Photosynthesis, a process that had its beginnings about 2.5 billion years ago, has an awesome responsibility; it keeps us breathing. It is a metabolic process in plants that uses the energy from sunlight to drive chemical reactions; reactions that produce amino acids, proteins, sugars and other compounds that create the architecture of plants. The process takes atmospheric CO2, converts the carbon plus other nutrients to organic compounds, then expels the left-over oxygen. Plants help regulate the composition of the atmosphere – they are our other set of lungs.
It has been shown experimentally that photosynthesis increases in many kinds of plants (some more than others), as the supply of atmospheric CO2 also increases. On a global scale, this is referred to as greening of the earth, where both regional studies, and more recently satellite data show an overall increase in plant growth, and an increase in growing seasons. In Europe and North America, the seasonal leaf-out (or bud-break) for the period 1950 to the 1990s was 2-4 weeks earlier than pre-1950. Continue reading →
Space may well be the final frontier (there are one or two on earth that still require some work), but the space around our own planet is decidedly crowded. Folk at NASA’s Goddard Space Center (Maryland) estimate about 2300 satellites now orbit Earth; vehicles in various states of repair, use or disuse, of which a little more than 1400 are operationalContinue reading →
Read any scientific paper or blog on climate and you’re bound to come across the phrase radiative forcing. Radiative forcing is central to all climate science. Radiation from the sun heats our atmosphere and earth surface. Some of this radiation is reflected back to space. If there is a balance between incoming and outgoing radiation then average global atmospheric temperatures neither increase or decrease. However, if the balance is perturbed, climate will warm or cool. Radiative forcing causes climate imbalances. Thus, volcanic aerosols tend to cool things off, decreasing albedo will tend to warm them. Continue reading →
Is there a relationship between volcanism and glaciation?
It is almost a truism that volcanic eruptions influence climate. Cold winters and even failed crops, particularly in the northern hemisphere, followed on the heels the Tambora, Krakatoa, and Pinatubo eruptions. But these climate aberrations were relatively short-lived, counted in years; the stratospheric aerosols and fine volcanic ash that reflect solar radiation back into space, eventually succumb to gravity and fall to earth. Eruptions of this kind do not result in long-lived, or permanent changes; they are temporary blips on an evolving earth and an evolving climate. Continue reading →
Of the two certainties in life, volcanoes offer the most excitement (death and taxes are basically the same thing). They are magnificent while asleep; a primeval ruggedness that stirs the imagination. We paint them, we eulogise them. And when they awaken, we run for cover. Whether in a state of dormancy or high agitation, they leave an impression on our inner and outer landscapes.
All active volcanoes emit gas; pre-, during and post-eruption. On average, 96% of volcanic gases are water vapour, the remaining components being CO2, SO2 (most common), plus a little helium, nitrogen, carbon monoxide, hydrogen sulphide, and a few halides. Volcano-derived carbon dioxide is frequently cited as a culprit for increasing atmospheric CO2 concentrations in Continue reading →
How to picture groundwater flow beneath the surface.
Analogues and analogies. Standard dictionaries define these as a comparison, correspondence, or similarity between one thing and another, that can apply to concepts, ideas or physical entities. They are tools, used to illustrate concepts, particularly abstract ideas, to help explain phenomena or theories. Science makes frequent use of analogies. It does so because many phenomena that it attempts to investigate and explain extend beyond normal human experience, beyond what is visible to the unaided eye, beyond what we can touch. Well-chosen analogies can help us understand the universe without, and the universe within. Continue reading →
Groundwater is always on the move. Under some conditions, in fractures or other large conduits, it can move quickly; almost at a walking pace. Under other conditions it moves inexorably slowly, like fractions of a millimeter a year. Regardless, it is always compelled to move. Movement requires energy. Where does this energy come from? What drives the flow of groundwater? Answers to these questions provide the foundations to the science of hydrogeology. Continue reading →
A rite of passage for many scientists is their elevation to some kind of editorial board, usually associated with a scientific journal. This is where they get to review the work of other scientists and become part of the decision-making process that results in publication – or rejection. It is an excellent means of extending one’s network of people who are interested in the same discipline. It is always a learning experience, no matter how many papers one reviews or edits over a lifetime; new ideas, new data, new methods, new ways of expression. Admittedly, the task of reviewing a paper can arrive on your desk at precisely the wrong time. But a good reviewer will understand that there is always a quid pro quo; your own paper under review may arrive on someone’s desk at a time most inconvenient for them. So you do the job anyway. Continue reading →
It seems that global catastrophes and the ensuing mass extinction of all manner of life-forms, asteroid impacts and Dinosaurs immediately come to mind, were made for Popular Science. Even Hollywood is in on the act. Perhaps it’s because, in the telling, they appeal to some innate sense of nihilism, a bit like the existential threats that politicians trot out from time to time.
