Climate benefit for cutting soot, methane smaller than previous estimates

Aug 12, 2013
Diesel smoke from a big truck. Credit: EPA

Cutting the amount of short-lived, climate-warming emissions such as soot and methane in our skies won't limit global warming as much as previous studies have suggested, a new analysis shows. The study also found a comprehensive climate policy would produce more climate benefits by 2050 than if soot and methane were reduced alone.

"Cutting back only on and will help the climate, but not as much as previously thought," said the study's lead author, climate researcher Steve Smith of the Department of Energy's Pacific Northwest National Laboratory. "If we want to stabilize the , we need to focus on greenhouse gases such as carbon dioxide, nitrous oxide and methane. Concentrating on soot and methane alone is not likely to offer much of a shortcut."

The new study will be published the week of Aug. 12 in Proceedings of the National Academy of Sciences Early Edition online. Smith works at the Joint Global Change Research Institute in College Park, Md., a joint venture between PNNL and the University of Maryland.

At least two studies have been published since 2010 that suggest reducing soot and methane would cut human-caused increases by half of a degree Celsius, or about 1 degree Fahrenheit, by 2050. International leaders took note and formed the Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants in 2012.

Soot and methane are called short-term climate forcers because they only remain in the atmosphere for a relatively short time: a couple weeks for soot and up to a decade for methane. Meanwhile, the better-known climate change culprit carbon dioxide can stick around for 1,000-plus years. Soot, also known as , is made of fine, carbon-based particles that are given off by car and truck tailpipes and wood stoves. Methane, the main component of natural gas, is released from leaking pipelines, , oil wells, cattle, and landfills.

A modeled future

Smith and his former research assistant Andrew Mizrahi used a PNNL computer model, the Global Change Assessment Model, or GCAM, to evaluate the impact of reducing soot and methane emissions on Earth's climate. GCAM is especially suited for projections such as this because it takes into account ongoing future changes in technology, society and the economy, including energy and land use. The model also incorporates greenhouse gases and pollutants that can result from those activities. Earlier studies of short-lived climate pollutants did not use an integrated, dynamic model such as GCAM.

With PNNL's climate model, Smith created more than 1,400 potential scenarios to reflect the many possibilities surrounding aerosols, tiny particles including soot that float in the atmosphere. The impact of aerosols on past and future climates has yet to be definitively determined. Ongoing PNNL research is evaluating how aerosol particles affect the atmosphere, including temperature and precipitation. The model also considered how reducing soot could impact other atmospheric emissions, including sulfur dioxide, nitrous oxide and organic carbon.

The study examined what the future could look like in an idealized world where soot and methane emissions were severely cut by 2035. All feasible and available technology was used to eliminate as much methane as possible. And all wood- and biomass-burning stoves were replaced with cleaner, modern stoves that use electricity or natural gas for energy. Finally, all cars and trucks were assumed to be equipped with advanced soot emission controls.

Highest possible reduction isn't so high

The research found that cutting soot and methane as described above produced an average temperature reduction of 0.16 degrees Celsius by 2050, which is substantially less than the 0.5-degree reduction found in earlier studies. When looking at individual scenarios that employed various assumptions about aerosols, temperature reductions varied from a low of just 0.04 degrees to a high of 0.35 degrees.

For further comparison, Smith also evaluated these results against what would happen if a comprehensive climate policy were enacted. Earlier PNNL research developed such a scenario, which includes substantially reducing all greenhouse gas emissions, instead of only limiting carbon dioxide as the previous short-lived climate pollutant studies did for their comparative scenario.

While focusing on reducing all greenhouse gas emissions, including methane, the comprehensive climate policy scenario also reduced the amount of soot in the atmosphere. As a result, the climate policy scenario lowered global average temperatures by 0.27 degrees in 2050, which is more than when only short-lived climate forcers were controlled. The comprehensive scenario also provided much larger temperature reductions through 2100.

"Focusing on soot and may be worth targeting for health reasons, as previous studies have identified substantial health benefits from reducing those emissions," Smith said. "To stabilize the global , however, the focus needs to be on carbon dioxide and other ."

