As both scientists (in many published papers) and political leaders (in the Paris Agreement) have now recognized, to stop global warming—to keep the global temperature from increasing indefinitely—we need to peak and then reduce emissions rapidly. We need to get our release of global warming pollution into the atmosphere, down to a level below the amount that carbon sequestration by the biosphere takes out of the atmosphere. This means that we have to work incredibly hard on two parallel tracks, simultaneously. On the one hand, cut pollution drastically. And on the other hand, regrow the biosphere.
At the annual climate negotiations going on in Marrakech, Morocco, various countries are presenting their visions of what they can do by 2050 to help achieve this goal, to which the world’s nations committed last year in Paris. Although the U.S. mid-century vision may be delayed because of the outcome of this week’s elections, we anticipate that when it comes out it will recognize how our forests can play a key role on the sequestration side—both preserving our current forest “sink”, which removes about three-quarters of a billion tons of CO2 from the air each year, and by reforesting to increase that sink over the next three-plus decades.
As a politically engaged scientist I try to keep in mind both the current reality—i.e. the grave threat to climate action represented by the incoming Trump administration and the new Congress—and also the longer-term needs of the planet. There’ll be lots of opportunities, and lots of need, to talk about the short term dangers in coming weeks and months. But this post will be about the longer-term, with the hope that if we better understand what can and must be done in the next few decades, it’ll help us change political reality so that it can happen.
A bit of climate and a bit of history
Earlier this year I worked with my UCS colleagues Jason Funk and Stu Sheppard to examine the climate potential of U.S. forests by mid-century. We found that some of the things people often think about doing first, such as stopping forest fires and planting more trees, are not actually the biggest opportunities.
To understand why, let’s take a quick look at the climate and the history of American forests. Oversimplifying, but not that much, we can say that the Eastern U.S. is moist, while the West is dry. In New England, the Mid-Atlantic, the Lake States, the South and a large part of the Midwest, we get about 40 inches (i.e. 1 meter) of precipitation annually, fairly evenly spread over all the months of the year. But as you travel west beyond the Mississippi, this diminishes steadily, and pretty soon it’s so dry that forests fade out, transitioning into prairie and eventually into desert.
The picture is complicated by the Rockies and the Sierras, and there’s also a narrow band of incredibly wet and productive forest in the far west (along the Pacific coast in northern California, Oregon, Washington and the panhandle of Alaska), but by and large, the eastern half of the U.S. is good forest country, while the western half is not. (See the numbers in the table below).
The contrast between the East and the West of the continental U.S., in terms of their land use, forests, carbon, and potential for future sequestration. Sources: Zhu, Zhiliang, and Reed, B.C., eds., 2012, Baseline and projected future carbon storage and greenhouse-gas fluxes in ecosystems of the western United States. U.S. Geological Survey Professional Paper 1797 (http://pubs.usgs.gov/pp/1797/), and Zhu, Zhiliang, and Reed, B.C., eds., 2014. Baseline and projected future carbon storage and greenhouse-gas fluxes in ecosystems of the eastern United States. U.S. Geological Survey Professional Paper 1804 (http://pubs.usgs.gov/pp/1804/)
This has consequences. It means that the East has much more forest carbon than the West, and also more potential for future forest sequestration. It means that wildfires are principally a threat in the montane West, but that the regions they threaten are mostly forests with less carbon, or ecosystems that aren’t forested at all.
That’s all a matter of climate geography, but there’s an important historical angle as well. The frontier of European settlement mostly moved westward from the Atlantic coast, and in the process, almost all the eastern forests were cleared and converted into farmland. But starting in the late 1800s, as farming reached the fertile soils of the prairies and the rangeland further west, agriculture declined back east, so that cleared land began to be recolonized by trees. This “reforestation” mostly came about from natural regeneration, not from tree-planting by people. Nonetheless, it was powerful enough to convert 2/3 of the East back into forest.
Where we are today
So now, a century or so later, we have large areas of middle-aged forest growing in the eastern half of the country, taking carbon out of the atmosphere and locking it up in wood. Nearly all of this is happening on private lands. In contrast, the big National Forests and other public lands are nearly all out west – where it’s drier, there’s less forest land, and the carbon stock of those forests, as well as their potential to sequester more carbon in coming decades, is much less. Here’s the map:
Federal lands are nearly all in the West. The red line shows the 100th meridian (100 degrees West longitude), the traditional dividing line between East and West.
What does this mean in terms of using our forests to protect our climate — not just to maintain the present-day sink but also to sequester significantly more carbon by 2050? It means that if we’re serious about doing it right, we should put our major emphasis on:
- The eastern half of the country, not the west. This is where most of the forest carbon is now, and where there can be a lot more in the future
- The privately-owned forests, not the public lands. This is a simple consequence of the lack of public lands in the East.
- Natural regeneration rather than tree-planting projects. This not only has considerable ecological advantages, but it’s what makes most economic sense, since tree-planting in the U.S. is expensive, especially in the West.
I hope and expect that there’ll be lots of good ideas about forests in the U.S. mid-century blueprint, including a few—e.g. building future cities using wood instead of steel and concrete—that would be truly visionary. But what we need to see is a plan for American forests that is as big as our enormous potential.