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Global Warming and Global Climate Change
A Short Article by Courtney
Mention global climate change or global warming and you will receive responses that vary from utter gloom to total denial. What cannot be denied is that the effect of infrared radiation on certain gasses in the atmosphere is to cause heating. What is also known is that the concentrations of these gasses, such as carbon dioxide (CO2), is rising in line with emissions from burning fossil fuels. If we release CO2 into the atmosphere, it has to go somewhere. If the natural reservoirs can only absorb it at a given rate, it will accumulate in the atmosphere. This is happening – we can measure it. A higher level of CO2 (and certain other gasses) means that the atmosphere absorbs more infrared radiation and heats up – we can demonstrate this in the laboratory. So global warming (and global climate change) as a result of human action is happening; what we don't completely understand is how big the effect is and how dire the consequences. But we have a pretty good idea.
In simple terms, global warming is the gradual raising of average surface temperatures (in our case caused at least in part by the accumulation of greenhouse gasses in the atmosphere). Global climate change is the gradual altering of global weather patterns around the world. Global climate change can occur as a result of global warming. While global warming means an overall rise in average surface temperature around the whole world, the localized effect of global climate change in certain regions can be a significant drop in average temperatures. In other words, whilst the world generally is getting warmer, some localities can actually see falling average temperatures.
THE GREENHOUSE EFFECT
Understanding the greenhouse effect is the key to understanding global warming and global climate change. The greenhouse effect is the warming that occurs when certain gasses in the Earth's atmosphere trap heat in the same way that the glass walls of a greenhouse do, hence the name. These gasses let in energy in the form of radiation from the sun, but prevent (some of) it from escaping into space. I must mention straight away that we need the greenhouse effect, without it our planet would be some 30°C colder than it is today - very cold. But just as too little would leave us a frozen ball in space, too much can lead to a runaway greenhouse effect - such is the case on Venus with surface temperatures over 400°C.
About 50% of the solar energy that reaches the Earth is infrared radiation. This causes a direct warming effect as it passes through the atmosphere and when it strikes the Earth's surface. The other 50% is of higher frequencies (shorter wavelengths), which is largely visible light and only has a heating effect on the atmosphere once it is absorbed by the Earth and re-radiated as (longer wavelength) infrared radiation.
This infrared radiation from the Sun and Earth can be absorbed by the atmosphere, but much of this heat escapes into space, especially during clear weather, creating a balance that prevents temperatures rising continuously. A portion of it is reflected back to the Earth (by clouds) where it causes further heating.
So, some infrared radiation (mainly) from the Sun and Earth is absorbed by gasses in the atmosphere and causes them to heat up - an increase in atmospheric temperatures. Just how big an increase depends on how much energy is absorbed in the atmosphere, and this, in turn, depends on the atmosphere's composition.
The Earth’s atmosphere is composed, in round figures, mainly of 78% nitrogen, 21% oxygen and 1% argon. For our purposes we can ignore these gasses as they do not absorb significant amounts of infrared radiation and thus do not contribute to the greenhouse effect or global warming. It is the other, less plentiful, trace components: water vapour, CO2, methane, ozone, nitrous oxide, and chlorofluorocarbons (CFCs) that absorb infrared and so raise atmospheric temperatures. We shall focus on the first three of these as they are representative of the greenhouse gasses and the ones that have the greatest effect on global warming and, thus, global climate change.
Now for a very short piece of science that is at the heart of global warming. To be a greenhouse gas, a gas must be a compound of more than one element (hence nitrogen, oxygen and argon are not) and its molecules must be stimulated to vibrate by interaction with infrared radiation. There must be a change in dipole moment within the molecules during the vibration.
Water vapor is produced from the evaporation of liquid water or from the sublimation of ice. Water vapour in the atmosphere is continuously generated by evaporation from water surfaces such as oceans and lakes, from plants and from the breath of animals. Water vapour also enters the atmosphere from volcanic eruptions. It is removed by condensation (the formation of clouds, mist and fog) and precipitation (rain or snow). On average a water molecule is resident in the atmosphere for about 10 days.
Water vapour is a significant greenhouse gas (therefore relevant to global warming) and is responsible for most of the weather we experience. The energy it carries powers our most destructive storms and generates lightning. Human activity increases the amount of water entering the atmosphere both directly from sources, such as power stations and motorized transport and indirectly through our contribution to global warming, causing increased evaporation.
