Those who acknowledge AGW, but attribute only minor contribution to the past 150 years of warming to it, are either ignorant or in denial of the science. In terms of radiative forcing, nothing understood to have occurred or likely to occur comes close to the radiative forcing produced by accumulating atmospheric CO2. Maybe some deeply mysterious mechanism, currently unknown or poorly understood factors could come to the rescue, but science is not about what we don’t know, it’s works with what we do know.
The array of scientific specialties which lead us to conclude that past warming has been caused predominantly by accumulating greenhouse gases and land use practices by humans, strongly implies that the future climate will continue to warm. The best scientific assessment places the degree of warming to expect from a doubling of CO2 or it’s equivalent radiative forcing at between 2C and 4.5C. That amount of warming positions the Earth’s climate significantly warmer than anything known to have occurred for at least several millions of years.
Those who argue for a very low climate sensitivity (<2C) need only to look to the arctic to see positive feedback at work. Is some of what is happening in the arctic due to factors other than a general warming of the planet? Of course, natural variability is always at work, but let’s not loose sight of what science says is the driving factor which has set this into motion. That driving influence continues to move in only one direction and will carry the effects of natural variability on it’s back.