First of all it is important to distinguish between the terms ‘global warming’ and ‘man made global warming’, and unfortunately the chances are neither is a hoax. Global warming means an overall increase in global temperatures, which is happening and you’d be hard put to find a single scientist who would deny this.
Climate is extremely complex and while the term global warming seems to indicate simply everywhere getting gradually warmer, the reality is both more complicated and more worrying. Some of the effects of global warming are hotter summers, colder winters, unusual flooding, unusual droughts, and other unexpected weather events worldwide.
Individually, none of these mean anything. Weather is not the same as climate and is notoriously unpredictable. One hot summer is just that. It doesn’t point to a climatic trend or indicate that there is anything strange happening. Culmutively, weather events can show climate.
It is natural for people to believe more strongly what they see themselves, especially if they don’t know much about climate. A hot summer has people panicking about global warming and predicting catastrophes. When this is followed by an unusually cold winter they let out a sigh of relief, and start worrying about sinister hoaxes.
The actual evidence comes from both the weather trends mentioned above, from the continuous meteorological monitoring that has been taking place for years, from glacial and sea level measurements. These show the world is indeed getting hotter.
Where the supposed controversy lies is whether or not humans are responsible. Much of the controversy has been manufactured for political and economic ends. The oil industry for example, which has a vested interest in ‘proving’ humans are not causing climate change, spends a fortune on campaigning and research to try and get people believing the hoax conspiracy. Major political parties, especially in the United States, have joined in. Neither actually bothers with hard science, they just want people to believe what suits their own ends.
Unfortunately most scientists disagree, especially those who work in the fields of climatology, meteorology, and related physical sciences. Nearly all agree that global warming is being caused by human activity.
Global warming is not a result of natural cycles. Climatologists naturally take these into account. For example the sun spot cycle is regularly cited by bloggers as the explanation for global warming. It isn’t. The sunspot cycle follows a regular 11 year cycle, which does indeed affect climate.
Or rather it did. Until the late seventies the sunspot cycle corresponded very closely to climate changes. Then it stopped being at all closely linked, a time that corresponded with the rise of greenhouse gases in the atmosphere.
Through burning fossil fuels, humans have released carbon that had been locked away for eons. The last time it was in the atmosphere it did indeed have an effect on climate, at a time when the sun was cooler. This time around we can’t really expect it not to have an effect simply because we do not want it to.
Global warming has become politicised, as major issues nearly always are, which distracts completely from the real problem. Global warming is happening, and it is almost certainly caused by us. What to do now is not to either panic or start worrying about enormous conspiracies. We need to figure out how to slow it down, and how to cope with the changes it has already made and will continue to make. It is too late to stop it.
Further reading: http://www.newscientist.com/article/dn11462-climate-change-a-guide-for-the-perplexed.html