 The job of the Inner Governmental Panel on Climate Change, or IPCC, is to assess the science on climate change and produce summary reports. Interestingly, when we look back at their past reports, it turns out the IPCC is much more likely to underestimate than overestimate climate impacts. But before we get into that, let me give you some background. The IPCC is organized by the United Nations. Since 1990, they've produced five reports. Each report is actually a series of books, almost a thousand pages. The books cover the physical science, the impacts adaptation and vulnerability, and the mitigation of climate change. The IPCC include climate models from more than 20 different climate laboratories around the world, each with their own supercomputers. Each lab's model is written independently from the others. They come from China, Norway, the United States, Canada, France, Australia, Germany, Korea, Russia, Japan, and the United Kingdom. The IPCC puts the report through a rigorous review process where each sentence is scrutinized. It produces a report that all authors agree on and that the governments of the member countries agree on. Because of this process, the IPCC reports tend to air on the side of being conservative. Here are three examples of the IPCC being conservative. First off, they've tended to underestimate how much greenhouse gases we'll emit. In fact, the carbon dioxide concentration and emission rates measured in the last few years indicate that we are currently on the worst case scenario path. This suggests that the IPCC should adjust its scenarios to give a better sample of future emissions in order to imagine a worse, worst case scenario, which it has done for its most recent reports. The second example is Arctic sea ice decline. The area of ice covering the Arctic ocean has been getting pretty small at the end of summer these days. Whenever this bright white ice melts, it reveals a darker ocean surface underneath it. Dark ocean water absorbs more sunlight, making the system even warmer, and melting even more ice. This is an amplifying feedback. If we graph the Arctic ice area at the end of the summer each year, we find it's decreasing much quicker than any climate model projected. This signifies that all of the climate models have underestimated the strength of this reinforcing cycle. The last example is sea level rise. Measurements indicate that sea level rise is accelerating faster than projected by climate models. Most recently, the IPCC estimate was 60 percent below the observed trend. When the fourth report of the IPCC came out, scientists studying glaciers had begun to report that the flow of ice discharge to the ocean was accelerating. Some glaciers were accelerating, others were not, and we didn't really know why. Giant meltwater lakes and drainage holes called mulans were observed on the Greenland ice sheet and fears were that the water might be getting to the ground, lubricating the ice sheet and its glaciers and causing it to accelerate its melt. Rather than include the dynamic ice melting process and their sea level rise projections, the IPCC scientists decided they didn't have enough information to include this effect properly, so they left it out entirely. This is a good example of their airing on the side of caution. One study has taken a more thorough look at the IPCC projections, looking at new scientific findings after the IPCC reports came out. What they found was that the new scientific findings were more than 20 times more likely to be worse than what the IPCC predicted. There were a few examples where the IPCC overestimated climate impacts, but overall the cautious approach of the IPCC means it's been systematically underestimating climate impacts. Why is this? Another study suggests that the IPCC and climate scientists in general tend to be conservative in their predictions because they're airing on the side of least drama. In other words, scientists underestimate the threat of climate change because they're worried about being accused of alarmism. One myth distorts the evidence for IPCC reports. That myth is that the IPCC and the impacts projected by the climate models are alarmist, exaggerating the danger of global warming in order to cause needless worry. This myth uses the technique of conspiracy theory. Some people believe the scientists of the IPCC are conspiring to trick people about the effects of global warming. This myth also uses cherry picking. It uses isolated examples where the IPCC overestimated climate impacts, but we've learned that the most data points towards the IPCC tend to underestimate climate impacts. They are the polar opposite of alarmist. In reality, the IPCC is 20 times more likely to underestimate rather than exaggerate climate impacts.