July 01, 2005
Reflector Satellites Proposed To Prevent Global Warming
James Pearson, John Oldson and Eugene Levin of Star Technology and Research in Mount Pleasant South Carolina propose construction of a system of satellites to control the amount of sunlight that reaches and warms Earth.
A wild idea to combat global warming suggests creating an artificial ring of small particles or spacecrafts around Earth to shade the tropics and moderate climate extremes.
There would be side effects, proponents admit. An effective sunlight-scattering particle ring would illuminate our night sky as much as the full Moon, for example.
And the price tag would knock the socks off even a big-budget agency like NASA: $6 trillion to $200 trillion for the particle approach. Deploying tiny spacecraft would come at a relative bargain: a mere $500 billion tops.
But the idea, detailed today in the online version of the journal Acta Astronautica, illustrates that climate change can be battled with new technologies, according to one scientist not involved in the new work.
Social anthropologist Benny Peiser of the British Liverpool John Moores University says this proposal demonstrates humans can prevent disastrous climate changes.
"I don't think that the modest warming trend we are currently experiencing poses any significant or long-term threat," Peiser told LiveScience. "Nevertheless, what the paper does show quite impressively is that our hyper-complex civilization is theoretically and technologically capable of dealing with any significant climate change we may potentially face in the future."
Here is the abstract to the research paper. The particle solution is too expensive but the ring of controlled satellites could be implemented for at most a half trillion US dollars.
An artificial planetary ring about the Earth, composed of passive particles or controlled spacecraft with parasols, is proposed to reduce global warming. A flat ring from 1.2 to 1.6 Earth radii would shade mainly the tropics, moderating climate extremes, and counteract global warming. A preliminary design of the ring is developed, and a one-dimensional climate model is used to evaluate its performance. Earth, lunar, and asteroidal material sources are compared to determine the costs of the particle ring and the spacecraft ring. Environmental concerns and effects on existing satellites in Earth orbit are addressed. The particle ring endangers LEO satellites, is limited to cooling only, and lights the night many times as bright as the full moon. It would cost an estimated $6–200 trillion. The ring of controlled satellites with reflectors has other attractive uses, and would cost an estimated $125–500 billion.
Satellites with reflectors could rotate to present more or less reflective surfaces toward the Sun. Also, a fancier design to such satellites could allow them to also function as communications or remote sensing satellites. One could even imagine adjusting the orientation of some of the satellites to reflect more light onto crops to make them grow more rapidly.
Whether global warming ever becomes a big enough problem to justify a climate engineering project remains to be seen. Many would see such a project as an intervention in nature that humans have no right to make. Some would claim that climate engineering amounts to "playing God". Also, such a project would inevitably change climate in some parts of the world in ways that residents of those parts would see as detrimental. However, should humans ever colonize Mars I expect proposals for climate engineering of Mars to meet far less resistance on ideological or consequential grounds. Mars is so inhospitable to human habitation that the debate would center around what is the best way to adjust Mars to human needs. There'd be no fear of making some parts of Mars worse for humans in order to make other parts better. Also, nature as we understand it with a large range species does not exist on Mars. So the threat to Martian lifeforms (if any still exist) would be small as compared how climate engineering on Earth would inevitably shrink some ecological niches while expanding others.
I am not a pessimist about global warming for the simple reason that humans are going to become orders of magnitude more technologically capable in the 21st century. All problems will become more solvable. I think it unlikely humans will have much need for fossil fuels 50 years from now. Other energy technologies will become more attractive long before significant global warming takes place.
If this proposal is supposed to cost hundreds of billions to put reflectors in space, wouldn't it be cheaper to lay reflective material in desert areas? I can see that being literally thousands of times cheaper and easier to maintain and adjust. You could also just float mirrors in the oceans if it's ocean temperatures you're worried about.
Using space mirrors for terraforming is usually thought of for warming, not cooling. For cooling, it makes a lot more sense to just make the surface shinier.
What's cheaper, putting a square meter of mylar into space or laying down a few cut up potato chip bags on the ground?
Off the top of my head I can see several problems with laying the reflective sheets on the ground:
1) More surface area would be needed on the ground than in space for three reasons:
- Some sunlight gets turned into thermal energy before it even reaches the surface.
- If sunlight is reflected back from the surface some of it will create thermal energy on the way back up into space.
