And consider that in 2009, scientists said that CO2 only produced around 40% of the warming:Abstract
The observed global-warming rate has been nonuniform, and the cause of each episode of slowing in the expected warming rate is the subject of intense debate. To explain this, nonrecurrent events have commonly been invoked for each episode separately. After reviewing evidence in both the latest global data (HadCRUT4) and the longest instrumental record, Central England Temperature, a revised picture is emerging that gives a consistent attribution for each multidecadal episode of warming and cooling in recent history, and suggests that the anthropogenic global warming trends might have been overestimated by a factor of two in the second half of the 20th century. A recurrent multidecadal oscillation is found to extend to the preindustrial era in the 353-y Central England Temperature and is likely an internal variability related to the Atlantic Multidecadal Oscillation (AMO), possibly caused by the thermohaline circulation variability. The perspective of a long record helps in quantifying the contribution from internal variability, especially one with a period so long that it is often confused with secular trends in shorter records. Solar contribution is found to be minimal for the second half of the 20th century and less than 10% for the first half. The underlying net anthropogenic warming rate in the industrial era is found to have been steady since 1910 at 0.07–0.08 °C/decade, with superimposed AMO-related ups and downs that included the early 20th century warming, the cooling of the 1960s and 1970s, the accelerated warming of the 1980s and 1990s, and the recent slowing of the warming rates. Quantitatively, the recurrent multidecadal internal variability, often underestimated in attribution studies, accounts for 40% of the observed recent 50-y warming trend.
http://m.pnas.org/content/early/2013/01 ... 1110.short
In summary, the new PNAS paper says that the amount of warming caused by humans putting colorless and odorless plant and tree fertilizer in the air should be about 50% of what's been measured and then adjusted and re-adjusted etc... And the 2009 comment by Gore said that CO2 only produces around 40% of warming because other human caused factors were causing warming.Those conversations led Gore to politically inconvenient conclusions in this new book. In his conversations with Schmidt and other colleagues at the beginning of the year, Gore explored new studies - published only last week - that show methane and black carbon or soot had a far greater impact on global warming than previously thought. Carbon dioxide - while the focus of the politics of climate change - produces around 40% of the actual warming.
http://www.guardian.co.uk/world/2009/no ... nt-climate
So if I'm doing the math right (and if there is no mention of some of the warming caused by soot or black particles in the PNAS paper), a more reasonable estimate for the total warming caused by humans releasing plant and tree food in the air should be 50% * 40% = 20%. Put another way, of the amount of warming that we have had since 1900, only 20% of it may have been caused by human released CO2.
Assuming my math is correct, this much smaller amount of human CO2 caused warming of just 20% looks more reasonable to me.
Given that the temperature recored has been adjusted and readjusted and that there are now known temperature biases from thermometer placement issues, I think it's possible that the amount of CO2 warming is more like 10% to 15%, an amount that I would not be skeptical of.