Carbon Sequestration: Another Reason for Good Stewardship

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Malka Pattison, Dr. Bradley Reed

 

Malka Pattison: Good afternoon, we've got the mic going. I'm Malka Pattison and I'd like to welcome you to the US Department of the Interior's Office of Policy Analysis seminar. Our speaker today is Brad Reed who is the US Geological Survey Associate Program Coordinator for Land Change Science. Brad's topic is carbon sequestration, an important tool in counter-balancing greenhouse gases.

Brad has been the Chief Researcher in the assessment of the 48 contiguous states, various carbon sequestration. He's also starting a new research program for assessing carbon sequestration in Hawaii and Alaska. Brad?

Dr. Bradley Reed: Thank you very much, Malka. I appreciate you inviting me to give this seminar. Thank you for all the arrangements that you and your staff have made to make this possible.

First and foremost, I want to say that this is a research project that's been undertaken by a large number of scientists. They'd taken the leads on various aspects of this study. I want to be sure to give them credit as we go through this presentation.

Biological carbon sequestration. We at USGS and DOI were mandated or legislated to undertake the study by the Energy Independent and Security Act of 2007, which called for the Department of Interior to determine the current stocks and flexes of ecosystem carbon and other greenhouse gases, conduct a national assessment covering all major terrestrial and aquatic ecosystems, estimate the potential capacity of ecosystems to increase carbon sequestration, consider policy application such as adaptation and mitigation options, consider the effects of climate change and other controlling processes, and to consult with other DOI bureaus and organizations.

I have this carton in the bottom corner here which might be difficult to see. It's put there to remind me to emphasize that we're looking at all ecosystems including forests, crop lands, wetlands, grass lands, tribe lands, and other lands such as urban lands.

We're looking at three different carbon tools -- living biomass, dead organic matter, and soil. We're looking at controlling processes such as wood harvesting, fires, land use change. We're looking at a lot of influences on the carbon cycle.

We've been publishing a series of assessment reports that began in 2010. It began with a publication of methodology that was to be undertaken by the research team, followed by regional assessments for the Great Plains, Western US, and Eastern US. These are complete now. The assessments for Alaska and Hawaii are well underway. We're hoping that they'll be published this year or 2015, I should say.

We're operating on a two different time scales here. One is the baseline assessment, and the other is projected changes and biological carbon sequestration. 2001 to 2005 were considered as the baseline years for these reports.

We conduct land change and carbon projections up to 2050 based on three climate models that have arranged of temperature and precipitation trends, and three IPCC scenarios -- SRES, special report on emission scenarios story lines.

These are called A1B, A2, and B1 scenarios with range of projected economic growth, innovation, and fused toward environmental sustainability. We'd like to say that these are not predictions. These are projections based on equally unlikely scenarios that we're looking at here.

This assessment has a unique use of remote sensing satellites in it. The current national greenhouse gas inventory is large, at least the land sector portion of the national greenhouse gas inventory.

It's largely based on the USDA Forest Inventory and Analysis, and National Resource Inventory Analysis, which are based on in situ observations. The assessment that we're conducting here uses these data and supplements them significantly with a remote sensing data, primarily from Landsat where we get land cover via the National Land Cover Database, land cover change. We're also looking through NLCD as well as vegetation change tracker and fires through land fires MTBS, Monitoring Trends and Burn Sovereignty.

We also look at courser as resolution satellite models for net primary production that helps in form our biomass modeling and irrigation.

Naturally, we also have extensive views of models. We have models for land change projections which is down-scaling those SRES story lines and for projecting land change through forecasting scenarios of land change.

We have fire extent and emissions models, biogeochemical models through the GEMS, General Ensemble Modeling System, with three different models, and hydrologic modeling.

We have teams of scientists responsible for each of these land change projections by scientists at Menlo Park as well as at the Aero Center in South Dakota, Fire extent and emissions by our team in Denver, the biogeochemical models by a team at Aeros, and hydrologic modeling by teams that in Denver and Sacramento. So, it's a very large effort by a number of scientists.

I'm going to jump right to some of the results here because I have a lot of things I want to cover here in a relatively short amount of time.

