If you wish to see behind the scenes of a real and ongoing conspiracy, do follow these links:
The American Denial of Global Warming - Naomi Oreskes
ExxonMobile Report: Smoke, Mirrors and Hot Air
Industry Ignored Its Scientists on Climate
Oreskes on her review of the climate literature from 1999 to 2003:
The drafting of such reports and statements involves many opportunities for comment, criticism, and revision, and it is not likely that they would diverge greatly from the opinions of the societies' members. Nevertheless, they might downplay legitimate dissenting opinions. That hypothesis was tested by analyzing 928 abstracts, published in refereed scientific journals between 1993 and 2003, and listed in the ISI database with the keywords "climate change" (9).
The 928 papers were divided into six categories: explicit endorsement of the consensus position, evaluation of impacts, mitigation proposals, methods, paleoclimate analysis, and rejection of the consensus position. Of all the papers, 75% fell into the first three categories, either explicitly or implicitly accepting the consensus view; 25% dealt with methods or paleoclimate, taking no position on current anthropogenic climate change. Remarkably, none of the papers disagreed with the consensus position.
Admittedly, authors evaluating impacts, developing methods, or studying paleoclimatic change might believe that current climate change is natural. However, none of these papers argued that point.
To my knowledge, not much has changed since. The work of even some of the more legit sceptics in no way undermines an anthropogenic forcing of climate change. All the works in this regard either don't undermine the current understanding or are very flawed. The sun's influence, clouds and tropospheric temperatures are all examples. You can check out the rebuttals to those ideas if you go to RealClimate's Wiki page, their index, their Start Here page or, to really understand climate, go to Spencer Weart's The Discovery of Global Warming page, which is created from, I believe, his book of the same name. Warning: it's an extensive site, but if you truly, honestly, don't quite get the whole Anthropogenically forced Climate Change thing, you will after reading that site/book.
If it's a conspiracy, it started a VERY LONG time ago. From Weart's website:
In 1896 a Swedish scientist published a new idea. As humanity burned fossil fuels such as coal, which added carbon dioxide gas to the Earth's atmosphere, we would raise the planet's average temperature. This "greenhouse effect" was only one of many speculations about climate, and not the most plausible...
In the 1930s, people realized that the United States and North Atlantic region had warmed significantly during the previous half-century... one lone voice, the amateur G.S. Callendar, insisted that greenhouse warming was on the way...
In the 1950s... new studies showed that, contrary to earlier crude estimates, carbon dioxide could indeed build up in the atmosphere and should bring warming. Painstaking measurements drove home the point in 1961 by showing that the level of the gas was in fact rising, year by year...
A 1967 calculation suggested that average temperatures might rise a few degrees within the next century...
The scientists' claims about climate change first caught wide public attention in the summer of 1988, the hottest on record till then. (Most since then have been hotter.)...
There is zero evidence of conspiracy, and logically it's idiotic to claim it is a conspiracy. However, as the links further up illustrate, not only is there a conspiracy to deny climate change and to prevent action to mitigate it, we actually have proof of this. It's historical fact. I've yet, in three years of trying, to get one of these deniers to even address this, let alone actually acknowledge it.