A California Commission has raised the possibility of sea level rise to 10 feet by 2100 (Scientific American). Its previous estimate for the maximum possible rise had been 6 feet. The new estimate was based on studies about the way floating ice shelves that hold back massive mainland glaciers can fracture and break away, causing an abrupt collapse of some glaciers that are not otherwise well-blocked. The probability of this happening is not measurable but it should not be neglected by coastal defense planners. In addition, “Even without the 10-foot rise, the draft guidance cautions, as much as two-thirds of Southern California beaches “may be completely lost due to rising sea level.”
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A special report for the coming international conference about the risks of global warming is said to have been watered down by scientists. There is a fear that hearing the truth would cause some of the biggest polluting nations to drop out (or stay out) of the Paris Agreement. According to a reviewer, “The scientists who produce reports like these try to summarise the latest knowledge, but they have a reputation for being conservative about the worst risks of climate change…..This time they have outdone themselves in pulling their punches, however.” That means the public is also kept in the dark, which raises questions about the ultimate value of this common practice.
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Dana Nuccitelli reviews a new study and the methods it used for determining climate sensitivity. The methods are not easy to grasp, but the study did come up with a simple conclusion for sensitivity that keeps it in line with mainstream estimates of around 2.9C for a doubling of atmospheric CO2 after all the regular slow-moving feedbacks have kicked in, which would take about a century. From this it follows that “under current international climate policies, we’re most likely headed for about 3.4C warming,” which is also a standard estimate, widely expressed by many persons who are seeking to have those policies tightened up
–Note: I have personally come to believe that studies like this one are flawed if they do not reveal an accounting for the destiny of all of the heat being taken up by the oceans. As discussed in recent Climate Letters (see CL#1254) that heat uptake has a way of subtracting from current air temperatures that would otherwise occur over ocean surfaces if oceans handled incoming radiation the same way it is handled on land. The difference is measurable, and growing, and meanwhile the heat that is buried in the oceans keeps building up. It will continue building up, at about today’s rate, even if the CO2 level in the atmosphere stops growing. How will that affect the decades and centuries that are to follow, assuming a great difficulty in attempts to actually reduce the CO2 level? I believe the ocean interiors would keep getting warmer and warmer, and before too long that warmth would start to reveal itself over an expanded surface area, inevitably affecting air temperatures above the ocean surface at some point. These temperatures would sooner or later be enabled to catch up with those over land. This entire process, which Hansen and others refer to as inertia, should not be thought of as a feedback. It is simply a more complicated way of raising the air temperature over 70% of the Earth’s surface, taking a longer route than the short and easy route taken above land, and adding maybe a century or so to the time needed for completing the uniform warmup of air temperatures over the entire globe.
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A study about the extraordinary effectiveness of ocean heat uptake in certain regions. This study, published late in 2017, is relevant to the above discussion. There are no reviews available to look at but it does have open access, found at the link below. The study explains why a type of cloud feedback that could add 1.5C to sensitivity estimates would likely be reduced to just 0.3C in the current century because the added radiation would apply to ocean surfaces in a region where ocean heat uptake would increase in a nearly corresponding way. Thus, from the Conclusion in section 5, “Observational constraints on cloud phase and shortwave radiation that produce a large ECS increase do not imply large changes in 21st century warming projections.” That sounds like good news for the 21st century, but leaves open any answer to questions about the end game when ocean heat at depth has finally built up enough to have an undiminished effect at the surface—maybe in the next century?
Carl