Dr Roy Spencer writes:
There is a continuing debate over sea level rise, especially how much will occur in the future. The most annoying part of the news media reporting on the issue is that they imply sea level rise is all the fault of humans.
This is why the acceleration of sea level rise is what is usually debated, because sea level has been rising naturally, for at least 100 years before humans could be blamed. So, the two questions really are (1) Has sea level rise accelerated?, and (2) how much of the acceleration is due to humans?
Yesterday’s spat between Gavin Schmidt and Willis Eschenbach dealt with the question of whether sea level rise has accelerated or not. Gavin says it has. Willis says not, or at least not by a statistically significant amount.
I’m going to look at the data in a very simple and straightforward manner. I’ll use what I believe is the same data they did (Church & White, from CSIRO, updated through 2013 here), and plot a trend line for the data before 1950 (before humans could reasonably be blamed), and one for the data after 1950:
If we assume that the trend prior to 1950 was natural (we really did not emit much CO2 into the atmosphere before then) and that the following increase in the trend since 1950 was 100% due to humans, we get a human influence of only about 0.3 inches per decade, or 1 inch every 30 years.
Even though it looks like there is some evidence of even stronger acceleration more recently, sea level has varied naturally on multi-decadal time scales, and it is dangerous to extrapolate any short-term trends far into the future.
Climate models aren’t of much help in determining the human contribution because we have no idea how much of recent warming and the glacial melt was natural versus human-caused.
Models still can’t explain why glaciers started melting in the mid-1800s, just like they can’t explain why it warmed up so much from the mid-1800s to the mid-1900s.
The bottom line is that, even if (1) we assume the Church & White tide gauge data are correct, and (2) 100% of the recent acceleration is due to humans, it leads to only 0.3 inches per decade that is our fault, a total of 2 inches since 1950.
As Judith Curry mentioned in her continuing series of posts on sea level rise, we should heed the words of the famous oceanographer, Carl Wunsch, who said,
“At best, the determination and attribution of global-mean sea-level change lies at the very edge of knowledge and technology. Both systematic and random errors are of concern, the former particularly, because of the changes in technology and sampling methods over the many decades, the latter from the very great spatial and temporal variability. It remains possible that the database is insufficient to compute mean sea-level trends with the accuracy necessary to discuss the impact of global warming, as disappointing as this conclusion may be.”
Read more at Dr. Roy Spencer’s website
Is this the same Gavin Schmidt who earlier this year coauthored a paper on exploring evidence in earth’s past of an alien race who were wiped out on earth (before homo sapiens developed ) because of their advanced use of fossil fuels causing CO2 to then cause runaway global warming? Gavin Schmidt leader of men and aliens NOT.
Western Australia and New South Wales are geologically stable. Both states show steady decline in sea level for 2000 years:
WA:
http://jonova.s3.amazonaws.com/graphs/sea-level/sea-levels-west-aust-lewis-20000-7000-years-ago.gif
NSW:
http://jonova.s3.amazonaws.com/graphs/sea-level/sea-levels-nsw-lewis-20000-7000-years-ago.gif
Courtesy of Jo Nova:
http://joannenova.com.au/2012/10/australian-sea-levels-have-been-falling-for-7000-years/
The late, great John Daly on Tasmanian sea level:
http://www.john-daly.com/deadisle/index.htm
No on 1 and 0 on 2.
Have to agree.
Humans haven’t warmed the air enough globally to have any impact on sea level rise since 1950, although we could possibly have had a minor effect from irrigation and similar activities.
Remember to tie all claims back to the CO2 molecule and its underlying physics:
1) The chart dog-legs. CO2 shows a log decay. It would not cause a dog-leg or acceleration.
2) Just look at the Battery Park tidal gauge, there is no trend or acceleration.
3) Thermal expansion can cause an increase in sea level. CO2 doesn’t warm the oceans, visible radiation does.
4) Sea Ice and the Greenland glaciers are melting from BELOW. CO2 doesn’t cause warm oceans or geothermal heat.
5) The dog-leg doesn’t match the dog-legs on the Hockeystick chart. Either way, CO2 can’t cause a dog-leg.
The lower the understanding of the basic drivers of major trends in the data, the lower the justification for expensive actions. How much evidence is appropriate for what level of spending is a political question, not a scientific one. We absolutely do not have enough justification for the extreme actions that are being proposed.
And scientists who overstate evidence are putting their thumb on the scale, and are thus betraying the public trust.
The volume of sea ice in the Arctic is currently the largest in 5 years.
Disappointing coming from a professional scientist.
There is no such thing as a “NATURAL RISE” in sea level: Changing SL is CAUSED by:
1) An increase in temperature (thermal expansion.
2) An increase in volume – caused by changes in the amount of ice (and water) on land.
3) Very slow changes in the volume of ocean basins.
The first two are caused by rising temperature, but the third is not. We know that the 3) is not responsible for the alleged “natural rise” in SL (0.5 inches/decade) between 1850 (when tide gauge records became useful) and 1950 (when the IPCC asserts rising GHGs became the predominant driver of temperature change). How do we know this? Simple. 0.5 inches/decade is 50 inches/millennium or 1.25 m/millennium. Over the last 4 millennia, we are positive that there hasn’t been 5 m of SLR. The rate of rise is indistinguishable from ZERO.
Some scientists even believe that SL may have FALLEN slightly since the end of the Holocene Climate Optimum in parallel with the fall in temperature.
