Mountain pine beetle upends the Canadian emissions picture?

The lastest Canadian greenhouse gas emissions data looks very different if Canadian forests are taking into consideration.

There was some rejoicing over the fact that Canada's GHG emissions grew by only 2 Mt CO2e (that includes CO2 plus other GHGs converted to "units" of CO2) or 0.25% from 2009 to 2010, despite the fact that the economy was rebounding from the recession. But if you include land cover, land use change and forestry, GHG emissions grew by 86 Mt from 2009 to 2010.

Why such a large change? According to the Canadian government model, forests went from a net sink of 17 Mt in 2009 to a net source of 72 Mt in 2010 (see Table 7-1 in NIR). If you

break the GHG balance of forests up by region, the driver of this change was the "Montane Cordillera", or #14 on the map to the left. These forests of western BC were a net source of 100 Mt. The only other net sources regions in 2010 were the "Boreal Shield West" (#9 at 22 Mt), the "Pacific Maritime" (#15 at 5.7 Mt) and the "Taiga Shield East" (#4 at 1.7 Mt).

There are large, natural year-to-year variations in forest carbon balance, so it's important not to read too much into the jump from 2009 to 2010. What the 2010 number does reflect, however, is the very large amount of carbon, in the form of dead wood, in BC that is waiting to be respired to the atmosphere (if we don't use sequester it in buildings). For that, we can largely thank the Mountain Pine Beetle, the outbreaks of which have been linked to climate change. From the National Inventory Report:

The upward trend in dead organic matter (DOM) decay since the year 2000 reflects the long-term, growing effect of past disturbances, especially insect epidemics that have left substantial quantities of decaying DOM. Over the last decade, insect epidemics have affected a total of over 56 Mha3 of managed forests, with 72% being located in the Montane Cordillera reporting zone and corresponding to the epidemics of Mountain Pine Beetle. In contrast, much of the interannual variability of the GHG budget of managed forests hinges on the occurrence and severity of fires.

Before you start screaming "cover-up", it is standard UN reporting practice, to not include land use, land cover and forestry in the "total" at the top of the GHG inventory tables. This is done for a number of legitimate reasons, not the least of which being that net emissions from forests must be estimated by models and, as I've said, the results vary from year to year because of climate variability. Nonetheless, it is striking that climate change, via its effects on Canadian forest, might be undoing the reported progress in curbing, or starting to curb is a better term, greenhouse gas emissions from some sectors of the Canadian economy.

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Nutrient limitation missing from an otherwise good NY Times story on forests and climate change

The NY Times published a lengthy article about the climate implications of the forest diebacks and fires. It is, on the whole, a great and all-too-rare example of longform science journalism.

The article does miss one important point about CO2 fertilization, the increase in plant growth thought to come from adding more CO2 to the air.

Climate-change contrarians tend to focus on this “fertilization effect,” hailing it as a boon for forests and the food supply. “The ongoing rise of the air’s CO2 content is causing a great greening of the Earth,” one advocate of this position, Craig D. Idso, said at a contrarian meeting in Washington in July.

Dr. Idso and others assert that this effect is likely to continue for the foreseeable future, ameliorating any negative impacts on plant growth from rising temperatures. More mainstream scientists, while stating that CO2 fertilization is real, are much less certain about the long-term effects, saying that the heat and water stress associated with climate change seem to be making forests vulnerable to insect attack, fires and many other problems.

The CO2 fertilization effect is limited, because plants require more than just CO2 to do their job:  photosynthesis. Water is certainly a limiting factor, but nutrients are just as important. In experiment after experiment, scientists find that the CO2 fertilization effect is short-lived without additional inputs of nutrients, particularly nitrogen.

One of the reasons CO2 fertilization may have accelerated plant growth in parts of Europe and North America over the past few decades may be the fact that we've inadvertently been fertilizing the plants with nitrogen, as well as CO2. We'll actually be talking about this in GEOB400 in a couple weeks. For the 6.7 billion or so of you who were unable to register this semester - yes, yes, the class is too small, I hear that all the time - I wrote about this on Maribo a few years ago, in a cross-post with Eli and Tamino:

One culprit is carbon’s chemical sibling nitrogen, that’s #7 on your periodic table if you’re scoring at home. Like many siblings, carbon and nitrogen are quite co-dependent, and, one might argue, a bit resentful about the whole thing. Carbon fixation - photosynthesis, plant growth – is limited by the availability of nitrogen. Though only up to a point. If there’s too much nitrogen, things get saturated, and the carbon-based plants pout and refuse to grow more.

