The surprising news from scientists about rising sea levels!

Summary: Rising sea levels have become a core element — perhaps the core — of climate activists’ warnings. What do scientists say? Should we worry, panic, or despair? Here is a brief answer, plus much supporting evidence. This is journalism for the public policy debate about climate change, not written by a subject matter expert.

As so many of the predicted effects of climate change have failed to appear on time (e.g., the end of winter, more and stronger hurricanes), rising sea levels have become the focus of climate activists. It creates easy (if unscientific, even daft) graphics of global flooding — hopefully panicking insurance companies and landowners. Unfortunately, as so often the case, the science has not supported their screams of “Wolf!”

Now a new cycle begins, with the first salvo being Jeff Tollefson’s “Satellite snafu masked true sea-level rise for decades” in Nature, 17 July 2017 — “Revised tallies confirm that the rate of sea-level rise is accelerating as the Earth warms and ice sheets thaw.” A mild tone, as such articles go. The mainstream news stories to follow, fed by activists, probably will be lurid — or even hysterical. People will be running for the hills if they take them seriously (but they don’t; even believers see them as entertainment).

Spoiler – Conclusions

Below you will find six charts and 2750 words from major institutional science websites plus eight works of cutting edge research. It describes the scientific basis for the terrifying news stories you have seen and will continue to see in the major news media. I’ll save you some time. Here are the four conclusions relevant to the public policy debate about climate change.

(a) The seas are slowly rising and will continue to do so. Europe is preparing many of its coastal cities for this. America is not. Unless we wake up, the results will not be pretty. Slow and stupid are the sins “Nature’s god” always punishes.

(b) There are some tentative signs that the rate of increase is already accelerating, rather than just fluctuating. But the data is noisy (lots of natural variation) and the (tentative) acceleration is small — near the resolving power of these systems (hence the significance of the frequent revisions).

(c) Graph E in paper (5) is the key. As the world continues to warm, the rate of sea level rise will accelerate (probably slowly). Understanding the four scenarios used in the IPCC’s AR5 is an essential first step to making sense of the stories in the news about rising seas (discussed below).

(d) Bottom line: activists are attempting to incite hysteria by exaggerating and misrepresenting what science tells us about rising sea levels.

What do the scientists say about the rising seas?

We start, as always, with the Working Group I of the IPCC’s Fifth Assessment Report: Chapter 3 – Observations: Oceans. The oceans have been rising at varying rates for a long time.

“It is very likely that the mean rate of global averaged sea level rise was 1.7 [1.5 to 1.9] mm/yr between 1901 and 2010 and 3.2 [2.8 to 3.6] mm/yr between 1993 and 2010. Tide gauge and satellite altimeter data are consistent regarding the higher rate during the latter period. It is likely that similarly high rates occurred between 1920 and 1950.”

The chapter also discusses at length the high degree of “interannual-to-multi-decadal variability” due to climate modes (e.g., the North Atlantic oscillation, the Atlantic multi-decadal oscillation, the Pacific decadal oscillation, and the El Niño–Southern Oscillation) which obscure long-term trends.

Also see NASA’s website about sea level projections. The rise over the past 25 years is aprox. 3.2 mm/year (12.6″ per century). Red emphasis added

“High quality measurements of (near)-global sea level have been made since late 1992 by satellite altimeters …This data has shown a more-or-less steady increase in Global Mean Sea Level (GMSL) of around 3.2 ± 0.4 mm/year over that period. This is more than 50% larger than the average value over the 20th century. Whether or not this represents a further increase in the rate of sea level rise is not yet certain.”

Now let’s look at research since AR5’s WGI report was published in 2013.

What do the satellites say?

The major databases of global mean sea level show no acceleration in recent years. Here are  two of them.

(a) AVISO – through 25 March 2017.

AVISO shows a 1993-2017 rise at a rate of  3.28mm/year (12.9″ per century) – and no acceleration. They are confident of their data. Aviso distributes satellite altimetry data from Topex/Poseidon, Jason-1, ERS-1 and ERS-2, EnviSat, and the Doris precise orbit determination and positioning products. It is a partnership of these major science institutions. They have not updated their graph since March 2017. See their interactive tool here. Click the graph to enlarge.

