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about Gavin Schmidt

Gavin Schmidt is a climate modeler, working for NASA and with Columbia University.

Why is future sea level rise still so uncertain?

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Three new papers in the last couple of weeks have each made separate claims about whether sea level rise from the loss of ice in West Antarctica is more or less than you might have thought last month and with more or less certainty. Each of these papers make good points, but anyone looking for coherent picture to emerge from all this work will be disappointed. To understand why, you need to know why sea level rise is such a hard problem in the first place, and appreciate how far we’ve come, but also how far we need to go.

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Nenana Ice Classic 2021

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And…. it’s that time again. The clock stopped on the Nenana ice classic this afternoon (April 30, 12:50pm AT). This is pretty much on trend and unsurprising given the relatively slightly cool winter in Alaska. The jackpot on offer this year was $233,591 but will likely be shared among several winners. This year’s ‘break up’ is a little odd, since the ice moved sufficiently to trigger the clock, but not enough to actually topple the tripod (which is still visible as this is being written (9pm ET) – Update 10:30pm ET: gone now though!). But, the rules are the rules…

Nenana Ice Classic break-up dates since 1917.

The trends in the break up date is about 8 days earlier per century (±4), estimated over the whole record, but substantially faster over the last 50 years (16 ± 12 days/century, 95% CI).

Other phenological records show similar trends, notably the longest cherry blossom record from Kyoto which dates back to 9th Century, and which had a record earliest peak bloom this year and a clear trend over the last few decades:

Kyoto Cherry Blossom trends (graph from Statista)

Feel free to link to your favorite such record in the comments…

Laschamps-ing at the bit

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A placeholder to provide some space to discuss the paper last week (Cooper et al, 2021) on the putative climate consequences of the Laschamps Geomagnetic Excursion, some 42,000 yrs ago.

There was some rather breathless reporting on this paper, but there were also a lot of sceptical voices – not of the main new result (a beautiful new 14C dataset from a remarkable kauri tree log found in New Zealand), but of the more speculative implications – both climatically and anthropologically.

On twitter there were some good threads covering multiple aspects of the paper (and the lead author):

https://twitter.com/tinyicybubbles/status/1362743531438227457?s=20

But let me make a couple of different points. We have occasionally discussed the Laschamps event here as a counter-example to the notion that changes in galactic cosmic rays have a major impact on climate. A reversal or near-reversal of the geomagnetic field would be expected to greatly increase the GCR getting to the lower atmosphere – in far greater amounts than over a solar cycle, or grand solar minimum (like the Maunder Minimum). So if people want to postulate a big role for GCR there, they needed to explain why there wasn’t a much bigger signal at 42kya too. These authors are thus not the only people to have looked for significant climate impacts at this time. They are perhaps the first to claim to have found them…

To be clear, the modeling that was done in this paper was good (if extreme) and suggested that the geomagnetic event combined with a severe grand solar minimum (much bigger than the Maunder minimum) would cause significant depletion of the ozone layer and some shifts in the annular modes. But the ozone depletion is less than we’ve seen due to anthropogenic ozone depletion since the 1980s, and the surface climate changes don’t seem very significant at all – especially compared to the massive variability exhibited in the ice cores throughout the last ice age (particularly in Marine Isotope Stage 3 – the Dansgaard-Oeschgar events). At best these are nuanced and subtle climate effects, and certainly not anything apocalyptic (despite Stephen Fry’s dulcet tones).

Finally, it should be called the Laschamps event (with a final, and etymologically correct, ‘s’) after the village in the Auvergne where it was first identified. There is unfortunately 50 years of legacy references to the “Laschamp” excursion, but hopefully it isn’t too late to fix!

