What causes global warming. Is global warming really happening? If it is, is human activity the cause? What will happen to the future climate if global warming is happening? How can we tell all this? This short primer will help to answer these questions.
A Global Warming Primer
Global Warming will be our demise! Or maybe, Global Warming is a fiction, foisted on us by environmental nutcases intent on wrecking our economy and way of life! Between these simplistic polar opposites lies the truth about climate change and global warming. The truth as best as we can tell. It's easy for non-scientists to become overwhelmed by the rhetoric surrounding this issue. But being a non-scientists does not necessarily mean being uninformed. Scientists and climatologists agree on many aspects of global warming. Controversy still exists, but more and more consensus exists as our ability to monitor and model our climate improves.
This is a little primer, for fellow non-scientists, of the picture of our climate today, and what kind of change we may expect in the near future - about one hundred years. This information will, hopefully, help lay people to understand the issues surrounding global warming and climate change.
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. Without the natural greenhouse effect the average temperature on Earth of 15 degrees Celsius (59 degrees Fahrenheit) 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, that trap heat from the sun in the atmosphere and provide a relatively mild and stable climate. The carbon dioxide is from the emission of CO2 from animals respiration, which is cycled into the atmosphere, and then taken up by plants in the process of photosynthesis.
Global Warming - Too Much of a Good Thing
We know that Earth has a natural greenhouse effect caused by the presence of carbon dioxide in the atmosphere. This greenhouse effect is the reason our planet has an average mean temperature of 59 degrees Fahrenheit. Without this natural greenhouse effect, the average global temperature would be about 0 degrees Fahrenheit. The greenhouse effect is a good thing.
The problem is that as civilization has industrialized, more and more carbon has been released into the atmosphere as carbon dioxide, or CO2, as a consequence of burning fossil fuels. Other human activities also contribute to the build up of greenhouse gasses, which include methane, nitrous oxide, and CFC's. However, the sheer volume of CO2 being released into the atmosphere from the burning of fossil fuels, makes this the principal contributor to the build up of greenhouse gases.
Just how much CO2 has been released since industrialization? 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. Also, since the last half of the twentieth century, the rate of increase in the concentration of CO2 has risen sharply.
It is clear that there has been a rapid increase in the amount of greenhouse gas, especially 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
We have records of daily temperature for many parts of the globe going back about one hundred and fifty years. The data available shows a wide variation in average global temperature but suggests that the temperature has risen about .5 degree Celsius since the middle of the nineteenth century.
But there are problems with these data when using them to construct an accurate picture of Earth's average temperature. Among these problems are changes in instrumentation, thermometer design and accuracy has changed in the past century and a half. Urban "heat islands" also effect temperature data. It is well known that the climate in and around urban areas is effected by the presence of the urban environment. It is also know that 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 a rural area, and is now in an urban area. Data collection points change over time. There is also a geographical bias in collecting temperature data. 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 associated with simply taking the temperature give an inaccurate picture toward global warming? Yes it can. However, climatologists are well aware of these problems and have taken care in factoring them in when analyzing the data. Thus, the figure of .5 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.
That the Earth's temperature has risen about a half a degree in the past hundred and fifty years is generally not in dispute by most scientists and is not the controversial question.
The controversial question then becomes 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 human activity?
Modeling the Climate
Climatologists have constructed models of the climate to show the expected rise in temperature given the increase of greenhouse gas in the atmosphere since the beginning of industrialization. These models suggest that about a one degree Celsius rise in temperature is expected. While this is not too far off the observed increase of .5 degree, it is double, and enough to cause concern about the accuracy of these models. Therefore, climatologists have generally been reluctant to ascribe the observed increase in global temperature to human induced global warming - until recently.
There is some new data which tends to support that global warming is, in fact occurring. As climatologists develop more sophisticated models other phenomenon are expected as a consequence of global warming. Such things as receding glaciers, rising sea levels, dying coral reefs, migrating plants and animals, reduced daily temperature fluctuations, and more pronounced and frequent "extreme precipitation events" are all suggested by climate models as a consequence of global warming. All these phenomenon are being observed in our climate to some degree.
Thus, while still a matter of some controversy among scientists and climatologists, it is becoming clearer to the majority of these experts that global warming is indeed occurring in our day and age.
The next controversial 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.
Ancient Climate
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 ancients times, and the fluctuations of temperature and climate through the eons. Thus we can differentiate between natural and human induced fluctuations.
The past several hundred thousand years show several climate trends. 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 usually about 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. Also, our current concentration of atmospheric CO2 is the highest it ever has been, based on our ice core data. Clearly, we have altered our atmosphere.
Do we really need to worry about a .5 degree Celsius change? We can start to answer this question by looking at the more recent past.
Medieval England
Using historical records, we can estimate the variations in average temperature in central England for the past thousand years. Overall, the average temperature in England during this time period has been about ten degrees Celsius (about fifty degrees Fahrenheit). There have been variations in average temperature of plus or minus a half a degree Celsius around the ten degree average. This variation caused significant changes in climate, including vineyards in England and the colonization of Greenland during warmer periods, and the formation of ice on the Thames river during the colder periods. Indeed, the 1600's has been called 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 about a half a 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 climatologists models predict between a 1 and 3 degree Celsius increase in average temperature in the next century. Some more, some less - no models predict a decrease in average global temperature.
We can therefore assume about a 2 degree Celsius increase in average temperature. Likely effects of this increase are rising sea levels by about one and a half to three feet, changes in precipitation patterns, and more extreme precipitation events (a large amount of precipitation in a short amount of time). As stated earlier these effects are already being observed.
Less clear, but possible, effects are increased storm intensity and forest/species destruction. It can 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.
Still harder to predict, and perhaps less likely effects of our predicted temperature variation 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.
Conclusion
Modeling our climate and predicting likely outcomes based on our buildup of greenhouse gasses is complex and controversial. The most complex models take months of continuous computer time to project over the next century. But as our understanding and models of the climate improve, more and more scientists are able to form a consensus over what were once controversial questions.
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 several thousand 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 about a half a degree rise in temperature in the past one hundred and fifty years.
* That our current rate of temperature change is ten to twenty times faster than that occurring in nature.
* That a fluctuation of about a half a degree over a few hundred years can cause significant climatic changes.
* That the signature of global warming is most likely present in today's climate.
And what is less certain:
* How much of an increase will actually occur in the next century
* What the effects will be of the rise in average global temperature.
As our understanding of this issue increases, it is becoming clear that what we do today to come to grips with our energy production and use, specifically the burning of fossil fuels, will have a significant impact on our children and our children's children. The future livability of our climate could very well rest in our hands.
No matter what we choose to believe regarding global warming and it's impact on future climate, I believe now is the time for citizens and their governments to deal effectively with this issue. For all we know, tomorrow may be too late.