“Comparisons between these altimetry data and those obtained using independent techniques, such as the drifting buoys of the Argo network, the GRACE gravimetry satellite, or the network of tide gauges, can not only corroborate these results but also help us establish which of the possible sources of variation in mean sea level might explain the rise observed.”

(b) Colorado University Sea Level Research Group (SLMG).

The CU SLMG provides another graph showing rising sea levels — but no acceleration. They have not updated it since June 2016, probably waiting for recalculation of satellite data. The trend is 3.4 mm/year (11.8″ per century).

“Since 1993, measurements from the TOPEX and Jason series of satellite radar altimeters have allowed estimates of global mean sea level. These measurements are continuously monitored against a network of tide gauges. When seasonal variations are subtracted, they allow estimation of the global mean sea level rate. As new data, models and corrections become available, we continuously revise these estimates (about every two months) to improve their quality.”

Global Mean Sea Level. Seasonal signals removed (10mm = 0.4″.).

Where do activists get those scary scenarios?

The climate change debate has entered what we might call the “Campfire Phase”, in which the goal is to tell the scariest story. /1

— Oren Cass (@oren_cass) July 12, 2017

When climate activists do not just make up stories, they use the worst-case scenario in the IPCC’s AR5: RCP8.5. Like a good worst case analysis, it assumes large changes in current trends in population (high) and technology (stagnant in the 21st century). The scenario is unlikely and becoming more so every day. RCP8.5 assumes that coal is the fuel of the late 21st century. Coal companies are going bankrupt now, replaced by natural gas and renewables.  Electric cars are already commonplace in Europe, with mass production coming to America eventually as the technology matures (it’s in the early stages now). The potential solar and even fusion remains bright for coming generations.

Scientists are responding to this, with papers increasingly focused instead on the middle scenarios (RCP4.5 and RCP6.0). With continued technological progress, we might reach the RCP2.6 scenario in the mid 21st C – with negative greenhouse gas emissions. For details see Manufacturing climate nightmares: misusing science to create horrific predictions.

Recent papers about new analysis of the data

Unlike what you read in the mainstream media about climate and economic data, collecting this data is not like counting apples. Hence the role of revisions and reanalysis of the data. The graphs of global sea level and atmosphere temperatures result from mind-blowingly complex calculations, whether based on instruments on satellites or Earth’s surface. See this presentation describing some of this complexity.

Improvements are an ongoing process, as seen in “Orbit related sea level errors for TOPEX altimetry at seasonal to decadal time scales” in Ocean Science, in press. The TOPEX mission ended in January 2006.

Scientists have attempted to understand the dynamics of rising sea levels, unlock their history, and detect the expected acceleration in the rate of rising sea levels. Here are samples of their recent work. Red emphasis added.

(1) “Timescales for detecting a significant acceleration in sea level rise” by Ivan D. Haigh et al in Nature Communications, 14 April 2014.

“Our results imply that if/when the currently understood components of the variability in the records are removed, then accelerations significantly different from zero are likely to become detectable in individual tide gauge records later this decade or early next decade, using the methods considered here.”

(2) “Unabated global mean sea-level rise over the satellite altimeter era” by Christopher S. Watson et al in Nature Climate Change, June 2015. Gated. Abstract…

“The rate of global mean sea-level (GMSL) rise has been suggested to be lower for the past decade compared with the preceding decade as a result of natural variability, with an average rate of rise since 1993 of +3.2 ± 0.4 mm yr−1. However, satellite-based GMSL estimates do not include an allowance for potential instrumental drifts (bias drift). Here, we report improved bias drift estimates for individual altimeter missions from a refined estimation approach that incorporates new Global Positioning System (GPS) estimates of vertical land movement (VLM). …

“Applying the bias drift corrections has two implications. First, the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 ± 0.4 mm yr−1 and +2.9 ± 0.4 mm yr−1, depending on the choice of VLM applied. These rates are in closer agreement with the rate derived from the sum of the observed contributions, GMSL estimated from a comprehensive network of tide gauges with GPS-based VLM applied and reprocessed ERS-2/Envisat altimetry.

