SHOOT: They're saying 350ppm is the yardstick. We're already at 387ppm.
In the 1980s scientists worried about a doubling of pre-industrial levels of carbon dioxide, to 550 parts per million. Then 450 started to look like a problem. Now you and others say that 350 is dangerous, and we’re already at 387. What did climatologists learn that caused them to lower the estimate of dangerous CO2 levels?
The new information came from observations of how the system is responding to 387ppm and to more detailed information on how earth responded in the past to different atmospheric compositions. For instance, we see that the ice sheets are not stable at 387ppm; the Greenland and Antarctic ice sheets are losing mass even with current warming. The Greenland ice sheet had been losing between 150 and 200 cubic kilometers a year in 2002, and now is losing almost 300 cubic kilometers a year. Antarctica had been losing less than 100 cubic kilometers a year, and is now losing more than 150, so it seems like we're heading into a period of much more rapid ice sheet loss. |
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