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‘Glaciers have always grown and receded’–A few glaciers melting does not mean global warming

(Part of the How to Talk to a Global Warming Skeptic guide) Objection: A few glaciers receding today is not proof of global warming. Glaciers have grown and receded differently in many times and places. Answer: Firstly, it is more than "a few glaciers" that are receding; it is a pervasive, sustained, and accelerating global trend. The National Snow and Ice Data Centre (NSIDC) maintains a chart of global glacier mass balance, and for as far back as their data allows us to look, all but a few years have shown a loss in ice volume of subpolar and mountain …

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‘One record year is not global warming’–Luckily, there are plenty more years to consider

(Part of the How to Talk to a Global Warming Skeptic guide) Objection: So 2005 was a record year. Records are set all the time. One really warm year is not global warming. Answer: This is actually not an unreasonable point -- single years taken by themselves can not establish or refute a trend. So 2005 being the hottest globally averaged temperature on record is not convincing. Then how about: every year since 1992 has been warmer than 1992; the ten hottest years on record occurred in the last 15; every year since 1976 has been warmer than 1976; the …

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‘The scientists aren’t even sure’ — No scientist ever is

(Part of the How to Talk to a Global Warming Skeptic guide) Objection: Even the scientists don't know that the climate is changing more than normal and if it's our fault or not. If you read what they write it is full of "probably," "likely," "evidence of" and all kinds of qualifiers. If they don't know for sure, why should we worry yet? Answer: Probability is the language of science. There is no proof; there are no absolute certainties. Scientists are always aware that new data may overturn old theories and that human knowledge is constantly evolving. Consequently, it is …

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‘One hundred years is not enough’–Yes it is

(Part of the How to Talk to a Global Warming Skeptic guide) Objection: One hundred and some years of global surface temperatures is not long enough to draw any conclusions from or worry about anyway. Answer: The reliable instrumental record only goes back 150 years in the CRU analysis, 125 in the NASA analysis. This is a simple fact that we are stuck with. 2005 was the warmest year recorded in that period according to NASA, a very close second according to CRU. Because of this limit, it is not enough to say today that these are the warmest years …

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‘Warming is due to the Urban Heat Island effect’ — No, it isn’t

(Part of the How to Talk to a Global Warming Skeptic guide) Objection: The apparent rise of global average temperatures is actually an illusion due to the urbanization of land around weather stations, the Urban Heat Island effect. Answer: Urban Heat Island Effect has been examined quite thoroughly (PDF) and found to have a negligible effect on temperature trends. Real Climate has a detailed discussion of this here. What's more, NASA GISS takes explicit steps in their analysis to remove any such spurious signal by normalizing urban station data trends to the surrounding rural stations. It is a real phenomenon, …

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‘Mauna Loa is a volcano’ — CO2 rise is measured on top of a volcano!

(Part of the How to Talk to a Global Warming Skeptic guide) Objection: CO2 levels are recorded on top of Mauna Loa ... a volcano! No wonder the levels are so high. (image courtesty of Global Warming Art) Answer: Yes, it's true, Mauna Loa is an active volcano. In fact it's the biggest volcano on earth! So, should we suppose that Charles Keeling didn't know that? Well, no, he did know it. And using subtle scientific indicators like "wind direction," he was even able to ensure that his readings were not contaminated by any out-gassing when it was occurring. OK, …

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‘There is no evidence’ — Yes, there is

(Part of the How to Talk to a Climate Skeptic guide) Objection: Despite what the computer models tell us, there is actually no evidence of significant global warming. Answer: Global warming is not an output of computer models; it is a conclusion based on observations of a great many global indicators. By far the most straightforward evidence is the actual surface temperature record. While there are places -- in England, for example -- that have records going back several centuries, the two major global temperature analyses can only go back around 150 years due to their requirements for both quantity …

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A brief post-preamble

As David said, I am going to be reposting, article by article, my How To Talk to a Climate Skeptic guide here at Grist. Before beginning, I would like to make a correction, present a plan, offer an explanation, and make a request. David said that after 60 or so articles the guide is a "mission accomplished." Unfortunately, there really is a lot left to cover! That's the correction. The plan is to present these articles roughly following the Stages of Denial sorting, so it will read like a "journey of discovery." The explanation is prompted by a few comments …

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