ITER Forum Website update 2/13
B.J.Green (23/2/13)
1. Scientists split on rate of sea-level rise
BY: GRAHAM LLOYD, ENVIRONMENT EDITOR From: The AustralianJanuary 16, 2013 12:00AM
SCIENTIFIC reports are split on whether the rate of global sea level rise is getting faster, a leaked IPCC draft report has confirmed.
A report published in Journal of Climate last month found "small or no acceleration, despite the anthropogenic (human) forcing".
The report adds to three being assessed by the Intergovernmental Panel on Climate Change.
Understanding whether the speed of sea level rise was increasing was critical to judging the accuracy of worst-case scenario predictions for rises of more than 1m over the next century.
A leaked draft of the fifth report of the IPCC, due to be released later this year, cited three other reports on the same issue.
IPCC chairman Rajendra Pachauri has criticised the leak and said the findings could change, but the oceans chapter of the leaked draft report said only two of the three reconstructions from tide gauge data extending back to 1900 or earlier indicated a "non-zero" acceleration.
The estimates of the rate of acceleration ranged from zero to 0.013mm a year.
The draft said it was "likely" that global-mean sea-level rise had accelerated since the early 1900s. It said a much higher trend since 1993 likely reflected a degree of natural variation.
It was unclear whether the Journal of Climate report findings would alter the panel' s deliberations. Key IPCC authors were meeting in Tasmania this week but would not comment on the state of discussions.
CSIRO sea level specialist John Church has rejected the abstract findings of the Journal of Climate report, by JM Gregory, to which he contributed. Dr Church did not return emails or calls from The Australian on Monday or yesterday but told a press conference: "Sea level clearly is linked to climate change. It is clearly linked to increases in greenhouse gases and that's actually in the paper which was quoted by The Australian. So the quote is, I'm sorry, inaccurate.
"The sea level has already increased the rate of rise from the 18th to the 19th century. The instrumental records would indicate an acceleration during the 20th century, and the projections will indicate a further acceleration during the 21st century," he said.
The JM Gregory paper sought to explain why observed sea level rises had been found to exceed the sum of estimated contributions, especially for the early decades of the 20th century.
"The reconstructions (of GMSLR) account for the approximate constancy of the rate of GMSLR during the 20th century, which shows small or no acceleration, despite the increasing anthropogenic forcing.
"Semi-empirical methods for projecting GMSLR depend on the existence of a relationship between global climate change and the rate of GMSLR, but the implication of our closure of the budget is that such a relationship is weak or absent during the 20th century."
Online discussion of the paper said the analysis was a criticism of semi-empirical method rather than the link between sea level rises and global climate change.
2. A rising tide of discord
BY: GRAHAM LLOYD, ENVIRONMENT EDITOR From: The AustralianJanuary 16, 2013 12:00AM
WHEN the Intergovernmental Panel on Climate Change releases its updated report on the state of climate science and outlook later this year its projections for future sea level rises will be among its most keenly scrutinised findings.
Some of the world's leading climate scientists are meeting in Hobart this week to thrash out what is supposed to be the best available science on what climate change means for future temperatures, weather and the oceans.
Sea level rises have been a core concern that have been used to capture headlines with doomsday scenarios of rises of several metres if the world's ice sheets collapse in a devastating, if unlikely, feedback loop.
Since the last IPCC report was published in 2007, projections for sea level rises have been steadily revised upwards by governments around the world.
The US National Research Council has estimated a sea level rise of up to 2m by 2100. This is the same figure contained in the US Climate Assessment released in December. Al Gore, in his documentary An Inconvenient Truth, forecast rises of more than 6m.
The IPCC has been sober by comparison. The 2007 IPCC report projected a worst-case scenario of sea level rises of between 26cm and 59cm by the year 2100. Its most optimistic scenario was for a sea level rise of 18cm to 38cm during the century.
But since the IPCC report was released, the CSIRO has put forward three scenarios that estimate a sea level rise of up to 1.1m by 2100.
If a global agreement can be reached to bring about dramatic reductions in global emissions the CSIRO estimates sea level rises can be limited to 50cm.
A medium scenario mirrors the IPCC's leaked draft report for its fifth assessment, estimating a rise of 80cm by 2100.
The high-end scenario includes the impact of "recent warming trends on ice sheet dynamics" beyond those already included in the IPCC projections. There has been particular concern about the extent of recent ice melts in the Arctic.
Within the scientific community there has been lively debate about both the past and potential sea level rises.
The debate has questioned the ability of models to account properly for what had been observed. Advances in satellite technology are expected to give a much higher level of confidence in measurements that are taken in future.