- Satellites could probably be positioned to reflect light more hours of the day. Remember surface material doesn't reflect light at night. Though perhaps in low orbit in fast orbits the satellites would suffer the same problem.
2) The surface reflective material would cover up areas where life forms live.
3) The surface material would require on-going maintenance due to rain, wind, wild animals, dust, and human interference. Space-based stuff could be much thinner and a satellite could have a huge thin metal material sheet projected out from itself. The poles that supported it would not need to be strong enough to withstand gravitational forces.
4) Oceans get storms. The materials would need to be floated on objects that could withstand that. But the floating objects would tend to wash up on shore.
5) The ground-based stuff would probably be less adjustable. Space-based satellites would be adjustable. They could be powered by solar collectors and use electrons for propulsion to slowly shift orientations.
I'm not saying you are wrong. I'm saying that it is not immediately obvious to me that the ground-based approach would necessarily be cheaper.
Another way to do the ground-based approach would be to use smaller scale weather enginering in cold regions (e.g. Alaska, northern Canada, Siberia) to cause more snowfall that would last longer into summers. Then more light would be reflected back from the surface into orbit.
Or bioengineer a tree that reflects more light back up into the atmosphere.
Blot out the stars with reflectors but don't put windmills within view of Senator Alexander's summer home on Nantucket. Yep, that's a good trade-off.
We may not use fossil fuels in 50 years but if global warming is real the changes it wreaks will be very well along on their course. I'm gonna keep smoking a couple of packs of cigarettes a day because by the time I get lung cancer stem cell research or cloning will make a lung transplant a snap.
As for terraforming Mars, James Lovelock's _The Greening of Mars_ is a good place to start. He started formulating the Gaia Hypothesis when he noticed the homeostasis of Earth's atmospheric chemistry as opposed to other planet's in the solar system. Or at least, that's what I've read.
We could put the satellites in orbits that keep them always over the light side of the Earth. Then they wouldn't blot out any stars.
I wonder what fraction of the sky the satellites would take up. Maybe we'd rarely see them.
If we stop burning fossil fuels within 50 years then, no, global warming will not become a big problem.
"We could put the satellites in orbits that keep them always over the light side of the Earth. Then they wouldn't blot out any stars."
Call me dumb, but wouldn't this mean they'd be making one revolution per year? Wouldn't this be way too slow to maintain orbit?
It is my understanding that there are places like Lagrange points where you can place stuff and it stays there. So somewhere between the Earth and the Sun the gravity of the two cancels out and an object with the right momentum will stay between the Earth and Sun at a distance that doesn't change all that much. Though Earth's orbit around the Sun is elliptical and so perhaps it is not so easy. Plus, may be the ideal stable area is not big enough to allow enough of the sun's light to be deflected.
I could be wrong. But that is my impression. I'm not a big space nut and I my knowledge in this area is pretty limited. Hopefully a more knowledgeable reader will pipe up and explain whether there is a way to position stuff between Eart and the Sun long term.
They would be in orbit; solar orbit, at L1, between Earth and the sun.
This point is roughly a million miles sunward of Earth, and an 800-mile diameter disc would block just about exactly the 1% of sunlight you'd need to restore Earth's radiative balance. As it would be visible only as a dark spot on the Sun, you would have no impact on the night sky or any of the species which depend on e.g. lunar cycles other than tides.
They would be better than anything in Earth orbit because 100% of them would be doing their job all the time, so you'd need less of them than for items in any other orbit. This is something I keep meaning to blog.
EP, there is no way you could keep a disk in L1 if you are blocking 1% of the Earth's sun light. The disk is basicly a huge solar sail and would be blown out of L1. So you would want to place it somewhere where the force acting on the disk from the Sun, Earth, and the light reflection balance out. Which begs the question of how to keep it in a stable orbit due to variation in solar output.
It would seem to me one would have to have some way to store the energy and then later to reuse the energy for propulsion. Perhaps one could store the energy as electric potential and then use that potential to accelerate protons or other ions coming from the sun to varying degrees as needed?
Dynamic orbit adjustment would obviously be necessary. A couple of ideas:
1) Make parts of the reflectors/solar sails dynamically retractable based on how much solar wind is hitting them.
2) Use solar photovoltaics to generate electricity to produce an electron stream for propulsion.