These are the baseline and projected land use, and land cover changes from these models. We're looking at ecosystems along the vertical part of the table -- forest, agriculture, shrub grass, wetland, and other. You can see the amount of land cover in the baseline timeframe and the percentage of total area of the conterminous US.

You can see the projected change up to 2050 and see that there are some minor changes in land cover on a conterminous US scale.

Regionally, the story differs. For example, the Eastern US baseline and projected land use and land cover change is significantly different.

The Eastern US is primarily forested almost 50 percent with significant agricultural lands and wetlands. Between 1992 and 2005, where we have some good information from Landsat about how much areas change, we can see that about nine percent of the Eastern US has changed. Projections out to 2050 indicate that about 20 percent of the area could change in land cover. Pretty substantial.

In parts of the east especially the Southeastern US, we could see up to 30 percent change out to 2050.

If we look at a series of Landsat images here and the projections, we can see how these may change. This is the area around Birmingham, Alabama, that's the big red block in the center of the upper left hand image.

The projections out to '20 based on the A1B, A2, and B2 models. You can see the projected area of urban increase by their red outlines and the proportion of projected timber harvesting in maroon. You could see it very clearly that the different models had different projections of land change for urbanization as well as for timber harvesting.

The demand for forest harvesting is going to be a big driver of land change in the Eastern US primarily in the Southeastern US. We're looking at increased urbanization and little new forest land.

Now, we're looking at the carbon stock for the conterminous US by ecosystem type. The units we're looking at here are teragrams of carbon, that's million metric tons.

These are the different ecosystems, the current carbon stocks, and projected stocks out to 2050. I mentioned that we used three different scenarios. We used three different climate models. We used different biogeochemical models as well. We're averaging the results of all of these for the numbers, and then we have a range of results in parenthesis.

You see that forests account for well over 50 percent of the carbon stocks in the conterminous US, and are expected to continue to do so throughout the range of the study.

Now, we're looking at carbon flux. This is the amount of either input of carbon into the ecosystem or output between the emissions of one type to another.

Here's the numbers for 2010. The total for the conterminous US is about 431 teragrams of carbon per year. The negative number indicates that the conterminous US is a carbon sink, absorbing carbon from the atmosphere.

If you look at the numbers as were projected out into the future, you can see that it continues to be a carbon sink. The numbers continue to be negative.

However, you can also see that these numbers are growing smaller. The strength of the carbon sink in the conterminous US is expected to weaken over the next 40 or so years. You can see that the total number of teragrams of carbon expected to be sequestered in these ecosystems goes from 431 million metric tons to 345 million metric tons.

Let me go back up. You can also see that there's a wide range of results in those parenthesis, according to the different climate models and BGC models. The wide range of results are highly dependent on what scenario is used, and what model is used for these projections. Most results indicate a growing carbon stock throughout the projected period, but under most scenarios, we also see a decreasing carbon sink in the conterminous US.

Let's look at these numbers in comparison to emissions. The US greenhouse gas inventory for 2012, which was published in 2014 by the EPA, shows total emissions of about 6,500 million metric tons of CO2 equivalent. We've changed units here from carbon to CO2 equivalent, because that's how it's reported in the EPA reports.

Total passenger car emissions in 2012 were about 755 million metric tons. Now, we're looking in the bottom table, is the ecosystem CO2 flux for Great Plains, Western US and Eastern US. We can see that the baseline sink is about 1,500 million metric tons, so about double the emissions of passenger cars. We also see that the projected flux is less than it is for the baseline period, so that's something that we need to keep in mind for counteracting emissions from not just cars, but from power plants and other sources of CO2 emissions.

We're very happy to report that the conterminous US is completed. We had our final report for the conterminous US in June of this year. The Alaska report, which is underway, is expected to be significant, due to large forested areas, warming of Alaska, large fires, and large scale thawing of permafrost. We're anxiously awaiting those results from our team in Alaska.

We have some early results, and I should have put a draft watermark across the next two or three slides, because these have not undergone peer review yet. We're going to report these anyway, at least in this talk.

