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Fall AGU 2017

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It’s that time of year again. #AGU17 is from Dec 11 to Dec 16 in New Orleans (the traditional venue in San Francisco is undergoing renovations).

As in previous years, there will be extensive live streams from “AGU On Demand” (free, but an online registration is required) of interesting sessions and the keynote lectures from prize-winners and awardees.

Some potential highlights will be Dan Rather, Baba Brinkman, and Joanna Morgan. The E-lightning sessions are already filled with posters covering many aspects of AGU science. Clara Deser, Bjorn Stevens, David Neelin, Linda Mearns and Thomas Stocker are giving some the key climate-related named lectures. The Tyndall Lecture by Jim Fleming might also be of interest.

As usual there are plenty of sessions devoted to public affairs and science communication, including one focused on the use of humour in #scicomm (on Friday at 4pm to encourage people to stay to the end I imagine), and a workshop on Tuesday (joint with the ACLU and CSLDF) on legal issues for scientist activists and advocates.

AGU is also a great place to apply for jobs, get free legal advice, mingle, and network.

A couple of us will be there – and we might find time to post on anything interesting we see. If any readers spot us, say hi!

O Say Can You CO2…

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Guest Commentary by Scott Denning

The Orbiting Carbon Observatory (OCO-2) was launched in 2014 to make fine-scale measurements of the total column concentration of CO2 in the atmosphere. As luck would have it, the initial couple of years of data from OCO-2 documented a period with the fastest rate of CO2 increase ever measured, more than 3 ppm per year (Jacobson et al, 2016;Wang et al, 2017) during a huge El Niño event that also saw global temperatures spike to record levels.

As part of a series of OCO-2 papers being published this week, a new Science paper by Junjie Liu and colleagues used NASA’s comprehensive Carbon Monitoring System to analyze millions of measurements from OCO-2 and other satellites to map the impact of the 2015-16 El Niño on sources and sinks of CO2, providing insight into the mechanisms controlling carbon-climate feedback.

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References

  1. J. Wang, N. Zeng, M. Wang, F. Jiang, H. Wang, and Z. Jiang, "Contrasting terrestrial carbon cycle responses to the two strongest El Niño events: 1997–98 and 2015–16 El Niños", 2017. http://dx.doi.org/10.5194/esd-2017-46
  2. J. Liu, K.W. Bowman, D.S. Schimel, N.C. Parazoo, Z. Jiang, M. Lee, A.A. Bloom, D. Wunch, C. Frankenberg, Y. Sun, C.W. O’Dell, K.R. Gurney, D. Menemenlis, M. Gierach, D. Crisp, and A. Eldering, "Contrasting carbon cycle responses of the tropical continents to the 2015–2016 El Niño", Science, vol. 358, 2017. http://dx.doi.org/10.1126/science.aam5690

1.5ºC: Geophysically impossible or not?

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Guest commentary by Ben Sanderson

Millar et al’s recent paper in Nature Geoscience has provoked a lot of lively discussion, with the authors of the original paper releasing a statement to clarify that their paper did not suggest that “action to reduce greenhouse gas emissions is no longer urgent“, rather that 1.5ºC (above the pre-industrial) is not “geophysically impossible”.

The range of post-2014 allowable emissions for a 66% chance of not passing 1.5ºC in Millar et al of 200-240GtC implies that the planet would exceed the threshold after 2030 at current emissions levels, compared with the AR5 analysis which would imply most likely exceedance before 2020. Assuming the Millar numbers are correct changes 1.5ºC from fantasy to merely very difficult.

But is this statement overconfident? Last week’s post on Realclimate raised a couple of issues which imply that both the choice of observational dataset and the chosen pre-industrial baseline period can influence the conclusion of how much warming the Earth has experienced to date. Here, I consider three aspects of the analysis – and assess how they influence the conclusions of the study.
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Sensible Questions on Climate Sensitivity

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Guest Commentary by Cristian Proistosescu, Peter Huybers and Kyle Armour

tl;dr 

Two recent papers help bridge a seeming gap between estimates of climate sensitivity from models and from observations of the global energy budget. Recognizing that equilibrium climate sensitivity cannot be directly observed because Earth’s energy balance is a long way from equilibrium, the studies instead focus on what can be inferred about climate sensitivity from historical trends. Calculating a climate sensitivity from the simulations that is directly comparable with that observed shows both are consistent. Crucial questions remain, however, regarding how climate sensitivity will evolve in the future.

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