Can We Feed an Expanded Population?

One argument you often see is that our farmland can easily feed even more people and that our technology will see that famines are a thing of the past. I am going to suggest that this may be an overenthusiastic view of our ability. First, the world is losing a surprising amount of good soil every year, to water and wind erosion. Seawater rising will remove a lot of prime agricultural land, but there is a much worse problem that needs attention. The 18th May edition of Science had some information that might give cause to rethink any optimistic view. Our high intensity agriculture depends on keeping pests, weeds and fungi at bay, and much of that currently depends on the heavy use of certain chemicals. The problem is what we are trying to keep at bay are gradually evolving resistance to our agents.

Looking at fungicides first, there are basically four classes of fungicides licensed for use, and some of these, such as the azoles, have a number of variations, but the variations tend to be those to differentiate the compounds from someone else’s, and to get around patents. The fundamental activity usually comes from one chemical group. As an example from antibiotics, there are a large number of variation on penicillin, but they all have beta lactams, and it is the beta lactams that give the functionality, so when bugs evolve that can tolerate beta lactams, the whole set of such penicillin-like drugs becomes ineffective. For fungi, the industrial scale production of single crops in some regions optimises the chance of a fungus developing a resistance, and there appears to be the possibility of gene transfer between fungi.

This has some other downstream issues. Thus medical advances lead to people having a much better chance of survival through cancer treatments, but they then become more susceptible to fungi. Apparently Candida auris is now resistant to all clinical antifungals, and is a worse threat in hospitals because it can survive most standard decontamination procedures. A number of other fungi are very threatening in clinical situations.

So what can be done about fungi? Obviously, seeking new antifungals is desirable, but this is a slow process because before letting such new chemicals out into the environment, we have to be confident that there will really be benefits and the chemicals are sufficiently effective under all circumstances, and we also need to know there are no unintended consequences.

Insecticides and herbicides (and following the article in Science, these will be collectively termed pesticides) have the same problem. It was estimated that even now the evolution of such resistance costs billions of dollars in the US. With regard to weeds, in 1996 plants were produced that were not harmed by glyphosate, and the effectiveness of this led to over 90% of US maize, soy and cotton being planted with such plants. (Some will recall the fact that some were bred so the plants did not produce viable seed, and further seed had to be purchased from the company that developed the plant.) Now there are at least forty serious weeds that have developed resistance to glyphosate. Plants have been engineered that are resistant to chemicals mimicking previous herbicides but the weeds are defeating that. Weed species have evolved to resist every known herbicide, and no herbicide has been developed with a new mode of action over the last thirty years.

In agriculture, it is easy to see how this situation could arise. When you spray a crop, not every part of every plant gets the same amount of spray. Some of what you don’t want will survive in places where the dose was less than enough. From the farmer’s point of view, this does not matter because enough of the pests have been dealt with that his return is not hurt by the few that survive. However, the fact that some always survive is just what evolution needs to develop life forms capable of resisting the chemicals.

So, what to do? Obviously, more effort is required, but here we meet some problems that might be intractable. Major companies have to invest large amounts of money to provide a possible solution, and they will only do so when there are likely to be guaranteed very large sales. However, to defeat resistance, it is most desirable to pulse agents, thus using agent A one year, agent B the next, and no repeat for a number of years. That maximises the chance of avoiding the generation of further resistance, but what company wants to participate in the sort of sales future? We could try natural procedures and live with the fact that yields are lower, but that implies we really do not want to eat that much more, which in turn suggests population growth needs to be curbed. Unfortunately, there are no easy answers.

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Agricultural Fix for Climate Change?

One of the sadder aspects of our problem with climate change is that the politicians simply do not appreciate the magnitude of the problem, which is illustrated by a briefing in the journal Nature (554, 404). It is all very well to say that emissions must be curbed, and fast, but there is a further problem. What is there is still there. The Intergovernmental Panel on Climate Change has argued that carbon emissions must peak in the next couple of decades, and then fall steeply if we want to avoid a 2 Centigrade degree rise in average temperatures. So how do we get a steep decline?