References

  1. A. Cooper, C.S.M. Turney, J. Palmer, A. Hogg, M. McGlone, J. Wilmshurst, A.M. Lorrey, T.J. Heaton, J.M. Russell, K. McCracken, J.G. Anet, E. Rozanov, M. Friedel, I. Suter, T. Peter, R. Muscheler, F. Adolphi, A. Dosseto, J.T. Faith, P. Fenwick, C.J. Fogwill, K. Hughen, M. Lipson, J. Liu, N. Nowaczyk, E. Rainsley, C. Bronk Ramsey, P. Sebastianelli, Y. Souilmi, J. Stevenson, Z. Thomas, R. Tobler, and R. Zech, "A global environmental crisis 42,000 years ago", Science, vol. 371, pp. 811-818, 2021. http://dx.doi.org/10.1126/science.abb8677

Don’t climate bet against the house

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Decades ago (it seems) when perhaps it was still possible to have good faith disagreements about the attribution of current climate trends, James Annan wrote a post here summarizing the thinking and practice of Climate Betting. That led to spate of wagers on continued global warming (a summary of his bets through 2005 and attempts to set up others is here).

There were earlier bets, the most well known perhaps was the one for $100 between Hugh Ellsaesser and Jim Hansen in 1989 on whether there would be a new temperature record within three years. There was (1990), and Ellsaesser paid up in January 1991 (Kerr, 1991). But these more recent bets were more extensive.

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References

  1. R.A. Kerr, "Global Temperature Hits Record Again", Science, vol. 251, pp. 274-274, 1991. http://dx.doi.org/10.1126/science.251.4991.274

Update day 2021

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As is now traditional, every year around this time we update the model-observation comparison page with an additional annual observational point, and upgrade any observational products to their latest versions.

A couple of notable issues this year. HadCRUT has now been updated to version 5 which includes polar infilling, making the Cowtan and Way dataset (which was designed to address that issue in HadCRUT4) a little superfluous. Going forward it is unlikely to be maintained so, in a couple of figures, I have replaced it with the new HadCRUT5. The GISTEMP version is now v4.

For the comparison with the Hansen et al. (1988), we only had the projected output up to 2019 (taken from fig 3a in the original paper). However, it turns out that fuller results were archived at NCAR, and now they have been added to our data file (and yes, I realise this is ironic). This extends Scenario B to 2030 and Scenario A to 2060.

Nothing substantive has changed with respect to the satellite data products, so the only change is the addition of 2020 in the figures and trends.

So what do we see? The early Hansen models have done very well considering the uncertainty in total forcings (as we’ve discussed (Hausfather et al., 2019)). The CMIP3 models estimates of SAT forecast from ~2000 continue to be astoundingly on point. This must be due (in part) to luck since the spread in forcings and sensitivity in the GCMs is somewhat ad hoc (given that the CMIP simulations are ensembles of opportunity), but is nonetheless impressive.

CMIP3 (circa 2004) model hindcast and forecast estimates of SAT.

The forcings spread in CMIP5 was more constrained, but had some small systematic biases as we’ve discussed Schmidt et al., 2014. The systematic issue associated with the forcings and more general issue of the target diagnostic (whether we use SAT or a blended SST/SAT product from the models), give rise to small effects (roughly 0.1ºC and 0.05ºC respectively) but are independent and additive.

The discrepancies between the CMIP5 ensemble and the lower atmospheric MSU/AMSU products are still noticeable, but remember that we still do not have a ‘forcings-adjusted’ estimate of the CMIP5 simulations for TMT, though work with the CMIP6 models and forcings to address this is ongoing. Nonetheless, the observed TMT trends are very much on the low side of what the models projected, even while stratospheric and surface trends are much closer to the ensemble mean. There is still more to be done here. Stay tuned!

The results from CMIP6 (which are still being rolled out) are too recent to be usefully added to this assessment of forecasts right now, though some compilations have now appeared:

CMIP6 model SAT (observed forcings to 2014, SSP2-45 scenario subsequently) (Zeke Hausfather)

The issues in CMIP6 related to the excessive spread in climate sensitivity will need to be looked at in more detail moving forward. In my opinion ‘official’ projections will need to weight the models to screen out those ECS values outside of the constrained range. We’ll see if other’s agree when the IPCC report is released later this year.