These are the carbon stocks for interior Alaska. We're looking at petagrams of carbon rather than teragrams, so this is billion metric tons, for the '80s, '90s, 2000s and 2010s.

You'll see that the large proportion of carbon stock is tied up in the soils for interior Alaska and living biomass. If we look at the estimated change in carbon stocks, this is interior Alaska, this is not including coastal Alaska in these slides, we can see that the stocks of living biomass and soil and total carbon is decreasing, while deadwood and litter is increasing.

Why is that? You can see that it's primarily driven by accumulated burn area. It's either the jump in fires in the early 2000s. You can see that this is in line with increased temperatures. As those fires occur, living biomass drops, change in litter goes up, and dead woody vegetation goes up as well, and soil carbon goes down as well, because some of the peat soils burn as does the living biomass.

The increase in fire frequency in the early 2000s has induced carbon loss from living vegetation and soil stocks. The change induced in this boreal region of Alaska has led to a transition from a carbon sink to a carbon source in about 2005, so this is something that we need to really keep our eyes on. We don't have the projected numbers yet, but we have to see what those projections bring. My guess is that it's going to stay around a neutral carbon source-carbon sink into the foreseeable future, maybe jumping back and forth.

To summarize the accomplishments of this study for the baseline period and projected period, out to 2050, land use, land cover change is identified as a key driver of carbon change. In the Western US, change in forest lands will likely drive change in carbon. We have significant uncertainties that result from the climate projections, and climate trends, and subsequent trends in wildfires in the Western US. Most projections point to increased fires, increased severe fires, in the Western US.

In the Eastern US, timber harvesting and urbanization will likely be the key drivers of changes in carbon. In the Great Plains, agricultural policies, such as the Conservation Reserve Program, biofuel subsidies, have been the primary drivers of land change, and subsequently of carbon change.

For the first time, we now have a National Inventory of Carbon Storage in all ecosystems and all carbon pools. This is at a spatially detailed scale, 250 meters by 250 meters, since a primary source of data is remote sensing data, so we are able to map it wall to wall at a 250-meter resolution.

We have an inventory of the aquatic component, and we have an ongoing assessment of Alaska and Hawaii. We now have the ability to monitor and account for change in greenhouse gas emissions on all DOI, all federal, or all US lands. I should say ecosystem greenhouse gas emissions on all DOI, federal or US lands.

We have a baseline from which to estimate the effects of potential mitigation strategies and tradeoffs. This is a major step in quantifying the degree to which land management practices might support or counteract other climate change mitigation policies.

Next step, completing Alaska and Hawaii, and we would like to get to the point where we're conducting regular assessments of all interior lands, and perhaps beyond. We also want to use this assessment to support decision making, decision support to land managers.

We want to develop capabilities to routinely update the assessment, track changes, track the effects of wildfire, drought, and other conditions on carbon storage. This is in partnership with other interior bureaus.

Federal lands occupy a lot of the conterminous US. In fact, at the bottom line here, this is carbon stocks in federal lands. About 22 percent of the carbon stocks of the US are in federal lands. If we project that out to 2050, it's still well over 20 percent, but a slight decrease -- 27 percent of the forested lands of the conterminous US are in federal ownership.

If we look at the carbon flux, the amount that's sequestered each year in this case, since they're negative numbers in most cases, we have about 126 teragrams of carbon per year sequestered in federal lands. As we project out to the future, you can see that is projected to drop quite significantly, primarily in the forested lands.

If we go back to one of my first slides on the Energy Independence and Security Act, the legislation that drove this work, I wanted to highlight a couple of bullets. These are to consider policy applications such as adaptation and mitigation applications. We were also legislated to consult with other DOI bureaus and other organizations.

In line with this, we've initiated a partnership with the US Fish and Wildlife Service over three of their National Wildlife Refuges, including Great Dismal Swamp, Pocosin Lakes and Alligator River.

This partnership was to provide information on the carbon balance in these refuges, and understand how management and/or restoration could potentially increase carbon storage. We want to estimate the effects of hydrologic management on carbon sequestration, fire management and establishing selected types of vegetation communities, and enhance carbon sequestration on these public lands while quantifying the other ecosystem service trade-offs that may be taking place.