The 2015 Paris agreement settled on negative emissions. That sounds good, until you start putting numbers on what has to be done. Consider the simple approach of putting silicates onto the land, where they will be weathered to produce silica and calcium/magnesium/iron bicarbonate or carbonate.

In an experiment (Beerling et al. 2018. Nature Plants: 4: 138 – 147) applied 3.5 t/ha of wollastonite powder (calcium silicate) to some New Hampshire land, which led to a 50% increase in the delivery of weathered calcium and silica to a stream. This was accompanied by a decrease in soil acidity and a decreased release of soil aluminium. So, carbon dioxide was taken from the atmosphere while improving the soil quality. Global cropland totals 12 million square km and additionally 1 – 10 million square km of marginal land is available.

Wollastonite is not the most readily available rock, but there is unlimited basalt. There are massive amounts of olivine, and this is potentially able to capture 0.8 – 0.9 t CO2 per tonne of applied rock, but olivines also tend to have higher levels of nickel and chromium. The authors suggest continental flood basalts, which have lower amounts of nickel and chromium and higher amounts of phosphorus, but now the carbon capture potential is about 0.3 t CO2 per tonne of applied rock. This suggests that applying 10 – 50 t /ha/y of rock to an area of farmland about the size of Texas could sequester 0.2 – 1.1 billion tonne (Gt) of CO2. That is a significant reduction, but of course about 1/3 of that would currently be emitted in the grinding/transportation. Suppose we wanted to put it on all agricultural land? There is a hundred hectares to a square kilometre, so in the worst case we would need to grind and apply 60 Gt of basalt per year.

The problem could be lessened if the 7 – 17 Gt of silicate waste were used. For example, it is estimated that quarrying for construction generates an estimated 3 Gt of “fines” that are too small to be used. There is about 1.4 – 5.9 Gt of construction/demolition waste dumped each year. Cement in particular is particularly suitable. Up to half a Gt of steel slag is produced each year, and this contains weatherable elements plus some fertiliser, such as phosphate. Besides these wastes, in some places there are historically accumulated dumps of material, although these materials are probably already sequestering CO2, so perhaps they should not be counted

A further benefit from this is that the silica will replenish eroded soil and aid replacement of further soil organic carbon, as the world’s cropland soil is eroding far faster than it can be replaced (about 5 t/ha/y). Such weathered material provides silicic acid for plants, which strengthens stems, and it is suggested that this might reduce the effect of pests.

To summarise, here is a method that could in theory take CO2 from the air, but think of the problems. Let us assume the most encouraging figures. Humanity currently burns about 9 Gt of carbon a year. To absorb all of that, we would have to apply 109 Gt of powdered basalt a year, and burn no carbon while we are doing it. That is 109 billion tonne of basalt, which is not a soft rock, and do that while running the risk of some serious adverse environmental issues, and try to avoid having a lot of silicosis amongst the workers. All of this is not going to be easy. Worse, as far as CO2 levels are concerned, that is merely standing still.

There is one other related option. The rock peridotite is a mantle rock, but occasionally there are large surface deposits. It is a relatively soft rock on the surface, and it is one of the faster rocks for sequestering carbon dioxide. For that reason, it tends to be rather rare because when it does get to the surface, it weathers and erodes relatively quickly under the effect of water and carbon dioxide. However, one proposal is to drill into a deposit and fracture hydraulically, and force CO2 in, where it will form dolomite. The problem here tends to be with location. One of the bigger masses of peridotite is in the Oman desert, which is not rich in water, nor in local CO2.

Thinking about this shows some of the problems of modifying a planet. People seem to think changing Mars into somewhere pleasant to live in would be easy. In my novel Red Gold I offered the suggestion that to do that you would need a dead minimum of at least a petatonne (a million billion tonne) of nitrogen to have enough pressure to have a tolerable outside air pressure that would last through the winter. Where do you find that?

Another small commercial break: from May 3 – 10, for those in the US and the UK, A Face on Cydonia will be at 99c or 99p respectively. For everyone else, Amazon requires it to be $2.99 – still a bargain!

How Earth Cools

As you may have seen at the end of my last post, I received an objection to the existence of a greenhouse effect on the grounds that it violated the thermodynamics of heat transfer, and if you read what it says it is essentially focused on heat conduction. The reason I am bothering with this post is that it is an opportunity to consider how theories and explanations should be formed. We start by noting that mathematics does not determine what happens; it calculates what happens provided the background premises are correct.