Frank wrote, “There is no such thing as a ‘NATURAL RISE’ in sea level…”
Of course there is. “Natural” sea-level rise is SLR which is not caused by man. Dr. Spencer was perfectly clear that that’s what he meant.
Sea-level has been rising and falling for as long as there have been oceans — and it’s perfectly natural.
.
Frank continued, “Changing SL is CAUSED by…
2) An increase in volume – caused by changes in the amount of ice (and water) on land…
… caused by rising temperature…”
Not entirely. Many things other than “rising temperature” can change the amount of ice/water sequestered on land.
The most important factor affecting ice sheet mass balance is snowfall, but climate alarmists rarely mention it. They talk plenty about melting ice and glacier calving, and mostly ignore the factor which is much more important and much greater in magnitude than either of those, because snowfall accumulation ADDS to ice sheet mass, and subtracts from sea-level, which means it is not useful to the alarmist narrative.
A warming climate causes processes which both increase and decrease sea-level rise. Based on the sea-level measurement record, it seems that when there’s no Laurentide ice sheet to melt those processes roughly balance each other.
The magnitude and importance of snowfall on ice sheet mass balance (and thus sea-level) is illustrated by the story of Glacier Girl.
She’s a WWII Lockheed P-38 Lightning which was extracted in pieces from beneath 268 feet of accumulated ice and snow (mostly ice), fifty years after she made an emergency landing on the Greenland Ice Sheet.
Do the arithmetic and you’ll calculate an astonishing number: more than 5 feet of ice per year, which is equivalent to more than seventy feet of annual snowfall!
That ice and snow represents evaporated water, mostly from the Arctic and North Atlantic Oceans, which then fell as ocean-effect snow on the Greenland Ice Sheet:
http://p38assn.org/glaciergirl/images/GPR-measurement-concept.jpg
The story of Glacier Girl is fascinating. You can read more about it here:
http://www.airspacemag.com/history-of-flight/glacier-girl-the-back-story-19218360/?all
and here:
http://p38assn.org/glacier-girl-recovery.htm
So, the key question is: what happens to snowfall in a warming climate?
The answer is that it increases, for two reasons.
First, it increases simply because warmer air holds more moisture. Every meteorologist knows that the biggest snowfalls occur when the temperature is not too far below freezing.
https://www.google.com/search?q=%22too+cold+to+snow%22
Second, a warmer climate should reduce sea-ice extent, increasing evaporation from the Arctic, North Atlantic, and Southern Oceans, and thereby increasing Lake/Ocean-Effect Snowfall (LOES) downwind. (Ice-covered water does not produce LOES.)
When additional snow falls on ice sheets and glaciers, it adds to ice mass accumulation and subtracts from sea-level.
So, which effects are greater in a warming world? Those which decrease ice mass and increase sea-level, or those which increase ice mass and decreases sea-level?
The best evidence to answer that question is history, because we already have some experience with the effect of temperature changes on sea-level. What it tells us is that those opposing processes must be very similar in magnitude, because the approximately 1°C of warming which the Earth has experienced since “pre-industrial” (Little Ice Age) conditions was associated with only a very, very slight acceleration in sea-level rise, all of it more than 85 years ago. Sea-level is rising no faster now than it was nine decades ago, when CO2 was under 310 ppmv, and CH4 was 1.0 ppmv. A 30% increase in CO2 and an 80% increase in CH4 have caused no acceleration at all in the rate of sea-level rise, and there’s no reason to suppose that similar future increases will cause dissimilar results.
.
Frank continued, “…Simple. 0.5 inches/decade is 50 inches/millennium or 1.25 m/millennium. Over the last 4 millennia, we are positive that there hasn’t been 5 m of SLR. The rate of rise is indistinguishable from ZERO.”
Your arithmetic would only be correct if you assumed that the rate of sea-level change has not varied over the last 4000 years. Why would you assume that?
Climate alarmists frequently do arithmetic like that, with sea-level or temperature, and declare that recent increases in either or both are unprecedented in thousands of years, because of evidence that temperatures or sea-levels were many degrees or meters different thousands of years ago. It is a common fallacy.
The evidence is very strong that there’s nothing at all unusual about the modest warming which the Earth has experienced over the last century, or the minute amount of sea-level rise.
That fallacy is a product of statistical confusion. Paleoclimate information, inferred from indirect evidence like marine sediments, is naturally “smoothed,” by processes which blend the evidence from consecutive decades, centuries, and millennia. As any engineer knows, when you smooth a graph, sharp fluctuations disappear. But many people apparently don’t know that. They see a paleoclimate graph and say, “look, it took x-thousand years to change by a few degrees or a few feet, that’s much slower than the 20th century!” But, of course, they have no way of knowing how many times it went up or down much more rapidly than that during a single decade during that x-thousand years.
What’s more, other than the recent higher CO2 levels, from fossil fuel use, the current Modern Climate Optimum is very similar to the Medieval Warm Period and the Roman Climate Optimum, and probably cooler than it was during the Holocene Climate Optimum and most of the Eemian interglacial.
.
Frank continued, “Some scientists even believe that SL may have FALLEN slightly since the end of the Holocene Climate Optimum in parallel with the fall in temperature.”
Not necessarily “slightly.” if you google search for “Holocene highstand” you’ll find a number of studies which concluded that, circa 3000 BC, in many places, and at least in most of the tropics, sea-levels were considerably higher than present.
That might be because, according Zwally (2015), the Antarctic ice sheet (especially the EAS) has been growing during the Holocene. Here’s an excerpt from the abstract (with my translations added in [brackets]):