Darwin and Fall Colors

In eastern France, one of the first plants to have red leaves is Virginia creeper (Parthenocissus quinquefolia). As the name suggests, the plant is originally from North America. Someone brought it from America and planted it in a European garden, and it spread widely from there, either by its vine branches, or by its seeds, which resemble grapes and are eaten by birds. Another plant species that has bright autumn leaf colors, including red, is another woody plant from North America: the sweetgum tree (Liquidambar styraciflua). This essay accompanies a YouTube video.

Leaves changing color in the autumn is part of a process known as senescence. It is part of a perennial plant’s way of getting ready for winter. It is a long, slow process. It must begin in late summer, before the temperatures even get chilly. The only way a leaf can “know” that autumn is coming is by measuring the length of the night, which gets longer every year starting on June 21 no matter what the temperature might be. Leaves use the pigment phytochrome to measure the length of the night.

Part of senescence is the formation of an abscission layer. This is essentially a layer of scar tissue at the base of the leaf that allows it to easily break off and blow away when senescence has finished. By the time this happens, the abscission layer has already healed up what would have been a gaping wound. As the abscission layer forms, the ability of the leaf to export molecules gradually declines. One of the reasons an old leaf is less valuable to a plant than a young leaf (as I will explain in a separate essay, with its own video) is that a young leaf does not have an abscission layer, and it is able to export sugar and other molecules rapidly to the rest of the plant. In an old leaf, there is some resistance to exporting photosynthetic products such as sugar. An old leaf produces less sugar, and in addition is less able to export that sugar to the rest of the plant.

Why do leaves turn yellow and red in the autumn? Let’s start with yellow. The yellow color is carotenoid pigments, which were present in the leaf throughout its life. In this photo, the non-water-soluble leaf pigments have been separated by a process of chromatography [ref]. You can see two green bands (chlorophyll a is emerald green, chlorophyll b is olive green) and yellow bands of carotenoids, including one faintly visible at the top. These pigments came from fresh young leaves of supermarket spinach.

Carotenoids are not directly photosynthetic, but they assist the chlorophyll in the process. When the plant recycles its chlorophyll—including the valuable magnesium atoms in the chlorophyll molecules—the yellow color that was there all along is revealed.

But why do leaves often turn red in the fall? The red color is anthocyanins. Of course, most of them do not. But in hundreds of woody plant species, autumn leaves turn red. The reason this happens is that a leaf in autumn has little photosynthesis, but it does have some, and it produces sugars, which are difficult to export. The leaf uses these sugars to manufacture anthocyanins. This especially occurs on crisply chilly but sunny autumn days.

It seems likely to me that the anthocyanins are the chance result of sugar buildup. That is, they do the plant no good, but just happen to be beautiful to us. But studies have shown that lots of woody plant species have independently evolved the ability to produce red leaves in the autumn. If something evolves over and over again, there is likely to be a good evolutionary reason for it. But what is that reason? It’s hard to say and impossible to prove.

One suggestion is that the red anthocyanins protect photosynthesis from ultraviolet radiation. When I first heard it, this explanation made no sense to me, since by the time a leaf turns red most of its useful life is past. But not quite all of it. Perhaps the red pigment protects the leaf cells from ultraviolet damage during the very important process of senescence itself.

Human plant breeders have selected many species that have bright red leaves even in the middle of the season. These plants do not grow as well as the ones with solid green leaves, but that does not matter. Their success depends not so much on growth and seed production as upon their ability to please human tastes.

We still do not know why most of the tree species that produce red leaves in the autumn are in northeastern North America and Asia. This photo shows bright autumn colors, due mostly to sugar maple (Acer saccharum) in New York.

In Europe, most native species just turn a dull yellow or maybe just degrade directly to brown. When American painters used bright red on their canvases, European painters thought they were just making it up, since there is nothing like it on the native landscapes of Europe.

If Darwin walked around his estate at Down, outside London, he would have seen red leaves in the autumn. The Down House website boasted about these colors earlier this year (the photos will probably be gone by the time you visit the site). But most of the plants with red leaves were Virginia creeper and sweetgum that were planted there.

Serious about Energy Efficiency, part three. Elon Musk's carbon footprint

Try putting “Elon Musk carbon footprint” into a search engine. You will find plenty. This is, you realize, the world’s richest man, who just managed to talk his company into giving Him a trillion-dollar pay package. This is all money that Tesla is not going to spend on making their products innovative and safe (hint to investors).

