Climate Change skeptics? [ot]

Outlook

For the past six years since publication of the AR4, the UN global climate negotiations were conducted on the basis that even without serious mitigation policies global sea-level would rise only between 18 and 59 cm, with perhaps 10 or 20 cm more due to ice dynamics. Now they are being told that the best estimate for unmitigated emissions is 74 cm, and even with the most stringent mitigation efforts, sea level rise could exceed 60 cm by the end of century. It is basically too late to implement measures that would very likely prevent half a meter rise in sea level. Early mitigation is the key to avoiding higher sea level rise, given the slow response time of sea level (Schaeffer et al. 2012). This is where the “conservative” estimates of IPCC, seen by some as a virtue, have lulled policy makers into a false sense of security, with the price having to be paid later by those living in vulnerable coastal areas.

Is the IPCC AR5 now the final word on process-based sea-level modelling? I don’t think so. I see several reasons that suggest that process models are still not fully mature, and that in future they might continue to evolve towards higher sea-level projections.

1. Although with some good will one can say the process models are now consistent with the past observed sea-level rise (the error margins overlap), the process models remain somewhat at the low end in comparison to observational data.

2. Efforts to model sea-level changes in Earth history tend to show an underestimation of past sea-level changes. E.g., the sea-level high stand in the Pliocene is not captured by current ice sheet models. Evidence shows that even the East Antarctic Ice Sheet – which is very stable in models – lost significant amounts of ice in the Pliocene.

3. Some of the most recent ice sheet modelling efforts that I have seen discussed at conferences – the kind of results that came too late for inclusion in the IPCC report – point to the possibility of larger sea-level rise in future. We should keep an eye out for the upcoming scientific papers on this.

4. Greenland might melt faster than current models capture, due to the “dark snow” effect. Jason Box, a glaciologist who studies this issue, has said:

There was controversy after AR4 that sea level rise estimates were too low. Now, we have the same problem for AR5 [that they are still too low].

Thus, I would not be surprised if the process-based models will have closed in further on the semi-empirical models by the time the next IPCC report gets published. But whether this is true or not: in any case sea-level rise is going to be a very serious problem for the future, made worse by every ton of CO2 that we emit. And it is not going to stop in the year 2100 either. By 2300, for unmitigated emissions IPCC projects between 1 and more than 3 meters of rise.

Nice Deletion sport.

Sketch is probably more accurate.

But, I gave you/them the benefit of the doubt by making it an 1/8th (3.2mm per Wilburs NASA propaganda chart) of inch per year.

Times 8 equals an inch (8 years) times 12 (88 years) times 3.28 feet equals a meter (281 plus years) etc etc etc.

Criticisms of the fourth report's incomplete sea-level predictions haunted them, said R. Steven Nerem, a professor of aerospace engineering at the University of Colorado at Boulder and an author of the chapter.

"From the get-go, we all knew we were going to be under the magnifying glass," he said.

If they got sea level wrong a second time, the climate world would be ready to pounce. If they underplayed their projections, they could reinforce the panel's reputation for conservatism, its reluctance to adopt recently unearthed evidence. If they went with bleeding-edge estimates, they might get ahead of accepted science and undermine their credibility with world governments. Dikes might be built too tall, or they might not be built where needed. And either way, groups on both sides of the climate debate would likely be dissatisfied with their results.

The final push in Stockholm lasted 24 consecutive hours. Mr. Clark tried to stay alert. Finally, the sea-level section came up. On the screen, their most important conclusion appeared: Under pessimistic estimates and with no climate action, sea levels will rise between 1.7 and 3.2 feet by the last two decades of this century; with robust, global action, in a lucky world, they would still rise—but by only 0.8 to 1.8 feet.

Then came the section they added to mollify Mr. Levermann:

"Based on current understanding, only the collapse of marine-based sectors of the Antarctic ice sheet, if initiated, could cause global mean sea level to rise substantially above the likely range during the 21st century," it read. "However, there is medium confidence that this additional contribution would not exceed several tenths of a meter of sea level rise during the 21st century."

Through such unlovely paragraphs is consensus forged.

Regarding my statement about "man caused some warming", my point was the criteria "man caused warming" is completely open ended. The level of man's contribution to global warming is undefined. The criteria allows for any amount of contribution by anthropogenic forcings.

You claim the criteria sets the minimum for anthropogenic contribution at 50 per cent. Where, in the criteria for levels 2 and 3, is that criteria stated?What's your basis for that claim?

I see. Since level 7 explicitly states that humans are causing less than half of global warming, any paper that implies humans are causing warming (without clarifying how much warming or minimizing the human impact) should be interpreted as saying humans are causing at least 50% of the warming.

Since you have been relying on the abstract and not the actual paper