Please let us know in the comments if you have suggestions for improvements to these figures/analyses, or suggestions for additions.

References

  1. Z. Hausfather, H.F. Drake, T. Abbott, and G.A. Schmidt, "Evaluating the Performance of Past Climate Model Projections", Geophysical Research Letters, vol. 47, 2020. http://dx.doi.org/10.1029/2019GL085378
  2. G.A. Schmidt, D.T. Shindell, and K. Tsigaridis, "Reconciling warming trends", Nature Geoscience, vol. 7, pp. 158-160, 2014. http://dx.doi.org/10.1038/ngeo2105

2020 Hindsight

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Yesterday was the day that NASA, NOAA, the Hadley Centre and Berkeley Earth delivered their final assessments for temperatures in Dec 2020, and thus their annual summaries. The headline results have received a fair bit of attention in the media (NYT, WaPo, BBC, The Guardian etc.) and the conclusion that 2020 was pretty much tied with 2016 for the warmest year in the instrumental record is robust.

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Flyer tipping

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You would be forgiven for not paying attention to the usual suspects of climate denial right now, but they are trying to keep busy anyway.

Last week (January 8), Roy Spencer [Update Jan 13: now deleted] posted a series of Climate Change “flyers” on his personal blog that purported to be organised by David Legates (NOAA, detailed to Office of Science and Technology Policy (OSTP), nominally on leave from (and soon to return to) U. Delaware). Each was a rather garishly colored rehash of standard climate denial talking points, but featuring the OSTP official logo, and claiming to be copyrighted by OSTP (a legal impossibility). Note that if this was an official US Govt. work, they could not copyright them, but if it wasn’t, they could not legally use the OSTP logo to indicate that it was.

Dubious use of an official government logo…

The reaction to this definitive refutation of mainstream science (ha!) was… silence. Spencer’s post was reblogged at WUWT but again, nothing happened [Update Jan 13: Also now deleted]. . Many of the authors of the pieces themselves – many of whom are active on social media – didn’t bother to tweet or post about them. Odd.

The whole thing seems to be Legates trying to get a pet project out into the world before the new administration comes in, but without bothering with all that messy peer-review, official permission, proper channels or, you know, actual science. Almost certainly this is also a violation of the Data Quality Act, something Patrick Michaels (one of the flyer authors) was quite exercised about in his effort. Consistency is also apparently optional.

Anyway, a couple of days ago (Jan 10), they were also posted on Willie Soon’s new website where they were noticed on twitter, and today there have been some media eyebrows raised.

Is there a there there?

The flyers themselves are remarkably thin on valid argumentation. Will Happer’s discussion of Radiative Transfer is mostly textbook stuff except for the last paragraph where he simply asserts that a radiative forcing of 3 W/m2 can’t possibly matter. That’s kind of the key issue, which he totally elides.

Christopher Essex purports to discuss climate models, without ever showing anything from a climate model. He seems to be arguing against some Aristotelian concept of climate models that never has to be bothered with actually looking at the real world (for instance). Weird, and totally pointless.

Spencer makes the remarkable assertion that climate has changed for natural reasons in the past (I’m shocked, shocked!), and ignores how attribution actually works (I’m not at all shocked).

The Connollys and Willie Soon’s flyer purports to talk about sun-climate connections, but they spend most of their effort talking about Milankovitch forcing before pivoting to imagining a universe where the temperatures have not in fact been steadily climbing but where they could conceivably have a higher correlation to out-of-date and unsupported reconstructions of solar activity. In so doing, they even have the chutzpah to cite a paper of mine. Meh.

Etc. If there is a demand in the comments, I could expand on the others, but for now, I think you get the idea.

Why should anyone care?