You might find it strange that nitrogen is limited, given that N2 or di-nitrogen gas makes up the majority of the atmosphere. However, N2 is unreactive. It only becomes available to plants when converted to reactive form by microbes. In the process of making fertilizer and burning fossil fuels, we not only have increased the rate at which this conversion happens, leaving more nitrogen in our soils and waterways, we've emitted nitrogen in other reactive, gaseous forms, like nitrogen oxides or NOx...

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Climate change: An accounting problem

The latest RealClimate post, which describes the latest ice melt data from Greenland, features this really important figure. It illustrates an issue that arises every semester in my climate change course, and is, in a sense, fundamental to understanding to biogeochemical cycles and issues like why carbon is accumulated in the atmosphere.

The figure shows model-based annual anomalies (thanks ED) of snowfall (reddish-orange), water loss through surface melt and runoff (yellow) and net accumulation of mass (blue), all in Gt/yr. The key point is that an ice sheet shrinks not simply because it is melting (yellow), but because the loss of water through melt (yellow) is greater than the gain through snowfall (red). The difference is the change in mass (blue). It is an accounting problem; like your bank account, you need to look at the debits and the credits to know whether the balance is changing.

This is the same fundamental concept that  underlies carbon dioxide accumulation in the atmosphere, and as MIT management expert John Sterman has shown, befuddles most people. Carbon dioxide is accumulating in the atmosphere not simply because we are burning fossil fuels and clearing land, but because the flux in to the atmosphere from those sources is greater than the flux out (to land, and the oceans).

As an aside, in my climate change course, one of the many ways we discuss these points is by watching the infamous "CO2 is life" advertisements created a few years back by the Competitive Enterprise Institute. The "Glaciers" video cites scientific evidence for snowfall-driven growth of ice sheets in the interior of Antarctica to suggest that ice sheets around the planet are not shrinking. The mistake in the ad is that in order calculating whether an ice sheet is shrinking, on net, you need to do the full accounting of all inputs (from snow) and all the outputs (from melt), not just cherry pick one part of the ice sheet, or one flux in or out.

The CEI ads, by the way, are hilarious. If you've not seen them, you really must. They are well worth two minutes out of your day; the Onion News Network couldn't have come up with fake ads that funny.

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The pine beetle and carbon cycle feedbacks

An important study from in last week’s Nature concluded that the mountain pine beetle infestation that have devastated the forest industry out here has also converted western Canadian forest from a carbon sink to a carbon source. In the simplest possible terms, the beetles kill the trees, decreasing carbon uptake (photosynthesis) and increase carbon loss (decomposition). This is not a new suggestion. The Kurtz et al. paper is, however, the most complete accounting to date.

A lot of people are labelling this a ‘positive feedback’ from climate change (e.g. like how warming melts sea ice, which reduces reflection of solar radiation, which accelerates the warming). The logic is that warmer weather promotes the beetle outbreak, which releases carbon from the forest, which further warms the climate.

The assertion appears correct. But be wary of the hyperbole. Not all positive feedbacks are made equal. There are only so many pines, the beetles can only do so much damage. At some point, they run out of trees to eat, and the infestation recedes. As the authors of the Nature study have said, the betters have almost eaten themselves out of house and home. And re-forestation initiatives could return the forests to being a carbon sink.

The type of positive feedback that should be included in carbon cycle assessments? Yes. Runaway positive feedback that will send the atmosphere to 1500 ppm? Probably not.

There is a sadly ironic policy twist to the beetle infestation. For one, the forests now might pump out more carbon than the entire BC economy, throwing a wrench into regional GHG reduction agreements. The Canadian government lobbied hard to include forest carbon sinks under the Kyoto process, under the expectation that our boreal forest would provide a big carbon credit and reduce the need to address emissions themselves. Safe to say, that stance has softened in recent years.

