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.

Return to carbon-land

Thanks to new, serious long-term climate change policies in the province of Saskatchewan and the state of Minnesota, I've had to update the carbon-land map. The original was a play on the Jesusland cartoon circulated after the '04 US election.

Expect more states to leave carbonland in the coming months. My current home state of New Jersey, already a member of the States United for Climate due to participation in RGGI, also just set one of the most aggressive emissions reductions policies in all of North America.

If you're wondering why there is still some carbon-land in (western) Canada, it is because this does not count. Admission to the States United for Climate requires real willingness, and at least some semblance of a plan, to meet the emissions target.

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.

The aftermath of Gonu

Maybe comprehensive coverage of a human tool of a storm in the Middle East is too much to expect of a N. American news media obsessed with things like, as a commenter on Chris Mooney's blog wrote, Paris Hilton going to prison?

In searching for updates on post-Gonu flooding in Iran, I found few articles that focused on anything other than oil prices. Those few that did had the "we interrupt this tale of human suffering for breaking news on oil prices" dynamic going. Is it really too much to ask that the news on oil prices and the news on the dead from Cyclone Gonu at least be divided into separate, maybe adjoining, articles?

Try this schizophrenic headline from an Environment News Service story this morning: "Cyclone Gonu kills 70, leaves oil ports unscathed". Sure, headlines today are rarely poetry. At best, they are a way to convey the most information in that least words. And maybe that is all the editors consciously aiming to accomplish by adding the comma and second sentence fragment. Sub-consciously? Might as well just add replace the comma with "but, don't worry, it".

For a short bit of news on the aftermath in Iran, try Reuters and this Iranian news service. The blog sadaboutgonu, mentioned in comments below, has a fascinating set of photos and video from Oman.

The G8 statement on climate change

The G8's climate change declaration has been called "a major step forward" (Tony Blair), an "important step" (Stephen Harper), a "big success" (Angela Merkel), a "very substantial coming together" (Tony Blair, he's good with the quotes) and "a bold, audacious plan that will unite the world against the problem of climate change" (George Bush).

Ok, I made that last one up. It is rather sad that the US agreeing to seriously consider greenhouse gas reduction targets is a big success. That shows how low the bar has been set for international climate negotiations with the Bush Administration. Ever been told you will be seriously consider-ed for a job? Did you get the job?

You can read the text of the agreement yourself. The very first item on climate change (#40) contains this statement: "Tackling climate change is a shared responsibility of all". True. There are more like this (#53):

We therefore reiterate the need to engage major emitting economies on how best to address the challenge of climate change. We embrace efforts to work with these countries on long term strategies.

True again. But in policy-speak, these statements mean the US refuses to accept a hard emissions target unless China and India accept a similar target (something both countries have already rejected, and that would be unfair). The stalemate will continue unless the US Congress overwhelmingly passes legislation in the fall, and there's so much political pressure that President Bush does not use his veto power. The real battle for international climate policy could happen not (at the UN negotiations) in Indonesia this fall, but on the floor of the US House.

In the end, I suppose the G8 declaration is a step forward, in that at least the Bush Administration is not rejecting the science, and is recognizing that someone out there might want to do something about greenhouse gas emissions. If I were the leaders of the other G8 nations, I would not be too proud, however. It sure looks like they just got bullied one more time by the Bush Administration.

More on Gonu

The remnants of Cyclone / Hurricane Gonu have caused severe flooding in southern Iran. The overall death toll on Oman and Iran has passed 70, including 12 killed in Iran from flash floods. These are places not accustomed to severe rainfalls. Based on the little decent news coverage (not to defend the source) I was able to find, it appears the Iranian villages were unprepared for a deluge of this size.

This image (scroll down) shows the cyclone tracks in the northwest Indian Ocean since 1985. Notice no storms passed into the Gulf of Oman (upper left). The global image on Wikipedia shows just how rare it is for cyclone to even approach the Arabian peninsula or Iran.

The anamously warm sea surface temperatures off Oman played a role in steering the cyclone on that unusual track. NOAA's Coral Reef Watch has a "bleaching watch" for the coast of Oman. That means sea surface temperatures are nearing a level at which some coral bleaching may occur. Since both can be driven by warm ocean temepratures, the concurrence of intense hurricanes and coral bleaching is not so unusual; the largest coral bleaching event in the Caribbean took place in 2005, also the strongest hurricane season.

Given that this blog is devoted in large part to climate change science and policy, I'm normally wary of writing about a specific storm or weather event as it can give the false impression that one could reasonably argue that that storm or event is a clear result of climate change.