You will get an answer right away. According to PC Magazine, “Elon Musk's two private jets alone—not including his emissions from other sources—generate 5,497 tonnes of carbon dioxide a year, or an average of 15 tonnes per day. This is equal to 11 average people's emissions in their entire lifetimes.” A tonne is a metric ton, that is, a thousand kilograms. Then you can click on a Guardian article that explains, worldwide, “Twelve billionaires’ climate emissions outpollute 2.1 million homes.” And that article is even out of date; it has gotten worse.

As if you did not already have enough reasons to hate Elon Musk. Imagine him trying to tell a government how to be more efficient.

But we will get nowhere complaining about how the richest people not only waste money while millions of people suffer, or complaining about how the rich do not deserve to be millions of times richer than the average person. Maybe a little, but not a million times. There is a serious point here.

The fault for global warming, caused by carbon emissions, is primarily due to rich nations (like America) and rich people in those rich nations. China emits more carbon than America, but it has over a billion people. The average Chinese person does not emit, directly or indirectly, as much carbon as an average American. I drove a small car when I was living in America, and my “guilt” was much less than an average American, certainly a rich American.

It is clear that one major contributor to global warming is that so many Americans are so rich and wasteful. You knew that. I just want to give you a couple of numbers to consider.

In France, where I now live, the richest ten percent are responsible for 31.2 percent of carbon emissions. But in America, the richest ten percent are responsible for 84.5 percent of carbon emissions. What this means is that rich Americans are really, really rich and wasteful. America needs to become more like France, in which the rich people (at least, the ones who live around Strasbourg) have only moderately showy wealth and are only moderately wasteful.

As long as rich Americans continue to be joyously wasteful, then there will be no solution to the problem of global warming.

Serious about Energy Efficiency, part two.

One of the major sources of greenhouse gases is automobiles. In America, in 2022, there were 283,400,986 automobiles registered in America, including corporate and government vehicles. Clearly, as we all know, Americans rely heavily on automobiles to go everywhere. Only in certain urban areas, and not even very many of these, have usable public transit. Also, much of America is simply not walkable for everyday purposes. To go to a large store, an American usually has to drive. Americans who have given up the use of automobiles have had to prepare carefully and greatly alter their daily schedules. I have known exactly one such person outside of New York City. But in urban areas in France, it is not unusual for people to simply not own cars.

And American cars are big. The average fuel efficiency in America is 6.7 liters per 100 km (35 mpg), down from 905 in 2004, which is an improvement, but is still less efficient than the 4.1 liters per 100 km in Europe. There are all kinds of consequences for this. In America, we have to have wide lanes and multiple lanes to accommodate the numerous big cars and pickup trucks. In Strasbourg, France, where I live, even major streets usually have just one lane each direction, and the lanes are narrow. I have seen five pickup trucks in two years in Strasbourg. Even panel trucks used for repair and delivery are smaller than those in America. In France, bicycle parking lots are larger, and every urban area has well-developed, reliable, and cheap public transit. People in France without cars, like me, can save the money and inconvenience of car payments, licenses, registration, driving school (mandatory in France), finding parking spaces, etc. That adds up to a lot of time and money.

One result of excessive car ownership in America is traffic jams. Most major cities, and even minor ones, have huge traffic jams at certain times of day. Even Tulsa, where I used to live, which is far from being among the largest American cities.

Traffic jams cost a lot of money for cars idling, and create headaches for governments that feel the obligation to build new roads. At least in America.

The traffic problem in Strasbourg seems ridiculously small to me, who has just moved from America. But the government of the Eurometropole of Strasbourg sees traffic as a problem. Too many cars? In America, no level of government would think that there are too many cars. A few American cities have provided incentives to not drive downtown. But in Strasbourg, there are incentives to actually get rid of your car.

According to the municipal website, if you sell your car (and can show the city officials your paperwork), you can receive a debit card (from MasterCard) with between 2,000 and 2,500 euros of funds, depending on your income. You can only use these funds for certain things. You can get tickets for buses, trams (trains within the metropolitan area), trains (between cities), official car-sharing services, or to rent, buy, or repair a bicycle. It would take a lot of tram rides (over 1,300, in fact, or 650 round trips) to use up 2,500 euros.

The trams in Strasbourg are quite efficient. They almost always run on time, and at intersections the trams get the right of way. Cars (and municipal buses) must wait for the trams to pass.

In America, municipal governments might try to encourage people to take public transit. But in France, they will pay you to do so. It seems like a good deal to me.