The objection mentioned convection as a complicating feature. Actually, the transfer of heat in the lower atmosphere is largely dependent on the evaporation and condensation of water, and wind transferring the heat from one place to another, and it is these, and ocean currents, that are the problems for the ice caps. Further, as I shall show, heat conduction cannot be relevant to the major cooling of the upper atmosphere. But first, let me show you how complicated heat conduction is. The correct equation for one-dimensional heat conduction is represented by a partial differential equation of the Laplace type, (which I would quote if I knew how to get such an equation into this limited htm formatting) and the simplest form only works as written when the medium is homogenous. Since the atmosphere thins out with height, this clearly needs modification, and for those who know anything about partial differential equations, they become a nightmare once the system becomes anything but absolutely simple. Such equations also apply to convection and evaporative transfer, once corrected for the nightmare of non-homogeneity and motion in three dimensions. Good luck with that!

This form of heat transfer is irrelevant to the so-called greenhouse effect. To show why, I start by considering what heat is, and that is random kinetic energy. The molecules are bouncing around, colliding with each other, and the collisions are elastic, which means energy is conserved, as is momentum. Most of the collisions are glancing, and that means from momentum conservation that we get a range of velocities distributed about an “average”. Heat is transferred because fast moving molecules collide with slower ones, and speed them up. The objection noted heat does not flow from cold to hot spontaneously. That is true because momentum is conserved in collisions. A molecule does not speed up when hit by a slower molecule. That is why that equation has heat going only in one way.

Now, suppose with this mechanism, we get to the top of the atmosphere. What happens then? No more heat can be transferred because there are no molecules to collide with in space. If heat pours in, and nothing goes out, eventually we become infinitely hot. Obviously that does not happen, and the reason becomes obvious when we ask how the heat gets in in the first place. The heat from the sun comes from the effects of solar radiation. Something like 1.36 kW/m^2 comes in on a surface in space at right angles to the line from the sun, but the average is much less on the surface of earth as the angle is at best normal only at noon, and if the sun is overhead. About a quarter of that is directly reflected to space, and that may increase if the cloud cover increases. The important point here is that light is not heat. When it is absorbed, it will direct an electronic transition, but that energy will eventually decay into heat. Initially, however, the material goes to an excited state, but its temperature remains constant, because the energy has not been randomised. Now we see that if energy comes in as radiation, it follows to get an equilibrium, equivalent energy must go out, and as radiation, not heat, because that is the only way it can get out in a vacuum.

The ground continuously sends radiation (mainly infrared) upwards and the intensity is proportional to the fourth power of the temperature. The average temperature is thus determined through radiant energy in equals radiant out. The radiance for a given material, which is described as a grey body radiator, is also dependent on its nature. The radiation occurs because any change of dipole moment leads to electromagnetic radiation, but the dipoles must change between quantised energy states. What that means is they come from motion that can be described in one way or another as a wave, and the waves change to longer wavelengths when they radiate. The reason the waves representing ground states switch to shorter wavelengths is that the heat energy from collisions can excite them, similar in a way to when you pluck a guitar string. Thus the body cools by heat exciting some vibratory states, which collapse by radiation leaving them. (This is similar to the guitar string losing energy by emitting sound, except that the guitar string emits continuous decaying sound; the quantised state lets it go all at once as one photon.)

Such changes are reversible; if the wave has collapsed to a longer wavelength when energy is radiated away, then if a photon of the same frequency is returned, that excites the state. That slows cooling because the next photon emitted from the ground did not need heat to excite it, and hence that same heat remains. The reason there is back radiation is that certain frequencies of infrared radiation leaving the ground get absorbed by molecules in the atmosphere when their molecular vibrational or rotational excited states have a different electric moment from the ground state. Carbon dioxide has two such vibrational states that absorb mildly, and one that does not. Water is a much stronger absorber, and methane has more states available to it. Agriculture offers N2O, which is bad because it is harder to remove than carbon dioxide, and the worst are chlorocarbons and fluorocarbons, because the vibrations have stronger dipole moment changes. Each of these different materials has vibrations at different frequencies, which make them even more problematical as radiation at more frequencies are slowed in their escape to space. The excited states decay and emit photons in random directions, hence only about half of that continues on it way to space, the rest returning to the ground. Of that that goes upwards, it will be absorbed by more molecules, and the same will happen, and of course some coming back from up there with be absorbed at a lower level and half of that will go back up. In detail, there is some rather difficult calculus, but the effect could be described as a field of oscillators.

