A Global Warming Primer
by Thomas D Schueneman
edited: Wednesday, July 09, 2003
Posted: Wednesday, July 09, 2003
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A brief overview of the realities of global warming.
The Deer, or the Boy
A deer in the headlights...
Or the boy that cried wolf...
How do you begin to make sense of the rhetoric surrounding the issue of global warming?
There are no simple answers. It’s natural for non-scientists to become overwhelmed by the shouting and contradictions. It’s easy to bury your head in the sand with thoughts of, "I like warm weather anyway".
Being a non-scientist does not necessarily mean being uninformed – or misinformed. Between these simplistic opposing views is a more realistic and constructive outlook toward global climate change.
Controversy does exist; this is natural for such a complex science. Science evolves; it is, and should be, open to debate. The debate in climatology is leading to a consensus that tells a tale of a world already experiencing the first signals of global warming.
This is a primer for fellow lay people. Presented here is a picture of our climate. How it was, how it is, and how it may be in the near future.
This picture is grounded in the basics of climatology.
Now is the time to abandon the paralyzing rhetoric based in misinformation and incrimination - on both sides of the issue.
Wouldn’t it be grand if we could leave to future generations a thriving economy, and a healthy and stable environment? The two do not need to be mutually exclusive.
The Greenhouse Effect
The greenhouse effect is a naturally occurring phenomenon of Earth’s environment, and is essential to the climate on Earth as we know it. With the natural greenhouse effect the average temperature on Earth is 15 degrees Celsius (59 degrees Fahrenheit). Without it, the average temperature would be about minus 18 degrees Celsius (or 0 degrees Fahrenheit).
The world would be a very cold place, indeed!
The greenhouse effect happens in nature by the presence of "greenhouse gases", principally carbon dioxide (CO2), that trap heat from the sun in the atmosphere and provide a relatively mild and stable climate. Carbon dioxide from animal respiration is cycled into the atmosphere, then taken up by plants in the process of photosynthesis. Animals take in the oxygen emitted from the plants, and the cycle continues.
The balance of nature is a wonderful thing...
Too Much of a Good Thing
Along comes humanity and our penchant to burn fossil fuels. This began in earnest with the start of the industrial revolution, around 1750. Burning these fuels - coal, oil, and natural gas - substantially augment the natural occurrence of CO2 in the atmosphere. CO2 isn’t the only culprit; other greenhouse gasses are produced from human activity. Agriculture produces methane and nitrous oxide, and aerosol propellants produce Chloroflourocarbons (CFCs - made famous mostly for the deleterious effect they have on the ozone layer). CO2 is the principal greenhouse gas due to the sheer volume released into the atmosphere from burning fossil fuels.
Around 1750, the concentration of CO2 in the atmosphere was about 275 parts per million. Today, the concentration is 350 parts per million, or a 30% increase, and rising. Since the last half of the twentieth century, the rate of this increase has risen sharply.
It is clear that there has been a rapid increase in the amount of carbon dioxide in the atmosphere since the start of industrialized society.
But what effect does this have on Earth’s climate?
Taking the Earth’s Temperature
Recording the temperature at a single location on Earth is one thing, but how do we take the Earth’s temperature as a whole?
We have daily temperature records for many parts of the globe going back about one hundred fifty years. As might be expected, there is a wide variation in average global temperature. But the overall trend is an increase of one-half degree Celsius (or one degree Fahrenheit) since the middle of the nineteenth century.
This doesn’t sound like much, does it? But it can have significant effects on climate, as we will discuss shortly.
First, let’s look at the problems associated with getting an accurate average temperature of the Earth over time. Among the problems are:
Instrumentation - thermometer design and accuracy has changed in the past century and a half.
Urban "heat islands". The climate in and around urban areas is effected by the presence of that urban environment. Much of the official data recorded for temperature is taken in and around cities. Also, some of the data collection points may have at one time been in rural areas, and are now in urban areas. Data collection points change over time.
Geographical bias. Most of the data collection points are located in the industrialized, urbanized world, where the known heat island effects are most pronounced.
Can all these problems give an inaccurate and misleading picture toward global warming?
Yes, of course.
However, these problems are well understood. Thus, the figure of one half-degree increase in average global temperature is not derived from raw data, but adjusted to compensate for the various factors that effect the raw data.
Our picture thus far shows a significant increase of CO2 in the atmosphere since the start of industrialization. It also shows an increase of one-half degree Celsius in average global temperature since the mid-nineteenth century.
What has caused this increase in average temperature? Is this just a natural fluctuation, or does it truly portend global climate change? If so, is this climate change due to industrialized human society?
We’ve got some groundwork laid. Now let’s continue constructing our picture.
Modeling the Climate
Climatologists construct computer models of the climate to show the expected rise in temperature given the increase of greenhouse gas in the atmosphere. These models suggest a one degree Celsius rise in temperature. This is not too far off the observed increase of one half degree. However, it is double, and enough to cause concern about the accuracy of these models, or the claim that we are now experiencing global warming. Traditionally, most scientists have been reluctant to ascribe the observed increase in global temperature to human induced global warming due, in part, to this discrepancy.
As stated earlier, science evolves. Improvements in climate modeling and observations of changes in the environment have eliminated this reluctance for the majority of climatologists.
Receding glaciers, rising sea levels, dying coral reefs, migrating plants and animals, reduced daily temperature fluctuations, and more pronounced and frequent "extreme precipitation events" (a large amount of precipitation in a short amount of time) are all suggested by today’s climate models as a consequence of global warming. All these phenomenon are being observed in our climate to some degree. The hottest year on record is 1995, with 1990 being the second hottest year. The hottest decade on record is the 1980’s.
It is becoming clear to the majority of these experts that global warming is indeed occurring now.