The initial work on this partnership has been taking place at the Great Dismal Swamp, which is located on the border of Virginia and North Carolina, about 15 or 20 miles from the Atlantic Coast.

This has an interesting land use history. In the 1760s, George Washington began draining and logging this area. Significant land use practices have taken place on the swamp for centuries, which has greatly changed its habitat. In 1974, the Great Dismal Swamp Act established it as a National Wildlife Refuge, over 100,000 acres of forested wetlands.

I mentioned that we wanted to look at carbon sequestration in line with other ecosystem services. Ecosystem services are the benefits that humans derive from nature, and they include services that can be divided into four types -- provisioning services, such as timber, regulating services, such as filtering water, providing clean water, mitigating fires, cultural services, such as bird watching or canoeing, other types of recreational activities, and supporting services, such as nutrient cycling, that support those other three ecosystem services.

We need to take all of these ecosystem services into account when looking at management practices. We typically do not manage just for carbon.

The idea here under ecosystem services and carbon is to enhance the service of carbon sequestration on public lands while quantifying the ecosystem service trade-offs such as the impact on wildlife, visitors, et cetera.

We'd like to produce regional and local scale carbon estimates such as carbon flux, ecosystem carbon balance and long-term sequestration rates to include in ecosystem service evaluations that support DOI land management, and to estimate the effects of refuge management practices on carbon sequestration and trade-offs with other services for stakeholders.

There are a lot of stakeholders that are dependent on ecosystem services on our federal lands. We recently held a stakeholder workshop in the Dismal Swamp area, which gave a list of potential ecosystem services that are provided to these stakeholders. These stakeholders included local entities such as cities, states, federal and national level refuge and environmental groups, academia, and non-profits as well.

This workshop was to provide a clear focus on benefits that people derive from nature and link the environmental processes with the value that's attached to these services. This is an ongoing dialogue that we will be having with these stakeholders as this project continues.

This is a multi-partner project, including Fish and Wildlife Service, Nature Conservancy, USGS and several universities. The hydrologic management of this project is, of course, led by the Fish and Wildlife Service. The hydrologic management is their primary management tool at the swamp. Through a series of water control structures, they are able to control to an extent the water levels.

Then, the carbon research and ecosystem service assessment for decision-making is led by the USGS with these other partnerships as mentioned above. We're establishing several in situ measurement sites, such as surface elevation monitoring, to see if the hydrologic practices lead to an accumulation of peat or a decline of peat.

We have gas chambers to look at atmospheric gas exchange. We have wells to look at the water levels. We have a number of sites to look at above-ground biomass. We have peat sampling, et cetera, as well as looking at ecosystem services modeling and remote sensing analysis from Landsat, radar and LiDAR.

I'm going to summarize what I've said so far, and then open it up to questions, if I may. The summary is that we've completed an assessment of biological carbon sequestration for the conterminous US. It appears that the US will continue to be a carbon sink. The ecosystems of the US will continue to be a carbon sink, although the strength of the sink may be weakening out to 2050.

Work is underway to integrate the assessment into land management actions that we hope to continue working on. We have a pilot project with Fish and Wildlife Service now, and we hope to get projects going with the other land management bureaus of the Interior as well.

Thank you for your attention.

Malka: Let's begin with questions from the audience here. Any questions?

Female Audience Member: Hello. I was wondering how often you're going to reassess the carbon assessment.

Dr. Reed: The question was how often will we reassess? That's a very good question. We're wondering that ourselves.

I think it's fairly realistic to do updates on this assessment by looking only at land change. We don't have to replicate the complete modeling again every year or every two years.

But we can look at areas that have changed. We have the satellite technology that we can do that. I think it's reasonable to say that we could do this every two years, and maybe even annually at some point. But we don't have a schedule to do that at this time. It depends on budgets and mandates from the Interior as well as other agencies.

The current greenhouse gas inventory that's conducted by the Environmental Protection Agency is updated every year. We would eventually like to get to the point where our information can be input into the annual inventory, but we're not quite there yet. We have a little bit of work left to do to get to that point.

Female Audience Member: Thank you.

