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• Rupert Neate
• The Guardian, Monday 24 February 2014 08.09 AEST
• Jump to comments (664)

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Sea-level rise in this century is likely to be 70-120 centimeters by 2100 due to climate change if greenhouse-gas emissions are not mitigated, a broad assessment of the most active scientific publishers on that topic has revealed.

The 90 experts participating in the survey anticipate a median sea-level rise of 200-300 centimeters by the year 2300 for a scenario with unmitigated emissions. In contrast, for a scenario with strong emissions reductions, experts expect a sea-level rise of 40-60 centimeters by 2100 and 60-100 centimeters by 2300. The survey was conducted by a team of scientists from the USA and Germany.

“While the results for the scenario with climate mitigation suggest a good chance of limiting future sea-level rise to one meter, the high emissions scenario would threaten the survival of some coastal cities and low-lying islands,” says Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research. “From a risk management perspective, projections of future sea-level rise are of major importance for coastal planning, and for weighing options of different levels of ambition in reducing greenhouse-gas emissions.”

Projecting sea-level rise, however, comes with large uncertainties, since the physical processes causing the rise are complex. They include the expansion of ocean water as it warms, the melting of mountain glaciers and ice caps and of the two large ice sheets in Greenland and Antarctica, and the pumping of ground water for irrigation purposes. Different modeling approaches yield widely differing answers. The recently published IPCC report had to revise its projections upwards by about 60 percent compared to the previous report published in 2007, and other assessments of sea-level rise compiled by groups of scientists resulted in even higher projections. The observed sea-level rise as measured by satellites over the past two decades has exceeded earlier expectations.

90 key experts from 18 countries

“It this therefore useful to know what the larger community of sea-level experts thinks, and we make this transparent to the public,” says lead author Benjamin Horton from the Institute of Marine and Coastal Sciences at Rutgers University in New Jersey. “We report the largest elicitation on future sea-level rise conducted from ninety objectively selected experts from 18 countries.” The experts were identified from peer-reviewed literature published since 2007 using the publication database ‘Web of Science’ of Thomson Reuters, an online scientific indexing service, to make sure they are all active researchers in this area. 90 international experts, all of whom published at least six peer-reviewed papers on the topic of sea-level during the past 5 years, provided their probabilistic assessment.

The survey finds most experts expecting a higher rise than the latest IPCC projections of 28-98 centimeters by the year 2100. Two thirds (65%) of the respondents gave a higher value than the IPCC for the upper end of this range, confirming that IPCC reports tend to be conservative in their assessment.

Half Expect 1.5m Or More

The experts were also asked for a “high-end” estimate below which they expect sea-level to stay with 95 percent certainty until the year 2100. This high-end value is relevant for coastal planning. For unmitigated emissions, half of the experts (51%) gave 1.5 meters or more and a quarter (27%) 2 meters or more. The high-end value in the year 2300 was given as 4.0 meters or higher by the majority of experts (58%).

While we tend to look at projections with a focus on the relatively short period until 2100, sea-level rise will obviously not stop at that date. “Overall, the results for 2300 by the expert survey as well as the IPCC illustrate the risk that temperature increases from unmitigated emissions could commit coastal populations to a long-term, multi-meter sea-level rise,” says Rahmstorf. “They do, however, illustrate also the potential for escaping such large sea-level rise through substantial reductions of emissions.”

Citation:

B. P. Horton, S. Rahmstorf, S. E. Engelhart, A.C.Kemp: Expert assessment of sea-level rise by AD 2100 and AD 2300. Quaternary Science Reviews (2013). [doi: 10.1016/j.quascirev.2013.11.002]

Link to the article when it goes online: http://dx.doi.org/10.1016/j.quascirev.2013.11.002

Source:

This report based on a story released by the Potsdam Institute for Climate Impact Research here.

23 February 2014

Arctic sea-ice loss adds 25% to carbon dioxide warming over last 30 years

First posted at robertscribler

What’s the difference between a majestic layer of white sea ice and an ominous dark blue open ocean?

For the Arctic, it means about a 30 to 50 per cent loss in reflectivity (or albedo). And when seasonal sea-ice states are between 30 and 80 per cent below 1979 measures (depending on the method used to gauge remaining sea ice and relative time of year), that means very, very concerning additional heating impacts to an already dangerous human-caused warming.

A dark and mostly ice-free Arctic Ocean beneath a tempestuous swirl of clouds on September 1, 2012, a time when sea ice coverage had declined to an area roughly equal to the land mass of Greenland. Image source: Lance-Modis/NASA AQUA.

How concerning, however, remained somewhat unclear until recently.

In the past, idealized climate simulations and physical model runs had produced about a two per cent overall loss in Arctic albedo based on observed sea ice losses. This decline, though minor sounding, was enough, on its own, to add a little more than a 10 per cent amplifying feedback to the already powerful human atmospheric carbon dioxide (CO₂) forcing during recent years. Such an addition was already cause for serious concern and with sea ice totals continuing to fall rapidly, speculation abounded that just this single mechanism could severely tip the scales toward a more rapid warming.

But, as has been the case with a number of Arctic model simulations related to sea ice, these computer projections failed to measure up to direct observation. In this case, direct satellite observation. The situation is once more worse than expected.

A new study produced by University of San Diego Scientists now shows that loss of albedo for the Arctic Ocean due to rapidly declining sea ice was four per cent during the period of 1979 to 2011. This amazing loss of reflectivity, on its own, created a powerful enough heat trap to produce an amplifying feedback to human warming equal to 25 per cent of the heat captured by CO₂ emitted during that time — when spread out over the entire globe.