“Second, in contrast to the previously reported slowing in the rate during the past two decades, our corrected GMSL data set indicates an acceleration in sea-level rise (independent of the VLM used), which is of opposite sign to previous estimates and comparable to the accelerated loss of ice from Greenland and to recent projections, and larger than the twentieth-century acceleration.”

(3)  “Refining satellite era estimates of global mean sea level rise” by Christopher S. Watson et al, slides presented at the International GNSS Service Annual Workshop in February 2016. This is an excellent introduction to the complexities of calculating sea levels from satellite data. A few of their conclusions.

• “Our work suggests TOPEX is yet to be fully understood and is presently slightly overestimating the trend in GMSL. {The TOPEX mission ended in January 2006!}
• “Our revised record seems more consistent with the sum of the observed contributions to GMSL. While not yet statistically significant, we see the emergence of an acceleration.
• “Further reprocessing of TOPEX is currently underway by mission agencies, first results seem commensurate with our findings, but this remains in progress.”

(4) “Revisiting the contemporary sea-level budget on global and regional scales” by Roelof Rietbroeka et al, PNAS, 9 February 2016 — “The simultaneous combination of sea-level anomalies from satellite altimetry and data from satellite gravimetry allows a partitioning of the sea-level rise into the different contributions.” Abstract…

“Dividing the sea-level budget into contributions from ice sheets and glaciers, the water cycle, steric expansion, and crustal movement is challenging, especially on regional scales. Here, Gravity Recovery And Climate Experiment (GRACE) gravity observations and sea-level anomalies from altimetry are used in a joint inversion, ensuring a consistent decomposition of the global and regional sea-level rise budget. …”

The thick grey line is the total change in sea level over the 2002–2014 period: 2.74 mm/year (10.8″/century).

(5) “Temperature-driven global sea-level variability in the Common Era” by Robert E. Kopp et al in PNAS, 15 March 2016 —

“We present the first, to our knowledge, estimate of global sea-level (GSL) change over the last ∼3,000 years that is based upon statistical synthesis of a global database of regional sea-level reconstructions.

“GSL varied by ∼±8 cm over the pre-Industrial Common Era, with a notable decline over 1000–1400 CE coinciding with ∼0.2 °C of global cooling. The 20th century rise was extremely likely faster than during any of the 27 previous centuries. Semiempirical modeling indicates that, without global warming, GSL in the 20th century very likely would have risen by between −3 cm and +7 cm {1.2″ to 2.8″), rather than the ∼14 cm {5.5″} observed. Semiempirical 21st century projections largely reconcile differences between IPCC projections and semiempirical models.”

“Graph A: Global sea level (GSL) under prior ML2,1. Note that the model is insensitive to small linear trends in GSL over the Common Era, so the relative heights of the 700–1000 CE and 20th century peaks are not comparable.” The sea level values are with respect to 1900 CE baseline. This graph is widely used, seldom with this important caveat. (1.0cm = 0.4″.)

“Graph E: 21st century projections for RCPs 2.6, 4.5, and 8.5. Red lines show the fifth percentile of RCP 2.6 and 95th percentile of RCP 8.5. …Sea level values are with respect to 2000 CE baseline.” By roughly 2025 the rate of sea level rise accelerates substantially under all four RCPs. (10cm = 3.9″.) The acceleration is steep only under the unlikely worst-case RCP8.5 scenario.

(6)  “Is the detection of accelerated sea level rise imminent?” by J.T. Fasullo et al, Scientific Reports, 10 August 2016 — Abstract.

“Global mean sea level rise estimated from satellite altimetry provides a strong constraint on climate variability and change and is expected to accelerate as the rates of both ocean warming and cryospheric mass loss increase over time. In stark contrast to this expectation however, current altimeter products show the rate of sea level rise to have decreased from the first to second decades of the altimeter era. Here, a combined analysis of altimeter data and specially designed climate model simulations shows the 1991 eruption of Mt Pinatubo to likely have masked the acceleration that would have otherwise occurred. This masking arose largely from a recovery in ocean heat content through the mid to late 1990 s subsequent to major heat content reductions in the years following the eruption.

