I first heard about the issue in school and at home, not in any real depth but just the basics such as that the arctic will melt if we keep going down the road we're on. This was about 15-20 years ago.
I thought it sounded serious, but didn't really give it much thought until An Inconvenient Truth came out. I live in Britain, and at least for us this film seemed to be the catalyst that sparked more interest in the subject. I decided to read a book on the subject and chose The Rough Guide To Climate Change. This really explained the science quite well, together with the history of the issue. It all seemed to tie up very well.
While I was still reading the book, I kept wondering why there wasn't a vigorous debate going on over the issue. After all, polititions had pretty much ignored it for ages until An Inconvenient Truth brought it to the attention of the public, due to the fact that it might be quite tricky to find a solution for. Also, corporations such as oil companies surely would stand to lose a lot of money if Co2 emissions were drastically reduced.
I discovered the answer one day when browsing on YouTube. There WAS a vigorous debate going on, but it was mostly taking place in the US. From the reading I had done, many of the arguments I saw were obviously rubbish. How could Al Gore have invented global warming when it was established long before he even mentioned it? Also most of the deniers seemed to be under the illusion that global warming meant that the world was rapidly cooking. They did not seem to understand that global warming refers to a change in average global temperature of less than 1 degree so far, which is problematic because of the climate changes it causes, NOT because of the heat itself. This was one of the most basic facts that I learned from the book. Another very common skeptical arguement relies on the wrong assumption that we are being told by 'warmers' that the world has never warmed or cooled before humans started interfering with it.
So I kept reading, and researching both sides of the argument. I discovered that all the sources I checked that supported AGW agreed with each other over the important points and created a watertight case. Skeptical arguements on the other hand claimed a whole range of things. While some misunderstood what GW even means in the first place, many others just pointed to individual examples of parts of the world that used to be warmer. Even the more complex arguments against GW were easily answered, and again all the answers from all the sources I checked agreed with one another. Never did GW science contradict itself the way that 'skeptics' appeared to.
Never have I believed that GW science is true beyond any shadow of doubt. After all, science has sometimes been wrong in the past and it could be wrong again. I just think that when highly researched science is giving us a warning so stark we would be crazy to ignore it.
Then there was this amazing discontinuity between the two sides of the argument, that almost seemed to be a mirror.
-It's the biggest threat in history/It's the biggest hoax in history
-Oil companies such as Exxon are funding denial/Governments are funding the hoax as part of a plot to tax us more or fulfil an environmental agenda
-There's an overwhelming consensus among scientists/30,000 scientists disagree with GW
-Not addressing the issue may well mean the end of life as we know it/the measures proposed to address the issue will ruin us and mean the end of life as we know it
-More and more evidence is being accumulated/the evidence is debunked and some day soon the world will realise it
Overall it's clear that one side or the other is lying, and in my view it's very clear that there is one side who has the motivation, the means and the money to spread this level of deception.
In fact, it turns out it's not even a secret that Exxon oil have been pouring a lot of money into climate change denial, and being a huge multinational company trading in one of the world's most lucrative resources, they have a great deal of money to throw around. On the other side, I never could see what in the world a goverment would stand to gain if they were indeed lying about GW. The issue has been around far longer than any government has been talking about it, and it is rather tricky for them to address.
The most damning piece of evidence against skeptics turned out to be the 30,000 scientists against GW (formerly 22,000 and before that 17,000). Nearly every skeptic refers to this, and it turns out to be nothing more than an internet peition that anyone with a degree in any area of science can sign. I looked it up myself to be sure, and so can you. It's right here: http://www.petitionproject.org/ and you can see through it's own wording that it hardly represents a group of experts whose opinion actually means something. If there really was a large body of experts disputing GW, they would certainly not need to rely on some lame internet petition for their figures.