The Greenhouse effect refers to the warming of the lowest layer of the Earth’s atmosphere due to carbon dioxide and other greenhouse gases (water vapour, methane and nitrous oxide, among others). A natural greenhouse effect enables life on our planet, and it occurs when greenhouse gases let the sun’s heat energy pass through the Earth’s atmosphere and in turn help to absorb most of that heat. This leads to a surface temperature of the atmosphere remaining about 33°C higher than without a natural greenhouse effect, which would otherwise be a temperature of around -18°C.

The greenhouse effect mechanism can be explained in more detail as follows: It is a phenomenon in which electromagnetic radiation with many different wavelengths warms the object, such as the Earth’s atmosphere and surface through absorption. A heated object emits only infrared radiation. Infrared’s, or simply heat radiation’s penetrating power is rather poor, and therefore it absorbs or re-radiates, for example, into gas-like mediums (in the case of climate change, greenhouse gases) easier than other wavelength ranges. In other words, in the greenhouse effect, electromagnetic radiation from the Sun penetrates the system (Earth’s atmosphere) quite effortlessly, but some heat becomes trapped within the atmosphere and warms it.

Currently, human activity is rapidly warming the globe by adding more greenhouse gases to the atmosphere. Climate change, a human expansion of the greenhouse effect, refers to growing greenhouse gas emissions warming the atmosphere. Carbon dioxide, methane and nitrous oxide in the atmosphere have increased steadily and significantly in the last two centuries after staying relatively steady for thousands of years. Most emissions come from housing, transport and food and the industries related to them. This raises socially important questions about the choices made by municipalities about energy sources, types of public transport and food catering.

The two major constituents of the Earth’s atmosphere, nitrogen and oxygen, do not contribute to atmospheric warming due to their molecular structure. The most important greenhouse gases that occur naturally in the atmosphere are water vapour (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and ozone (O3). All the greenhouse gases have molecules with three atoms or more, which vibrate when they absorb heat. The most potent greenhouse gas in the lowest layers of the atmosphere is water vapour, which accounts for about 50% of the warming effect. The second largest contributor is carbon dioxide. Additionally, humans have released into the atmosphere large amounts of many gases of natural origin and many new, man-made greenhouse gases, such as halogenated hydrocarbons.

Greenhouse gas molecules are able to absorb heat radiation within certain wavelengths and re-radiate the heat out towards the space, but some are re-radiated back towards the Earth, warming the surface and lower atmosphere.

Plants need carbon dioxide for photosynthesis. As the source of available carbon in carbon cycle, atmospheric carbon dioxide is the primary carbon source for life on Earth. In normally encountered concentrations, carbon dioxide is colourless, odourless, and non-toxic in small amounts and a weakly reactive gas denser than air. It occurs naturally in the air and water. The Carbon dioxide molecule (CO2) consists of a carbon atom and two oxygen atoms. The molecular shape is linear (O=C=O) and its atoms are double bonded. Carbon dioxide is a significant greenhouse gas contributing to climate change, since like the other greenhouse gases, it lets the visible radiation through itself, but absorbs strongly infrared i.e. heat radiation. Heat radiation makes the CO2 molecule vibrate and radiate, in other words, emit the heat radiation it absorbed.

In nature, all aerobic organisms manufacture carbon dioxide when they metabolize carbohydrates and lipids to produce energy through respiration. Most of the human-produced carbon dioxide comes from fossil fuels, such as oil, coal and natural gas. Another primary cause of carbon dioxide is tropical deforestation.

Carbon dioxide is not necessarily the most potent of all the greenhouse gases humans produce, but due to its large proportions and long lifespan, it is the most significant climate change accelerator. The global average concentration of carbon dioxide in the atmosphere has increased since the Industrial era from about 280 ppm (ppm=parts per million) to 390 ppm, in other words, almost by 40%. CO2 will continue to rise around 2 ppm per year. Currently, it occurs in the Earth’s atmosphere at a concentration of about 0,039% by volume. The levels are higher than they have been at any time in the past 600,000 years, exceeding the levels at the end of the last Ice Age by a third.

