Tuesday, 22 February 2011

What Evidence Is There That Carbon Dioxide Is Causing Global Warming?

Science is not every one's favourite subject but the quest to understand how the world around us works has been one of the enduring themes of mankind's history. We don't always get it "right" in that a scientific theory can be overturned by new thinking but the process of scientific inquiry is rigorous and well understood. It has also delivered great advances for us meaning that many illnesses that were once fatal have now been conquered, we have an enormous capacity to build things and move around and our ability to communicate with each other and entertain ourselves is greatly enhanced.
But there is a flip side to science as well. The generation living in the 1960's through the 1980's lived under the fear of a MAD war where the use of atomic weapons would mean Mutually Assured Destruction. The weapons are still there, but the fall of the Berlin Wall and collapse of communism in the Soviet Union means that the threat of an all out war seems rather remote, now. Perhaps, with that worry out of the way, the world began to look a little more to its future and it was not a pleasant prospect.
Scientists had for some time been warning about the dangers of pollution on the capacity of Nature's systems to continue to support the burgeoning human population and in particular about the impact of the gases that were being released by burning fossil fuels. These gases, it was said, could affect the temperature of the Earth causing it to rise. This in turn would lead to higher sea levels as the ice melted, stronger and more frequent storms in some areas and a vast increase in the amount of deserts on the planet. This was serious stuff. In 1988, the governments of the world instituted the Intergovernmental Panel on Climate Change (IPCC) to look at the scientific evidence and make recommendations on what the world should do. They have made four reports since then, the first in 1990 and the latest in 2007, and each one has become surer about the diagnosis: human activity is raising the level of various gases in the atmosphere and the outcome will be a higher average temperature across the globe. To avoid the adverse affects of this, the recommendation is to cut the amount of these gases we are adding to the atmosphere by an enormous 80%. As modern civilisation is essentially based on energy use, many people find this a near impossible concept. However, rather than provoking a serious discussion on the relative responsibilities of one generation to its children, many people have simply claimed that the problem "doesn't exist" or that carbon dioxide (referred to from here on as CO2, the scientific notation for it) is not responsible. This article will try to answer, in simple terms:
"What is the evidence that CO2 is causing global warming?"
The simplest and most complete answer is to say "read the IPCC reports". They are very thorough and very meticulous but they are difficult for laypeople to read and I will try to avoid language that is too technical.
The very first thing to note is about how science works. The basic scientific process is that scientists look at the known properties of a system and form a theory that describes how that system is thought to work. They then can observe or imagine a change of some sort, and predict what will happen if the theory is right. The next step is usually to perform an experiment and so confirm or deny your hypothesis when your expectations are or are not met. When the scientist thinks they have discovered something new, the work is shared with other scientists to check it. It is a pretty robust system and it is the same one that was used to generate all the fun stuff we have.
In the case of global warming the system in question is the earth, its oceans and atmosphere; the known properties are those of different gases that make up the atmosphere and what happens when the proportions change, how heat behaves (called thermodynamics) and electromagnetic radiation. The change to the system is a slow and steady increase in the amount of CO2 in the air. That this is happening is unequivocal, since the late 1950's the concentration of CO2 in the atmosphere has been measured and the steady increase is clearly recorded.
That this is happening has been described as a giant experiment on this one and only home planet of ours and as we have only one chance to see it through, if the outcome is disastrous, we have no way back. However, rather than wait and see what will happen, scientists have developed model to predict the outcome and it is those models ability to describe what has already been recorded that gives them validity.
As long ago as 1824 a scientist called Joseph Fourier discovered that the Earth's atmosphere kept the planet warmer than would otherwise have been expected and this became know as the "greenhouse effect" The knowledge that that CO2 is an active gas that allows the visible (sunlight) radiation from the sun into the climate system but slows that same energy down on its way out as heat (infrared) radiation came more than 100 ago and was described in 1859 by a scientist called John Tyndall. Another called Svante Arrhenius made the first calculations of the impact of adding more CO2 from human activities to raise the average temperature of the earth's surface before the end of the 19th century. Pretty much since then, scientists have been improving our knowledge and watching closely for generations now.
So, it makes sense that it should happen. Is it?
Yes, it is. Weather data from more than 1000 meteorological stations around the world, satellite observations of sea surface temperature and Antarctic research station measurements are showing global average temperatures are on the increase: 2010 was the tied as being the warmest since record began and 9 out of the 10 warmest years have been since 2002. And there are other indicators besides direct measurements of surface temperature.
Well, say some, because expected things can happen for unexpected reasons, and just because the two things happen does not mean that one causes the other. What about other potential causes. Maybe it's the sun? Maybe it's natural causes? Maybe it's volcanoes? Maybe it's geothermal? Maybe it's galactic cosmic rays?
The truth is, they have been considered by the IPCC reports: it was never just taken it for granted that because we expect it and it has happened we therefore understand it. The sun has not changed its output significantly since the fifties, or enough overall to explain the degree of warming. Saying "natural causes" is really just a cop out: what natural cause? That is a bit like saying there is no need to look at automobile safety because "cars crash all the time" The impact of volcanoes or geothermal has also been looked at and found not to be the source. Theories about cosmic rays is a pretty far fetched grasp at straws and is bears as much standing with climate scientists as homeopathy has with medical doctors. In all of this hard researching, no other primary candidate cause has emerged that can explain the observations.
As well as the temperature measurements being in line with expectations for the CO2 levels in the atmosphere there are some other observations that fit in well with an enhanced greenhouse effect and these observations do not fit with the other potential causes. For example, temperatures have risen more at night than during the day. This really defeats the notion of sun powered climate change. Also the stratosphere, the second layer of the atmosphere, is cooling. Models that predict the warming we are seeing at surface level also predict the cooling stratosphere as a particular feature of the current climate change. And, an increasingly enhanced greenhouse effect should cause an energy imbalance between incoming sunlight and outgoing infrared radiation, which has been detected.
So to summarize: we know man made climate change is real because there is no other likely candidate cause, the CO2 rise is unquestionably the result of our activities, the effects that are being observed are consistent with an enhanced greenhouse effect and the whole phenomenon is entirely consistent with very long standing theories and expectations. The science is certain: the challenge remains, what do we do about it?
Harold Forbes is Author of "How to be a Humankind Superhero: a manifesto for individuals to reclaim a safe climate". The book has been described by Jonathan Porritt as "An enjoyable read that manages to hit the elusive balance between the analytic and the practical". You can read chapter summaries athttp://www.hksuperh.com or download the first chapter as a FREE PDF at http://bit.ly/freehksh
Article Source:
Harold Forbes - EzineArticles Expert Author