But there is a lot at stake in getting the right answers.
Rising sea levels would displace millions of people living in low-lying areas, many of them already among the world's poorest.
The Pacific nation of Kiribati is preparing an evacuation plan as some of its 32 flat coral atolls have started to disappear below the water.
In developed nations, billions of dollars worth of infrastructure and property is vulnerable to rising sea levels and the impact of increased storm surges. Accurate modelling will allow governments to plan and potentially save billions of dollars in infrastructure.
Equally, overly pessimistic projections can have an expensive cost in lost opportunity. There is a broad agreement that global sea levels are now rising by about 3mm a year.
However, a recent report by the US National Oceanic and Atmospheric Administration says global sea levels had risen by only 1.1mm to 1.3mm a year from 2005 to last year, which is less than half of the rate claimed by the IPCC.
Another peer-reviewed report estimates unsustainable groundwater use, artificial reservoir water impoundment including dams and the loss of water from closed basins had contributed to a sea level rise of about 0.77mm a year between 1961 and 2003, about 42 per cent of the observed sea-level rise.
Another paper, published in the Journal of Climate last month, found there has been "little or no acceleration in sea level rises despite the increasing anthropogenic forcing".
One difficulty in making projections is the high level of "inertia" in the ocean system which, like turning a large ship, takes a long time to respond to change. Another difficulty is accurately reconstructing the long-term sea level record because of the lack of real data.
Records for northern hemisphere sea levels date back to 1700 from Amsterdam, with three more sites in northern Europe starting after 1770. By the late 1800s more gauges were being operated in northern Europe and along the North American east and west coast.
The first measurements of sea level from the southern hemisphere began after 1880, all in Australia and New Zealand. There were no tide gauges on islands within the Pacific, Indian or Atlantic oceans until the 1950s, and the majority were not in place until the 80s. A precise record for sea levels is therefore relatively recent in geological terms.
But according to a leaked draft of the IPCC's fifth assessment report on oceans, due to be released late this year, it is "virtually certain" that global mean sea level rose at a mean rate between 1.4mm and 2.0mm a year during the 20th century and between 2.7mm and 3.7mm a year since 1993.
Projections on sea level rises will be contained in a separate chapter of the updated report.
The IPCC chairman Rajendra Pachauri has described the leak of the draft report as "unfortunate".
"I wouldn't at this stage come to any conclusions," he says. "We're still working hard with this report and it's entirely possible that what we get in the final version may be far stronger or in some cases maybe a little more moderate.
"I wouldn't go by any of the conclusions that people have seen as part of the draft report," Pachauri says.
However, the draft says the assessment on sea level rises is based on high agreement between multiple studies using different methods and independent observing systems since 1993.
The draft report says it is likely the GMSL rose between 1930
and 1950 at a rate comparable
to that observed since 1993, possibly due to "multidecadal climate oscillation".
Individual tide gauges around the world and reconstructions of GMSL show increased rates of sea level rise during this period.
It is considered "very likely" that estimates of the global average rate of sea level change are affected by land motion.
And it is "very likely" that warming of the upper 700m of the ocean has been contributing an average of 0.6mm a year of sea level change since 1971.
The draft report said it is likely that warming between a depth of 700m and 2000m has been contributing an additional 0.1mm a year to sea level rise since 1971 and that warming below 2000m has been contributing another 0.11mm a year since the early 1990s.
There is some conflict, however, in whether or not the rate of sea level rise is accelerating.
This is crucial to understanding whether the more extreme sea level rise projections are likely.
The draft report says two out of three reconstructions of the GMSL from tide gauge data extending back to 1900 or earlier indicate a non-zero acceleration.
These estimates range from zero to 0.013mm a year.
The draft report therefore says it is "likely" that the GMSL rise has accelerated since the early 1900s.
"While there is more disagreement on the value of a 20th century acceleration in GMSL when accounting for possible multi-decadal fluctuations, two out of three records still indicate a significant positive value," it says.
However, it says the much higher trend in GMSL calculated since 1993 "likely" reflects, in part, multidecadal oscillation.
The oceans chapter of the draft report does not include the findings of a paper published in Journal of Climate last month that has caused some controversy due to its wording on the relationship between global climate change and sea level rises.
The JM Gregory report shows "small or no acceleration, despite the anthropogenic forcing".
The paper published in the online Journal of Climate has attempted to piece together the factors behind the global mean sea-level rise during the 20th century.
There are contributions to sea level rise from ocean thermal expansion (sea water expanding as it gets hotter), melting from glaciers and ice sheets, groundwater extraction and reservoir impoundment of water.