When measuring carbon footprints, a standard unit of carbon dioxide equivalent is often being used. The idea is to express the impact of each different greenhouse gas in terms of the amount of CO2 that would create the same amount of warming.

Another method used to compare different gases is the so-called global warming potential (GWP). It is a standard ratio, which describes the total warming impact of each gas. It is measured relative to CO2, which scores 1,0. The impact is measured over a set period – usually 20, 50 or 100 years. For example, methane scores 86 (20 years) and 34 (100 years).

Carbon is constantly recycled and reused between the reservoirs (atmosphere, oceans, plants, animals, soil). The natural flow of carbon is so rapid that a single carbon dioxide molecule remains in the atmosphere only about five years. However, most of the carbon dioxide stored by terrestrial vegetation and oceans is finally being released back into the atmosphere.

During photosynthesis plants converse inorganic carbon (carbon dioxide, O=C=O) and release free oxygen. Sugars (glucose monosaccharides) are synthesized from carbon dioxide and free oxygen comes from water molecules that dissolve in light. The bacteria and fungi use cellular respiration to extract the energy contained in the chemical bonds of the decomposing organic matter, and so release carbon dioxide into the atmosphere. Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into their use. Nutrients that are commonly used by cells in respiration include glucose and oxygen and the products of this process are water and carbon dioxide.

Most carbon dioxide is stored in the oceans. Large amounts of carbon dioxide from the atmosphere dissolve in the surface waters of the oceans, but at the same time much of it gets released into the atmosphere. However, single-cellular plankton keeps the carbon cycle going in the seas. Through photosynthesis, plankton consume carbon dioxide in the surface waters and once they die, they begin to sink and release carbon dioxide into the deep seawater and sediment. Since the sea floor is not in contact with the atmosphere, carbon dioxide cannot be released into it.

For a long time, the oceans, terrestrial vegetation and soil have absorbed carbon dioxide from the atmosphere and represented so-called carbon sinks. However, scientists suggest that climate change weakens these carbon sinks. When humans add carbon dioxide to the atmosphere, it is divided according to the carbon cycle between the oceans, vegetation and atmosphere. About 45% of CO2 remains in the atmosphere, while about 30% is taken up by the oceans and the remaining 25% is absorbed by the terrestrial biosphere.

Atmospheric Infrared Sounder

In addition to carbon dioxide, other greenhouse gases contribute to climate change in many ways and through different mechanisms. Here is some information regarding the most significant greenhouse gases, along with carbon dioxide.

Methane is distinctly stronger than carbon dioxide, but short-lived and accounts for considerably less emissions, so it is only the second most prevalent greenhouse gas emitted by human activities. A methane molecule consists of one atom of carbon and four atoms of hydrogen (CH4).

Metaania syntyy eloperäisen aineksen hajotessa hapettomissa oloissa: riisipelloilla, lehmien ja muiden märehtijöiden suolistossa ja kaatopaikoilla, sekä kosteikoilla, soilla ja vesistöjen pohjakerroksissa. Metaania karkaa ilmakehään myös hiilikaivoksista ja maakaasuputkien vuotaessa. Noin 2/3 metaanin päästöistä arvellaan olevan ihmiskunnan aikaansaannosta.

Methane lasts about twelve years in the atmosphere before it gets oxidized and turns into water and carbon dioxide. However, the concentration of methane in the atmosphere has more than doubled since preindustrial times.

Water on the sea floor and soil in the permafrost regions has vast quantities of methane hydrates – solid compounds of methane. If the temperature of the atmosphere rises further, it might cause degradation of methane hydrates, which will then escape into the atmosphere. If vast quantities of methane would be released into the atmosphere, it could dramatically change the global climate. Such a phenomenon would be one of the many climate change feedbacks – processes that amplify the effect of each climate forcing. It is unlikely that methane hydrated would release significant amounts of methane during the 21st century, but there might be a potential risk further in the future.