This is a feedback double what we were led to expect from climate model simulations. Perhaps more importantly, the local feedback in the Arctic — a region containing gigatons and gigatons of additional carbon waiting to be released during a period of rapid warming — is not 25 per cent greater, but four times greater than the total human CO₂ forcing since the start of the industrial revolution.

It is important to step back for a moment and consider the implication of this new information. If you took all the emissions from cars in the world, all the buses, all the aircraft, all the land use CO₂ emissions, all the agriculture, and all the amazing extra atmospheric heat capture that an emission equal to 160 times that of all the volcanoes on Earth would entail and added it all together, just one insult to our natural world in the form of Arctic sea-ice loss has now equaled a 25 per cent addition to that amazing total.

Or just add enough extra heat equal to forty times the CO₂ emitted by Earth’s volcanoes (for a total of X200). And the burden of all that extra heat is directly over a region of the world that contains a number of very large ice sheets which, if rapidly warmed, result in catastrophic land change and sea-level rise, and a number of outrageously enormous carbon deposits that, if rapidly warmed and released make the current albedo loss feedback look like child’s play.

In short, the game just got a lot uglier. Such an increase is a very big deal and will have strong implications going forward that affect the overall pace of human caused warming, the pace of Earth and Earth Systems changes, and the degree to which we might contain ultimate temperature rises under a scenario of full mitigation. From the study contents:

We find that the Arctic planetary albedo has decreased from 0.52 to 0.48 between 1979 and 2011, corresponding to an additional 6.4 ± 0.9 W/m² of solar energy input into the Arctic Ocean region since 1979. Averaged over the globe, this albedo decrease corresponds to a forcing that is 25 per cent as large as that due to the change in CO₂ during this period, considerably larger than expectations from models and other less direct recent estimates.

It is worth noting that the period measured by the study did not include the unprecedented sea-ice area, extent and volume losses seen during 2012. So it is likely that albedo loss and related Arctic additions to human warming are somewhat worse than even this study suggests. It is also worth noting that the total additional radiative forcing from all human CO₂ emissions since the industrial age began is estimated to be about 1.5 W/m². 

No way out through increasing cloud cover

The study also found that:

Changes in cloudiness appear to play a negligible role in observed Arctic darkening, thus reducing the possibility of Arctic cloud albedo feedbacks mitigating future Arctic warming.

Though seemingly innocuous, this statement is a death knell for one proposed method of geoengineering — namely cloud generation via spray ships deployed throughout the Arctic basin. The proposal had suggested that numerous ships could be spread about the Arctic during summer. These ships would be equipped with large machines that would dip into the ocean and spray sea water into the atmosphere to form clouds. The notion was that this would somehow increase albedo. Proponents of the plan neglected to provide scientific evidence that such a scheme would actually work or wouldn’t make matters worse by increasing atmospheric water vapor content — a substance with known heat-trapping properties.

Others had hoped a cloudier Arctic would take care of itself by producing a negative feedback naturally. Numerous studies have found that an Arctic with less sea ice is a much stormier, cloudier Arctic. And a number of specialists and enthusiasts hinted that the extra clouds would provide some cooling.

Not so according to the San Diego study. And this makes sense as clouds, while reflective of direct radiation contain large quantities of heat-trapping water vapor and tend to also trap long-wave radiation — which is more prevalent in the Arctic due to low angle of light or extended periods of darkness.

Extraordinarily rapid arctic amplification

Despite the various hollow conjectures and reassurances, what we have seen over the past seven years or so is an extraordinarily rapid amplification of heat within the Arctic. Arctic sea ice continues its death spiral, hitting new record lows at various times at least once a year.

Heat keeps funneling into the Arctic, resulting in heatwaves that bring 90 degree temperatures to Arctic Ocean shores during summer and unprecedented Alaskan melts during January. We have seen freakish fires in regions previously covered by tundra, in the Yakutia region of Russia, Alaska and Canada and in Arctic Norway during winter time. And we see periods during winter when sea ice goes through extended stretches of melt, as we did just last week in the region of Svalbard.

One need only look at the temperature anomaly map for the last 30 days to know that something is dreadfully, dreadfully wrong with the Arctic:

Global temperature anomaly vs the, already warmer than normal, 1981 to 2010 baseline. Image source: NOAA/Earth Systems Research Laboratory.

And one need only begin to add the number of amplifying feedbacks in the Arctic together to start to understand how much trouble we’ve set for ourselves:

1. Arctic albedo decrease due to sea ice loss.
2. Arctic CO₂ release due to thawing tundra.
3. Arctic methane release due to thawing land tundra.
4. Arctic methane release due to thawing subsea tundra and venting seabed methane.
5. Arctic albedo loss due to black carbon deposition.
6. Arctic albedo loss due to land vegetation changes.
7. Warming Arctic seas due to runoff from warming lands.
8. Arctic albedo decrease due to land snow and ice sheet melt.
9. South to north heat transfer to the Arctic due to a weakening, retreating Jet Stream and increasing prevalence of high amplitude atmospheric waves.

We all know, intuitively what an amplifying feedback sounds like. Just hold a microphone closer to a speaker and listen to the rising wail of sound. And it is becoming ever more obvious with each passing day, with each new report that the Arctic is simply screaming to us.

How deaf are we? How deaf are those of us who continue to fail to listen?

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