Great question! I don’t think anyone should. But this whole effort is emblematic of how far the climate question has moved. With a new US administration poised to act on climate across a whole series of fronts, this feeble throwback (were they released on a Thursday?), serves to underline how out-of-touch these old school deniers and their talking points really are. This is perhaps the last weak ‘hurrah’ of a bankrupt cause.

Good riddance to bad rubbish.

Update (4pm, Jan 12): that was quick:

Unforced Variations: Jan 2021

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According to the somewhat* arbitrary customs of our age, the 1st of January marks the beginning of a new year, a new decade and, by analogy, a new start in human affairs. So shall it be at RealClimate too**.

This month’s topics will no doubt include the summaries of the 2020 climate (due Jan 14th or so), ongoing efforts to understand and predict extreme weather in a climate context, and the shift by the weather organizations (WMO, NWS) to a new set of climate normals (i.e. moving from 1981-2010 to 1991-2020).

In the spirit of this new year, please make a renewed effort to stay vaguely on climate science topics, try to stay constructive even when you disagree, refrain from posting abuse, and don’t bother with cut-and-paste climate denial (that stuff was tedious enough when it was originally wrong, and is simply boring now). Thanks!

*completely

**Seriously, we are thinking about how to update/re-position this blog, and would welcome constructive suggestions from readers.

2020 vision

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A meeting of smoke and storms (NASA Earth Observatory)

No-one needs another litany of all the terrible things that happened this year, but there are three areas relevant to climate science that are worth thinking about:

  • What actually happened in climate/weather (and how they can be teased apart). There is a good summary on the BBC radio Discover program covering wildfires, heat waves, Arctic sea ice, the hurricane season, etc. featuring Mike Mann, Nerlie Abram, Sarah Perkins-Kilpatrick, Steve Vavrus and others. In particular, there were also some new analyses of hurricanes (their rapid intensification, slowing, greater precipitation levels etc.), as well as the expanding season for tropical storms that may have climate change components. Yale Climate Connections also has a good summary.
  • The accumulation of CMIP6 results. We discussed some aspects of these results extensively – notably the increased spread in Equilibrium Climate Sensitivity, but there is a lot more work to be done on analyzing the still-growing database that will dominate the discussion of climate projections for the next few years. Of particular note will be the need for more sophisticated analyses of these model simulations that take into account observational constraints on ECS and a wider range of future scenarios (beyond just the SSP marker scenarios that were used in CMIP). These issues will be key for the upcoming IPCC 6th Assessment Report and the next National Climate Assessment.
  • The intersection of climate and Covid-19.
    • The direct connections are clear – massive changes in emissions of aerosols, short-lived polluting gases (like NOx) and CO2 – mainly from reductions in transportation. Initial results demonstrated a clear connection between cleaner air and the pandemic-related restrictions and behavioural changes, but so far the impacts on temperature or other climate variables appear to be too small to detect (Freidlingstein et al, 2020). The impact on global CO2 emissions (LeQuere et al, 2020) has been large (about 10% globally) – but not enough to stop CO2 concentrations from continuing to rise (that would need a reduction of more like 70-80%). Since the impact from CO2 is cumulative this won’t make a big difference in future temperatures unless it is sustained through post-pandemic changes.
    • The metaphorical connections are also clear. The instant rise of corona virus-denialism, the propagation of fringe viewpoints from once notable scientists, petitions to undermine mainstream epidemiology, politicized science communications, and the difficulty in matching policy to science (even for politicians who want to just ‘follow the science’), all seem instantly recognizable from a climate change perspective. The notion that climate change was a uniquely wicked problem (because of it’s long term and global nature) has evaporated as quickly as John Ioannidis’ credibility.

I need to take time to note that there has been human toll of Covid-19 on climate science, ranging from the famous (John Houghton) to the families of people you never hear about in the press but whose work underpins the data collection, analysis and understanding we all rely on. This was/is a singular tragedy.