Water vapour is the most potent greenhouse gas in the lowest layers of the atmosphere, contributing more than half of the global warming caused by the natural greenhouse effect. Humans add water vapour to the atmosphere in many ways. However, the natural water cycle is such a global-scale process that man-made evaporation is insignificant compared to it. Climate change increases the amount of water vapour in the atmosphere since warm air holds more moisture than cold air. One could say that emissions of other greenhouse gases indirectly increase the amount of water vapour in the atmosphere. This is one of the many climate change feedbacks. (For further information, read the text about climate change and physics.)

Nitrogen dioxide, also known as nitrogen oxide, deutoxide of nitrogen and laughing gas is produced in nitrate degradation of soil. It is an important greenhouse gas and its amount in the atmosphere has been increased by human activities. Its total concentration in the atmosphere is relatively small, but it is a prominent air pollutant, which increases global warming, and it lives much longer than, for example, methane – about 110 years. One-third of all nitrogen dioxide emissions are caused by human activities, particularly by nitrogen-based fertilizers for field crops. The other two-thirds come from natural sources including soils and the oceans. Nitrogen dioxide molecules degrade in the highest atmospheric layers due to bombardment by solar ultraviolet radiation.

Ozone (O3) protects the Earth from the highly hazardous solar ultraviolet radiation. However, in high quantities it can be harmful to animals and plants. Most ozone is found high in the region called the stratosphere, where there has been a steady decline in the amount of ozone due to depletion caused mainly by halogenated hydrocarbons. The ozone hole itself has a minor cooling effect and it has slightly weakened the impacts of the greenhouse effect. However, ozone is an important greenhouse gas in the lower atmosphere called the troposphere. Ozone is produced when nitrogen dioxides, carbon monoxides and hydrocarbons from car fumes react in the sunlight with oxygen in the air. In addition, it is generated in the reactions of plant-originated hydrocarbons and the oxidation of methane. Ozone is a short-lived gas, so its levels in the atmosphere are not known before the era of industrialization and motorisation. Therefore, it is hard to estimate the rate of increase of ozone in the lowest layers of the atmosphere compared to its natural occurrence.

Halogenated hydrocarbons are potent greenhouse gases. Their ability to absorb heat radiation is several thousand times greater than carbon dioxide’s. However, they exist in the atmosphere only in small amounts so their contribution to the greenhouse effect is much less than carbon dioxide’s. There are tens of different types of halogenated hydrocarbons. Their molecular formula is similar to light hydrocarbons, with one or more hydrogen atoms being replaced by fluorine and/or chlorine. Depending on the molecule type, halogenated hydrocarbons’ lifespan varies from one year to 50,000 years. The longest-living gas molecules, such as tetrafluoromethane (CF4), have carbon-fluorine bonds.

Most of the halogenated hydrocarbons do not occur naturally in the atmosphere but are caused by human activities. They are used, for example, in refrigeration, and also different industries produce large amounts of halogenated hydrocarbon emissions. In addition, chlorofluorocarbons that contain chlorine are responsible for man-made ozone depletion as well as being contributors to the Earth’s greenhouse effect.

brunobord

Fossil fuels have formed by natural processes when microorganisms break down plankton and other biodegradable material in the absence of oxygen under water millions of years ago. Over thousands of years, this organic matter, mixed with mud, got buried under heavy layers of sediment. The resulting high levels of heat and pressure caused the organic matter to chemically alter.

Oil, coal and natural gas are the most widely used fossil fuels. They consist of a mixture of various hydrocarbons and the specific mix gives fuels their characteristic properties, such as boiling point and density. Because fossil fuels are formed in natural processes from organic matter, they all contain high percentages of carbon. As it is the case with other organic compounds when burning (oxidizing), the carbon and hydrogen atoms combine with oxygen atoms to produce carbon dioxide and water vapour. Combustion also releases chemical energy, which is transferred to the surroundings as thermal energy and light. Our energy production system is currently widely based on this mechanism.

Before the Industrial era, wood fuel, water wheels and windmills generated most of our energy. After the Industrial Revolution, world energy use increased by more than ten-fold in the 20th century; from 911 million tonnes of oil to 9645 million tonnes as the world’s population went up from 1 billion to 6 billion.
Today coal, oil and natural gas are the most important non-renewable energy sources. Compared to them, the share of nuclear energy usage is relatively small. Renewable energy technologies are constantly under development around the world, and lately, wind and solar power, geothermal energy and hydroelectricity technologies have improved by leaps and bounds.