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Reporting and promoting science

Science sells these days. In the push for advertising dollars and readership, the conventional and electronic media strive to link new scientific results to the pressing issues of the day.

And, to be fair, in the push for tenure and grant dollars, we academics can be guilty of the same. The holy grail used to be getting a paper in Nature or Science. Now it is getting a paper in Nature or Science so that the paper will be reported on CNN or the BBC.

The intent, in either case, can be benign. A lot of the published science today, on subjects like climate change, is important news. But in the effort to "frame" - to use the terminology in the Matt Nisbet and Chris Mooney article that created buzz earlier this year - science for public and political consumption, a lot of mistakes are being made. It ranges from the inaccurate reporting and questionable publicity of the mythical lake that would resolve the very real crisis in Darfur to outright abuse of statistics to throw stones at solid science.

Take these three recent headlines... please.

1) Red faces at NASA over climate-change blunder

I call this is a "false positive". There's been a huge and unnecessary uproar over the discovery of a minor mathematical error in the NASA GISS historical temperature dataset. The error means that 1998 was no in fact the warmest year in US history, but is tied with 1934. As the NASA scientists themselves report (pdf), the error has a negligible impact on the global temperature, no impact on global rankings of the warmest years, and absolutely no impact on the evidence for human influence on the climate (see Tamino or Realclimate for details).

2) Warming will pause then full steam ahead, scientists contend

This is the "we didn't read the whole paper". These reports of a "global warming" forecast for the next decade come from a innovative short-term climate modeling study published in Science. The goal of the study was to test the ability to predict climate on decadal or shorter time-scales, a specially developed climate model that explicitly considers the frequency of large-scale atmosphere-ocean oscillations like El Nino (see Tamino). At the end of the study, after a lengthy model validation against observed data from the recent past, the authors discuss the model's predictions for the next ten years, stressing they are contingent on stochastic variables like the occurrence of El Ninos. The headlines made it seem as though the scientific community had confidently concluded that 'warming will pause' for a couple years.

3) Trees won't fix global warming

And finally, "we just didn't understand the paper". The headlines are based on research, presented at last week's ESA meeting, from Duke University's Free Air Carbon Enrichment (FACE) site, where scientists have been testing the effect of higher CO2 levels on tree growth for the past ten years. In the past, scientists had thought that higher atmospheric CO2 would effectively 'fertilize' plants. The Duke experiments showed that this fertilization effect was limited by the availability of water and nutrients (press release). In an effort to link the result to a public issue - carbon offsets - the media stories reported that new research shows planting trees won't work to combat global warming. In other words, planting trees won't take up ANY carbon. Of course it would; all that wood is made of carbon, where else could it come from? The Duke research only showed that there won’t be an extra growth bump because there’s more CO2 levels in the air, not that there won't be any growth at all.

This is the danger of popularizing science. As we saw with the coverage of the Darfur Lake, more attention was given to the initial headline than to the later reports that the 'lake' did not in fact hold any water. Unfortunately, with such quick turnaround in reporting, it is vital that all of us, the one's doing the research, the one's writing the press releases and the one's writing the news story, get it right the first time. It's not a trivial task. But otherwise, these misrepresentations (about global temperature) or misintepretations (about short-term climate prediction) or mistakes (about trees and carbon) make it into the public consciousness.

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Where does all that carbon go? Part II

Last week, Tamino at Open Mind, Eli at Rabbet Run and I began an experiment in mob-blogging’ about the carbon cycle. Following on our initial posts, profilic Eli has posted a couple interesting CO2 concentrations maps that highlight forest fires and fossil fuel emissions.

For a refresher on where all the carbon goes, the graph at right shows the IPCC's breakdown of the resting place, for now, of fossil fuel emissions over the past 25 years. The atmospheric build-up is measured (see Tamino's post) and the ocean uptake in well-constrained by measurement: that allows us to back-out the land uptake.