Suppose Tulsa, my previous home, checked into building a tram service. It would be so expensive that it would not get seriously considered. But most cities in France have had tram service for decades and have simply maintained and expanded it.

It is a nice day today (rare enough in the rainy, chilly autumn of northeastern France). I think I will take a hike in one of the forest preserves. If I had a bicycle, something I’m still working on, I could ride there safely on paved trails and dedicated bike lanes. But instead I will take the tram to the bottom of the hill in La Robertsau, hike into the Parc de Pourtalès, then on the paved walking/biking trail to the Cascades, and back. Or I could walk all the way to the Rhine River and look into Germany. Suppose I had more time. I could take the tram to the train station, and take a bus up to a medieval monastery in the mountains, where I could look across the Alsatian plain to the Rhine River, and hike back down to catch a train home.

When I retired to France, I said there were two things I would not do: drive a car, or tie my shoes. They have both been equally easy investments: walking shoes with straps, and tram/bus tickets. Life is good in this socialist paradise.

Serious about Energy Efficiency, part one.

France is an ecologically imperfect society. One writer called it “the light green society.” But at least it is trying to decarbonize its energy production and use energy more efficiently than the United States. I described this in a previous essay, and provide a little more detail here.

France relies heavily on nuclear power. Many ecologically-oriented citizens dislike this. But it does mean that France imports less natural gas from Russia. The existing nuclear plants seem to be operating safely, although France has not yet fully thought through a plan for eventually dismantling them when they are old. But at least France has no plans to build new nuclear facilities. Instead, France wants to rely more on sustainable energy, an important component of which is solar energy. Here in Strasbourg, we have solar panels all over the place, especially the roofs of parking structures—at least, those parking structures that do not have gardens on the roof.

Alsace, in eastern France, has a lot of hydropower electricity. Much of this comes from water that flows from the Vosges Mountains down the Ill, Aar, Muhlwasser, and other rivers, and the canals, such as the Marne-Rhine canal very near where I live. As it flows downhill, the water runs electrical turbines. There are no major dams, just small barriers. Also, electricity is used to pump water to higher levels, and the water generates electricity as it descends back to the canal or river.

In France, each electrical consumer can log into a website. In the middle of the day, 65 percent of the electricity came from nuclear power, and 25 percent from solar power. Four percent of the electricity was from hydropower, and three percent from wind. When the sun set, of course, solar electricity went to zero percent. The most expensive part of solar electricity is storing the energy, something in which France has not invested. At sunset on October 2, nuclear power provided 75 percent of the electricity and hydropower provided 14 percent.

Coal, at least here in Alsace, comes in consistently at zero percent.

A quick comparison to America is irresistible. Is there ever a time, anywhere in America, where solar energy provides 25 percent of the electricity, or coal provides zero percent? And yet President Trump wants to make America more dependent on fossil fuels and to discourage the development of wind and solar energy. He is leading America boldly back into the twentieth century, a century of war and waste, while France is moving meekly into the twenty-first.

The news outlets that reported Trump’s $8 billion in sustainable energy cuts made it sound like Trump was taking revenge on the blue states (according to one source) or the states that Harris won (according to another). While I believe Trump was, in fact, intending retribution (he has an ego that is almost unparalleled in recent history), the facts do not prove it. This may be what we could call a false correlation. Of course most of the sustainable energy projects are in blue states; those are the only states that want sustainable energy. Maybe Trump just hates energy production that is not based on coal and oil, and this explains the pattern, rather than antipathy towards Democrats or Harris.

The energy system in Alsace is so efficient that it generates a surplus of electricity, which is sold primarily to nearby Germany. There is a surplus despite the electricity used to pump the water.

There are a number of advantages to this system.

• First, there are few electrical interruptions—none in the nearly two years I have lived here—because nuclear energy is absolutely constant and predictable.
• Second, there are few interruptions because the electrical cables are all underground, except for the ones that provide voltage to the electric trams. There are no tornadoes to knock down power lines or twist them up in tree branches. France does have a few major storms, but is less vulnerable to them.
• Third, the various sources will share their electricity with one another. This does not happen as much in America, especially in Texas, where the power grid is mostly independent of the rest of the country. 

Back in America, our family was very unusual. We used less electricity than not only the average household, but even the average energy-conserving household, according to information provided on our monthly bills. But here in France, our energy use is about average.

An energy-efficient economy, even if imperfect, is attainable. France is doing it. According to the American Council for an Energy Efficient Economy, France is the most energy-efficient country in the world. America comes in at tenth, which is not bad, but there is a lot of room for improvement.