Malka: Questions from the Internet? More questions from this room?

Jonathan Steele: Hi. This is Jonathan Steele from Office of Policy Analysis. You had a slide that showed amongst the different ecosystems that there would be a net loss to some of those acres, but then your slide showed that there would be actually a net gain in the carbon sink ability. Can you explain that phenomenon?

Dr. Reed: It's a little bit confusing when we're talking about carbon stocks and carbon flux. In this table, we're looking at carbon stocks. You see that, let's just look at forests, for example. We're looking at 26 billion metric tons in about 2000, out to almost 40 billion metric tons by 2050. The carbon is increasing in this ecosystem through time.

If we look at the next slide, we're looking at carbon flux. This is the annual amount of carbon that's sequestered. You can see that negative sign indicates it's a carbon sink. It's still sequestering carbon. You can see that it continues to sequester carbon, so the carbon stocks are increasing with time.

But the annual rate is decreasing. We're down to only 225 million metric tons per year. Our stocks are still increasing, but at a decreasing rate. That's what we were getting at with that.

Malka: Internet questions? More questions from the room?

Indur Goklany: Hi. Indur Goklany, Office of Policy Analysis. How much confidence do you have in your projections?

Dr. Reed: There are a lot of uncertainties in many aspects of this. It's even difficult to quantify the uncertainties. We have uncertainties in the input data. We have uncertainties in the projections, the climate projections, the land use change projections. We have uncertainties and biases in the different models.

That's why we did a range of these scenarios. We did a range of climate models. We do a range of biogeochemical models, in addition.

What we're really looking for is a convergence of evidence. Do all these different sources point in a certain direction?

I can't put a number on how confident we are in these results. But I will say that our information, as well as other scientific input, points in the same direction. I'm not going to say we're going to be sequestering 225 teragrams of carbon per year in 2050, but what I am fairly confident in saying is that the strength of the carbon sink looks to be decreasing. The absolute numbers? No.

Indur: Do you have any idea at all how good the projections are? Have you done an end-to-end analysis of the uncertainties? Because you're using different models, and you're using the output of one model and feeding it to the next model. The uncertainties will...

Dr. Reed: We can look at...

Indur: I don't know whether multiplication is the right word, but they get bundled together and they go down the systems.

Dr. Reed: Right, absolutely. It's a ripe area of research, and we're putting some of our resources in the next couple of years into uncertainty analysis because the uncertainties aren't even very well known at this point. We know, in general, what they are, but to quantify them, we're not real sure about that at this time. Like I said, we can see that the results are quite different from the different scenarios.

We know that these scenarios, as I mentioned earlier, they're all equally unlikely. They're not really very realistic scenarios. That just gives us a guideline to go to when we're looking at these projections. It's a framework from which we can guide our decision making and policy making.

Male Audience Member: We have a question from one of our viewers. According to one of your slides, agricultural land is projected to be a greater carbon sink in the future. Could you tell us why this is so?

Dr. Reed: It's projected to be about the same. It's a very small increase. To be honest, I cannot tell you why that modest increase might be taking place. Remember, this is an average of three different story lines. In some of these story lines, we're looking at high population increase. Other story lines, we're looking at a more green, if you will, scenario.

If we were looking at one of these story lines, I might be able tell you why the agricultural lands might be increasing in sequestration or even becoming a source under some of these scenarios. We would have to track that down to the individual story lines that we're looking at. Some of them call for massively increased agricultural production to support a rapidly increasing population. Those would be the carbon sources.

In other scenarios, we're looking at very conservation oriented agricultural practices. Those are the ones which would increase the carbon storage.

On average, it looks like they're about the same but there's a wide range of potential results from these different scenarios.

Male Audience Member: A follow on question. Do the results for agriculture represent net sequestration changes since some agricultural processes are also carbon sources?

Dr. Reed: Yes, that includes all agricultural lands. It indicates fertilizer additions, it indicates no till agriculture in some areas. It includes a wide range of agricultural practices that are currently taken from agricultural data. Those are the inputs to the models.

Malka: Any questions in the room? We have another Internet question.

Male Audience Member: Could you also say a bit about how these results compared to global studies?