The paper says an "enigma" of the 20th-century sea level rise has been that the observed rise has been found to exceed the sum of estimated contributions, especially for the earlier decades.
The paper proposes thermal expansion simulated by climate models may previously have been understated owing to the absence of factoring in volcanic forcing.
The rate of melting from glaciers was larger than previously estimated, and was not smaller in the first than in the second half of the century. The Greenland ice sheet could have made a positive contribution throughout the century.
Ground water use and storage in reservoirs may have been approximately equal in magnitude.
The Gregory et al paper says it is "possible to reconstruct the time series of GMSLR from the quantified contributions, apart from a constant residual term, which is small enough to be explained as a long-term contribution from the Antarctic ice sheet".
"The reconstructions account for the approximate constancy of the rate of GMSLR during the 20th century, which shows small or no acceleration, despite the increasing anthropogenic forcing.
"Semi-empirical methods (a combination of observations and modelling) for projecting GMSLR depend on the existence of a relationship between global climate change and the rate of GMSLR, but the implication of our closure of the budget is that such a relationship is weak or absent during the 20th century."
The paper has also been cited as further evidence of uncertainty about the "acceleration" of sea level change that would be needed to produce the extreme sea level rises that have been predicted.
One analysis of this finding of a "weak or absent" relationship between global climate change and the rate of sea level rise is that it is an attempt to discredit the accuracy of semi-empirical modelling.
One of the report's authors, John Church from CSIRO, has rejected analysis that the paper weakens the case that sea level rises are speeding up or that the link to climate change is questionable.
He told an IPCC press conference in Hobart yesterday sea level was clearly linked to climate change.
"It is clearly linked to increases in greenhouse gases. And that's actually in the paper. The sea level has already increased the rate of rise from the 18th to 19th century.
"The instrumental records would indicate an acceleration during the 20th century, and the projections will indicate a further acceleration during the 21st century," he said.
In its 2012 State of the Climate report, the Bureau of Meteorology says the observed global-average mean sea level rise since 1990 was near the high end of projections from the 2007 IPCC fourth assessment report.
Rates of sea level rise were not uniform around the globe. Since 1993, the rates of sea level rise to the north and northwest of Australia had been 7mm to 11mm a year, two to three times the global average.
Rates of sea-level rise on the central east and southern coasts of the continent were mostly similar to the global average.
CSIRO says the variations are at least in part a result of natural variability of the climate system.
For the RealClimate blog the bottom line is the rate of sea-level rise was very low in the centuries preceding the 20th, very likely well below 1mm a year in the longer run. In the 20th century the rate increased, but not linearly due to the non-linear time evolution of global temperature.
"The diagnosis is complicated by spurious variability due to under sampling," says RealClimate.
"At the end of the 20th and beginning of the 21st century the rate had reached 3mm a year, a rather reliable rate measured by satellites.
"This increase in the rate of
sea-level rise is a logical consequence of global warming, since ice melts faster and heat penetrates faster into the oceans in a warmer climate."
3. Rising uncertainty about sea level increases
BY: GRAHAM LLOYD, ENVIRONMENT EDITOR From: The AustralianJanuary 19, 2013 12:00AM
FOR a measure of scientific uncertainty the high-water mark may well be what impact climate change will have on rising ocean levels over the coming 100 years.
When it releases its fifth report later this year the Intergovernmental Panel on Climate Change (IPCC) is considered certain to revise upwards its estimate of what may happen by 2100.
The estimates will still be less than what Australian coastal planners have been told to expect but dramatically more than a casual appraisal of what occurred in the past century.
The worst case scenario , in a leaked IPCC draft document discussed by climate scientists in Hobart this week, is for sea levels to rise by 56cm to 96cm by 2100, with a rate rise of 8mm to 15mm a year over the last decade of the century.
This compares with the IPCC's 2007 worst case forecast of 26cm to 59cm and a current annual mean-global sea-level rise of about 3mm a year. The difference will be the latest projections are expected to include a contribution from melting ice sheets.
Some models have predicted far worse outcomes from melting ice but the draft IPCC document says while this cannot be excluded "scientific understanding is insufficient for evaluating their probability".
For a window into the complex and uncertain world of sea level predictions, it is difficult to go past a paper published last month which explores sea level rises over the 20th century.
To set the record straight. The JM Gregory paper published in the Journal of Climate, "Twentieth-century global-mean sea-level rise: is the whole greater than the sum of the parts", did not say there was no link between global warming and sea level rises as initially incorrectly reported, and corrected, in The Australian.
Attempts to contact the authors both prior to and after publication were unsuccessful. And it was a mistake RealClimate, an online forum for "climate science from climate scientists" said could be easily made.