The climate change deniers come in two camps, those who try to deny that global temperatures are increasing at all, and those who deny that the increase is due to human activity. There are also some who out of ignorance, stupidity or intellectually dishonesty (i.e., they are motivated by ideology to completely deny everything having to do with climate change), straddle both camps. Those who deny that there is a real warming trend tried to use the hacked emails from the climate research center in East Anglia to cast doubt on the temperature data. As I pointed out in my previous post, despite their desperation to find evidence that scientists were cooking the books, so to speak, the few things they did find were taken completely out of context and did nothing to disprove the science. What's more, this center is not the only place conducting climate research, nor is it the only source of such temperature data. Though it is one of the major centers for collecting global temperature data, there are several others, including NASA. All of these places have come up with the same results. Some attempt to cast doubt on the credibility of all of these research centers despite the large amount of data they have, but when it comes right down to it, no one has reliable global temperature data that differs markedly from that of these centers, and in fact, as the video I referred to last time (http://www.youtube.com/watch?v=P70SlEqX7oY) points out, the few actual scientists who question the current consensus about climate change generally accept that there has recently been a warming trend (i.e., they are in the second of the two camps). So there is much less reason to question the credibility of all the mainstream climate research centers than there is to question that of their critics.
Some also cite "evidence" that seems to question global warming such as cold winters in particular areas, cooling trends in certain regions, and so forth. In fact, these misleading arguments are one of the reasons why "climate change" is now the preferred term. As is commonly stated by scientists, an increase in the overall global temperature has complex consequences around the world. While most places will warm up, some places will actually get cooler. Likewise rainfall patterns will change, so some places will become drier and others wetter, and so on. Also, a lot of people confuse weather and climate. Climate, roughly speaking, is average weather over a long period of time. So even if the climate warms somewhat, you can still have very cold days and even cold winters. The key is the overall climate, not weather on any given day in a particular location. This also why arguments like "they can't even be sure if it'll rain tomorrow, how can they tell if the Earth is warming" are ignorant. In fact, while modelling climates is not easy, it is a lot easier than predicting short-term weather (just as it's easier to predict certain things about a population than it is about an individual person). Of course the reverse is true as well. Some are far too ready to attribute every weather event (a hurricane, a drought, a hot spell) to global warming. While global warming may influence some such things, it's impossible to say for sure, and in many cases it's merely a short term variation unrelated to the overall climate. Basically, individual weather events are not good arguments either for or against climate change, unless they can be shown to be part of a trend.
An example of climate change deniers misleadingly citing local trends is Antarctica. Studies have shown that outlying parts of Antarctica are clearly warming, while the central part of the continent actually cooled slightly. Deniers cite the latter point as evidence against global warming, while ignoring the former. However, cooling in one region does not mean that the globe as whole is not warming. In fact, there are many reasons for such local variations. In this case, I have recently read that the hole in the ozone layer over Antarctica means a certain amount of heat that would otherwise be trapped is escaping, meaning that area has cooled slightly. So in this case, our previous disruption of the atmosphere is counterbalancing our ongoing disruption (though of course only a crazy person would suggest such a balance is a good thing, given the hazards created by the lack of an ozone layer). What's more, one of the scientists whose study of Antarctic temperatures has been cited by deniers as evidence against global warming has been quoted as refuting assertions that his work disproves global warming.
Then there is the recent claim that the globe has actually been cooling over the last decade. This claim (using the same temperature data that the deniers claim to doubt) is based on disingenuous use of the year 1997 as a starting point. That year,global temperatures were being affected by El Nino, which combined with the general warming over the 20th century made that year the hottest on record. This means, of course, that years since then, when there has been no El Nino effect, have not been as hot. However, if you use either 1996 or 1998 as a starting point, you still see a warming trend. So basically the "global cooling" claim is based on a highly misleading use of statistics, as was shown when statisticians were given the data without being told what it was and yet they still all agreed that the data showed an upward trend (http://news.yahoo.com/s/ap/20091026/ap_on_bi_ge/us_sci_global_cooling and http://news.yahoo.com/s/ap/20091026/ap_on_sc/us_sci_global_cooling_methodology). What's more, despite 1997 still being the hottest year (a record that is expected fall in the next few years), the decade that is just ending was still overall the hottest ever, hotter even than the 1990s (http://news.yahoo.com/s/ap/20091208/ap_on_sc/climate).