A recent scientific paper by Steven Stanley published by the US National Academy of Sciences, provides some good news on this score; past estimates of life forms snuffed out by such global events, have been exaggerated. Stanley’s reassessment accounts for the fact that extinctions are taking place all the time, in the background, and that these individual, long-term biotic events need to be subtracted from the total species loss resulting from some catastrophe. Continue reading →
Venus and Mars. Popular mythologies aside, neither planet has a particularly hospitable temperament. Both are rocky planets, like earth, and both have atmospheres of carbon dioxide (about 95%) and nitrogen (about 3%). Surface temperatures on Venus hover around 450oC; those on Mars about -53oC. Venus is not only a tad warm, its surface atmospheric pressure is 92 times that on earth; that on Mars about 6 one thousandths of earths comfort zone. Venus’ inclemency is the result of run-away Greenhouse processes; Mars’ is due to virtually no Greenhouse effects. Earth resides in that ‘Goldilocks zone’, being neither too hot nor too cold. Lucky us!
An energy budget
The sun heats the earth’s surface, atmosphere and oceans; earth’s internal heat contributes very little to this process. For the climate to be stable over a reasonable length of time (decades, centuries) there must be a balance between incoming heat from the sun and outgoing heat lost to space; this heat is lost via reflection, convection and conduction. Perturbations in this balance result in the surface either heating up or cooling down. We know that these long-term imbalances do occur because there have been glaciations and intervening periods of more clement surface conditions. Major climatic variations like these are mainly the result of (predictable) periodic perturbations in earth’s orbit and rotation, namely the Milankovitch cycles.
The total energy that earth receives from the sun is called the total radiance. It is primarily in the form of visible and infrared light, with lesser proportions of short wave-length UV, gamma and x-ray frequencies, and longer wavelength frequencies like microwaves. Partitioning of the incoming light is illustrated in the cartoon below. About 30% is reflected directly back to space by clouds, aerosols and the earth’s surface, especially ice sheets (referred to as the albedo); 70% is absorbed by the atmosphere, and both the solid and liquid earth.
However, to maintain an energy balance, some of this absorbed light energy must be converted and re-radiated back to space. We witness this re-radiation in our everyday lives. The many hues of red, blue, green, and yellow in my backyard are visible because a part of the light spectrum is reflected. If the entire spectrum is reflected, we see white; the red flowers are reflecting only light in the red part of the spectrum – the remaining light energy is absorbed. The absorbed energy is absolutely necessary for biological growth. If no light or heat energy is reflected, we see nothing – black.
The greenhouse blanket
The Martian surface is frigid because most of the light-heat energy that gets to the planet’s surface is reflected and re-radiated back to space – Mars has no blanket. Our own atmosphere is made up of 78% nitrogen, 21% oxygen, and very small amounts of carbon dioxide, methane, and water vapour. Nitrogen and oxygen are almost completely transparent to sunlight in the visible and infrared part of the spectrum – they do little to help warm or cool the planet. That task has been appointed to the greenhouse gasses; water vapour (most abundant), carbon dioxide, methane, nitrous oxide, and more recently certain industrial hydrocarbons that have chlorine and fluorine in their molecular structure. Despite their very low concentrations in the atmosphere (water vapour is most abundant, CO2 is 0.04%, methane is even less), they are solely responsible for maintaining the kind of climatic conditions we have become accustomed to. All except the chlorofluorocarbons occur naturally.
How does this greenhouse process work? As an example, a carbon dioxide molecule consists of a carbon atom bonded to two oxygen atoms. Bonding is loose enough such that infrared light energy will cause the atomic bonds to vibrate; in doing so the molecule absorbs heat. All the greenhouse gasses operate on the same principle. However, they also react to heat energy at different frequencies in the infrared part of the spectrum – this is illustrated below, comparing water and CO2. Water vapour absorbs energy over certain frequencies across the light spectrum, but importantly there is a ‘window’ between about 8-15 micrometres (part of the infrared frequency range) where it does not absorb heat; heat can escape through this frequency window.
This creates for us a wonderfully fortuitous balance between some infrared heat being absorbed by water vapour and other parts of the heat energy spectrum that can escape to space. Part of theenergy balance is also moderated by CO2 that absorbs heat in parts of the infrared spectrum that water does not. Nitrous oxide and methane also play an important role in maintaining the balance between heat that is absorbed, and heat that is redirected to space. It is worth reiterating that, except for water, the concentrations of these greenhouse gasses are very low and that even minor changes to these amounts will result in some degree of warming or cooling of the atmosphere.
An additional factor in the greenhouse effect is the amount of aerosol and extremely fine particulate matter in the atmosphere. Volcanic eruptions contribute some of these although addition to the atmosphere is sporadic. The potential cooling effect from violent eruptions is well documented (Krakatoa 1883, Pinatubo 1991). Soot from industrial burning and clearing of forests is also present and may influence atmospheric heating.
Although oxygen has no role in greenhouse maintenance, it does interact with certain ultraviolet light frequencies to produce ozone (O3) in the upper atmosphere; this happy circumstance means that most of the harmful UV energy is filtered out by ozone before it reaches the surface.
Postnote
There is an enduring image of Earth rising above the moon’s horizon, taken during the first manned lunar mission. Small, cloud swirled, seemingly fragile. Our atmosphere looks thin. When you look at this image, and then consider some of the details of how the atmosphere works, the balancing acts among all the gas components, the partitioning of heat and mass from air, earth and oceans, you realize how precarious the conditions conducive to our well-being really are. I’m not sure who said it first, but it really is all we’ve got.
