The vast majority of scientists will say that these fuels give a 20 to 30 percent carbon reduction.

Judge as of 2007-09-28 against peer-reviewed lifecycle analyses and scientific assessments then available of greenhouse-gas reductions from first-generation (corn) ethanol compared with gasoline (e.g. Farrell et al. 2006, Argonne GREET, Wang). True: most of the scientific literature then estimated reductions of roughly 20–30% (about 15–35% counts). Mostly true: the consensus range was close but somewhat wider, or centred a little outside it (e.g. 10–30%). Mixed: the estimates were widely spread, with a large share outside the range or doubting any reduction. Mostly false: the 'vast majority' wording overstates agreement, or most estimates were well below 20% (e.g. close to 0–15%). False: the literature then mostly found no reduction or an increase in emissions. Studies published after the claim date (e.g. Searchinger 2008 on land-use change) do not count.

Set before the research began.

1. E1 Ethanol can contribute to energy and environmental goals - PubMed PubMed (NCBI/NLM), citing Science 311(5760):506-8 · 27 January 2006

   “All studies indicated that current corn ethanol technologies are much less petroleum-intensive than gasoline but have greenhouse gas emissions similar to those of gasoline.”

2. E2 Corn biofuel 'dangerously oversold' as green energy | New Scientist New Scientist · 18 July 2007

   “The report includes a recent study by the US Department of Energy (PDF), concluding that corn ethanol could reduce greenhouse gas emissions by 18% to 28%.”

3. E3 Corn biofuel 'dangerously oversold' as green energy | New Scientist New Scientist · 18 July 2007

   “Conclusions vary widely from being worse than gasoline to being about the same.”

4. E4 A First-Law Thermodynamic Analysis of the Corn-Ethanol Cycle - Natural Resources Research Springer (Natural Resources Research) · 22 February 2007

   “Equivalent CO2 emissions from corn ethanol are some 50% higher than those from gasoline, and become 100% higher if methane emissions from cows fed with DDGS are accounted for.”

The Farrell et al. 2006 review in Science (E1) concluded that the studies it reviewed found current corn ethanol has greenhouse-gas emissions similar to gasoline's, which is well short of a 20–30% reduction. A 2007 New Scientist report (E3) said conclusions varied widely, from worse than gasoline to about the same. One 2007 peer-reviewed analysis (E4) found emissions 50% higher than gasoline's. Among the evidence reviewed, only a US Department of Energy study (E2) gave a reduction in the claimed range (18–28%), while a review of studies (E1), a news report (E3) and a peer-reviewed paper (E4) reported emissions similar to or higher than gasoline's, so the evidence does not support the claim that the 'vast majority' of scientists agreed on that range.