Wednesday, September 29, 2010

Bio-geoengineering - Musings on a Satellite Photograph

Your humble blogger is in full-on real-estate exploration mode at the moment.  In doing so I have spent a fair amount of time staring at satellite pictures from Google Maps, much like the one above.  For the sake of my privacy, that particular picture is a randomly selected piece of the countryside not too far from Ithaca.  However, it's not too dissimilar from the kinds of property we have been looking at - plots that are former farms with 5 or 10 or 20 acres of land, some pasture, maybe a pond, maybe some woods.  The rest of my family's goal is to have a place of great natural beauty where our kids can grow up catching frogs in the stream, running in the field with the family dog (that we don't have yet, but are very eagerly anticipating), and so on.

However, I am thinking in terms of my goal to get us to the point of being climate neutral.  Obviously a lot of that involves thinking about the traditional issues of building energy efficiency, renewable power, etc.

However, staring at the aerial photos and thinking about the solar energy budget of a particular piece of property is starting to make me think about the problem rather differently.

The most striking thing about the picture to me is the albedo variation across the property.  Recall, if you've forgotten your high school science that the albedo of an object is defined thus:
The albedo of an object is a measure of how strongly it reflects light from light sources such as the Sun. It is therefore a more specific form of the term reflectivity. Albedo is defined as the ratio of total-reflected to incident electromagnetic radiation. It is a unitless measure indicative of a surface's or body's diffuse reflectivity. The word is derived from Latin albedo "whiteness", in turn from albus "white", and was introduced into optics by Johann Heinrich Lambert in his 1760 work Photometria. The range of possible values is from 0 (dark) to 1 (bright).
So in lots of these satellite pictures of old farms (or current farms for that matter), there are stock ponds, and they invariably show up as jet black.  So clearly the albedo of a pond is pretty close to zero.  That means that pretty much all of the incident radiation is absorbed.  Now, these kinds of farm ponds are generally only 0-15 feet deep, so this must be even more strongly true of the ocean, which is really deep.   Recalling that the oceans cover something like 2/3 of the planets surface, it's clear that the planet's energy absorption will be strongly dominated by the ocean.

Furthermore - recall the basic physics of the greenhouse effect.  The atmosphere is relatively transparent to incoming visible light, but carbon dioxide, water vapor, etc, make it less transparent to outgoing reradiated infrared.  By keeping some of this reradiated heat in, the greenhouse gases warm the planet.

Now, if we guess that the land in the picture above has average albedo of around 0.3 (the average for the land on earth generally), that means a third of the incoming solar radiation is immediately reflected back out into space still at visible wavelengths.  So that reflected portion is largely not subject to greenhouse gas capture.  By contrast, thermal radiation from the high albedo ponds is all subject to the greenhouse gas (it's important to note that the albedo also applies to emission of thermal radiation from objects, as well as their absorption - Kirchoff's law).

So the oceans not only dominate the earth's energy budget, but they are also the place where the bulk of the change in energy flow due to greenhouse gases is occurring.  The wiki actually has a picture that illustrates this:

The 'total sky' one include the effects of cloud, whereas the "clear sky" one is only the albedo without clouds.  Note how the world's deserts show up as bright spots, while the tropical oceans are dark.

Now, the oceans are very large and slow to change, so the effects of pumping extra energy into them will be slow to show up.  However, in the long term, it seems likely that's where we are making the most important changes to the energy balance.

Anway, returning to the individual property above:

The other thing that's striking is that the land-uses have clear and large effects on the albedo.  The forests are much darker than the pasture.  Generally, forests have an albedo of 0.08-0.18, while green grass has an albedo of about 0.25.  Note that these kinds of variations are large compared to human changes in the greenhouse gases.  For example, here's an illustration of the effects of various "climate forcings" since 1850 (from Hansen and Sato here):

These are W/m2, and for comparison, the solar illumination averaged across day and night is about 342 W/m2. So for example, the effect of CO2 increases since 1850 is about 1.4/342 = 0.4%.  By contrast, changing from forest to pasture changes the amount of incoming solar radiation absorbed by around 10% - a much larger effect (locally).

This suggests that one can exert significant climate leverage by changing what is grown.  If somehow one could cover the pasture in plants that had pretty white flowers all summer, as well as pale waxy leaves, that could have a pretty substantial effect on the energy balance of a particular piece of property.

I googled around a little bit, and it seems climate scientists are starting to think along similar lines.  I found a paper Tackling Regional Climate Change By Leaf Albedo Bio-geoengineering from last year, which has this to say:
The likelihood that continuing greenhouse-gas emissions will lead to an unmanageable degree of climate change [1] has stimulated the search for planetary-scale technological solutions for reducing global warming [2] (‘‘geoengineer- ing’’), typically characterized by the necessity for costly new infrastructures and industries [3]. We suggest that the existing global infrastructure associated with arable agricul- ture can help, given that crop plants exert an important influence over the climatic energy budget [4, 5] because of differences in their albedo (solar reflectivity) compared to soils and to natural vegetation [6]. Specifically, we propose a ‘‘bio-geoengineering’’ approach to mitigate surface warm- ing, in which crop varieties having specific leaf glossiness and/or canopy morphological traits are specifically chosen to maximize solar reflectivity. We quantify this by modifying the canopy albedo of vegetation in prescribed cropland areas in a global-climate model, and thereby estimate the near-term potential for bio-geoengineering to be a summertime cooling of more than 1􏳢C throughout much of central North America and midlatitude Eurasia, equivalent to seasonally offsetting approximately one-fifth of regional warming due to doubling of atmospheric CO2 [7]. Ultimately, genetic modification of plant leaf waxes or canopy structure could achieve greater temperature reductions, although better characterization of existing intraspecies variability is needed first.
That sounds pretty promising.


