Global forest carbon stocks are estimated at 861 billion tons, more than half of which is stored in tropical forests (Pan et al. 2011). When trees are harvested, they stop absorbing carbon from the atmosphere, but the resulting wood products, including solid wood and paper-based products, continue to store carbon through their lifetime (Box 11: What does ‘carbon neutrality’ mean?).
The amount of carbon stored in wood products is estimated to be increasing by 189 million tons per year (Pan et al., 2011). The amount of carbon stored in wood products varies significantly among product types and depends on the method of disposal. On average, solid wood products last longer than paper-based products (Larson et al., 2012) and carbon in both forests and products is released back to the atmosphere either slowly through decomposition or quickly by burning.
Establishing new forests on suitable land and replanting on formerly forested areas can store additional carbon (Box 12: The rate of carbon sequestration). The Global Partnership on Forest and Landscape Restoration estimates that over 2 billion hectares of deforested and degraded landscapes worldwide can potentially be restored (WRI, 2011). Thanks to growing recognition of forest and landscape restoration’s role in reducing carbon dioxide emissions and increasing carbon sequestration, countries have pledged over 20 million hectares to the Bonn Challenge—a global commitment to restore 150 million hectares of lost and degraded forests by 2020. Countries committed to the challenge, including Brazil, Costa Rica, El Salvador, Rwanda, and the United States, are beginning to announce their restoration pledges (IUCN, 2012).
Voluntary carbon markets
Companies seeking to supplement greenhouse gas (GHG) emissions reductions and further reduce their net carbon footprint may choose to purchase carbon credits from voluntary carbon markets to offset their emissions. In 2012, carbon offsets from conserving and expanding 26.5 million hectares of forest (an area about the size of New Zealand) were valued at $216 million USD (Forest Trends, 2013) (Box 13: Reducing Emissions from Deforestation and Forest Degradation (REDD)). The private sector continues to make up the majority of the demand, purchasing 70 percent of the total carbon offsets in 2012 as a way to demonstrate corporate social responsibility and commitment to addressing climate change (Forest Trends, 2013). A number of voluntary carbon markets are now operating and standards are in place to verify the validity of projects offering carbon credits (Table 12).
Table 12. Voluntary carbon markets and voluntary carbon standards
Voluntary carbon markets
Carbon Trade Exchange
Members of the exchange can sell and buy carbon credits generated from four types of projects: renewable energy, forestation and afforestation, energy efficiency, and methane capture. Projects are verified by a third party.
Carbon Farming Initiative
Farmers and landholders can participate and earn carbon credits for storing carbon and reducing emissions on their land. They can then sell the credits to interested businesses as carbon offset.
Awards carbon credits to forest landowners committed to long-term maintenance of biomass stocks and helps them sell credits within voluntary carbon markets.
Voluntary carbon standards
Verified Carbon Standard
Provides methodologies for certifying projects and calculating carbon credits; certified projects must go through independent auditing. Verified Carbon Standard is one of the most widely used standards for the agriculture, forestry and other land use sector.
The Gold Standard
A certification body that verifies the quality of carbon credit projects. Carbon credits that have been certified by the Gold Standard are sold through intermediary companies.
Plan Vivo Standard
Certifies carbon credit projects led by rural smallholders and rural communities. The 2013 updated standard emphasizes community participation and ownership, and non-carbon benefits.
The forest industry is a major user of biofuels derived from wood. Sawmills and pulp mills both burn those parts of the tree that they cannot convert into merchantable products. Co-generation of heat and electricity is common, and some mills even export electricity to the grid (Asikainen et al., 2010). Using wood waste for fuel can help reduce the use of fossil fuels.
Harvesting wood to produce wood-based biofuels, however, is a different scenario. To determine whether harvesting wood for biofuels can reduce carbon dioxide emissions, additional factors must be considered. First among these factors is the amount of emissions associated with harvesting, transporting, and using wood-based biofuels. Second, the long-term productivity of the land and its ability to replace the carbon stock lost to harvesting (Mitchell, Harman, and O’Connell, 2012) should be considered. Finally, the biological changes resulting from continuous harvesting— such as change in stand age and soil fertility—may reduce productivity (Schulze et al., 2012). Additionally, while the emissions from harvesting wood can be offset with regrowth on the same land, the calculation of carbon savings should account for the amount of carbon that could have been sequestered if the trees were not harvested for biofuel production (Haberl et al., 2012; Searchinger, 2010; Hudiburg et al., 2011).
Contributions to Climate Change
An estimated 13 percent of global carbon dioxide emissions are attributable to land-use changes and forestry activities (Pan et al. 2011). When forests are logged, destroyed, or burned at a faster rate than the rate at which they regrow, they can contribute to climate change. Additionally, while logging of tropical hardwoods is sometimes the primary purpose of forest clearing, it can also trigger and enable other drivers of deforestation by providing other users with access roads. Other drivers of deforestation include expansion of large-scale agricultural production such as palm oil, cattle ranching and coffee; small-scale subsistence farming; and urban sprawl. When forest land is converted to other uses, there can be a significant net contribution to greenhouse gas emissions (Figure 9).
However, logging does not necessarily have to lead to deforestation. In a sustainably managed forest area, the growth of new trees can compensate for the carbon lost through annual logging within the area. In contrast, a forest that is subjected to land-use change or over-harvesting that leads to permanent forest cover loss will release more carbon than it takes up.
Compared with other materials (e.g., concrete, steel, plastic), products made from sustainably managed forests are generally advantageous from a GHG perspective because wood is produced by taking carbon from the atmosphere while producing other materials require use of fossil fuels.
Logging operations: machinery and equipment that use fossil fuels for harvesting.
Transportation: Transport of wood products from forest to shelf requires fossil fuels.
Manufacturing: Most types of forest product manufacturing operations require fossil fuel energy. Some operations can rely entirely on biomass fuel from residuals of the forest products manufacturing process, in which case, less fossil fuel energy would be needed (Tonn and Marland, 2006).
Disposal: Emissions may result when products decompose in the landfill, though paper products that end up in landfills can sequester carbon for a long time (Micales and Skog, 1996).
Factors to consider regarding climate change
Some argue that old-growth forests with stable carbon stocks should be replaced with stands of young, vigorously growing trees as a way to increase carbon uptake. However, this would reduce the amount of carbon stored on the land, and it would take decades, or even centuries, for the GHG benefits of the newer stands to overcome the loss of carbon from the original forest. Furthermore, old-growth forests, particularly in the tropics, are important to preserving the world’s biological diversity, and therefore should not be considered on the basis of carbon stocks and flows alone.