So the take-away message is the physics are well understood, the effect of the greenhouse gases is it slows the cooling process, so the ground stays warmer than it would if they were not there. Now the good thing about a theory is that it should predict things. Here we can make a prediction. In winter, in the absence of wind, the night should be warmer if there is cloud cover, because water is a strong greenhouse material. Go outside one evening and see.

Summer Storms

New Zealand has just had some more bad weather. Not an outstanding statement, but it does add a little more to the sort of effects that climate change is bringing to us. We have had quite a warm summer. Certainly not as hot as Australia, but where I live we have had many days hotter than what before were outstandingly hot days. On many days, we had temperatures about ten degrees Centigrade above the January average. Apart from one day of rain shortly after Christmas, we had almost no rain from October and the country was in a severe drought. You may say, well, a lot of countries have months without rain – so what? The so what is that October and November are usually the rather wet months here.

Then a week ago we got a storm. It was supposed to be “a depression that was the remains of a tropical cyclone” but with wind speeds of 86 knots reported, by my count that is still a tropical cyclone, except it is no longer in the tropics. (It just limps in to a category 2 hurricane.) Why did it not die down? Probably because the surface waters of the Tasman are at record high temperatures, and seven degrees Centigrade above average in places, and warm sea waters feed these systems with extra energy and water.

Where I am, we were lucky because the system more or less passed us by. The highest wind speed here was 76 knots, but that is still more than a breeze. We also missed most of the rain. Yes, we did get rain, but nowhere near as much as South Westland, where 0.4 meters of rain falling in a day was not uncommon.

The rain did some good. A couple of scrub fires broke out in Otago, and it looked like they would be extremely difficult to contain, thanks to the drought. The best the fire service could do would be like spitting at it compared with what the cyclone brought to bear.

However, the main effect was to be a great inconvenience, especially to Westland. Westland is largely a very thin strip of flat land, or no flat land, running through very tortuous mountain country. If you have nothing better to do, go to Google Earth and zoom in on the town of Granity (41o37’47″S; 171o51’13″E). What you will see is the hill, which goes up very steeply to over 300 meters before rising more “gently to the town of Millerton at about 700 meters. Between the road and the sea is one layer of houses, and the storm was washing up into their back doors.

The hills and mountains are very young, which means they have very little erosion, whole a lot of the rock is relatively soft sedimentary rock. There are some granitic extrusions, and these merely provide another reason for the rest to be even more tortuous. The whole area is also torn apart, and constructed, from continuing earthquakes. Finally, there is fairly heavy subtropical rain forest, parts getting over ten meters of rain a year. The area is quite spectacular, and popular with tourists, and it is very well worthwhile driving through it. Once you could see glaciers flowing through rain forest; now, unfortunately, the glaciers have retreated thanks to global warming and they only flow down mountainsides but they are still worth seeing.

The net result of all this is that when this cyclone struck, the only road going north-south and was west of the mountains got closed thanks to slips (one was a hundred meters wide of fallen rock from a hill) and trees knocked over by the wind. Being stuck there would be an experience, especially since the place is basically unpopulated. If you want to see the wild, you tend to be short of facilities. Some were quite upset about this, but my question to them was, this cyclone was predicted for about three days in advance. If you really could not put up with it, why go there? One grump was recorded as saying, “This sort of thing would not happen in . . . ” (I left out the country – this person did not define them.) Well, no, it would not. They don’t get tropical cyclones, hurricanes typhoons, or whatever you want to call them, and they don’t have this difficult terrain. One way or another, we have to put up with weather.

However, the real point of this is to note there is still glacial progress being made to do anything sensible to hold global warming. There is a lot of talk, but most of it is of the sort, “We have to do . . . by the next fifty years.” No, we have to start a more determined effort now.

