the global warming threshold beyond which any of those four elements (including the AMOC itself) could be expected to tip, as opposed to thresholds established from studying those elements in isolation. A 2021 assessment of the economic impact of climate tipping points found that while tipping points in general would likely increase the social cost of carbon by about 25%, with a 10% chance of tipping points more than doubling it, AMOC slowdown is likely to do the opposite and reduce the social cost of carbon by about -1.4%, since it would act to counteract the effects of warming in Europe, which is more developed and thus represents a larger fraction of the global GDP than the regions which would be impacted negatively by the slowdown. The following year, this finding, and the broader findings of the study, were severely criticized by a group of scientists including Steve Keen and Timothy Lenton, who considered those findings to be a severe underestimate. The authors have responded to this criticism by noting that their paper should be treated as the starting point in economic assessment of tipping points rather than the final word, and since most of the literature included in their meta-analysis lacks the ability to estimate nonmarket climate damages, their numbers are likely to be underestimates. Impacts of a shutdown The possibility that the AMOC is a bistable system (which is either "on" or "off") and could collapse suddenly has been a topic of scientific discussion for a long time. In 2004, The Guardian publicized the findings of a report commissioned by Pentagon defence adviser Andrew Marshall, which suggested that the average annual temperature in Europe would drop by 6 Fahrenheit between 2010 and 2020 as the result of an abrupt AMOC shutdown. In general, a shutdown of the thermohaline circulation caused by global warming would trigger cooling in the North Atlantic, Europe, and North America. This would particularly affect areas such as the British Isles, France and the Nordic countries, which are warmed by the North Atlantic drift. Major consequences, apart from regional cooling, could also include an increase in major floods and storms, a collapse of plankton stocks, warming or rainfall changes in the tropics or Alaska and Antarctica, more frequent and intense El Niño events due to associated shutdowns of the Kuroshio, Leeuwin, and East Australian Currents that are connected to the same thermohaline circulation as the