Be it global warming or climate change, the idea that we can be certain about the former world temperature rests upon a number of assumptions and challenging methodologies. It's important that people understand some of the more significant critiques and issues related to the endeavor of dating.
Our technology chronology complicates innovation in the space sciences; & our weather & climate theories can become confused as a result. Our understanding of space physics has undergone dramatic changes over the past half-century, & these discoveries are just now trickling into the other domains.
In Nov of 2009, somebody released 1000 emails obtained from the Climatic Research Unit at the Univ of East Anglia. The event was named Climategate, and it taught us that some climate scientists are willing to hide and misrepresent the data in order to create a motivating fear in the public.
It is premature to discount the Sun as a cause for climate change / global warming, given that there remain numerous anomalous solar observations. These anomalies are trying to tell us that our Standard Solar Model is either wrong or incomplete. AGW advocates should be fluent in these anomalies.
Venus is not an example of a runaway greenhouse effect. The Venus Pioneer mission revealed that Venus is not in thermal equilibrium; that it is releasing 15% more heat than it takes in (!); and that this heat is coming from the ground (!). This data was so inexplicable that it was thrown out.
There was a 30-yr period of warming from 1910-1940, then a cooling from 1940 to 1970, just as CO2 emissions began to rise exponentially, and then a 30-yr warming from 1970-2000 that was very similar in duration and temperature rise to the rise from 1910-1940. This suggests natural cycles.
The decentralization of science has traditionally played a role in keeping science honest. By contrast, climate science has behaved as a research monopoly which seeks to protect funding for researchers that support man as the cause, while actively undermining researchers convinced it is the Sun.
World temperatures are increasing over time, thus, the world is actually warming, which is scientifically undeniable. If there is any dispute, it is over the cause, not the existence, or even the impact.