Climate Change Horrors

By now a lot of people are probably getting sick of hearing about climate change, but it needs to be continuously emphasized because the problem is not going away any time soon. People are now starting to realize that global warming means stronger storms, but that is the least of our problems. Worse than that, most people don’t actually know what many of our problems are going to be. Let us forget about storms and look at what else could happen.

The most frightening is if warming gets out of control and melts the Arctic tundras. We have to be careful about this, but we know that about 252 million years ago there was the most massive mass extinction ever. What happened? We cannot be entirely sure, but one account has it that global warming of about four degrees caused the release of Arctic methane, and 97% of life on Earth died. Now, of course we cannot be sure of what happened and the Earth is not like what it was then. The continents are not even the same, and those land forms that were there then are not in the same place now. Nevertheless, we can be sure that if the Arctic methane is released due to warming, there will be a very serious enhancing of temperature. Amongst other things, for the first two decades methane is 87 times worse than carbon dioxide.

The most obvious consequence is from the heat. Already there are parts of the world where heat becomes a problem for people working, and this is not helped by humidity increases. In 2003 there was a European heat wave that killed as many as 2000 people every day it maintained its high temperatures. If we add 2 degrees to the average temperatures, cities in the middle east, like Bahrain, and further east like Karachi and Kolkata will be almost uninhabitable, and for Muslims, the hajj would be impossible. We could try air conditioning, but with what fuel? Our current energy systems would simply add to the problem.

Warming of agricultural areas reduces crop yields. At present, most crops are grown in as near ideal conditions for them, and most foods are produced in quantities to feed the population, but not with a huge excess. So the biggest problem is starvation. You may say, move the agriculture away from the equator to newly warmed regions. That is possible to some extent, but what we forget is that the current colder regions do not have good soil. Trying to grow crops in Greenland is fine, until you discover that most of the newly exposed surface is stone.

There are also secondary issues, thus the recent flooding in Bangla Desh that covered almost half the country with water also largely destroyed the crops being grown there. Other places may suffer droughts, with the same result. My view is this is uncertain, because I do not believe that modeling is good enough. You will hear that in Jurassic times temperatures were significantly warmer than now. Yes, but much of the land was desert, the continents were also in a greatly different configuration, and mammals were not predominant.

Everyone now knows that as the ice melts, the sea levels will rise. Depending on how much ice melts, the seas could rise by seventy meters. At present, about 600 million live within ten meters of sea level. Given that even modest sea level rising predicts a seven to fourteen meter rise, you can see that an awful lot of infrastructure will have to be rebuilt, and perhaps a billion people moved and rehoused, followed by somehow finding them employment. That means more carbon dioxide emissions. Cement manufacture alone produces about three billion tonne of carbon dioxide per annum now, and if we have to rebuild the entire coastal infrastructure, a huge amount of additional cement will be required. If the sea absorbs too much carbon dioxide, and a lot of organic matter gets trapped in it, parts may go anoxic and emit large amounts of hydrogen sulphide. Excessive hydrogen sulphide is the agent that is believed to have enhanced the great extinction in the late Permian. Higher levels of carbon dioxide are often used to explain coral bleaching, but the problem is much worse. Shellfish that depend on aragonite, one of the two crystalline forms of calcium carbonate, will not be able to form shells if the oceans absorb significantly more carbon dioxide because aragonite will no longer crystallise.

The removal of ice from the poles will also alter weather patterns. Wind changes may lead to greater air pollution in certain areas if we try to maintain current industries. China has recently suffered from this. Places that are now livable will become desert, or near desert, and this will force people to move. The problem, is, where to? Where will they get work? Which countries are going to accept them, particularly bearing in mind the numbers also displaced from the shores? With few options, various wars are more likely to break out. Unless we solve the energy crisis, what next? If we stop burning fossil fuels, how will our economies progress? The real driver of economic growth since the mid 19th century has been cheap energy from fossil fuels. However, if we do not stop such burning, and if we do not find alternatives, GDP will drop significantly, which will make it more difficult for a large fraction of the population to earn a living. To survive, one outcome is enhanced war and a proliferation of crime.