“A consequence of this finding is that barring another major volcanic eruption, a detectable acceleration is likely to emerge from the noise of internal climate variability in the coming decade.“

Update: (7)  “New estimate of the current rate of sea level rise from a sea level budget approach” by H. B. Dieng et al in Geophysical Research Letters, 28 April 2017 — Gated. Abstract.

“We revisit the global mean sea level (GMSL) budget during the whole altimetry era (January 1993 to December 2015) using a large number of data sets. The budget approach allows quantifying the TOPEX A altimeter drift (amounting 1.5 ± 0.5 mm/yr over 1993–1998). Accounting for this correction and using ensemble means for the GMSL and components lead to closure of the sea level budget (trend of the residual time series being 0.0 ± 0.22 mm/yr).

“The new GMSL rate over January 1993 to December 2015 is now close to 3.0 mm/yr. An important increase of the GMSL rate, of 0.8 mm/yr, is found during the second half of the altimetry era (2004–2015) compared to the 1993–2004 time span, mostly due to Greenland mass loss increase and also to slight increase of all other components of the budget.“

Figure 3a: Ensemble mean (EM) GMSL without TOPEX A drift correction (black curve), sum of EM components (red curve), and individual EM components over January 1993 to December 2015. Shaded areas represent one standard error as described in text.

Update: (8)  “A Consistent Sea-Level Reconstruction and Its Budget on Basin and Global Scales over 1958–2014” by Thomas Frederikse et al. in Journal of Climate, February 2018. Gated. Abstract.

“Different sea level reconstructions show a spread in sea level rise over the last six decades and it is not yet certain whether the sum of contributors explains the reconstructed rise. Possible causes for this spread are, among others, vertical land motion at tide-gauge locations and the sparse sampling of the spatially variable ocean. To assess these open questions, reconstructed sea level and the role of the contributors are investigated on a local, basin, and global scale. High-latitude seas are excluded. Tide-gauge records are combined with observations of vertical land motion, independent estimates of ice-mass loss, terrestrial water storage, and barotropic atmospheric forcing in a self-consistent framework to reconstruct sea level changes on basin and global scales, which are compared to the estimated sum of contributing processes.

“For the first time, it is shown that for most basins the reconstructed sea level trend and acceleration can be explained by the sum of contributors, as well as a large part of the decadal variability. The sparsely sampled South Atlantic Ocean forms an exception. The global-mean sea level reconstruction shows a trend of 1.5 ± 0.2 mm yr−1 over 1958–2014 (1σ), compared to 1.3 ± 0.1 mm yr−1 for the sum of contributors. Over the same period, the reconstruction shows a positive acceleration of 0.07 ± 0.02 mm yr−2, which is also in agreement with the sum of contributors, which shows an acceleration of 0.07 ± 0.01 mm yr−2. Since 1993, both reconstructed sea level and the sum of contributors show good agreement with altimetry estimates.”

See the slidedeck, especially #4 — showing the wide range among sea level reconstructions.

Update: (9)  “Climate-change–driven accelerated sea-level rise detected in the altimeter era” by R. Steven Nerem et al. in PNAS, in press. Abstract and Significance summary.

“Using a 25-y time series of precision satellite altimeter data from TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3, we estimate the climate-change–driven acceleration of global mean sea level over the last 25 y to be 0.084 ± 0.025 mm/y2. Coupled with the average climate-change–driven rate of sea level rise over these same 25 y of 2.9 mm/y, simple extrapolation of the quadratic implies global mean sea level could rise 65 ± 12 cm by 2100 compared with 2005, roughly in agreement with the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (AR5) model projections.”

“Satellite altimetry has shown that global mean sea level has been rising at a rate of ∼3 ± 0.4 mm/y since 1993. Using the altimeter record coupled with careful consideration of interannual and decadal variability as well as potential instrument errors, we show that this rate is accelerating at 0.084 ± 0.025 mm/y2, which agrees well with climate model projections. If sea level continues to change at this rate and acceleration, sea-level rise by 2100 (∼65 cm) will be more than double the amount if the rate was constant at 3 mm/y.”