Such a reflector would be somewhat sunward of the L1 point, of course.
- Make the reflector of segments which can be flat or angled relative to each other. Reflect light straight back at Sol when solar output is lower, to the sides when it's higher. Voila, balance.
- Make the reflector more massive. Use an artificial magnetosphere to balance the extra gravitational force against the solar wind. Voila.
C'mon, man. Let's have a hardball problem, there's no points for the gimme's.
"If we stop burning fossil fuels within 50 years then, no, global warming will not become a big problem."
As far as I know, most if not all of the global reinsurance industry already believes that global warming is a problem.
Changing the world's atmospheric chemistry is a long-term problem which requires long-term solutions. We are not going to be able to filter the world's atmosphere in a year or two to avoid climate effects even with some now imaginary super-science. Might be wise to start dealing with cost-effective measures now before the freshwater alters the Gulf Stream, for one example, especially since most of those cost-effective measures reduce energy waste, save money and resources, and make the USA less reliant on foreign sources of fossil fuels.
The earths temp has fluctuated dramatically throught its long history and life goes on. Global warming is the least of the meny problems associated with the air polution are so called modern sociaty produces. So blocking the suns rays will not save the human race, what a joke. Any more BRIGHT ideas. Maybe we should ask are replacements the robots in 2050. But I dought polution well be a concern of theres or mine, because if I am still alive. I will be 80 years old and serviving without health insurance.
IIRC, the latest paleoclimate research has associated 6°/century temperature spikes with the worst mass extinctions on record. This happens to be in the range expected from a doubling of atmospheric CO2.... so no, what we are looking at is not a run-of-the-mill climactic variation, it's a crisis.
It'll be a lot easier to survive without health insurance if you can still grow traditional crops, most plants haven't died off because it's gotten too warm or too dry for them, there aren't multiple 110° F heat waves every summer, and you don't have to contend with a bunch of diseases which were once confined to the tropics by the needs of their vectors.
I read orders of magnitude more reports on climate research than I post on this site because I don't want to bore people with it. But my impression from all my reading is that the Earth has been warmer than it is now at a number of points since the last glacial. It was warmer 1000 years ago. It was warmer during the Roman Empire era. It was warmer during other inter-glacials. Yet we have all these species that survived those periods and surived the glacial periods. They probably can adapt.
For example, 7000 years ago the Alpines had no glaciers.
The Alpine glaciers are shrinking, that much we know. But new research suggests that in the time of the Roman Empire, they were smaller than today. And 7,000 years ago they probably weren't around at all. A group of climatologists have come up with a controversial new theory on how the Alps must have looked over the ages.
He may not look like a revolutionary, but Ulrich Joerin, a wiry Swiss scientist in his late twenties, is part of a small group of climatologists who are in the process of radically changing the image of the Swiss mountain world. He and a colleague are standing in front of the Tschierva Glacier in Engadin, Switzerland at 2,200 meters (7,217 feet). "A few thousand years ago, there were no glaciers here at all," he says. "Back then we would have been standing in the middle of a forest." He digs into the ground with his mountain boot until something dark appears: an old tree trunk, covered in ice, polished by water and almost black with humidity. "And here is the proof," says Joerin.
Just two problems with that:
- It's one thing to sustain a 6°C change over a thousand years; it's quite another to handle it over a hundred. Ten times the rate means many (most?) plant species will not be able to move their range fast enough to survive.
- The characteristics of climate change from solar variations and atmospheric composition changes are different, and perhaps not commensurable.
For more on that, you'd have to ask the folks at realclimate.org; it's beyond me.
What suggests to you that anyone should expect a 6°C change over the coming century?
Climate change models attempting to project the effects of 570 ppm CO2 in the atmosphere, that's what.
What makes you think all the warmings and coolings of the past required a thousand years? Looked at some historical temperature graphs? Lots of the changes are fast.
Climate change models: They are all over the map. Also, the CO2 change to date has barely been enough to create a recognizable temperature change signal above the background variation that happens for lots of other reasons.
But I don't expect the pessimistic CO2 increase projection to happen anyway. There isn't enough oil and natural gas in the ground to do it and we'll shift to fission, fusion, and photovoltaics by 2050. The rate of technological progress is accelerating and will accelerate a lot more in the future.