Scary? Hopefully these consequences are sufficient to persuade those in power to do a lot. I am far from convinced that current politicians recognize what the problem even is, let alone how to address it.

Hurricanes Harvey, Irma, What next?

By now just about everybody on the planet will have heard of Hurricane Harvey, and we all feel deeply sympathetic to the people of Houston. This was a dreadful time for them, which raises the question, why did this happen? As the disaster abates, the words “Global Warming” keep coming up. Global warming did not cause that Hurricane, it did not cause it to land on Houston, and with one reservation, it almost certainly did not cause hurricanes to be more common. However, global warming would have made the ocean a little warmer than usual, and that will have increased the intensity of any hurricane that was generated, made it more expansive, and more powerful. While it might have been the most newsworthy event, it was by no means the worst event attributable to an effect of global warming.

Hurricanes and Typhoons are just local names for tropical cyclones, and they originate because the earth is a rotating sphere, and because surface temperatures are uneven, therefore in places air rises because it is warmer, and in other places it falls. In the former you get low pressure, while in the latter, high pressure, and because there are pressure differentials, air flows towards and away from these systems respectively. Air moving in the north-south directions has different velocities in the east-west directions because of the different rotational velocities, and this generates some circular air motion (the Coriolis force) the direction depending on whether the air is being sucked in or being pushed out. In the normal course of events this would generate modest circulation, which would affect nobody badly.

However, there is an additional aspect. When the circulation goes over water, it evaporates moisture, and when this is sucked upwards in a low pressure event, eventually the air gets colder and the water comes out as water droplets, which generate clouds, and if there is enough moisture, rain. Of course, this is somewhat oversimplified, especially in mid-latitudes where you get fronts, etc, to complicate matters as air at different temperatures starts to mix, but the above, while oversimplified, at least lets us see what happened with Harvey. The reason the tropical storms are so bad, when you get away from the equator so as to get some effect from the Coriolis effect, is that the warmer the water, the more moisture gets sucked up. Water has a rather high latent heat of evaporation, so when it condenses out, that energy has to go somewhere. The warmer air rises, generating lower pressures below, and hence more suction, which means more water sucked up, leading to even more air being sucked in, leading to the extremes of rotational kinetic energy that we see.

So, the warmer the water, the more energy is available to power stronger winds, and more rain comes down. Harvey was particularly bad because it stalled over Houston. Normally, tropical cyclones run out of strength as they cross land, because there is no further moisture to power them, but Harvey had half of itself over land, and half over the Gulf of Mexico, so it was able to keep itself going longer than you might expect. So the hurricane would have been a little stronger than without the global warming, it would have dropped much more rain than without the global warming, but its path greatly accentuated the damage. Irma will do the same wherever it hits.

What global warming will also do is increase the number of tropical cyclones around the world. That is simply because by increasing the surface temperatures of the seas, there is more energy available for a weather event, hence more of the systems that would normally just qualify as storms or cyclones get upgraded to the tropical cyclone status. Worse, they do not have to be in the tropics. In Wellington, where I live, this winter the Tasman was 1.5 degrees C hotter than usual for this time of the year, and when a resultant system somehow met some colder sub Antarctic air, we got a storm with wind speeds that qualified for a category 3 hurricane, with a lot of rain, but it was cold. So, what we can expect in the future is many more of these storms, and not just in the tropics. The storms do not need to be hot; they merely need to have been powered initially with warmer seawater.

I mentioned that Harvey was not the worst event. At the same time, the monsoon over parts of India and Bangla Desh, thanks to increased sea temperatures, gave record rainfall that put about half the country under water, thus probably wiping out a large fraction of the country’s crops. It also killed about twelve hundred people and severely affected the lives of forty-one million people. And Bangla Desh in one of the poorest countries on the planet. There may be a tendency to think Houston, being part of the richest country on the planet, will get over this, and it probably will, but these changing events are going to happen everywhere, and as with Bangla Desh, many places will not be able to cope easily. It is the richer countries that have to start doing things to control these disasters, if for no other reason than they are the only ones with the means to make an impact. We really need to work out how to deal with such events, because they will occur, but better still, we need to take real action to minimize the number that do happen, and that means really doing something about global warming. Those who deny its existence should be made to exchange positions with people in Bangla Desh

Reducing Greenhouse Gas Emissions

Leaving aside the obstinate few, the world is now coming to realize that our activities are irreversibly changing the climate through sending so-called greenhouse gases into the atmosphere. Finally a number of politicians (but not President Trump) have decided they have to do something about it. Economists argue the answer lies in taxes on emissions, but that will presumably only work if there are alternative sources of energy that do not cause an increase in emissions. The question is, what can be done?