Fig. 1 - Atmospheric water vapour condenses into clouds that generate
Our atmosphere contains CO2 at a concentration of 0.038% (380 parts per million or ppm) and methane at a little below 0.0002% (2 ppm) and this is enough to keep our atmosphere at the comfortable temperature it is today. Without these gasses (and water vapour) in the atmosphere, the Earth's average surface temperature (today 15°C) could be as low as -18°C. As you can see, it doesn't take a lot of greenhouse gasses to cause a lot of global warming and to have a big effect on temperatures; less than 0.04% of the Earth's atmosphere accounts for about 33°C of heating. Methane is about 20 times more effective as a greenhouse gas than CO2 and nitrous oxide is 300 times more powerful than CO2. Other gasses, such as CFCs (banned in most places because of their devastating effect on the the ozone layer), have heating potential thousands of times greater than CO2, but because their concentrations are so much lower, none of these gasses adds as much warmth to the atmosphere as CO2 does.
Fig. 2 – Space-borne instruments are essential in the study of atmospheric carbon
In order to understand the effects on global temperatures of all the gasses together, scientists refer to all greenhouse gasses in terms of the equivalent amount of CO2 - the amount of CO2 that would have the same greenhouse effect as, say, a given quantity of methane. Just since 1990, annual global emissions have gone up by about 6 billion metric tonnes of carbon dioxide equivalent, more than a 20% increase.
Fig. 3 – Atmospheric CO2 levels in 2003 (left) and 2008.
For millions of years, emissions of CO2 into the atmosphere have been balanced by those that were absorbed by plants and other natural carbon reservoirs – carbonate rocks (limestone and chalk) and our oceans are by far the largest carbon reservoirs. Consequently, concentrations and global temperature were reasonably stable, apart from massive geological or astronomical events that occasionally, briefly influence global temperatures. Volcanic eruptions, for example, emit particles that cool the Earth's surface, but these have no lasting effect beyond a few years or so. Other cycles, such as El Niño, also work on fairly short and predictable cycles.
Now, humans have increased the amount of CO2 in the atmosphere by more than a third since the industrial revolution. Changes this large have historically taken thousands of years, but are now happening over the course of decades.
Fig. 4 - The long-term record of atmospheric CO2 obtained from Antarctic ice cores
Methane is the second most important greenhouse gas after CO2 and is estimated to have been responsible for 20% of the enhanced greenhouse effect over the past 200 years. Fortunately, methane is comparatively short-lived in the atmosphere; ultraviolet radiation removes more than 90% of it in a matter of about 8 years.
Atmospheric concentrations of methane increased sharply during the 1980s, causing a spike in global warming, after which levels rose more slowly. This slower growth may have been caused, at least in part, by the industrial collapse of the former Soviet Union (a major emitter) and efforts to reduce methane emissions from landfill sites in North American and Europe.
However, since pre-industrial times, the amount of methane in the Earth's atmosphere has nearly tripled. About a third of this comes from natural sources (wetlands, oceans, forest and grass fires, etc). The remaining two-thirds appear to come from human activities (production and transportation of oil and natural gas, landfills, coal mining, sewage and ruminant livestock). Since the beginning of the 20th century, methane emissions from human activities have increased again (coincident with China's industrial boom), but their effect on the atmosphere has been counteracted over the same period by a reduction in emissions of methane from wetlands as they been drained or have dried out, especially in the Northern Hemisphere. Of course, one could reason that if the drying trend were reversed and emissions from wetlands return to normal, atmospheric methane levels may increase again, worsening the problem of global warming and global climate change.
Fig. 5 – Atmospheric methane concentrations at the surface
Reducing methane emissions and, therefore, atmospheric methane levels may help to reduce the overall rate of global climate change. Methane from fossil fuels can be captured cost-effectively and burned to produce electricity, but this does produce CO2. Producing more CO2 instead of methane is the lesser of two evils because, as we have seen, CO2 is a far less effective greenhouse gas than methane. In chemical terms:
CH4 + 2O2 → 2H2O + CO2
meaning that burning one molecule of methane in oxygen produces two molecules of water and one of CO2, which has only one twentieth of the heating potential of the original methane molecule. This process can be used to generate power. Chemistry over!
Overall, increasing levels of atmospheric greenhouse gasses is raising the global average surface temperature - our definition of global warming. Clearly, each gas makes its own contribution. In order of their contribution to global warming, the most significant gasses can be ranked as follows (the percentages indicate approximately how much of the greenhouse effect each gas produces):
The rapid rise in greenhouse gasses is a problem (among other reasons) because it is causing global warming and changing the climate faster than some living things may be able to adapt. A new and more unpredictable climate poses challenges to all life.
Historically, the Earth's climate has regularly alternated between temperatures like today's and temperatures cold enough that large sheets of ice covered much of North America and Europe. The difference between average global temperatures today and during those ice ages is only about 5°C and these swings happen slowly, over hundreds of thousands of years.
Now, with concentrations of greenhouse gasses rising, the Earth's remaining ice sheets, such as Greenland and Antarctica, are starting to melt. The water released from this "permanent" ice could potentially raise sea levels significantly. Consider that the Maldives are only an average of 1.5m above sea level; we don't need too much more water in the seas before the effect on such places becomes catastrophic. More on this to follow.
