Can planting trees help us avoid climate disaster?

Every country on Earth has now signed on to the Paris international climate agreement and pledged to dramatically reduce their carbon emissions. Fulfilling this ambition will require international cooperation at a historic level and time is running out. While many long-term changes are needed across nearly every corner of the global economy, increasing the “carbon sink” in the short term may be our best hope to offset the emissions we can’t reduce. This may buy us the time we need to fundamentally reshape society’s relationship with energy production and consumption and avoid climate disaster.

The problem

Current best-case scenarios for renewable energy deployment over the next few decades fall short of where they need to be to reach global climate goals. Governments have the capability to eliminate fossil fuel usage, but they are not putting those plans in motion fast enough. Traditional energy sources (coal, natural gas, and oil) are still dominant in almost every projection through mid-century, in large part due to the massive investments that have already been made. World energy demand is also growing rapidly as developing countries industrialize and fossil fuels are still the cheapest form of energy in many countries. Between now and 2040, global net electricity generation is projected to increase by 45 percent and fossil fuels may meet a large part of that demand.

Unless there are immediate and dramatic worldwide shifts in energy usage, there may be no way to avert catastrophic global warming without technologies that remove carbon dioxide (CO₂) from the atmosphere. These are known as “negative carbon” technologies; or sometimes, unsettlingly, as geo-engineering. The world’s leading authority on climate science, the Intergovernmental Panel on Climate Change (IPCC), has included some sort of negative carbon technology in 100 of their 116 scenarios modelling ways to keep global average temperature below 2°C of warming, over pre-industrial levels, by the year 2100 (the goal of the Paris Agreement).

Reports of the changing climate and the daunting scale of the sustainability challenge ahead make it easy to be pessimistic. Indeed – and even though climate change as a policy topic never seems to rise to the top of the list of concerns during election season – a sense of societal doom about the future seems to be increasing. Pop-culture imagery is full of dystopian visions of the future where humanity has irreversibly ravaged the natural world. The answer to this, for some, is to put their faith in technology. There are risks to allowing nation states or corporate entities to test products and techniques that could actually harm the environment even more. Thankfully, a large-scale negative carbon technology already exists that we know works, is economical, and is environmentally safe: plants.

The big idea

Trees and grass take in CO₂ through their leaves and stalks, making them one of the best available tools for reducing carbon. In 2014, U.S. forests, grasslands, and other natural sources sequestered 762 million metric tons (MMT) of CO₂ which offset around 11 percent of total U.S. greenhouse gas (GHG) emissions. This is what is referred to as the “carbon sink” (as opposed to “carbon source”).

When European settlers first arrived in the early 1600s, forests covered roughly half of what would become the landmass of the United States. Since then, total U.S. forestland has seen a net reduction of approximately 257 million acres. That is more than three times the size of the total acreage under management by the National Park Service which manages all of U.S. national parks, national monuments, national historic battlefields, trails, seashores, and more. It also equates to a great deal of stored carbon released back into the atmosphere. For plants to serve a much more significant role in carbon sequestration, along the lines of global climate goals, their coverage needs to increase – a lot.

If U.S. forests and long-living perennial grasses expand by 40 to 50 million acres they could potentially offset up to 50 percent of U.S. GHG emissions by mid-century. This is according to the United States Mid-Century Strategy for deep decarbonization (MCS), released by the Obama Administration, which provides a vision for an economy-wide net GHG emissions reduction of 80 to 100 percent below 2005 levels by 2050. The MCS is the culmination of decades of policy conversations at the domestic level, international negotiations, and ever-increasing scientific understanding of the challenges posed by climate change. The 80 to 100 percent reduction goal is in line with Article 4, Paragraph 19 of the Paris Agreement that calls on all countries to “formulate and communicate long-term low greenhouse gas emission development strategies.”

The MCS divides policy priorities into three categories: 1) transforming to a low-carbon energy system; 2) sequestering carbon through forests, soils, and CO₂ removal technologies; and 3) reducing non-CO₂ emissions. For each of these categories, well-researched policy plans are detailed with projection scenarios showing multiple pathways through which these policies might help achieve the MCS’s long-term goal. While the Trump Administration has rolled back some of the climate change mitigation efforts initiated under previous administrations, the MCS nevertheless remains a valuable assessment of strategies the U.S. will need to eventually return to in order to achieve long-term goals consistent with international climate agreements.