Another thing climate change deniers like to bring up is the fact that there was a period following the middle of the century when global climate actually cooled slightly. They point to a few articles in the mainstream media a few decades back talking about the possibility of a new ice age, and imply that climate scientists and the media are simply prone to exaggerate any recent trend in temperatures into a non-existent apocalyptic threat. They also seem to imply that the whole idea that the globe is warming due to human activity (anthropogenic global warming, as it is called) is something that only appeared in the last couple of decades.
In fact, the idea that human industrial activity could lead to an increase in temperatures goes back over a hundred years. It was apparently first hypothesized by Svante Ahrrenius in 1898, when human production of greenhouse gases was a small fraction of what it is now (http://news.yahoo.com/s/ap/climate_timeline;_ylt=Ai.JKlZRotSa4KFFyX2z7bxH2ocA;_ylu=X3oDMTE2aWNwa29sBHBvcwM1BHNlYwN5bi1yLWItbGVmdARzbGsDLWtleWRhdGVzYWJv). And by the 1970s, the predicted increase in temperatures over the first part of the 20th century had already been observed. A downturn in temperatures beginning in the 1940s which wiped out some of the increase had also been observed, but by no means all scientists agreed that a new ice age was the cause. Nor did this decrease cause them all to discard the idea of anthropogenic global warming. Isaac Asimov, best known as a science fiction writer but also a qualified biochemist, wrote a book on science for the general reader back in the early 1980s in which he briefly discusses global warming. He explains how humans were loading the atmosphere with carbon dioxide at a rate 200 times that of the world's volcanoes. He then talks about the downturn in temperatures, which was still happening at the time. He suggests that it was caused by an increase in smog particles in the atmosphere which cut off sunlight, so "it would seem that two different types of human atmospheric pollution are currently canceling each other's effect, at least in this respect and at least temporarily." While I don't know if his explanation for the downward trend (which of course ended about the time he wrote this) is the currently accepted one, but this clearly shows that the idea of anthropogenic global warming was current among scientists in the 1970s and 1980s, despite the slight downward trend in temperatures at the time.
Aside from the clear evidence of an upward trend in global average temperatures over the past centuries, there are plenty of other indications of a warming trend. One well known example is glaciers, which are retreating in many places around the world. Some deniers try to cast doubt on this evidence as well, claiming that some glaciers are growing, or that those that are shrinking are doing so for reasons other than global warming. No doubt a few glaciers are growing, because, as explained above, warming on a global scale can actually cause certain regions to cool, and also in some cases other factors may be at work (as in the cooling trend in some parts of Antarctica mentioned above). Likewise, in a few cases factors other than temperature may cause a glacier to shrink, such as a region becoming significantly drier. However, the fact that a majority of glaciers, in locations all around the world including the Alps, the Andes, Greenland and, most importantly the Himalayas (source of much of the water supply for Asian countries that are home to over a third of the world's people), are shrinking is a clear indication that more than regional factors are at work. Another worrying sign is increased melting of the Greenland ice sheet (which contains a substantial percentage of the world's fresh water) and of Arctic ice. There is no question that these phenomena are occurring, and they are clear indications of a warming pattern. What's more, if they continue, they will have dramatic effects on the climate of the northern hemisphere.
