Bored Wombat wrote:
I can say for a fact that participating here has led me to believe that human activity has some impact on rising temperatures over the last 100 years.. when I first started researching and discussing, I believed that human activity had little impact, which looks stupid from my perspective right now. Natural Factors are probably dominant though for the warming over the last Century, and I have not wavered on that view, since there is no compelling evidence to suggest otherwise.
What about you?
Changing the subject, no scientific paper
with the ISI keywords "global climate change" in the decade 1993-2003 would say that natural factors are probably dominant for the last 50 years.
For the last 100, it must be more of a toss-up, but I would suspect that most people would say that that warming is probably mostly due to anthropogenic forcing.
The way to separate the response of the global mean surface temperature into its response to natural forcing and its response to anthropogenic forcing would probably be with climate models. I would have thought that there was compelling evidence there.
For my part I notice that if I stay on forums for too long, the repeated view that the science is wrong gets to leak into my psyche, and I have to recalibrate by going to scientific sources. Which, ironically for the nomenclature, tends to be via the skeptics community. Not climate skeptics, but actual skeptics society skeptics.
It's not a matter of if AGW is real or not, it's a matter of how much warming is due to AGW. I can see how most of the warming could be due to Anthropogenic sources over the last 50 years, but I can also see how most of the warming over the last 50 years could be due to natural climate change. The CO2 concentration from 1970-2000 increased by 18%. During this timeframe, the temperatures rose. This would give you a forcing of around 0.66 w/m^2 from Carbon Dioxide, assuming a radiative forcing per doubling of CO2 to be 3.7 w/m^2 (which is generally accepted as the value for a doubling of CO2). Assuming that this was the only forcing during this timeframe that caused the temperature increase from 1970-2000, it's no wonder how one can get unimaginably high sensitivities. However, the sun's activity has increased during this timeframe, and the PDO/AMO became positive, representing a substantial natural forcing. According to Yu 2002
, the Cosmic Ray Flux could have decreased by as much as 8% during the late-20th Century, which represents a substantial increase in Solar Activity during this timeframe.
With the sun's magnetic field over the last 100 years more than doubling, and with CO2 concentrations increasing by 30% during the 20th Century, this represents substantial forcing from both natural and anthropogenic sources, however, when one properly accounts for the observationally measured amplification mechanism from Cosmic Rays, the Natural Forcing appears to have contributed more than the anthropogenic forcing. Note that this does not include any forcing from the PDO/AMO over a multidecadal timeframe.
The Oreskes study that you cite is not very robust.