Global Warming is one of those hot-button issues that's highly politicized, controversial and somewhat arcane, due to the highly technical nature of the information. This is compounded by the fact that very there's a great deal of money that stands in opposition to the Science; Exxon can't afford for Global Warming to be a Scientific fact any more than Philip Morris could afford for cigarettes to cause cancer. In both cases, the companies funded 'research' that challenges the conclusions of objective scientists in order to create doubt in the public's mind on sound Science. George Monbiot at The Gaurdian shows the conflict of interest (emphasis added);The website Exxonsecrets.org, using data found in the company's official documents, lists 124 organisations that have taken money from the company or work closely with those that have. These organisations take a consistent line on climate change: that the science is contradictory, the scientists are split, environmentalists are charlatans, liars or lunatics, and if governments took action to prevent global warming, they would be endangering the global economy for no good reason. The findings these organisations dislike are labelled "junk science". The findings they welcome are labelled "sound science".
Among the organisations that have been funded by Exxon are such well-known websites and lobby groups as TechCentralStation, the Cato Institute and the Heritage Foundation. Some of those on the list have names that make them look like grassroots citizens' organisations or academic bodies: the Centre for the Study of Carbon Dioxide and Global Change, for example. One or two of them, such as the Congress of Racial Equality, are citizens' organisations or academic bodies, but the line they take on climate change is very much like that of the other sponsored groups. While all these groups are based in America, their publications are read and cited, and their staff are interviewed and quoted, all over the world.
By funding a large number of organisations, Exxon helps to create the impression that doubt about climate change is widespread. For those who do not understand that scientific findings cannot be trusted if they have not appeared in peer-reviewed journals, the names of these institutes help to suggest that serious researchers are challenging the consensus.
Of course, without proper education about the peer-review process and the scientific basis of climate change, this strategy has proven quite effective (as it has in the past with other issues). So how can you decide (objectively) for yourself? Fortunately, the information you need to understand the issue is freely available online and ready for private use. I'll try to make the case here with the evidence easily available.
First, let's establish that our Earth is warming; NASA First Goddard Institute for Space Study's direct surface temperature analysis shows a steady increase of one degree Celsius from 1880 to 2000 (usisng Radiosondes). Satellite temperature measurements arrive at the same conclusion (from 1982 on), as do the direct surface temperature analysis at the Climate Research Unit at East Anglia. From here, we need to use more abstract methods of temperature measurement, because we didn't measure temperature in a verifiable way before 1880. Using dendrochronology, the study of the rings in trees to verify temperatures, we can get accurate temperature readings for up to 26,000 years ago. We also get accurate temperatures from the last five centuries by drilling bore holes and analyzing the results. The temperature rise is also concluded by indirect analysis; for instance, glaciers melting, sea ice melting, permafrost melting, sea levels rising, sediments and other proxy reconstructions. Yes, there has been melting in past centuries, but it's always been almost trivial compared to the extreme melting of today.
So, we've established that the earth is warming. How do we know that's it man-made though? After all, climate goes through highs and lows naturally- there's a cyclical process that repeats. The cycles that are often cited (but seldom understood) by climate skeptics are called Milankovitch cycles, after the Serbian climatologist. These cycles are caused by slight changes in Earth's tilt and orbit. Wikipedia summarizes it well; "The Earth's axis completes one full cycle of precession approximately every 26,000 years. At the same time, the elliptical orbit rotates, more slowly, leading to a 23,000-year cycle between the seasons and the orbit. In addition, the angle between Earth's rotational axis and the normal to the plane of its orbit moves from 22.1 degrees to 24.5 degrees and back again on a 41,000-year cycle. Currently, this angle is 23.44 degrees and is decreasing."
The temperature change predictions derives from these cycles are fairly exact, and they aren't anywhere near the temperature changes we're seeing in terms of speed and intensity. So why the difference? The claims that in the Middle Ages, warming was just as extreme are patently false, as are claims that we're 'recovering' from a 'little ice age' (I specifically address these because they're such common falsehoods among climate change deniers). So we have an observation; the climate is becoming warmer more rapidly than we can naturally account for. Scientifically, we'll need a hypothesis to explain the observation, then experiment to test the hypothesis.
We have the benefit of hindsight; a hypothesis has already been proposed. Certain gases, referred to as 'greenhouse gases', absorb infrared radiation. These differ from gases like nitrogen and oxygen that make up most of our atmosphere because those gases reflect, rather than absorb, that radiation. So what happens when that radiation gets absorbed? As I'm sure you've guessed, the temperature rises. We can confirm the correlation (but not the causation) of greenhouse gas levels to temperature changes through ice core data and construct a history of the temperatures relating to green house gases. However, it is true that greenhouse gas levels rise and fall naturally; over a 400,000 year period CO2 levels rose over 100ppm (100 carbon atoms, in parts per million atoms). Unfortunately, we've had that same rise (100ppm) in just the last 150 of our history!
So, we've established that the Earth's temperature is growing faster than ever before, that it's not a naturally occurring Milankovitch cycle, that the Greenhouse gas rises correlate with temperature rises, that Greenhouse gases absorb infrared radiation (causing temperature rises) at predictable levels over time and that we can predict the warming that occurs as a result. The effects of the rise in temperatures are also widely debated (again, by Exxon shills and honest scientists), but the information here demonstrates the reality of the change itself and it's cause.
For more information, I recommend these resources;
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