Fig. 6 – The Earth's northern ice cap in 1979 and 2003 showing the marked reduction in size, about 20%
So let's look at how global warming affects global climate change. As the temperatures rise, the climate can change in unexpected ways. In addition to rising sea levels, weather can become more extreme, meaning more intense storms, more rain, longer and more severe droughts, changes to the ranges in which certain plants and animals can survive and loss of water supplies from glaciers, ground water and rainfall. Different parts of the globe can experience very different effects. There is even a scenario that suggests that North-East Europe could see temperatures fall significantly due to disruption to the massive Atlantic currents that circulate huge amounts of energy and moderate our climate (thermo-haline circulation). A description of this process is far beyond the scope of this article, but I mention it to illustrate that the effects of global warming on the global climate are not always what we might expect.
Scientists are already seeing some of these changes occurring more quickly than they had anticipated. According to the Intergovernmental Panel on Climate Change (IPCC), eleven of the twelve hottest years since thermometer readings became available occurred between 1995 and 2006.
SOME IMPACTS OF GLOBAL CLIMATE CHANGE
The effects of global warming and the impacts of global climate change are far too numerous to list in full here. But here are some of them:
The video below from National Geographic illustrates the main points. I have included a link to the National Geographic site at the bottom of this page - you can view a larger version of this video there.
Even if we were to halt all greenhouse gas emissions right now, the Earth would continue to warm by a further degree or so - global warming and global climate change would not simply stop. Obviously this isn't going to happen because we couldn't suddenly stop all emissions, but what we do next will make the big difference. Depending on our chosen course of action, scientists predict that the Earth could eventually warm by between 1.5°C and 6°C. Compare this with the 5°C difference between the average global temperature during an ice age and that during an inter-glacial period and you will see the significance.
Many governments have stated that they intend to stabilize greenhouse gas concentrations at around 450-550 ppm, which is about twice the pre-industrial level, because this is thought to be the point beyond which the most damaging impacts of climate change will occur. That means there isn't much further to go before we will have done serious, possibly irreversible, damage to our atmosphere. According to the IPCC, we would have to reduce greenhouse gas emissions by 50 - 80% of what they are anticipated to be in the next century to reach this level. Many people and governments are already working hard to cut greenhouse emissions, but this is a global problem requiring action by all parties to resolve. There is little point in, say, the United Kingdom making radical reductions to its emissions if, say, China continues to emit ever more carbon.
Global warming and global climate change are complex issues with many challenges, not the least being convincing people that it is real and its consequences potentially dire. Moreover, governments and individuals are often unwilling or unable to take the actions necessary for a plethora of reasons - cost is often the main one. Dealing with climate change is the subject of many, many papers and way outside the scope of this article. However, we can look, briefly, at the areas that we should all be aware of.
Clearly, the most effective method is to reduce greenhouse gas emissions from a variety of sources (ideally every one) across the globe, rather than relying on an enormous change in any single area. This approach, applied globally could hold emissions around current levels for the immediate future and this would put us on track to stabilize around 500 ppm.
These measures include:
These technologies are not without their challenges and different communities and nations will make different decisions about how to power their lives. The good news is that there is a variety of options to put us on a path toward a stable climate. It's now up to us – all of us – to make it happen. Doing nothing really is not an option. Global warming and global climate change are not things that happen somewhere else or caused by someone else.
You can gat a .pdf version of this article here.
So, to conclude, what is being done about global warming and global climate change? Well, basically a lot of talking. Way back in 1998, 39 countries signed the Kyoto Protocol (a protocol to the United Nations Framework Convention on Climate Change - UNFCCC) and agreed that they would cut global carbon emissions. Article 3 states, "The Parties included in Annex I shall, individually or jointly, ensure that their aggregate anthropogenic carbon dioxide equivalent emissions of the greenhouse gases listed in Annex A do not exceed their assigned amounts... ...with a view to reducing their overall emissions of such gases by at least 5 per cent below 1990 levels in the commitment period 2008 to 2012."
Subsequent meetings of the signatories continue to reaffirm the desire to cut emissions, but frequently reports failure to achieve targets. So I have to leave you with the disturbing thought that we continue to pour some 30 billion tonnes of CO2 into the atmosphere every year. The greenhouse effect shows little sign of abating anytime soon!
And who is responsible for all those greenhouse gasses and, therefore, global warming? See below. Interesting to note that China, the USA and the EU between us account for over half the world's output. Also of interest is that the USA did not sign-up to the treaty.
ANNUAL CO2 EMMISSIONS
(Tonnes per Year)
|% OF GLOBAL TOTAL|
|3 -||European Union||4,177,817,860||14.0|
|9 -||United Kingdom||539,617,000||1.8|
|10 -||South Korea||503,321,000||1.7|
|National Geographic - Global Warming 101|
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