Unpublished research.

Tollefson’s Nature article mentioned research presentations at the “Regional Sea Level Changes and Coastal Impacts” Conference in July 2017 (see the abstracts here). The eventual papers published from these might have a large impact on the public policy debate. Here are two.  First, the one by Nerem that Tollefson mentions.

(10)  “Sea Level Budget of the Altimetry Era Revisited” by Anny Cazenave el al.  Gavin Schmidt tweeted a graph (below) which I believe is from this presentation, similar to but apparently better documented than in previous papers associated with Cazanave (#2 and #7 above). This shows a slight acceleration during the past two decades, and a small acceleration since 2014 (to 0.14″/year). But the former might be natural variation and the latter might be a temporary effect from the 2014-2016 El Nino period. Click to enlarge the below graph.

“We revisit the global mean sea level (GMSL) budget during the whole altimetry era (1993 –  present) and show that using a large number of data sets to estimate the different components of the sea level equation improves the budget closure. Moreover, the budget approach allows to detect bias and drifts in the observations.

• Six different altimetry-based sea level data sets have been considered over the period January 1993-December 2015. They include the Climate Change Initiative (CCI) sea level products from the European Space Agency (ESA).
• The steric data include three data sets for January 1993-December 2004 and four Argo data sets afterwards.
• Three glaciers time series are considered. For the ice sheets, the IMBIE data set is used until December 2003 and the CCI ice sheet products afterwards. Both IMBIE and CCI products combine a large number of individual data sets.
• Changes in land water storage and atmospheric water vapour content are also accounted for.

“For each term of the sea level equation we use the mean of available data sets. The sum of components agree very well with the altimetry-based GMSL except at the beginning of the record (1993-1998). During the later period a single altimeter (Topex A) was operating. Moreover Topex A suffered significant instrumental drift. Previous studies attempted to estimate this drift by comparing with tide gauges and the experimental Poseidon altimeter data onboard the Topex/Poseidon mission.

“Here we use another approach and estimate the Topex A drift from the sum of components over January 1993-December 1998. Accounting for this correction leads to much improved agreement between observed sea level and sum of components. Using ensemble means for the GMSL and components rather than individual data sets leads to closure of the sea level budget.

“The trend of the residual time series is 0.0 +/- 0.2 mm/yr. The RMS is 2.4 mm/yr for the whole altimetry record. It decreases to 1.7 mm when the steric sea level is estimated with Argo (as of January 2005). We attribute the slightly larger RMS of the first decade to uncertainty of the steric component.

“For the whole altimetry period (January 1993-December 2015), the GMSL rate is now close to 3 mm/yr. However, significant GMSL rate difference is found between the 1st and 2nd decade of the altimetry era (2.7 mm/yr and 3.5 mm/yr respectively), suggesting sea level acceleration in the recent years.”

“We don’t even plan for the past.”
— Steven Mosher (member of Berkeley Earth; bio here), a comment posted at Climate Etc about our unpreparedness for the inevitable repeat of past weather.

For More Information

There is a serious problem with Earth’s seas: we’re killing them. See the ugly details here, and more here.

Please like us on Facebook and follow us on Twitter. For more information see The keys to understanding climate change, all posts about computer models, and especially these about rising seas…

• Good news: rising seas might not cover these Pacific islands.
• Assigning blame for the flooding of Pacific atolls.
• A massive melting problem in Antarctica!
• The New Yorker’s “The Siege of Miami” reveals a serious problem.
• Rising seas alert! Watch how science becomes a sensational news story.
• Focusing on worst case climate futures doesn’t work. It shouldn’t work.

To learn more about the state of climate change…

… see The Rightful Place of Science: Disasters and Climate Change by Roger Pielke Jr. (Prof of Environmental Studies at U of CO-Boulder). From the publisher…

“In recent years the media, politicians, and activists have popularized the notion that climate change has made disasters worse. But what does the science actually say? Roger Pielke, Jr. takes a close look at the work of the Intergovernmental Panel on Climate Change, the underlying scientific research, and the data to give you the latest science on disasters and climate change. What he finds may surprise you and raise questions about the role of science in political debates.”