Oh, and realclimate.org is just one set of viewpoints. You ought to read more widely on climate. For example, Amplifiers may be enhancing the effect of changes in sun spot activity.
Another example of other views: Ecological Modelling Volume 171, Issue 4 , 1 February 2004, Pages 433-450.
Climate change: detection and attribution of trends from long-term
Craig Loehle. NCASI, 552 S. Washington Street #224, Naperville, IL 60540, USA
Two questions about climate change remain open: detection and attribution. Detection of change for a complex phenomenon like climate is far from simple, because of the necessary averaging and correcting of the various data sources. Given that change over some period is detected, how do we attribute that change to natural versus anthropogenic causes? Historical data may provide key insights in these critical areas. If historical climate data exhibit regularities such as cycles, then these cycles may be considered to be the "normal" behavior of the system, in which case deviations from the "normal" pattern would be evidence for anthropogenic effects on climate. This study uses this approach to examine the global warming question. Two 3000-year temperature series with minimal dating error were analyzed. A total of seven time-series models were fit to the two temperature series and to an average of the two series. None of these models used 20th Century data. In all cases, a good to excellent fit was obtained. Of the seven models, six show a warming trend over the 20th Century similar in timing and magnitude to the Northern Hemisphere instrumental series. One of the models passes right through the 20th Century data. These results suggest that 20th Century warming trends are plausibly a continuation of past climate patterns. Results are not precise enough to solve the attribution problem by partitioning warming into natural versus human-induced components. However, anywhere from a
major portion to all of the warming of the 20th Century could plausibly result from natural causes according to these results. Six of the models project a cooling trend (in the absence of other forcings) over the next 200 years of 0.2-1.4 °C.
I could come up with a dozen more links of research which paints a more complex and qualified picture of what various climate researchers think. The scenarios like a 6 degree C change in the next century strike me as calculated to be alarmist in order to rouse the public to support bigger policy changes. E-P, if you want to get on a private list where someone sends out abstracts and articles on climate change studies contact me about it in private email. I'll ask the guy to put you on his list and you can read more than you ever wanted to know about climate research.
Smog particles seed clouds which reflect sunlight pretty well. If memory serves there was a Scientific American article about this phenomenon. Releasing enough of the right kind of particles in the right places to cool the Earth without causing health problems for humans might be a bit of a challenge, but I'll bet it would cost far less than one hundred billion.
Kim Stanley Robinson proposed something like this in his Mars trilogy, only for the purpose of increasing sunlight to Mars by about 25% as part of the terraforming effort. To reduce the cost of lifting into orbit, a silcate asteroid was flown to L1 (Mars'), melted down, and gently spun out into a giant magnifying glass. Just reverse the concavity to reduce sunlight.
...Newly released data show that Portland, America's environmental laboratory, has achieved stunning reductions in carbon emissions. It has reduced emissions below the levels of 1990, the benchmark for the Kyoto accord, while booming economically.
What's more, officials in Portland insist that the campaign to cut carbon emissions has entailed no significant economic price, and on the contrary has brought the city huge benefits: less tax money spent on energy, more convenient transportation, a greener city, and expertise in energy efficiency that is helping local businesses win contracts worldwide.
"People have looked at it the wrong way, as a drain," said Mayor Tom Potter, who himself drives a Prius hybrid. "Actually it's something that attracts people. ... It's economical; it makes sense in dollars."
I've been torn about what to do about global warming. But the evidence is growing that climate change is a real threat: I was bowled over when I visited the Arctic and talked to Eskimos who described sea ice disappearing, permafrost melting and visits by robins, for which they have no word in the local language.
In the past, economic models tended to discourage aggressive action on greenhouse gases, because they indicated that the cost of curbing carbon emissions could be extraordinarily high, amounting to perhaps 3 percent of G.N.P.
That's where Portland's experience is so crucial. It confirms the suggestions of some economists that we can take initial steps against global warming without economic disruptions. Then in a decade or two, we can decide whether to proceed with other, costlier steps.
In 1993, Portland became the first local government in the United States to adopt a strategy to deal with climate change. The latest data, released a few weeks ago, show the results: Greenhouse gas emissions last year in Multnomah County, which includes Portland, dropped below the level of 1990, and per capita emissions were down 13 percent.
This was achieved partly by a major increase in public transit, including two light rail lines and a streetcar system. The city has also built 750 miles of bicycle paths, and the number of people commuting by foot or on bicycle has increased 10 percent.