Explore further: Researchers constrain the sources of climate- and health-afflicting air pollution from China

More information: Steven J. Smith and Andrew Mizrahi," Near-Term Climate Mitigation by Short-Lived Forcers," PNAS, Aug. 12, 2013, DOI: 10.1073/pnas.1308470110

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julianpenrod
2 / 5 (21) Aug 12, 2013
I had said that the fossil fuel related suggested causes for climate change were not legitimate. Frankly, even carbon dioxide does not appear significant. Carbon dioxide has been building in the atmosphere for a century or more from industry. In the past decade, it has risen only a few more percent. But the past decade saw a period of massive and accelerated climate change manifestations. The amount of climate change effects in the past decade is out of keeping with the extra added amount of the gas. If there were no such effects in the century or so preceding, the miniscule extra amount during the past decade or so seems unable to explain the effects. It seems that it is chemtrailing, the doping of the atmosphere with weather control chemicals from high flying jets that is responsible for climate change.
NikFromNYC
1.8 / 5 (19) Aug 12, 2013
Is julianpenrod yet another sockpuppet account spewing nonsense as a smoke screen to make all discussion below Global Warming news appear to be mere noise?

http://s24.postim..._Bot.jpg

This study is all just a computer model raised to the level of headlines. It's exactly as competent as the competing claims of what the stock market will do on TV, quite similar to that especially since all Global Warming researchers have an immediate vested conflict of interest, namely that if soot really does have a big influence, their whole field of science no longer qualifies for emergency level funding. Actual on-the-ground studies are creeping up on the CO2 bandwagon:

http://esciencene....climate
NikFromNYC
1.7 / 5 (17) Aug 12, 2013
Ugh, my link is just a climate model too.

"Show me the data!" - Burt Rutan

All of these models ignore the elephant in the room: climate is dominated by ocean heat cycles that trap and release energy and which fluid dynamics alone renders chaotic and thus fundamentally unpredictable since tiny perturbations are amplified for decades at a time. This is not controversial, but talking about it certainly is.
thermodynamics
3.5 / 5 (11) Aug 13, 2013
Nick said: "All of these models ignore the elephant in the room: climate is dominated by ocean heat cycles that trap and release energy and which fluid dynamics alone renders chaotic and thus fundamentally unpredictable since tiny perturbations are amplified for decades at a time. This is not controversial, but talking about it certainly is."

Would you please tell me what models you are talking about that do not couple the oceans into the global climate models?

Let me give you a quote from Wikipedia: "Atmospheric and oceanic GCMs (AGCM and OGCM) are key components of global climate models along with sea ice and land-surface components." So, it seems that global climate models look at the atmosphere, oceans, land, and ice. They may not do the best job yet, but they are constantly improving.

Here is the link: http://en.wikiped...te_model

Continued:
thermodynamics
3.5 / 5 (11) Aug 13, 2013
Continued: Nick- Let's look at what the dreaded IPCC has to say about the models. I am sure you figure they don't look at the ocean coupling. They say: "Numerical models (General Circulation Models or GCMs), representing physical processes in the atmosphere, ocean, cryosphere and land surface, are the most advanced tools currently available for simulating the response of the global climate system to increasing greenhouse gas concentrations (criterion 1 -- see list here)." Oh, wait, they do talk about the same things Wikipedia talks about. Here is their link:

