(Part of the How to Talk to a Global Warming Skeptic guide) Objection: H2O accounts for 95% of the greenhouse effect; CO2 is insignificant. Answer: According to the scientific literature and climate experts, CO2 contributes anywhere from 9% to 30% to the overall greenhouse effect. The 95% number does not appear to come from any scientific source, though it gets tossed around a lot. Please see this paper (PDF), the textbook referenced here, and this article at RealClimate. There is a very important distinction to be made, as you will read if you follow the link to Real Climate, between …

Amory Lovins is rightfully admired by environmentalists. But nobody is right all the time, and the hydrogen path is one of his few mistakes. He summarizes his argument for hydrogen in Twenty Hydrogen Myths (PDF). More extensive discussion is embedded in his book Winning the Oil Endgame (book-length PDF). His basic proposal: Since most gas stations already have access to natural gas, put natural gas reformers in enough stations to make sure everyone has access to hydrogen within 25 miles. For stations without natural gas, they can reform hydrogen from LPG or ethanol -- or use off peak electricity. Build …

(Part of the How to Talk to a Global Warming Skeptic guide) Objection: Climate scientists never talk about water vapor -- the strongest greenhouse gas -- because it undermines their CO2 theory. Answer: Not a single climate model or climate textbook fails to discuss the role water vapor plays in the greenhouse effect. It is the strongest greenhouse gas, contributing 36% to 66% to the overall effect for vapor alone, 66% to 85% when you include clouds. It is however, not considered a climate "forcing," because the amount of H2O in the air basically varies as a function of temperature. …

(Part of the How to Talk to a Global Warming Skeptic guide) Objection: Today's warming is just a recovery from the Little Ice Age. Answer: This argument relies on an implicit assumption that there is a particular climatic baseline to which the earth inexorably returns -- and thus that a period of globally lower temperatures will inevitably be followed by a rise in temperatures. What is the scientific basis for that assumption? There is no evidence of such a baseline. The climate is influenced by many factors, which change or remain stable in their own ways. The current understanding of …

(Part of the How to Talk to a Global Warming Skeptic guide) Objection: It's clear from ice cores and other geological history that CO2 fluctuates naturally. It is bogus to assume today's rise is caused by humans. Answer: We emit billions of tons of CO2 into the air and, lo and behold, there is more CO2 in the air. Surely it is not so difficult to believe that the CO2 rise is our fault. But if simple common sense is not enough, there is more to the case. (It is worth noting that investigation of this issue by the climate …

Members of the Navajo Nation and their supporters have been blockading the site of a proposed coal-fired power plant in northwestern New Mexico for more than a week now, hoping to halt construction of what they believe will be a social and ecological disaster. If completed, the Desert Rock Power Plant will cover 600 acres in the largest American Indian reservation in the nation, and it will be the third coal-fired plant on Navajo land. The protesters have been camped at the site since Dec. 12, and are demanding that officials show them the permits required to begin survey work …

Many environmentalists are reverse size queens -- "small is beautiful." When Schumacher wrote the book of that title, he was responding to a real tendency to ignore diseconomies of scale -- a tendency that still exists. Up to a certain point, both organizations and physical plants produce more output for each unit of input as they grown in size. Past that point, costs of gigantism kick in, and efficiency begins to fall instead of rising. But Schumacher assumed that this point always occurs at small or medium sizes. In fact, there are many cases in which you get economies of …

People talk about the "politicization" of science all the time, usually in the form of an accusation designed to paint an opponent as biased or corrupt. Let's take a moment to think about the term and what it means. Science is a multi-layered, collective, and impersonal process consisting of three parts: individual scientists working under the scientific method, the results of the individual scientists undergo peer-review and are published for the community to evaluate, and important claims are then re-tested in the "crucible of science" -- they are either reproduced by independent scientific groups or have their implications tested to …

(Part of the How to Talk to a Global Warming Skeptic guide) Objection: According to the IPCC, 150 billion tonnes of carbon go into the atmosphere from natural processes every year. This is almost 30 times the amount of carbon humans emit. What difference can we make? Answer: It's true that natural fluxes in the carbon cycle are much larger than anthropogenic emissions. But for roughly the last 10,000 years, until the industrial revolution, every gigatonne of carbon going into the atmosphere was balanced by one coming out. What humans have done is alter one side of this cycle. We …

(Part of the How to Talk to a Global Warming Skeptic guide) Objection: Climate has always changed. Why are we worried now, and why does it have to be humans' fault? Answer: Yes, climate has varied in the past, for many different reasons, some better understood than others. Present-day climate change is well understood, and different. Noting that something happened before without humans does not demonstrate that humans are not causing it today. For example, we see in ice core records from Antarctica and Greenland that the world cycled in and out of glacial periods over 120Kyr cycles. That climate …