Portland offers all city employees either a $25-per-month bus pass or car pool parking. Private businesses are told that if they provide employees with subsidized parking, they should also subsidize bus commutes.
The city has also offered financial incentives and technical assistance to anyone constructing a "green building" with built-in energy efficiency.
Then there are innumerable little steps, such as encouraging people to weatherize their homes. Portland also replaced the bulbs in the city's traffic lights with light-emitting diodes, which reduce electricity use by 80 percent and save the city almost $500,000 a year.
"Portland's efforts refute the thesis that you can't make progress without huge economic harm," says Erik Sten, a city commissioner. "It actually goes all the other way - to the extent Portland has been successful, the things that we were doing that happened to reduce emissions were the things that made our city livable and hence desirable."
Mr. Sten added that Portland's officials were able to curb carbon emissions only because the steps they took were intrinsically popular and cheap, serving other purposes like reducing traffic congestion or saving on electrical costs. "I haven't seen that much willingness even among our environmentalists," he said, "to do huge masochistic things to save the planet."
So as he heads to the summit meeting, Mr. Bush should get a briefing on Portland's experience (a full report is at www.sustainableportland.org) and accept that we don't need to surrender to global warming.
Perhaps eventually we will face hard trade-offs. But for now Portland shows that we can help our planet without "wrecking" our economy - indeed, at no significant cost at all. At the Group of 8, that should be a no-brainer.
- end of quote -
It is much less sexy and far more effective to do the small, daily things that can make a difference right now on both greenhouse gas emissions and the economy than to imagine big projects at the LaGrange point orbits. Housekeeping is boring but spaceships are kewl!!!!
With all due respect, that sounds pretty immature to me. Ah, the attraction of the spectacular! Guy DeBord, that glorious drunken Frenchman, knew whereof he spoke.
Face it, climate is GOING to change. It has changed continuously in the past and it will change continuously in the future. Instead of dithering and finger pointing about what may or may not CAUSE it, we should be expending our efforts to learn to DEAL with it.
Turning "global warming" into some kind of political football match does exactly nothing to help matters. Even if humans had a zero footprint on the earth's environment, climate would still change! North America was covered in ice only seven or eight thousand years ago. Wake up and smell the smell the sunlight. As a species we will HAVE to learn to deal with changing climates if we don't want to become extinct. Whining about the policies of one president or movement is just about the most short sighted action possible.
"Deal with it"? Screw that. If the climate is influenced by changes on the scale of human activity, it is time we learned to control it.
I like my electric lights, thank you; I am not about to learn to "deal with" the night as you imply.
And I have done an analysis on controlling it with our energy systems.
The choice isn't electric lights or no electric lights. That's as false as Reagan's definition of conservation, "Freezing in the dark."
The choice is compact fluorescents, cold cathode fluorescents, or LEDs rather than incandescent bulbs. Or task lighting over area lighting. And that's just a start.
That was just for the sake of analogy. I meant "dealing with" climate change in the sense of "accepting it" - "dealing with" electricity shortages in the same way would mean exactly what Reagan meant.
Check the link for my ideas on climate control. More coming on economics and politics when I can get my thoughts together.
Well, this would certainly stick it to the solar energy people!
Just when they get all the solar panels deployed, the sun goes dim thanks to high tech shading ....
How about a heat-sink.
We have all heard about the carbon fiber "space elevator" project. Well, I wonder what the heat conductivity of a few of those fibers, one end on our equator on the ground and one end shaded in -300 degF orbit would do?
Thermodynamics would allow heat energy to be conducted away from the surface of the earth to an area of low energy (orbit).
Wait, energy has to be radiated into a medium that is able to accept more energy. Space is low on "mediums".
Why not just build a giant Ray-Ban lens and place it in orbit around the sun an appropriate distance between the sun and earth?
The problem with reflective (white) highways and roofs floated by Randall Parker will not do the trick of cooling the Earth's surface. True, during the sunny day it will not heat up as much. But, on the other hand, during the night it won't cool down as much either. The heat radiation by a black surface
is higher than that of the white surface.