Given all the evidence (and I've only given an extremely cursory overview), there is no question that the average global temperature has been rising over the last century (except the above mentioned period between about 1950 and 1980) and that the warming has accelerated over the last two decades. As mentioned previously, this is even accepted by many of those few deniers who have real scientific qualifications. So the next question is whether this warming is a natural cycle or whether humans are responsible. Some people make the argument that the climate has fluctuated ever since the Earth and its atmosphere formed (i.e., since long before humans existed) and therefore any fluctuations are natural. On the fact of it, this argument is illogical. Yes, the climate has fluctuated throughout geologic history and previous fluctuations have been natural. That does not mean that this fluctuation must necessarily be natural, any more than the fact that you haven't died yet means you can't die. The fact that the climate can and does change without human help does not mean that humans can't affect the climate. Right-wing trolls will sometimes sarcastically comment regarding any mention of climate change in the Earth's geologic past or even other planets that environmentalists, liberals, Al Gore, et al. are no doubt concerned about the case of "global warming" being discussed, implying that because these groups believe in the reality of anthropogenic climate change, they must think all climate change is anthropogenic. This is patently absurd. Climate change is like the course of a river; it can and does change naturally, but humans can also change it, and the fact that it happens one way (naturally or through human action) does not mean it can't happen the other way.
Those who claim that the present warming is not anthropogenic obviously have to come up with another explanation for the unusually rapid increase in temperature. A favorite is solar activity. The theory is that the sun has recently begun putting out more energy, and this has warmed up the Earth. It is true that in the past variation in solar activity has been responsible for global warming, and a number of scientists believe it may also be contributing to current warming. However, after repeated studies, the vast majority of researchers have concluded that greenhouse gases added to the atmosphere by humans are responsible for the majority of the current warming effect.
Others simply claim that since the climate has changed in the past, the fact that it is changing now (whether or not humans are responsible) is no big deal. They point out that the Earth will adjust and life will go on. Certainly it is true that any claim that the Earth itself is in any danger is complete hyperbole. The planet is no danger from humans. The same cannot be said for much of the life on it. Even though the carbon cycle will probably eventually compensate for an increase in carbon in the atmosphere and oceans by locking more carbon into limestone, this process takes tens of thousands of years. In other words, we'll be stuck with elevated temperatures and all the attendant effects for that length of time. While life on Earth couldn't be wiped out by anthropogenic climate change (unless we managed to push greenhouse gas levels high enough to create a runaway greenhouse effect like that Venus experienced), that doesn't mean that we should be casual about the effects. While nature will eventually adjust, many individual species are not likely to adjust fast enough to survive a rapid change in global climate. As for humans, while we are famously adaptable, it's not like we are still a relatively small population of hunter-gatherers who can just move if some regions become less congenial. There are six and half billion people in the world now, and hundreds of millions, even billions, will be negatively affected by climate change. They can't just pick up and move without causing massive disruption. So observing that life on Earth can survive major changes in climate is like observing that it can survive the Earth being hit by a sizable asteroid. It can, but is the extinction of large numbers of species and the death of millions of people (and possibly even the end of modern civilization, if the disruption is bad enough) a price we want to pay?
A review of some basic facts is in order. First, carbon dioxide, methane and other gases are greenhouse gases. That is to say, they all trap solar energy of certain wavelengths in the atmosphere, causing it to heat up. A certain amount of this is good; in fact if it weren't for the greenhouse effect, Earth would be too cold for life. The amount of warming caused by each gas also varies; carbon dioxide is not the most effective greenhouse gas. But too much of any greenhouse gas, including CO2, is definitely a bad thing. To see this, we need look no further than the nearest planet, Venus. Though it is a near twin to Earth in terms of mass, Venus has an average surface temperature of about 450 degrees Celsius, thanks to a thick atmosphere of carbon dioxide, the result of a runaway greenhouse effect which boiled any oceans the planet may once have had and baked all the carbon out of the rocks and into the air. So while carbon dioxide is not the only or even the most potent greenhouse gas, too much of it can create a hellish atmosphere.
