This month’s open thread.
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Thoughts on 2014 and ongoing temperature trends
Last Friday, NASA GISS and NOAA NCDC had a press conference and jointly announced the end-of-year analysis for the 2014 global surface temperature anomaly which, in both analyses, came out top. As you may have noticed, this got much more press attention than their joint announcement in 2013 (which wasn’t a record year).
In press briefings and interviews I contributed to, I mostly focused on two issues – that 2014 was indeed the warmest year in those records (though by a small amount), and the continuing long-term trends in temperature which, since they are predominantly driven by increases in greenhouse gases, are going to continue and hence produce (on a fairly regular basis) continuing record years. Response to these points has been mainly straightforward, which is good (if sometimes a little surprising), but there have been some interesting issues raised as well…
[Read more…] about Thoughts on 2014 and ongoing temperature trends
A new sea level curve
The “zoo” of global sea level curves calculated from tide gauge data has grown – tomorrow a new reconstruction of our US colleagues around Carling Hay from Harvard University will appear in Nature (Hay et al. 2015). That is a good opportunity for an overview over the available data curves. The differences are really in the details, the “big picture” of sea-level rise does not change. In all curves, the current rates of rise are the highest since records began.
The following graph shows the new sea level curve as compared to six known ones.
Fig 1 Sea level curves calculated by different research groups with various methods. The curves show the sea level relative to the satellite era (since 1992). Graph: Klaus Bittermann.
All curves show the well-known modern sea level rise, but the exact extent and time evolution of the rise differ somewhat. Up to about 1970, the new reconstruction of Hay et al. runs at the top of the existing uncertainty range. For the period from 1880 AD, however, it shows the same total increase as the current favorites by Church & White. Starting from 1900 AD it is about 25 mm less. This difference is at the margins of significance: the uncertainty ranges overlap. [Read more…] about A new sea level curve
References
- C.C. Hay, E. Morrow, R.E. Kopp, and J.X. Mitrovica, "Probabilistic reanalysis of twentieth-century sea-level rise", Nature, vol. 517, pp. 481-484, 2015. http://dx.doi.org/10.1038/nature14093
Diagnosing Causes of Sea Level Rise
Guest post by Sarah G. Purkey and Gregory C. Johnson,
University of Washington / NOAA
I solicited this post from colleagues at the University of Washington. I found their paper particularly interesting because it gets at the question of sea level rise from a combination of ocean altimetry and density (temperature + salinity) data. This kind of measurement and calculation has not really been possible — not at this level of detail — until quite recently. A key finding is that one can reconcile various different estimates of the contributions to observed sea level rise only if the significant warming of the deep ocean is accounted for. There was a good write-up in The Guardian back when the paper came out.– Eric Steig
Sea leave rise reveals a lot about our changing climate. A rise in the mean sea level can be caused by decreases in ocean density, mostly reflecting an increase in ocean temperature — this is steric sea level rise. It can also be caused by an increase in ocean mass, reflecting a gain of fresh water from land. A third, and smaller, contribution to mean sea level is from glacial isostatic adjustment. The contribution of glacial isostatic adjustment, while small, has a range of possible values and can be a significant source of uncertainty in sea level budgets. Over recent decades, very roughly half of the observed mean sea level rise is owing to changes in ocean density with the other half owing to the increased in ocean mass, mostly from melting glaciers and polar ice sheets. The exact proportion has been difficult to pin down with great certainty. [Read more…] about Diagnosing Causes of Sea Level Rise
References
- S.G. Purkey, G.C. Johnson, and D.P. Chambers, "Relative contributions of ocean mass and deep steric changes to sea level rise between 1993 and 2013", Journal of Geophysical Research: Oceans, vol. 119, pp. 7509-7522, 2014. http://dx.doi.org/10.1002/2014JC010180
Unforced Variations: Jan 2015
Absolute temperatures and relative anomalies
Most of the images showing the transient changes in global mean temperatures (GMT) over the 20th Century and projections out to the 21st C, show temperature anomalies. An anomaly is the change in temperature relative to a baseline which usually the pre-industrial period, or a more recent climatology (1951-1980, or 1980-1999 etc.). With very few exceptions the changes are almost never shown in terms of absolute temperatures. So why is that?
[Read more…] about Absolute temperatures and relative anomalies
Clarity on Antarctic sea ice.
I’ve always been a skeptic when it comes to Antarctic sea ice. I’m not referring here to the tiresome (and incorrect) claim that the expansion of sea ice around Antarctica somehow cancels out the dramatic losses of sea ice in the Arctic (NB: polar bears don’t really care if there is sea ice in Antarctica or not). Rather, I’m referring to the idea that the observation of Antarctic sea ice expansion represents a major conundrum in our understanding of the climate system, something one hears even from knowledgeable commentators. In this post, I’ll try to provide some clarity on this subject, with some basic background and discussion of a couple of important recent papers.
[Read more…] about Clarity on Antarctic sea ice.
AGU 2014
Once more unto the breach!
Fall AGU this year will be (as last year)
…the largest Earth Science conference on the planet, and is where you will get previews of new science results, get a sense of what other experts think about current topics, and indulge in the more social side of being a scientist.
Ten Years of RealClimate: Where now?
The landscape for science blogging, the public discourse on climate and our own roles in the scientific community have all changed radically over the last 10 years. Blogging is no longer something that stands apart from professional communications, the mainstream media or new online start-ups. The diversity of voices online has also increased widely: scientists blogging and interacting directly with the public via Twitter and Facebook are much more prevalent than in 2004. The conversations have also changed, and (for the most part) have become more nuanced. And a bunch of early career researchers with enthusiasm, time to spare and things to say, have morphed into institute directors and administrators with lots of new pressures. Obviously, blogging frequency has decreased in the last year or so in response to these pressures and this raises the question: where does RealClimate go now?
Ten Years of RealClimate
In the spring of 2004, when we (individually) first started talking to people about starting a blog on climate science, almost everyone thought it was a great idea, but very few thought it was something they should get involved in. Today, scientists communicating on social media is far more commonplace. On the occasion of our 10 year anniversary today it is worth reflecting on the impact of those changes, what we’ve learned and where we go next.