The drawback to this logic is that the land is both a prominent anthropogenic carbon dioxide source (e.g., deforestation, biomass burning) and a prominent carbon dioxide sink (e.g., net regrowth of vegetation). The positive uptake by land means that the sink is greater than the source. That, however, could change in the future, which would mean a larger fraction of carbon emissions would remain in the atmosphere. To answer that, it helps to study where the net carbon uptake occurring on land, and why?

One culprit is carbon’s chemical sibling nitrogen, that’s #7 on your periodic table if you’re scoring at home. Like many siblings, carbon and nitrogen are quite co-dependent, and, one might argue, a bit resentful about the whole thing. Carbon fixation - photosynthesis, plant growth – is limited by the availability of nitrogen. Though only up to a point. If there’s too much nitrogen, things get saturated, and the carbon-based plants pout and refuse to grow more.

You might find it strange that nitrogen is limited, given that N2 or di-nitrogen gas makes up the majority of the atmosphere. However, N2 is unreactive. It only becomes available to plants when converted to reactive form by microbes. In the process of making fertilizer and burning fossil fuels, we not only have increased the rate at which this conversion happens, leaving more nitrogen in our soils and waterways, we've emitted nitrogen in other reactive, gaseous forms, like nitrogen oxides or NOx. (eli, thanks for the suggestion - ed)

The IPCC map to the right shows nitrogen oxide (NOx) concentrations in the lower atmosphere. Notice the high levels above and downstream of North American, Europe and China. Deposition of this nitrogen could be increasing carbon fixation in forests.

A recent paper in Nature found just that: nitrogen fertilization, not forest regrowth after logging, may explain the majority of the net carbon sink in northern forests. The authors used chronosequences – yes, that’s a real word, not some star trek science word referring to data taken from a forest with trees of varying age that can be used to represent different stages of tree growth – to estimate mean carbon uptake at sites across the northern hemisphere.

By integrating uptake over entire rotations (from planting to forest replacement), the authors were able to get a more complete representation of carbon uptake by forests. Using that data, they found a strong relationship between nitrogen deposition and carbon sequestration, implying nitrogen fertilization may be driving the land carbon sink.

Nitrogen oxide emissions and nitrogen deposition are expected to increase in the future without tougher air pollution policies here and especially in Asia (see this paper). That could increase the carbon sequestration in northern forests, presuming those forests do not become N-saturated. Of course, hopefully the world will reduce NOx emissions and improve air quality. Unfortunately, that could also reduce carbon uptake and thus allow a larger fraction of carbon emissions to stay in the atmosphere.

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Where does all the carbon go?

This is the first in a series of group posts by a few of us bloggers interested in the science of climate change. For our first “mob” post, Tamino at Open Mind, Eli at Rabbet Run and yours truly here at Maribo are all writing about the carbon cycle and atmospheric carbon dioxide.

Much of the discussion on Maribo centers around the science politics of setting a short- and long-term GHG or carbon emissions target in order to stabilize atmospheric concentrations and avoid ‘dangerous’ climate change.

The emissions targets depend on how much - and for how long - the carbon dioxide we emit actually remains in the atmosphere. We need to understand the ability of the planet to take carbon out of the atmosphere, and how that itself is sensitive to climate change. The figure (IPCC WG1, Fig. 7.4) shows the annual fraction of fossil fuel emissions that remained in the atmosphere (black line is a five year mean). I'll come back to this.

The atmosphere is often compared to a bathtub. The emissions of carbon dioxide – the flow into the bathtub – are currently greater than the uptake of carbon – the flow out the drain. So carbon dioxide is accumulating in the atmospheric tub.

Personally, I like to say emissions are currently faster than the planetary uptake. Over geological time, millions of years, carbon is removed from atmosphere by weathering of rock and by burial in marine sediments. Burning fossil fuels releases this ‘fossil’ carbon to the atmosphere; deforestation and biomass burning quickly releases carbon that was stored over decades or centuries in trees. We’ve effectively sped up the flow of carbon into the atmosphere.

The increase in atmospheric CO2 since the Mauna Loa record began in the 1950s is only about half (~55%) of fossil fuel emissions. The rest has been absorbed by the oceans and terrestrial ecosystems.