USMCS Potential Land Use Scenario

Expanding U.S. forests by 40 to 50 million acres by 2050, as called for under the MCS, would recover one third of all U.S. forestland lost since 1850. This is a daunting task, but federal land management agencies theoretically have the tools needed to get the job done. The U.S. Forest Service directly manages 193 million acres and “supports sustainable management” on 500 million acres of private, state, and tribal forests. The Bureau of Land Management manages another 250 million acres and the National Park Service manages 84 million acres. Not all of this acreage is suitable for forest or grass land but it is plausible that a coordinated effort between federal and state agencies, as well as private and tribal land owners, could result in the needed carbon sink expansion.

Next steps

From 1987 to 2012, tree planting efforts helped U.S. forests expand by roughly 1 million acres per year – with federal land agencies accounting for roughly a third. To reach the mid-century reforestation goal, this annual expansion rate needs to double on average. However, since it takes time for trees to grow and reach their full carbon sequestration potential, even more planting has to occur in the short term. Projections call for 2.7 million acres per year of forest expansion from now through at least 2035 – almost three times the current rate.

The policy implications from achieving such a rapid expansion are numerous. U.S. forestland produces a variety of goods and services essential to the economy. Residential development and agriculture, while necessary for population growth and food, are large drivers of forest loss. A significant portion of U.S. energy production, including 40 percent of coal production, comes from federally-managed lands.

While the challenges are great, so too are the potential rewards. On private lands, planting more trees in urban locations, constructing more large buildings out of wood, and agricultural partnerships could usher in new economic opportunities. The MCS presents one example of the latter:

[I]n Iowa alone, an estimated 27 percent of cropland, or 7 million acres, may not be profitable in commodity crop production but could be well-suited to perennial grasses or agroforestry (Brandes et al. 2016). Focusing nationally on such areas could minimize land use competition and help increase rural landowner incomes while delivering environmental benefits like improved soil health and reduced nutrient runoff.

The Iowa case is one of many partnerships that will be required to ensure climate change-related land use changes do not lead to lost economic profitability. Any plan to increase forests and grasslands will need to carefully balance wood and food production, living space, and energy needs over the next few decades. Fortunately, the MCS estimates that up to 50 million acres of trees could be planted on agricultural land without impacting production. Through precision agriculture and agroforestry, the MCS makes many recommendations regarding enhancing agriculture to support large-scale carbon sequestration. This will “improve soil quality, water and nutrient retention, and crop yields, all with minimal competition for land use.”

Another exciting potential is biomass energy. There is an estimated 31 million acres of farmland that could be used to grow energy crops. According to the Biomass Energy Resource Center (BERC) in Burlington, Vermont, perennial grasses were used on the prairie for heat before the industrial revolution and in places with little forest land. These grasses came to be known as prairie coal. They are also very easy to grow and sequester a great deal of carbon in their roots and soil. BERC states that, “switchgrass used for heating has an energy output to input ratio of at least 10 to 1, compared to other bioenergy sources with output to input ratios around 1 to 1.” A recent study on herbaceous, another type of grass, found that one acre of farmland is capable of producing an “average annual yield of herbaceous biomass sufficient to meet the annual space- and water-heating needs of an average home.”

With any biomass energy source, the stored carbon is released when burned for energy and will need to be capped and stored. This process is known as bioenergy with carbon capture and storage (BECCS). According to a July 2017 paper in Energy Procedia, if implemented on a large-scale, models project BECCS could remove up to 616 gigatons (616,000 million metric tons) of global CO₂ from the atmosphere by 2100.

Alongside better coordination with private landowners and precision agriculture, land management at the federal level will also need to improve to facilitate carbon sink expansion. Twenty-eight percent of the total U.S. land mass is federally managed lands. Implementing large-scale planting projects may prove easier on federal land given the existing structure of land-management agencies. There may also be more accountability in tracking results.

Conclusion

2050 might seem a long way off, especially in the context of policy making. However, from a global climate standpoint, the importance of urgent action over the next few years cannot be overstated. The private sector will help drive emissions reductions in all sources of energy production and consumption — from electric vehicles to “green” buildings. These changes will reshape our society’s relationship with energy and will usher in many new and exciting technological advancements. But without bolstering the carbon sink through better land management and other policies discussed here, we are unlikely to achieve the United States Mid-Century Strategy for deep decarbonization and therefore unlikely to achieve global climate stability. Todd Stern, who led President Obama’s climate policy at the State Department in the years building up to the passage of the Paris Agreement, recently evaluated the future of the agreement and stated, “we can accomplish what we need to – if we have the political will.” Let us hope that our politicians can eventually create the policies we need to safeguard future generations.