(Part of the How to Talk to a Global Warming Skeptic guide) Objection: Global warming is a hoax perpetrated by environmental extremists and liberals who want an excuse for more big government (and/or world government via the U.N.). This is a common line, regardless of how ridiculous it is, so it should not go unanswered. Answer: Here is a list of organizations that accept anthropogenic global warming as real and scientifically well-supported:
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: Some stations, in the U.S. for example, show cooling trends. If there were really global warming, it would be warming everywhere. Answer: Global warming is the long-term increase in globally and seasonally averaged surface temperatures. It is not the case, nor is it expected, that all regions on the planet, let alone all weather stations, will show the same changes in temperature or rainfall patterns. Many stations have shown cooling, and some small regions have shown modest cooling as well. This does not invalidate global warming theory; it is merely the result of regional variation, and an example of how varied and complex the climate system is. (source: NASA)
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: Taking into account the logarithmic effect of CO2 on temperature, the 35 percent increase we have already seen in CO2 concentrations represents about three-quarters of the total forcing to be expected from a CO2 doubling. Since we have warmed about 0.7 degrees Celsius so far, we should only expect about 0.3 degrees more for a doubling from pre-industrial levels, so about 1 degree total, not 3 degrees as the scientists predict. Clearly the climate model sensitivity to CO2 is much too high. Answer: Even without addressing the numbers in this argument, there is a fundamental flaw in its reasoning.
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: According to the latest state-of-the-art satellite measurements from over the Arctic, sea levels are falling! Guess all that ice isn't melting after all. Answer: Yes, a new study using Europe's Space Agency's ERS-2 satellite has determined that over the last 10 years, sea level in the Arctic Ocean has been falling at an average rate of about 2 mm/year. This is very new and very interesting news, though it is preliminary and not published in any peer-reviewed journals yet. But even if these results hold up to time and scrutiny, it is not evidence that globally sea levels are not rising, because they are.
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: Sure, sea ice is shrinking in the Arctic, but it is growing in the Antarctic. Sounds like natural fluctuations that balance out in the end. Answer: Overall, it is true that sea ice in the Antarctic is increasing. Around the peninsula, where there is a lot of warming [PDF], the ice is retreating. This is the area of the recent and dramatic Larsen B and Ross ice shelf breakups. But the rest of the continent has not shown any clear warming or cooling and sea ice has increased over the last decade or so. This is not actually a big surprise.
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: Sure, some glaciers are melting. But if you look at the studies, most of those for which we have data are growing. Answer: This is simply not true, rumors on "the internets" aside. The National Snow and Ice Data Centre and their State of the Cryosphere division, on their Glacial Balance page, report an overall accelerating rate of glacial mass loss. The World Glacier Monitoring Service has similar findings, the most recent data coming from 2004.
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: Global temperatures have been trending down since 1998. Global warming is over. Answer: At the time, 1998 was a record high year in both the CRU and the NASA GISS analyses. In fact, it blew away the previous record by .2 degrees C. (That previous record went all the way back to 1997, by the way!) According to NASA, it was elevated far above the trend line because 1998 was the year of the strongest El Nino of the century. Choosing that year as a starting point is a classic cherry pick and demonstrates why it is necessary to remove chaotic year-to year-variability (aka: weather) by smoothing out the data. Looking at CRU's graph below, you can see the result of that smoothing in black.
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: The Antarctic ice sheets are actually growing, which wouldn't be happening if global warming were real. Answer: There are two distinct problems with this argument. First, any argument that tries to use a regional phenomenon to disprove a global trend is dead in the water. Anthropogenic global warming theory does not predict uniform warming throughout the globe. We need to assess the balance of the evidence.