With the La Niña now peaking in the tropical Pacific, we can expect a slightly cooler year in 2021 and perhaps a different character of weather events, though the long-term trends will persist. My hope is that the cracks in the system that 2020 has revealed (across a swathe of issues) can serve as an motivation to improve resilience, equity and planning, across the board. That might well be the most important climate impact of all.

A happier new year to you all.

References

  1. P.M. Forster, H.I. Forster, M.J. Evans, M.J. Gidden, C.D. Jones, C.A. Keller, R.D. Lamboll, C.L. Quéré, J. Rogelj, D. Rosen, C. Schleussner, T.B. Richardson, C.J. Smith, and S.T. Turnock, "Current and future global climate impacts resulting from COVID-19", Nature Climate Change, vol. 10, pp. 913-919, 2020. http://dx.doi.org/10.1038/s41558-020-0883-0
  2. C. Le Quéré, R.B. Jackson, M.W. Jones, A.J.P. Smith, S. Abernethy, R.M. Andrew, A.J. De-Gol, D.R. Willis, Y. Shan, J.G. Canadell, P. Friedlingstein, F. Creutzig, and G.P. Peters, "Temporary reduction in daily global CO2 emissions during the COVID-19 forced confinement", Nature Climate Change, vol. 10, pp. 647-653, 2020. http://dx.doi.org/10.1038/s41558-020-0797-x

An ever more perfect dataset?

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Do you remember when global warming was small enough for people to care about the details of how climate scientists put together records of global temperature history? Seems like a long time ago…

Nonetheless, it’s worth a quick post to discuss the latest updates in HadCRUT (the data product put together by the UK’s Hadley Centre and the Climatic Research Unit at the University of East Anglia). They have recently released HadCRUT5 (Morice et al., 2020), which marks a big increase in the amount of source data used (similarly now to the upgrades from GHCN3 to GHCN4 used by NASA GISS and NOAA NCEI, and comparable to the data sources used by Berkeley Earth). Additionally, they have improved their analysis of the sea surface temperature anomalies (a perennial issue) which leads to an increase in the recent trends. Finally, they have started to produce an infilled data set which uses an extrapolation to fill in data-poor areas (like the Arctic – first analysed by us in 2008…) that were left blank in HadCRUT4 (so similar to GISTEMP, Berkeley Earth and the work by Cowtan and Way). Because the Arctic is warming faster than the global mean, the new procedure corrects a bias that existing in the previous global means (by about 0.16ºC in 2018 using a 1951-1980 baseline). Combined, the new changes give a result that is much closer to the other products:

Differences persist around 1940, or in earlier decades, mostly due to the treatment of ocean temperatures in HadSST4 vs. ERSST5.

In conclusion, this update further solidifies the robustness of the surface temperature record, though there are still questions to be addressed, and there remain mountains of old paper records to be digitized.

The implications of these updates for anything important (such as the climate sensitivity or the carbon budget) will however be minor because all sensible analyses would have been using a range of surface temperature products already.

With 2020 drawing to a close, the next annual update and intense comparison of all these records, including the various satellite-derived global products (UAH, RSS, AIRS) will occur in January. Hopefully, HadCRUT5 will be extended beyond 2018 by then.

In writing this post, I noticed that we had written up a detailed post on the last HadCRUT update (in 2012). Oddly enough the issues raised were more or less the same, and the most important conclusion remains true today:

First and foremost is the realisation that data synthesis is a continuous process. Single measurements are generally a one-time deal. Something is measured, and the measurement is recorded. However, comparing multiple measurements requires more work – were the measuring devices calibrated to the same standard? Were there biases in the devices? Did the result get recorded correctly? Over what time and space scales were the measurements representative? These questions are continually being revisited – as new data come in, as old data is digitized, as new issues are explored, and as old issues are reconsidered. Thus for any data synthesis – whether it is for the global mean temperature anomaly, ocean heat content or a paleo-reconstruction – revisions over time are both inevitable and necessary.

References

  1. , 2021. https://www.metoffice.gov.uk/hadobs/hadcrut5/HadCRUT5_accepted.pdf