The next question now rests on the causes of this apparent global climate change, and the real effect it will have on the future of our climate and civilization.
The best way to answer this question is to look back at our climate, one hundred thousand years and more…
If we have so much trouble taking Earth’s temperature over the past century, how can we hope to know the climate of ancient Earth?
By taking ice core samples at the polar ice caps, scientists are able to tell the molecular composition of the precipitation as it fell to Earth. These ice-trapped clues are indicative of the temperature of these ancient times, and the fluctuations of temperature and climate through the eons. Thus we can differentiate between natural and human induced fluctuations.
There have been regular patterns of ice ages lasting about one hundred thousand years. These ice ages are punctuated by warmer "inter-glacial" periods lasting around twenty thousand years. We are presently in an inter-glacial period.
From our ice core samples, we know that the temperature difference between an ice age and an inter-glacial period is five to six degrees Celsius (nine to twelve degrees Fahrenheit). We also know from ancient air bubbles trapped in these samples that these temperature variations closely correlate with variations in atmospheric concentrations of CO2.
The rate of temperature change in these natural fluctuations has been about one degree Celsius per one thousand years, much slower than current changes. Our concentration of atmospheric CO2 is the highest it has ever been, based on our ice core data.
Clearly, we have altered our atmosphere.
Still, do we really need to worry about a one-half degree Celsius change? We can start to answer this question by looking at the more recent past.
Medieval England and The "Mini Ice Age"
Using historical records, scientists can determine the variations in average temperature in central England for the past thousand years. Overall, the average temperature in England during this time period was ten degrees Celsius (fifty degrees Fahrenheit). There have been variations in average temperature of plus or minus one half degree Celsius around the ten degree average.
This variation caused significant changes in climate, including vineyards in England, the colonization of Greenland during warm periods, and the formation of ice on the Thames River during the colder periods. Indeed, the 1600’s are described as a "mini ice age".
Using the Past to Look to the Future
We now have a picture of temperature change since industrialization, and the rapid and unprecedented rise in atmospheric carbon dioxide.
We have a picture of ancient climates, and the pattern of variation between ice age and inter-glacial periods, including the temperature fluctuation needed to drive these variations.
We also have a picture of the more recent past, in central England, and how variations in average temperature of only one-half degree Celsius during the past millennium has caused significant climatic change.
How can we use this data to create a realistic prediction of climate change for the next one hundred years?
Most climate models conservatively predict an increase in average temperature of between one and three degrees Celsius in the next century. Nobody’s climate model is predicting a decrease in global temperature.
Let’s split the difference and assume a two degree Celsius increase in average temperature. Likely effects of this increase are rising sea levels of one-and-a-half to three feet, changes in precipitation patterns, and more extreme precipitation events. As stated earlier these effects are already being observed.
Other probable effects are increased storm intensity and forest/species destruction. It can certainly be argued that these effects are also being observed in our climate. Some of these effects can also be attributed to pollution and habitat destruction not directly related to global warming.
Harder to predict, perhaps less likely effects of our predicted temperature increase over the next century are changes in ocean circulation patterns and ice sheet surges. These effects would cause a drastic disruption of our climate.
We need to remember that the rate of temperature change is an order of magnitude ten to twenty times greater than that of the natural fluctuations of the past. Also, keep in mind that the difference between an ice age and an inter-glacial period is between five and six degrees Celsius. A rapid two-degree change could have significant effects on our global climate.
Modeling the climate and predicting likely outcomes based on the buildup of greenhouse gasses is complex and controversial. The most complex models take months of continuous computer time to project over the next century. As the science evolves, so does the consensus among scientists.
Here is what we are reasonably certain of:
That we have significantly increased the amount of carbon dioxide and other greenhouse gasses in our atmosphere since the start of industrialized society.
That these levels of carbon dioxide are greater than at any time for which we have data, or thousands years.
That there is a close correlation between rising CO2 levels and rising temperature, based on ice core samples of ancient climates.
That we have observed a one-half degree rise in temperature in the past one hundred fifty years.
That our current rate of temperature change is ten to twenty times faster than that what has occurred in the past.
That a fluctuation of one half degree over a few hundred years can cause significant climatic changes.
That the signature of global warming is present in today’s climate.
And what is less certain:
How much of a temperature increase will actually occur in the next century, though a one to three degree Celsius rise is expected.
What the effects will be of this rise in average global temperature.
A Call for Reason
We live in times of unprecedented wealth and abundance. Our levels of consumption are enormous.
As we have seen, climatology is a complex endeavor. We surely cannot know all there is to know in the workings of our planet. But the growing body of evidence would suggest that prudence and caution are called for.
Is it not arrogant for us to ignore this mounting evidence? The future is always uncertain, and taking steps to guard against undesirable outcomes is not unusual.
Remember"Y2K"? Some claimed that it was just a hoax, others prepared for the end of the world as we knew it. Undeniably, Y2K pales in comparison to the complexity of global climate change. But Y2K is an example of how reason dictated prudent caution, and reasonable people undertook basic steps to insure that the "Y2K" bug would not bite, despite the inconvenience and expense involved.
Reason is called for here. Now is the time to develop a unified consensus and plan of action to mitigate the probable effects of global warming.
It starts with people like you and me. We need to look at our own habits and think about what we can do to curb the spiraling consumption that fuels the unprecedented rise in greenhouse gas.
Change is inevitable. Could anyone at the beginning of the twentieth century have foreseen the world we live in today? We need to let institutions and government know that we expect leaders of courage and vision to guide us into the twenty first century.
The burden is on leaders, industry, and citizens. It is, indeed, on every one of us.
The future livability of our climate could very well rest in our hands. Not just for humans, but for all life on Earth.
For all we know, tomorrow may be too late.
Are we really willing to take that risk?
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