The first thing to note is the climate is significantly out of equilibrium, that is to say, the effects have yet to catch up with the cause. The reason is, while there is a serious net power input to the oceans, much of that heat is being dissipated by melting polar ice. Once that melting process runs its course, there will be serious temperature rises, and before that, serious sea level rises. My point is, the net power input will continue long after we stop emitting greenhouse gases altogether, and as yet we are not seeing the real effects. So, what can we do about the gases already there? The simplest answer to that is to grow lots and lots of forests. There is a lot of land on the planet that has been deforested, and merely replacing that will pull CO2 out of the air. The problem then is, how do we encourage large-scale tree planting when economics seems to have led to forests being simply cut and burned? In principle, forest owners could get credits through an emissions trading scheme, but eventually we want to encourage this without letting emitters off the hook.

Now, suppose we want to reduce our current rate of emissions to effectively zero, what are the difficulties? There are five major sources that will be difficult to deal with. The first is heating. Up to a point, this can be supplied by electricity, including the use of heat pumps, but that would require a massive increase in electrical supply, and an early objective should be to close down coal-fired electricity generators. We can increase solar and wind generators, but note that there will be a large increase in emissions to make the construction materials, and there is a question as to how much they can really produce. Of course, every bit helps.

The second involves basic industrial materials, which includes metal smelting, cement manufacture, and some other processes where high temperatures and chemical reduction are required. In principle, charcoal could replace coal, if we grew enough forests, but this is difficult to really replace coal.

The third includes the gases in a number of appliances or from manufacturing processes. The freons in refrigerators, and some gases used in industrial processes are serious contributors. There may not be so much of them as there is of carbon dioxide, but some are over ten thousand times more powerful than carbon dioxide, and there is no easy way for the atmosphere to get rid of them. Worse, in some cases there are no simple alternatives.

The fourth is agriculture. Dairy farming is notorious for emitting methane, a gas about thirty-five times stronger than carbon dioxide, although fortunately its lifetime is not long, and nitrous oxide from the effluent. Being vegetarian does not help. Rice paddies are strong emitters, as is the use of nitrogen fertilizer, thus ammonium nitrate decomposes to nitrous oxide. Nitrous oxide is also more powerful and longer lived than carbon dioxide.

The fifth is, of course, transport. In some ways transport is the easiest to deal with, but there are severe difficulties. The obvious way is to use electric power, and this is obviously great for electrified railways but it is less satisfactory without direct contact with a mains power supply. Battery powered cars will work well for personal transport around cities, but the range is more questionable. Apparently rapid charge batteries are being developed, where a recharge will take a bit over a quarter hour, although there is a further issue relating to the number of charging points. If you look at many main highways and count the number of vehicles, how would you supply sufficient charging outlets? The recharge in fifteen minutes is no advantage if you have to wait a couple of hours to get at a power point. Other potential problems include battery lifetime. As a general rule, the faster you recharge, the fewer recharges the battery will take. (No such batteries last indefinitely; every recharge takes something from them, irreversibly.) But the biggest problem is power density. If you look at the heavy machinery used in major civil engineering projects, or even combine harvesters in agriculture, you will see that diesel has a great advantage. Similarly with aircraft. You may be able to fly around the world in a battery/solar-powered craft, but that is just a stunt, as the aircraft will never be much better than a glider.

One answer to the power density problem is biofuels. There are a number of issues relating to them, some of which I shall put in a future post. I have worked in this field for much of my career, and I have summarized my thoughts in an ebook “Biofuels”, which over the month of July will be available at $1 at Smashwords. The overall message relating to emissions, though, is there is no magic bullet. It really is a case of “every bit helps”.