Mike Aucott said...

Modifying plants to be more reflective does sound promising. But, since plants need light mostly in the visible spectrum for photosynthesis, it doesn't seem likely that changing important crop plants to be highly reflective will be dramatically successful.

Regarding albedo of land in western New York; don't forget there will be major seasonal differences. Those ponds generally freeze over all winter and will continue to do so in most winters, for a while anyway.

When we lived in rural America 25 years ago - in northcentral PA - we found that the biggest chunk of our energy usage was driving. And we had to do more of it than we anticipated; to get the kids to the school bus, to visit friends, to buy groceries, etc.

Gary said...

There is a bit of a paradox with the albedo / ecosystem question. Healthy, complex ecosystems usually have a much lower albedo than degraded systems. Consider rain forests vs deserts. The argument from a thermal ecosystem perspective is that living systems evolve to degrade in incoming solar radiation as completely as possible. Any energy gradient that can be exploited by some organism, will be; and in the processes the energy is "used" by the organism rather than reflected back into space directly. In practice, the water cycle is an important part of this process. So although a forest may be very efficient at absorbing sunlight, you find that the forest floor is cool. Transpiration, powered by sunlight on tree leaves, generates evaporative cooling. Down wind, the water vapor pumped into the atmosphere by the trees might condense into clouds which will then reduce the albedo. One can argue that a low albedo is a signature of healthy forests, especially if accompanied by abundant downwind cloud formation.

Robert said...

My daughter got married at a friends nearby small 'farm' while at Cornell. I recall being told that almost all of the original forest was cleared but has been partially replaced with secondary growth. I assume that much of this will be lost post peak??

Stuart Staniford said...


Yes, I think this area was pretty much completely cleared for farming in the century following the Sullivan expedition, but a lot of the more upland farms failed, especially during the great depression. The government reacquired much of the land for state forests, and there's also a lot of private forest where farms have been allowed to go back to nature. So now it's a quilt of forest, with remaining working farms wherever the glaciers left particularly good soil, especially in the valleys.

I guess I would tend to agree that post peak, biomass production will become a higher priority and marginal farmland might become profitable again, and there would be a tendency for places like this to come back into production more. However, I think it will probably be a relatively gradual decades-long thing.

Stuart Staniford said...

Mike: yes on driving. The general idea there is to use electric cars (personally, I bike around much of the time, but I probably won't in the depth of winter, and my wife won't even in summer :-)

Stuart Staniford said...


You raise a good issue that I also wondered about - what the effects are of forest vs pasture on transpiration and H2O. Obviously, it could potentially cut either way - water vapor is a potent greenhouse gas itself, which would tend to increase the greenhouse effect. However, if there's so much that it increases cloudiness, clearly that cuts the other way by increasing the albedo.

I agree that issue could be important and I don't understand it.

However, it seems less likely to be a factor in the kinds of situations the paper I linked to is talking about (do we use Barley variety A with a more reflective waxy coating and higher albedo, or B without).

Alexander Ac said...

Hi Stuart,

me thinks that even the possibility that yoz can look at such images means that you are not carbon neutral. And if you aim to, forget the aerial images :-)


Stuart Staniford said...


:-) I think the pictures will be taken whether or not I look at them...

Alexander Ac said...

Ok, you won that argument ;-)

Stuart Staniford said...

Ha - amusing. The satellite photo above I really did pick at random on Google maps (which didn't show it for sale). However, I see in Zillow that it actually has been for sale for over three months, if anyone wants it. Listed at $450k, but probably badly overpriced for this area at that.

James said...

Current warming is nearly 2 Watts per meter squared.

A small Christmas tree light is about 1 watt. So two of these small bulbs per square meter, 8000 per acre, more than 5,000,000 per square mile, giving off tiny bits of
heat, 24/7/365, over the entire surface of the earth is one way to think about our strange moment on Earth. And to understand, if only a bit, how this year has been one of the warmest in the last 1000 years, if not much longer than that.

BOP said...

Just found this article on albedo and it inspired a question.

We know that placing an ice cube in a drink will lower the temperature of the liquid. The temperature will reach some minima and then all of the liquid will slowly rise to ambient temperatures.

If we consider melting in the high latitudes it must be the case that any temperature rise is being countered by ice melting and that this will continue to be the case until all of the ice melts. It seems at this point there is a discontinuity and a sudden jump in temperatures due to the lack of any cooling effect due to ice melt.

Extend this to all areas of glaciation, all of which appear to be melting, and there appears to be a future point at which we are committed to a sudden and immediate temperature increase.

Was actually looking for your post on the cooking temperature of human proteins.