Sugarcane cools climate

Apr 17, 2011

Brazilians are world leaders in using biofuels for gasoline. About a quarter of their automobile fuel consumption comes from sugarcane, which significantly reduces carbon dioxide emissions that otherwise would be emitted from using gasoline. Now scientists from the Carnegie Institution's Department of Global Ecology have found that sugarcane has a double benefit. Expansion of the crop in areas previously occupied by other Brazilian crops cools the local climate. It does so by reflecting sunlight back into space and by lowering the temperature of the surrounding air as the plants "exhale" cooler water. The study is published in the 2nd issue of Nature Climate Change, posted on-line April 17.

The research team, led by Carnegie's Scott Loarie, is the first to quantify the direct effects on the from sugarcane expansion in areas of existing crop and pastureland of the cerrado, in central Brazil.

The researchers used data from hundreds of satellite images over 733,000 square miles—an area larger than the state of Alaska. They measured temperature, reflectivity (also called albedo), and evapotranspiration—the water loss from the soil and from plants as they exhale water vapor.

As Loarie explained: "We found that shifting from natural vegetation to crops or pasture results in local warming because the plants give off less beneficial water. But the bamboo-like sugarcane is more reflective and gives off more water—much like the natural vegetation. It's a potential win-win for the climate—using sugarcane to power vehicles reduces carbon emissions, while growing it lowers the local air temperature."

The scientists found that converting from natural vegetation to crop/pasture on average warmed the cerrado by 2.79 °F (1.55 °C), but that subsequent conversion to sugarcane, on average, cooled the surrounding air by 1.67 °F (0.93°C).

The researchers emphasize that the beneficial effects are contingent on the fact is grown on areas previously occupied by crops or pastureland, and not in areas converted from natural vegetation. It is also important that other crops and pastureland do not move to natural vegetation areas, which would contribute to deforestation.

So far most of the thinking about ecosystem effects on climate considers only impacts from greenhouse gas emissions. But according to coauthor Greg Asner, "It's becoming increasingly clear that direct climate effects on local climate from land-use decisions constitute significant impacts that need to be considered core elements of human-caused climate change."

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Provided by Carnegie Institution

3.2 /5 (5 votes)

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Doug_Huffman
2 / 5 (4) Apr 17, 2011
Anyone else here know how cane is traditionally harvested, like in the third world? What do you imagine happens to the leaves and the bagasse? Their carbon is released and not sequestered, just NIMBY, but in a power plant.
Cave_Man
2.8 / 5 (8) Apr 17, 2011
Seems like everyone is also conveniently forgetting that while ethanol from sugarcane doesnt produce as much CO2 it does produce huge amounts of acetaldehyde vapor which is what causes hangovers after you drink alcohol, it is also one of the worst known chemicals for ecosystems and human health.

So whats the benefit if we just wind up killing ourselves in a different way.

Solar wind geothermal and clean nuclear fusion are our only viable choices. Period.
jselin
2.2 / 5 (5) Apr 17, 2011
I would love to take geothermal off that list... I know the quanity of heat in the planet is staggering but we have no clue what were getting into with that. What if our appetite for power is 1000 or 10000 times current consumption in a few hundred years? What if we find that the magma goes through various transformations/viscosity changes in the liquid state that have an effect on the flow patterns in the mantle? We know very little about what exactly is going on down there including -precisely- how our magnetic field is generated (let alone its minimum requirements). Sound crazy? So would global warming warnings in the 1800s... (or to those still living in them)
NotParker
2.5 / 5 (8) Apr 17, 2011
"corn-based ethanol CO2 output was less than 5% different than from gasoline."

On top of that ethanol has a lot less energy than gasoline.

So you have to burn more of it to travel the same distance.

Ethanol has 6,100 Wh/litre of energy
Gasoline has 9,700 Wh/litre of energy

So you need to burn over 50% more ethanol (assuming 100% ethanol) to travel the same distance.
Shootist
3.4 / 5 (5) Apr 17, 2011
Using scarce land, to grow food, to burn for fuel. Harmless, really.

Move along citizen, nothing to see here.
PinkElephant
4.2 / 5 (5) Apr 17, 2011
@DougHuffman,
Their carbon is released and not sequestered
Sugarcane gets is carbon from the atmosphere; burning the resulting ethanol returns the carbon back to the atmosphere. This makes the fuel cycle carbon-neutral: it does not add new carbon into the atmosphere. Which cannot be said of fossil fuels.

@Cave_Man,
acetaldehyde vapor which is what causes hangovers after you drink alcohol, it is also one of the worst known chemicals for ecosystems and human health.
As compared to gasoline? Are you trying to be funny? Just like gasoline, that ethanol is meant for burning, not for drinking or inhaling.

@NotParker,
ethanol has a lot less energy than gasoline
Yes, so make your fuel tank 50% larger by volume: problem solved. Or, instead of an internal combustion engine, use a much higher-efficiency direct ethanol fuel cell (needs more R&D, but not even remotely possible with gasoline.)
PinkElephant
4.2 / 5 (5) Apr 17, 2011
@Shootist,
Using scarce land, to grow food, to burn for fuel
Which is just another way of harvesting solar energy. Yes, I agree that it should be possible to do this much more directly and efficiently. Thus, ethanol from sugarcane is a stopgap -- not the final answer.

Cellulosic ethanol from crop waste, as well as fermented ethanol or methane from food waste, on the other hand, do potentially have a long-term future.
SemiNerd
5 / 5 (1) Apr 18, 2011
Ethanol from corn only gives you about 30% more energy than you put into it when you consider the chemicals for pesticides, harvesting etc.

For sugarcane the number is more like 700% which is respectable. This is right up there with cellulose based sources without the problems with lignin separation.

In my mind it is just another way of extracting energy from the sun, and a pretty good one at that.
deepsand
3 / 5 (10) Apr 18, 2011
On top of that ethanol has a lot less energy than gasoline.

So you have to burn more of it to travel the same distance.

Given your proclaimed faith in engineering's ability to solve the direst possible outcomes of climate change, one would have expected you to realize that this is a trivial engineering problem. :lol:
NotParker
1 / 5 (3) Apr 26, 2011
Sugarcane gets is carbon from the atmosphere


But it gets nitrogen from fertlizer.

Brazil uses more fertilizer per hectare of arable land than the USA.

Most fertlizer is fossil fuel based.

http://http://www.tradingeconomics.com/united-states/fertilizer-consumption-kilograms-per-hectare-of-arable-land-wb-data.html
NotParker
1 / 5 (2) Apr 26, 2011
For sugarcane the number is more like 700% which is respectable.


I doubt that. The claim is that burning the bagasse helps the energy balance.

But if you burn the bagasse, it can't rot and fertilize the next crop.

And that 700% totally ignores the massive amounts of fertilizer Brazil uses - more per hectare than the USA.
NotParker
1 / 5 (2) Apr 26, 2011
One other thing. It is claimed by Brazilians that over 3.5 million people are in the the ethanol industry.

Thats the advantage Brazil has. Cheap labor.

I think that is worthwhile, but in terms of CO2, those people are producing vast quantities of CO2 in the production of ethanol, which when burned, produces even more CO2.

I personally don't care about Co2.

But the backflips people have to go through to convince us the "energy balance" is acceptible are quite silly.

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