http://www.ipcc-d...ide.html

So, I will be waiting for you to give me the links to those models that don't include oceans coupled to the atmosphere. You seem to think none do - and we can see from my two references that those who use them think they all include the fluid coupling. Weren't you the one who said "show me the data?"
thermodynamics
3.7 / 5 (12) Aug 13, 2013
Continued: So, now that we know they all take the ocean circulation into account, you are probably going to talk about how it is chaotic and can't be computed. I know that has been explained to you multiple times but I will go over it again. What they do is they run models many times with different boundary conditions. They then put the model results together to show an ensemble of results which give them statistics on the probable outputs. It is the same process we use with any complex modeling where we know the system is unstable or chaotic. If you are not familiar with the process you need to relearn modern numerical methods. We don't just throw up our hands when working with coupled differential equations in my combustion codes. We produce an ensemble of solutions that we can use for prediction. We also look at sensitivity to initial conditions to better understand the responses. Let me know if you are not familiar with the process.
NikFromNYC
1.7 / 5 (17) Aug 13, 2013
thermodynamics, I don't see any sign of the grids that your climate models use, in actual ocean currents. Can't you even switch to geodesic triangles instead of grids that get smaller away from the equator? Until your field loudly rejects Hockey Stick Team charlatanism, nothing you say or report even after peer review can be trusted and you force us chemists to delve into your dirty laundry instead.

Van Gogh is rolling in his grave: http://postimg.or...pvd84k1/

Science requires real data, not computer models alone. The biggest experiment of all has been carried out by China by vastly boosting their CO2 output over the last two decades that the best Argo buoy and satellite data show correspond to no further warming. Your climate models are thus bluntly falsified because they do not correspond to reality, even in basic shape let alone predictive ability.

Movie of real ocean dynamics: http://svs.gsfc.n...0p30.mp4
NikFromNYC
1.8 / 5 (15) Aug 13, 2013
"Philosophy will clip an Angel's wings." – John Keats ("Lamia," 1820)

http://alexruizar...15823393

"Before you hire an expert, determine that this expert status comes from experience, not theory." – Dan S. Kennedy ("The Ultimate Marketing Plan," 1991)
QuixoteJ
2.3 / 5 (16) Aug 13, 2013
"If we want to stabilize the climate system...", says the study's lead author, Steve Smith. Does he even realize how ridiculous of a statement that is? I couldn't read the article after that statement.
runrig
3.7 / 5 (6) Aug 13, 2013
"If we want to stabilize the climate system...", says the study's lead author, Steve Smith. Does he even realize how ridiculous of a statement that is? I couldn't read the article after that statement.


In that case you don't have an open mind as to the AGW threat, as that statement came in the second paragraph in. Not big and not clever.
Water_Prophet
1 / 5 (9) Aug 13, 2013
@Julianpenrod
Thou hast seen the light, the blessing of the most Holy Element, Water, be upon you.
Water is twelve times twelve times more important than the other foul Earth and Air Elements, yet man's pacts with the base Elements is blamed.
Why is it that so many models are used when nature can simply be observed? The way of Water, it's melting and not, the parables of Air-migrations from the Capricorn and Cancer to the Lands of perpetual ice clearly show us the way things will be, are and have been.
Howhot
2.6 / 5 (5) Aug 14, 2013
Hay NikfromNYC, isn't this more your style;

http://www.youtub...LkIqu1c8

Howhot
4.2 / 5 (5) Aug 14, 2013
Hay @Water_Prophet;
The way of Water, it's melting and not, the parables of Air-migrations from the Capricorn and Cancer to the Lands of perpetual ice clearly show us the way things will be, are and have been.

That is deep.
Gmr
3 / 5 (6) Aug 14, 2013
After hearing for the umpteenth time about the superior intellect of chemist PhD's, I feel like the guys did about pumas after watching 'Pumaman.'
Crow: You know I have almost no respect for pumas now? I now know that if I ever run into a puma I can just push it the hell over.

http://www.imdb.c...0/quotes
Howhot
4.3 / 5 (4) Aug 15, 2013
From the article;
Cutting the amount of short-lived, climate-warming emissions such as soot and methane in our skies won't limit global warming as much as previous studies have suggested, a new analysis shows.

That is what I've concluded too. Diesel Soot while not have a global impact (although it is a carcinogen just so you know). Methane is a concern because it is a green house gas and will impact the climate globally. It maybe short lived only lasting 12 years instead of the 1000s from CO2, but methane is also 20 times a better greenhouse gas. If you look at the situation with the Arctic ice melt, and the Russian permafrost melt, in the next decade, we can see a spike in methane that might be like a quantum leap higher in global green house gasses.