Fossil fuels and industrial energy generation have increased industrial production and improved our wellbeing and living standards. Cheaper goods and services are being produced rapidly in ever-increasing amounts and transported to consumers from faraway places. This has increased energy use significantly. Consumer goods are affordable to more and more people, and aggressive marketing creates a need to consume more. This contributes to a lifestyle based on burning fossil fuels which has created global problems, such as climate change.

Louis Vest

Petrochemistry is a branch of the chemical industry that plays a big role in causing global warming, but also provides building blocks for climate change solutions.

Petrochemical processes are used in petroleum refineries to transform crude oil into fossil fuels, such as fuel oil, diesel, kerosene, gasoline and flammable mixtures of hydrocarbon gases, used in liquefied petroleum gas. In addition to fuels, crude oil is processed and refined into plastics and other materials, such as fibres (nylon, polyesters) and synthetic rubber. The oil industry is one of the most significant contributors to climate change.

At the same time, petrochemistry is providing new solutions to boost low-carbon transport, improve weather resistance of wind power turbines and produce new materials. The Xperimania website lists the following sustainable petrochemical solutions:

• Insulation: enhanced insulating materials enable more energy-efficient buildings.
• Lightweight plastic composites help reduce cars’ and airplanes’ fuel consumption.
• Fuel cells: when used to power cars or motorbikes, hydrogen fuel cells produce water vapour instead of exhaust gases.
• New lighting technologies (such as organic light emitting diodes-OLEDS), which produce more light with less electricity.
• Wind turbines and solar panelling, both of which rely on materials produced by the chemical industry. Blades made of carbon-fibre reinforced plastics which are able to stand up to the severest weather have largely replaced the metal blades of wind turbines.

Bioenergy is energy made available from materials derived from biological sources. Biofuels, in turn, are fuels derived from biomass, which may include wood, straw, food waste, manure and sewage wastewater. Biomass can be combusted in incineration plants or it can be made into renewable biofuels from wood or combustible municipal and manufacturing waste. Additionally, biomass can be converted into biogas or biofuel, such as bioethanol or biodiesel.

Hopes to increase the use of bioenergy are high in many countries and it is a subject of much political debate. Minimizing greenhouse gas emissions is one of the most important factors for bioenergy expansion. However, its lifecycle has an impact on climate change on many levels. On the one hand, biofuels produce less greenhouse gas emissions than fossil fuels, but on the other hand they also contribute to climate change. Bioenergy is not necessarily environmentally friendly; its pros and cons depend on the energy source.

When evaluating the advantages and disadvantages of bioenergy, not only climate change, but also energy efficiency, economical and social sustainability and biodiversity should be taken into account. Natural resources should be used sustainably and preserved for future generations. If we are going to use bioenergy, we need to make sure that its production does not cause conflicting issues related to food production, soil sustainability and deforestation.

Solar radiation consisting of moving photons is the foundation of solar cell technologies. They can be traditionally divided into three generations. The first generation of solar cells dominating the market are mainly based on silicon wafers or polychrystelline silicon. The second generation of solar cells are so called thin-film solar cells. Their technology is based on photovoltaics and semiconductors formed between a photosensitized anode and an electrolyte, a photoelectrochemical system.

The third generation of solar cells are still at the beginning stages of their development cycle. One example of modern solar cells is nanochrystal solar cells, also known as dye-sensitized solar cells or Grätzel cells. The cells are prepared by using a simple screen-printing method on a titanium dioxide plate. The dye molecules on the surface of the plate absorb light. This means that nanochrystal cells have no electric current created by a p-n junction, rather the movement of photoelectrons is based on chemical reactions. In other words, as opposed to physics-based silicon thin-film cells, the operational principle of nanocrystal solar cells is based on photoelectrochemical reactions.

In addition to nanocrystal cells, there are also other solar cell types being studied and developed. For example, concentrator photovoltaics (CPV) and flexible solar cells with diverse applications, which are already being used and tested.

Jason-Morrison