Secondly, human activity such as the burning of fossil fuels is currently producing large amounts of greenhouse gases, primarily carbon dioxide but also others such as methane. The amount of carbon dioxide produced by humans at present is many times greater than that produced by natural processes, such as volcanic outgassing. The amount of carbon dioxide in the atmosphere (and in the oceans as well) is increasing noticeably, and it is clear that the main reason is human activity.
Finally, as explained above, the average global temperature has increased noticeably over the past decades. So is there a connection between the human production of greenhouse gases and the increase in temperatures? Well, if many smokers get lung cancer but relatively few nonsmokers do, is there a connection between smoking and lung cancer? If people who have close contact with a sick person also get sick, is there a connection between their illnesses? It seems obvious to conclude that in the first case, just as in the other two, there is a connection. It would be nice to think there isn't, but there's no point in deluding ourselves (http://www.belfasttelegraph.co.uk/opinion/johann-hari-i-wish-that-the-climate-change-deniers-were-right-14587028.html).
So where does that leave us? Basically, we can either act as if this is a problem that we need to solve or just ignore the issue and continue behaving the same way. Even if we believed that there was some room for doubt about the cause of global warming, it is clear that taking action is the logical choice. If climate change is being caused by us, drastic action is necessary to prevent the severe consequences of continued warming. If, as the deniers assert in the face of all contrary evidence, humans are not causing global warming, what would be the consequences of taking action against it? We would increase our use of cleaner energy, reduce our dependence on fossil fuels (simultaneously decreasing the attendant pollution -- and here I'm not talking about greenhouse gases but all the even more obvious pollutants), and become less profligate in our use of energy. Yes, there might be some temporary economic pain as we adjust our lifestyles and people have to switch from less environmentally sound professions to more sustainable ones, but in the long run we'd still be better off -- and that's even if there was no climate problem to solve. On the other hand, if we do nothing and continue as we are, we will eventually run out of fossil fuels, other resources will be drained faster as populous nations like China and India start consuming energy at rates comparable to the developed world, and other types of pollution will become more and more of a problem. So even if climate change weren't an issue (which it clearly is), we are better off changing our ways now.
Unfortunately, there are many people with a vested interest in the current system (far more than could possibly have a vested interest in creating a false climate change scare, delusions about socialist conspiracies notwithstanding). Others simply don't want to change their bad habits, and will listen to anyone who assures them that they don't have to. While in most cases delusions about the way things are tend to be relatively harmless (such as superstitions, belief in the supernatural, or the idea that aliens visit Earth secretly), in this case these people can do real harm, as evidenced by Barack Obama's inability to commit the US to major cuts in carbon emissions at Copenhagen, which in turn resulted from the fact that he knows he would never get Congress to agree to major cuts, because it is filled with delusional people like James Inhofe (admittedly few are as bad as him, but they are bad enough). So while the conclusion that action is necessary is obvious enough, we still have to keep making the argument until the majority of people realize this and take action.
Update -- For those who try to use the recent winter weather in North America to question the reality of global warming, the following article from Time entitled "D.C. Snowstorm: How Global Warming Makes Blizzards Worse" should be required reading: http://news.yahoo.com/s/time/20100210/hl_time/08599196229400 . As for the minor, though embarrassing, errors in the IPCC report on climate change, as explained in this report (http://news.yahoo.com/s/ap/20100210/ap_on_sc/sci_climate_report_woes;_ylt=AviWT1kIzu4HYei22ptbobqHgsgF;_ylu=X3oDMTJrYm5kZ3FlBGFzc2V0A2FwLzIwMTAwMjEwL3NjaV9jbGltYXRlX3JlcG9ydF93b2VzBHBvcwM4BHNlYwN5bl9tb3N0X3BvcHVsYXIEc2xrA3NjaWVudGlzdHNzZQ--), they have no affect on the underlying science on global warming.
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