Dr. Reed: We've compared them to other studies of the conterminous US, let's put it that way. The general trends agree with what is currently being put into the greenhouse gas inventory from our colleagues at US Forest Service. Looks like a decreasing carbon sink into the future. Our numbers are a little bit higher than theirs, more carbon sequestration than what they're projecting. We also include all ecosystems in our assessment.

The assessment currently done for the EPA's greenhouse gas inventory does not include federal grasslands and shrub lands in the West or in all of the conterminous US. It does not include wetlands, so our numbers should naturally be higher in that respect.

Our numbers are also a little bit lower than numbers that are collected at carbon flux towers and then extrapolated across the landscape. We're sort of in the middle of a range of studies that are put out there for the conterminous US.

Male Audience Member: Are there any similar studies for other areas of the world?

Dr. Reed: Yeah, there are. To my knowledge, there are no global scale studies at the level of detail that this has been done. I'm confident in saying that. This covers all ecosystems, all carbon pools at a 250-meter resolution. That's never been done before for the conterminous US, and it's never been done before for the globe. The scale of this work is new, let's say.

Malka: More questions here.

Male Audience Member: You've done soils also. This includes the soils also, right?

Dr. Reed: Yes.

Male Audience Member: How deep are you going down the soils?

Dr. Reed: We're going down 20 centimeters for this study.

Male Audience Member: Does that cover it all, because some areas, it would not?

Dr. Reed: It does not cover it all.

Male Audience Member: The carbon stock would be much higher than lots of its resource.

Dr. Reed: Yes, the carbon flux, however, would not change.

Malka: Another question from the Internet?

Male Audience Member: Is there a question of reaching saturation point with carbon stocks? As a follow-on, is there any expected adverse effect from increasing carbon stocks?

Dr. Reed: Saturation point on carbon stocks, I guess you'd be looking at the potential natural vegetation of the conterminous US. We are looking at that as well because that gives you the capacity of the ecosystem to sequester carbon if it all went back to its natural state.

We don't have peer reviewed results on that yet, but it is possible to reach a maximum point of carbon sequestration. Can you repeat the second part?

Male Audience Member: If there are any expected adverse impacts from increase in carbon stocks.

Dr. Reed: Yeah, that's sort of what we're trying to get at with these studies with the other management bureaus. Typically, we don't manage for carbon. We manage for other priority ecosystem services such as timber. We manage for recreation or we manage for biodiversity. What we're trying to get at with these cooperative projects with the other bureaus is to see what the tradeoffs are.

What if we did manage for carbon and planted nothing but trees in a land management area, one of some kind? What would that do to fire control? What would that do to biodiversity?

We want to put these things into this ecosystem services models to see what those tradeoffs would be. That is indeed a good question and one that we're interested in seeing what these tradeoffs are according to the different stakeholders. Some might think it's a worthwhile tradeoff other stakeholders might not think so.

Male Audience Member: Just as a clarification, would you expect to see any negative biophysical impacts from simply managing?

Dr. Reed: For increasing carbon, one potential is increased fire. It depends how all this management is done and the tradeoffs that you take into account along the way. Yeah, there are potential negative impacts but these have to be balanced with the positive impacts. More forests might lead to more fires, but it also might lead to increased biodiversity and increased carbon sequestration. You have to look at these different tradeoffs, depending on the environment, of course.

Female Audience Member: I have one more question, if you allow me. Any guidance for the user who is looking for carbon sequestration estimates. We know we have a lot of Federal agencies, a lot of private and universities. What should guide a researcher's use of estimates as he looks for a source?

Dr. Reed: If you're looking for a source of data to inform your studies, you can look at our website. We provide all of these data through cooperation with University of California, Berkeley. They're helping us with some data visualization. You can go to "landcarbon.org," to access these data. These data are freely available for download either on a continental basis or you can interactively draw a box of interest for your area of interest and download whichever data sets you want.

We have the projected data out to 2050, on a 250-meter resolution basis. We have an abundance of data that would support any kind of research.

Malka: Thank you, any other questions? If not, thank you very much, Brad.

Dr. Reed: My pleasure, thank you.

 

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