In this case, I'm writing about the storm because it is a rare event, because of the human impact, and because, frankly, the North American news coverage has been just abominable. CNN.com interrupts its coverage of the human toll to discuss oil prices. This is a direct quote:

At least 35 people were dead, most of them in Oman, and 30 were missing.
The storm spared the region's oil installations, and oil futures fell Friday on a wave of profit-taking that followed a surge in prices a day earlier. News that Cyclone Gonu had spared major oil installations in the Gulf of Oman also alleviated supply concerns. Light, sweet crude for July delivery fell 62 cents to $66.31 U.S. a barrel in morning trading on the New York Mercantile Exchange after dropping as low as $65.55 early in the session.
At least 32 Gonu-related deaths were reported in Oman, including members of police rescue squads, and 30 others were reported missing, police said. Rescue teams were searching for victims using helicopters and boats, he said.

Hurricane Gonu strikes Oman and Iran

This is an amazing, rare and possibly devastating event. Thanks in part to the warm surface temperatures (NOAA Coral Reef Watch anomaly data) in the northwestern Indian Ocean, Cyclone / Tropical Storm Gonu veered north into Oman and is moving into Iran.

As Jeff Masters' wunderblog explains, it may be entirely without precedent in the observed record. And, sadly, that means the region is underprepared. The only predictable part of this: the news coverage seems to be more concerned about the impact on oil infrastructure and oil prices than the impact on the people living there.

Hopefully, not too many commentators will be tempted to scream "aha - it must be global warming" and, if anything, stick to some reasonably informed winking.

China, the G8 and emissions intensity

Earlier, this week China announced a vague climate change policy that includes no GHG emissions targets. While hardly a surprise, the refusal to consider any emissions targets, or even any aspirational emissions goals pretty much destroyed whatever little chance there was that UK, Germany, Japan and the G8 countries would oppose the US effort to block the use of hard emissions targets.

China may be one place where the intensity-based metrics make some sense. With low per capita emissions and a smaller historical contribution to emissions, forcing China to drastically restrict economic development would hardly be a globally equitable solution to climate change.

As I discussed a couple weeks ago, China’s GHG emissions intensity rose in the past decade. China is at the stage of development where “carbon” generation is outpacing economic development. In terms of carbon efficiency, you can imagine China being around where the West was back in 1920s, before the global peak in emissions intensity (see the global intensity graph)

So at least new Chinese policy calls for a 20% decrease in energy intensity, the energy consumption per $ of GDP. Whether that policy has any teeth, or whether the emissions data is trustworthy, who knows? But it is a start.

The Canadian government proposal that G8 countries adopt intensity-based targets is ridiculous for Western nations. Europe, Japan, Australia and North America passed their peaks in emissions intensity, or lows in carbon efficiency, decades ago. For those countries, targets have to be based on the actual emissions.

For China and other rapidly developing nations, however, setting initial targets based initially on the “carbon” efficiency or intensity of the economy may be the only sensible solution to the global policy stalemate. Perhaps the only global plan that is equitable is one in which: i) the U.S., Europe, Canada and other Annex 1 nations accept hard caps on their own emissions, and ii) China and other developing nations use intensity-based targets until the per-capita emissions reach some threshold, beyond which hard emissions caps should be applied.

Exporting a bad idea to the world

First, the US proposes setting a global GHG emissions "goal" - an object to which effort or ambition is directed, rather than a "target" - an amount set as a (minimum) objective. Then, the effort to undermine the push for a global emissions agreement at the G8 Summit was savaged, by foreign governments, by Democrats and by commentators, like a tofurkey at a Greenpeace rally.

Now, quel horreur, the Canadian PM says his government wants to play peacemaker (CBC).

Prime Minister Stephen Harper told a German business audience Monday Canada won't meet its Kyoto targets to lower greenhouse gas emissions, but can be a world leader in battling climate change.

And here it comes:

Harper did say he believes his government's plan for intensity-based targets to limit greenhouse gas emissions will be more effective than setting overall reduction targets.

I was so dumbfounded by this, I double-checked on the CBC's French language service:

Selon la solution canadienne, il n'y aurait pas une réduction draconienne des gaz à effets de serre, mais l'encouragement de mesures moins polluantes dans chaque unité de production industrielle.

That's right. Canada is championing the emissions intensity policy as the solution to it all. Could it work? Only if the intensity-based targets, not aspirational goals, are set such that total emissions actually decline. However, that is not the case in the Canadian policy.

The joke is, er, the tragedy is, not only has the Canadian policy been ridiculed by experts across the spectrum, it is not even original. It was lifted, almost digit for digit, from the equally toothless American policy.

Let's hope the rest of the world looks at this graph. And that someone out there has a calculator that can do compound interest.

Ok, this biofuels thing has gone too far

MEXICO CITY (Reuters) - Mexican farmers are setting ablaze fields of blue agave, the cactus-like plant used to make the fiery spirit tequila, and resowing the land with corn as soaring U.S. ethanol demand pushes up prices.

The switch to corn will contribute to an expected scarcity of agave in coming years, with officials predicting that farmers will plant between 25 percent and 35 percent less agave this year to turn the land over to corn.