BY MARILIS AZZOPARDI
A greenhouse receives incoming radiation from the sun through the glass, as the earth does through its atmosphere. Part of that incoming sunlight is absorbed by the surface inside the greenhouse but the rest is reflected back into space and tries to escape the greenhouse by convection. Due to the lack of airflow the heat cannot escape and so the temperature rises, a process called the greenhouse effect. This is not what happens to Earth though.
What helps keep the earth warm is the presence of the gases in the atmosphere that absorb some of this heat radiation and re-emit it back to the surface, thus blanketing Earth and preventing the heat being lost to outer space. If it wasn’t for these gases creating the ‘greenhouse effect’ and warming the surface by 33°C, Earth would be a much colder place – around -18°C instead of the average temperature of 15°C.
The greenhouse gas that keeps Earth warm is water vapour.
Earth receives visible shortwave radiation from the sun through its atmosphere; some is reflected back by clouds, some is scattered by particles in the atmosphere, and some is absorbed by the ozone and other gases. The rest makes it to Earth’s surface where it can either be absorbed, or reflected back into space as long wave radiation. Highly reflective surfaces such as ice and snow reflect a lot of radiation, whereas darker surfaces such as the oceans tend to absorb more than they reflect. The loss of sea ice cover with exposure of the darker ocean beneath causes the Earth to absorb more radiation and less is reflected; this in turn causes more warming at the surface which can then lead to more ice loss.
Earth’s atmosphere is composed of 78% nitrogen, 21% oxygen, and the rest is composed of trace elements such as argon. Carbon dioxide (CO2) makes up 0.04% of the earth’s atmosphere and is released naturally in the carbon cycle through volcanic activity and respiration in organisms.
Since the Industrial Revolution, anthropogenic activities such as the burning of coal and other fossil fuels and deforestation have led to increases in concentration from around 280ppm (parts per million) in the early 1800s, to around 400ppm at the present time. The greatest rise has occurred in the last thirty years and since CO2 is very long-lived in the atmosphere (having a half-life of 100-10 years) this could have consequences and is a cause for concern.
You may be surprised to learn that the most abundant greenhouse gas that keeps Earth warm isn’t carbon dioxide but water vapour. Water vapour is the most important regulator of the Earth’s climate and as the Earth’s atmosphere warms, more water vapour evaporates from the oceans contributing to the formation of clouds and precipitation; this creates a positive feedback loop which contributes to the greenhouse effect.
The Other Greenhouse Gases
Methane is another greenhouse gas produced on Earth during the anaerobic breakdown of organic material such as occurs in the decomposition of wastes in landfills, agriculture and rice fields, or as a product of digestion in the guts of ruminants, e.g. cattle. Although it only makes up 1.8ppm of the Earth’s atmosphere, each molecule of methane contributes 25 times more to global warming than one molecule of carbon dioxide.
Nitrous oxide is 300 times more warming than CO2 but only comprises 0.3ppm of the earth’s atmosphere. Human activities such as biomass burning, fossil fuel combustion and the use of agricultural fertilisers have increased its atmospheric concentration by around 15% and it too is very long-lived in the atmosphere.
Methane contributes 25 times more to global warming than carbon dioxide.
Ozone is formed at the earth’s surface due to pollution, especially from traffic emissions reacting with sunlight, and functions very differently higher up in the atmosphere where it forms part of the greenhouse gases and specifically helps to block ultra violet run from the sun, protecting Earth and its living things from the harmful effects of UV radiation. Each ozone molecule is 1000 times more warming than CO2.
The Difference Between Weather and Climate
The weather is the short-term variation that we see in temperature, sunshine, cloud cover, rainfall, and wind whereas the climate refers to how the average of these conditions change over longer periods of time, usually around thirty years. By looking for significant changes of a 30-year time period it is possible to observe whether the climate is changing. Although the climate is always naturally changing, the term ‘climate change’ is usually understood to mean systematic, large-scale and long-term changes in the earth’s weather patterns and average temperatures.
The Consequences of Climate Change
Since the Industrial Revolution, Earth has warmed by around 1°C, and recently the warming has accelerated by an increase of 0.2°C per decade; the unprecedented rise over the past 200 years means that there could be a total increase of around 2 to 5°C by the end of this century. The concern is that species living on earth are not able to adapt fast enough to such rapid increases in temperature. The direct impacts could be heatwaves, exposure and an increase in infectious diseases such as malaria. Temperature and precipitation patterns may affect the distribution and abundance of species, as well as their habitats.
Although the effects of climate change are hard to predict, it can be expected that Earth will get warmer, which will increase evaporation from water bodies and precipitation; some regions may become dryer while others could become wetter. Communities living near the sea could be disproportionately affected.
Species living on earth are not able to adapt fast enough.
The higher atmospheric conditions of carbon dioxide could benefit plant growth, enabling them to grow more vigorously with less water, as well as changing the areas where crops grow best. Higher temperatures could allow types of agriculture to thrive in areas that have previously been unsuitable.
Although most of us associate climate change with negative effects, climate change can also be seen as a global opportunity for better health by giving us the opportunity to do things differently, and by developing healthier, less polluting and more sustainable communities. By developing innovative technologies in the provision of clean energy and low-carbon technologies we can maintain economic development without sacrificing health, and the future of the planet.