Scientific Data on Sea Level Rise
by Daniel Bailey
(Michigan, United States)
Greenland Mass Loss
When calculating sea level rise, we need to take many different factors into account. Hence, we cannot just look at the melting of glaciers.
What about the ice sheets themselves?
We have to examine the Greenland Ice Sheet (GIS), the West Antarctic Ice Sheet (WAIS) and the East Antarctic Ice Sheet (EAIS).
Greenland Ice Sheet
Looking at the GIS, we find the sheet to be losing mass, with the rate of loss itself increasing (30 Gigatonnes/yr2), In fact, from 2002 to 2010, the rate of mass loss from the GIS doubled (Velicogna 2009 updated with further GRACE data through July 2011).
Additionally, Tedesco and Fettweiss (2011) show that the mass-loss experienced in southern Greenland in 2010 was the greatest in the past 20 years.
West Antarctic Ice Sheet
Looking at the bottom of the world, we find the WAIS losing mass at accelerating rates, partially offset by mass gains in some parts of the EAIS (King et al 2012). The maps suggests growth of parts of coastal East Antarctica, little change in the interior and ice mass loss in West Antarctica.
Explanation for Ice Gain
However, a study published in Nature shows that a lot of the ice gain due to increased snowfall is countered by an acceleration of ice-flow to the ocean (Winkelmann et al 2012). Thus Antarctica’s contribution to global sea-level rise is probably greater than hitherto estimated (snow piling up exerts pressure on the ice, thus it flows faster to the coast).
Arctic Sea Ice
Which leaves the ongoing death spiral of the Arctic sea ice. Per Kaufman et al 2009, Arctic temperatures have reversed a 2,000 year long cooling trend and are now the warmest they have been in over 2,000 years. Correspondingly, sea ice extent is the smallest it has been in over 1,400 years.
Can it be Natural Causes?
Vinnikov et al 1999 examined the chances of this decline in the sea ice being due to natural causes and found the probabilities of well under 0.1% of being due solely to natural variability.
Day et al 2012 found that between 5% and 30% of the Arctic sea ice decline from 1979 to 2010 could be attributed to the natural cycles of the Atlantic Multidecadal Oscillation (AMO) and Arctic Oscillation (AO), and even less can be attributed to natural cycles since 1953, since these natural cycles tend to average out over longer timeframes (as Vinnikov also found).
More Likely Manmade
Despite increased observational uncertainty in the pre-satellite era, the trend in [Arctic sea ice extent] over this longer period [1953–2010] is more likely to be representative of the anthropogenically forced component.
Per Notz and Marotzke (2012):
The available observations are sufficient to virtually exclude internal variability and self-acceleration as an explanation for the observed long-term trend, clustering, and magnitude of recent sea-ice minima. Instead, the recent retreat is well described by the superposition of an externally forced linear trend and internal variability. For the externally forced trend, we find a physically plausible strong correlation only with increasing atmospheric CO2 concentration.
Our results hence show that the observed evolution of Arctic sea-ice extent is consistent with the claim that virtually certainly the impact of an anthropogenic climate change is observable in Arctic sea ice already today.
Per Halfar et al 2013:
The algae show that, while fast short-term changes have occurred in the past, the 20th century exhibited the lowest sea-ice cover in the past 646 years.
The past 150 y instead have been characterized by sea ice exhibiting multidecadal variability with a long-term decline distinctly steeper than at any time since the 14th century.
Arctic Sea Ice Volume
As for the most relevant metric of Arctic sea ice health, none is more important than volume. And it is here that the death spiral is most evident.
So unlike those who claim that the glaciers and the Arctic are just fine, but who actually are unmasked as prevaricators and dissemblers, the cold parts of our world (the cryosphere) are very loudly telling us that things are very much NOT OK.
And that the demise of our cryosphere, with attendant increasing impacts on sea levels, are proceeding apace and in unrelenting fashion.
Finally, we need to look at glacial mass balance as well.