The ocean ‘sink’ is best understood and easiest to measure. It can be almost entirely explained by the dissolution of CO2 in sea water, the reason the pH of the oceans is declining. Since solubility of CO2 decreases with temperature, much of this uptake has occurred in cold waters of the Southern Ocean. Other potential, but currently negligible on a global scale, ocean sinks include increases in photosynthesis by plankton [and deep-water burial of the ‘fixed carbon’] and changes in ocean circulation.

So we know with good confidence that about 30% of fossil fuel emissions have been absorbed by the oceans and the remainder by terrestrial ecosystems. The remainder must be taken up by terrestrial ecosystems.

The land sink is more challenging to quantify. We know there has been a net uptake of carbon on land. The knowledge of anthropogenic emissions and good estimate of the ocean sink allow us to infer this total land uptake or land sink. So that means carbon uptake by photosynthesis by terrestrial ecosystems is greater than carbon emissions by those ecosystems, from respiration, but also from disturbances like fires and deforestation.

Notice that I did not include deforestation as a CO2 sources above – just fossil fuel emissions. Deforestation is responsible for about 20% of total anthropogenic CO2 emissions; fossil fuels and the like for the other 80%. But since I’m talking about the net exchange of carbon between land and the atmosphere, carbon emissions from deforestation is folded into the equation.

Anyhow, field observations, including forest inventories, satellite observations of terrestrial productivity, data from ‘flux’ towers at specific locations, and modeling point to a few key players:

- Re-growth of forests on abandoned farmland in the Northern Hemisphere has led to a net uptake of carbon (at least until the trees reach maturity)
- Higher concentration of atmospheric CO2 can increase rates of photosynthesis and hence carbon uptake (“CO2 fertilization”).
- Deposition of nitrogen, emitted by burning of fossil fuels and application of fertilizer, may also be unintentionally ‘fertilizing’ forests

Knowledge of the sinks lets us calculate how anthropogenic CO2 emissions translate into increases in atmospheric concentration. Eli’s post provides a model for doing some simple experiments.

Why does this matter? Our understanding of the modern-day carbon cycle underpins to all that stuff about climate policy that you read, see, hear and smell in the news. Right now, we emit about 8 Gt of C per year, and that translates to, as Tamino points out, an increase of about 2 ppm of CO2/year in atmosphere. But what if climate change alters that way the oceans and the land take up carbon? Then the model has to change.

This is one of the great challenges in climate change science AND climate change policy. To work out what percent reduction is necessary to hit a stabilization level, we need to understand carbon cycle feedbacks: how will climate change alter the fraction of emissions that remain in the atmosphere? Here are three (of many) possible feedback effects:

i) Atmospheric CO2 affect on photosynthesis: Will there be carbon fertilization – higher photosynthesis - or will water stress and nutrient limitation reduce the fertilization affect?
ii) Drying in the tropics: Reduced rainfall in the Amazon would reduce carbon uptake and increase carbon release through fires
iii) Ocean circulation: A slowing of ocean circulation could limiting productivity in the surface ocean and sinking of carbon (via increasing stratification – topic for another day)

One way to get at these questions is to examine the year-to-year variability in CO2 growth in the atmosphere. What you see in that IPCC figure at the top of the post is that the rate of uptake by the planet varies widely year to year, from less than 20% of emissions, to over 70% of emissions.

There are a few interesting features. The year-to-year variability mostly originates from tropical forest. For example, you can see high airborne fractions or high growth rates during El Nino events (e.g., 1997-1998, 1972-3, 1982-3) due to related droughts (less C uptake) and fires (more C release). That’s not too surprising. It does serve as a warning: future drying in the tropics, due to climate and/or deforestation, could reduce the carbon sink.

In the past, most of the general circulation or climate models used in the IPCC assessments did not included a complete carbon cycle. The atmospheric CO2 concentrations were imposed based on externally generated scenarios. With a complete representation of the carbon cycle, we could instead impose emission, and allow the model to simulate the change in concentrations and uptake by land and oceans.

The latest IPCC assessment includes a comparison of some ‘coupled’ climate-carbon cycle models. All the models predict a decrease in the sink or an increase in the fraction of emissions that remain in the atmosphere. But more on that next time.

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