This week marks the beginning of the annual U.N. climate negotiations in Bonn, chaired by the nation of Fiji, and this year it’s going to be different. At most of the negotiating sessions from the early 90s up to the Paris Agreement in 2015, the emphasis was, reasonably, on reaching a broad consensus on how to prevent dangerous climate change. But Paris achieved that, and all the world’s countries, with one exception—the United States—have accepted that agreement. So now the question is, how can we make it work? A real challenge—particularly since a key delegation to the talks is now led by the climate-denialist Trump administration.
A new scientific paper, published two weeks ago in the Proceedings of the National Academy of Sciences by Bronson Griscom and colleagues, will be extremely helpful in this task. (The multi-authored effort was led by The Nature Conservancy.) The paper’s title is “Natural climate solutions,” and it shows that changes in how we use forests, agricultural lands and wetlands can be a sizeable part of the solution. (Simplifying a bit, 37% of the solution by 2030, according to their calculations).
Among the many natural approaches that they evaluated, reforestation turns out to be one with the most potential (although also the largest uncertainty.) Here’s the key graphic summarizing the estimates:
The potential of 20 “natural climate solutions” by the year 2030, measured in PgCO2 per year. A Pg (petagram) is the same as a gigaton, i.e. a billion tons of carbon dioxide; current global greenhouse gas emissions total a bit over 50 gigatons of CO2/year. Solutions which also have benefits for the air, water, soil and biodiversity are indicated by the small colored bars just to the left of the vertical axis. Source: Figure 1 of B. Griscom et al. 2017, “Natural climate solutions”, Proceedings of the National Academy of Sciences; DOI:10.1073/pnas.1710465114
The second-largest potential lies in reducing deforestation (or as the graph calls it, “Avoided Forest Conversion”), which also has the greatest low-cost potential and the benefit of lowering emissions immediately, and the third is improving natural forest management. So in terms of climate potential, forests are fundamental. But both agriculture (e.g. biochar, trees in croplands) and wetlands (e.g. protecting high-carbon peat swamps and mangrove forests, which also are important as buffers against storms and flooding) can make appreciable contributions, too. Furthermore, most of the potential solutions offer benefits not only to the climate, but also in terms of water, air, soil and biodiversity.
One notable feature of the paper is that it’s conservative, in the best sense of that word. The estimates take as a basic premise that natural approaches should only be implemented with safeguards for food security, biodiversity and people’s rights and livelihoods. Thus, for example, the calculations for reforestation assume that it will done using native species and only be implemented on grazing lands that were previously forested, so that afforestation of croplands and of natural grasslands is excluded. “Solutions” whose technical feasibility or social impact are questionable—e.g. Biological Energy with Carbon Capture and Storage (BECCS) or no-till crop production—are also excluded. And the authors go to great lengths (literally—there are over 90 pages of Supporting Information) to make sure that they’re not double-counting any of the potentials.
The paper does omit, at least in its explicit calculations, the kinds of solutions that involve changing how human societies consume rather than how we use nature to produce. In other words, the approaches it considers are supply-side ones, not demand-side ones such as changing our diets or reducing how much food we waste.
But the authors clearly realize the importance of consumption, and indeed they point out that the reforestation of grazing lands will have important impacts on livestock products, particularly beef. These effects could be of several kinds: shifting human diets away from beef, reducing herd sizes, improving the quality of cattle pastures or the nutritional value of their feed, and others. But what they have in common is that they would tend to reduce emissions of methane and nitrous oxide—both considerably more powerful greenhouse gases than CO2—from beef cattle and their manure. So there’d be an additional benefit in terms of emissions reduction, in addition to large amounts of carbon that will be sequestered by the new forests.
Just as important as the paper’s demonstration that natural solutions can be an important part of solving the climate problem, is their emphasis that they can only work if accompanied by massive cuts in fossil fuel emissions. Here’s their graphic showing the scenario they envisage, which includes cutting greenhouse gases from fossil fuels by 93% by 2050:
The scenario combining a dramatic reduction in fossil fuel emissions with Natural Climate Solution (NCS) mitigation to keep global temperature increases less than 2 degrees C. above the pre-industrial level. Source: Figure 2 of B. Griscom et al. 2017, “Natural climate solutions”, Proceedings of the National Academy of Sciences; DOI:10.1073/pnas.1710465114
Combined with the natural climate solutions, this would achieve the “negative emissions” needed to keep global warming below the 2 degrees C. recognized as dangerous for the future of humanity. And it would do it without using BECCS or other approaches whose feasibility and acceptability remains to be seen.
The critical but at the same time secondary role of natural solutions is the reason I wrote “(help)” in my title, despite my dislike of the post-modern fad for excessive parenthesization. With its conservative approach, the paper by Griscom et al. demonstrates that forests, agriculture and wetlands can’t solve the climate problem alone, but are nonetheless a critical part of an approach that can solve it. Thus, it’s a key step forward in how we think about, and what we do about, the most important environmental challenge of our time.