I like the idea of reflective screens in the deserts better. The screens don't need to reflect 100% of the solar radiation - that requires too expensive materials. It will be enough to paint them bright white. But they need to be collapsible, so that they won't interfere with the Earth radiation into space during the night. The task of maintaining them may be laid upon the local tribes, that people's labor isn't terribly expensive, after all. And the screens may bring very favorable local climate changes for those folks.
Future nanotech for the creation of surface materials will provide ways to make materials that can dynamically change colors. I think we'll be able to make our houses change colors by the season and time of day.
Upon further review, once VW TANK removed his shirt, the Earth's mean temperature dropped by approx ~2.8C thus completely reversing GLOBAL WARMING and restoring the Polar ice caps. Renowned Canadian theorist Ferris Buehler also noted that Winnipeg no longer suffers from unseasonably cold winters and snow cones have replaced slurpee's as the new "in" ice drink. He also just got in TANK's sisters pic's and it makes you wonder if they have the same mom.
I had a similar idea to Mark, but my solution may cost several billion $ less than an orbiting sun shade.
My invention is a a practical method of siting reflectors in the desert and it benifits the local communities too.
I did the approximation on the maths, if 10% of just the Sahara desert were covered in solar reflectors then a colossal 288,809 TWh per year can be radiated back into space.
My web site www.wwn-oneworld.co.uk goes into it in more detail with calculations to download. But I do need it all to be checked out before I ask the United Nations or a rich environmentalist to come up with the money.
Bye for now.
Hi, would it be feasible to put a large space sun filter in space to filter out the precise percentage of sunlight to correct global warming? I am thinking tha the closer you get to the sun the smaller the filter needs to be....Possible?
What about a simple solution of changing the colour of roofing material to white or another reflective colour, that would mean all new roofs and re-roofing of older properties would reflect all unnecessary solar-gain. We all know we need to move away from fossil fuels, but it won't be overnight.
All of the issues with global warming are as a result of human over-population of the planet, it's funny that if we see a proliferation of other animal species they are immediatley classed as vermin and destroyed, but we continue to breed at an exponential rate with no thought of the impact on the earth's resources. We need to cap the ammount of offspring we each have on a plannetary scale. Just think about it...hypothetically if each couple had two children there would be no change to the population as it stands...add-in usual mortality, homosexuality, abstinence, choice etc. there would be a managable decrease in over-population. This could be used as a chance to rid the world of poverty...with only two children to provide for.
Light passes through greenhouse gases but heat gets trapped by them (ref 'The Weather Makers' by Tim Flannery). So sun light comes in to Earth passing through the CO2. When the light hits the darker surfaces of the earth (trees, the oceans, lakes, roads etc.) these warm up and then radiate out heat in longer wavelength radiation. But the long wave radiation does not easily penetrate out through the CO2. So it figures that the more CO2 in the atmosphere, the hotter we will get - hence global warming.
The immediate solution to global warming whilst we struggle to reduce CO2, is to reflect back into space about 2% of the incoming sun light. Ground or sea based silver foil reflectors could be implemented tomorrow with known technology. And the cost is not great. Indeed in the case of road surfaces, roofing etc. these can be made white at no additional cost at all. On land, desert areas shaded with reflectors can be watered underneath and planted out with carbon absorbing plants for food or fuel. On the seas, oceans can be kept cooler saving essential marine life from death.
Of all the problems to be solved, the greatest priority is to stop the ice caps from melting and thus save our land and cities from destruction through rising sea levels. Ground and sea reflectors are I believe the easiest and most cost effective answer to keeping the earth cool.
Please take personal action and copy or edit this comment to local politicans, newspapers and friends.
We probably all agree that action is needed, can I recommend an excellent BBC web site that illustrates some of the options. The BBC http://news.bbc.co.uk/1/hi/programmes/6298507.stm
They have not mentioned the solar reflectors placed in the desert and as Martin says above; light passes through the green house gas layer (i.e. up or down) A physicist friend of mine (Jim Austin BSc, PhD, University of Keele) has done the calculations to calculate the area of reflectors needed to cool the climate by 1 degree gradually, the answer is approximately an area of the worlds deserts equal to 37% of the Sahara desert.
I would argue that of all the solutions, the easiest to manage, the cheapest and quickest to put into place is the desert based reflectors. More info at www.wwn-oneworld.co.uk
For starters, why not pass zoning ordinances requiring houses and other structures to be painted very light reflective colors?
Also, require gradual recoloring of all roads to lighter colors as well.