## “Frequency-comb-based remote sensing of greenhouse gases over kilometer air paths”

G. B. Rieker, F. R. Giorgetta, W. C. Swann, J. Kofler, A. M. Zolot, L. C. Sinclair, E. Baumann, C. Cromer, G. Petron, C. Sweeney, P. P. Tans, I. Coddington, And N. R. Newbury, “Frequency-comb-based remote sensing of greenhouse gases over kilometer air paths”, Optica, 1(5), November 2014, 290-298, by the Optical Society of America, http://dx.doi.org/10.1364/OPTICA.1.000290, with supplemental information available at http://dx.doi.org/10.1364/optica.99.099999.s1.

Abstract

Increasing our understanding of regional greenhouse gas transport, sources, and sinks requires accurate, precise, continuous measurements of small gas enhancements over long ranges. We demonstrate a coherent dual frequency-comb spectroscopy technique capable of achieving these goals. Spectra are acquired spanning 5990 to 6260 $cm^{-1}$ (1600–1670 nm) covering ~700 absorption features from CO2, CH4, H2O, HDO, and 13CO2, across a 2 km path. The spectra have sub-1-kHz frequency accuracy, no instrument lineshape, and a 0.0033 $cm^{-1}$ point spacing. They are fit with different absorption models to yield dry-air mole fractions of greenhouse gases. These results are compared with a point sensor under well-mixed conditions to evaluate the accuracy of models critical to global satellite-based trace gas monitoring. Under heterogeneous conditions, time-resolved data demonstrate tracking of small variations in mole fractions, with a precision less than one ppm for CO2 and less than three ppb for CH4 in 5 min. Portable systems could enable regional monitoring.

Such techniques are bound to be less expensive than satellite-based monitoring. Such systems are essential to support the happy day when emitters of carbon dioxide are assessed fines for doing so, in proportion to their emissions, whether these emitters are power plants, landfills, highway systems, cities, or suburban tracts.

## Land and Ocean Temperatures for 2014 through 3Q2014

(Hat tip to Dan’s Wild Wild Science Journal on “Five things to know about 2014 global temperatures” which had a link to this image.)

## Brian Hayes on clear climate models for the curious public

American Scientst has a nice article by Brian Hayes recounting the basic physics of climate, and then recommending both public engagement with clear, simple climate models, at least by the curious and scientifically literate, and the development of models which can be thus understood. He goes on to offer a number of resources offering such models. This is great.

However, this is both hardly a new phenomenon, especially with Python, and it doesn’t relieve the curious student of climate from the public of knowing some of the physics contributing to these calculations. Toward that end I would recommend the course by Professor David Archer, accompanying textbook, video lectures, and computer codes, and my favorite textbook by Professor Ray Pierrehumbert (Principles of Planetary Climate), with data and Python code, allowing the student to not only understand details of these physics, but see them through a graded series of models and calculations.

dr. Geert Jan van Oldenborgh offers the KNMI Climate Explorer which has many series of climate data collected in one place.

NOAA also has a number of Web pages devoted to climate and weather data:

## “Anthropogenic influence upon the climate: past and future prospects” (Professor Myles Allen)

Summary of the IPCC 2013 assessment (“physical science basis”), and Professor Allen’s thoughts moving towards Paris in 2015. Long lecture, in 4 parts. Slides are here.

Abstract:

This lecture provides an overview of the climate change issue, highlighting what are, in my view, the most important findings of the latest IPCC report and their implications for climate negotiations under the United Nations Framework Convention on Climate Change (UNFCCC). We will focus on three numbers that matter a lot, and mention along the way some other numbers that matter rather less than you might think.

The first important number is 95%, the level of confidence the climate science community now has that human influence is the dominant cause of the warming observed over the past 60 years. I will explain where this number comes from, with a quick (and colourful) introduction to the methods used for “detection and attribution” in the IPCC Working Group I report, and explain why the apparent “pause” in ocean surface warming over the past decade or so doesn’t really change the big picture.

The second important number is 40.3 degrees C (105 degrees F), the national average temperature high over Australia on January 7th, 2013. While bad enough for Australia, the significance of that “Angry Summer” for the rest of the world is as an example of the kind of damaging weather event that, subsequent studies have shown, was made substantially more probable by human influence on climate. With the IPCC Working Group II finding that the impacts of climate change on human and natural systems are now evident on all continents and across the oceans, understanding the links between climate change and harmful weather events is becoming important for the UNFCCC’s new “Loss and Damage” agenda, and a key focus of Oxford’s climateprediction.net/weatherathome project.

The third number is the big one: one trillion tonnes. That is the total amount of fossil carbon that the IPCC estimates can be dumped into the atmosphere over the entire Anthropocene epoch while keeping the resulting warming to likely less than two degrees Celcius. Over half a trillion tonnes has already been emitted, and accounting for warming due to other forms of pollution cuts down the remaining “carbon budget” further still. This puts the mitigation challenge into perspective, and helps explain why the IPCC Working Group III report found such a pivotal role for carbon capture and storage in scenarios that have some chance of meeting the two degree goal.

What are the numbers that matter less than you might think? One of them, although much tweeted, is “97% of scientists agree…” I’ll explain how this kind of opinion poll isn’t really relevant to how science, or the IPCC, actually works. Another over-rated number is the Equilibrium Climate Sensitivity (the subject of earlier climateprediction.net experiments), which turns out to matter much less than people thought. Finally, if you are hoping for a purely scientific argument that two degrees is the threshold for dangerous anthropogenic interference in the climate system, you will be disappointed: the IPCC reports make it clear that the assessment of what is dangerous has an ethical and moral dimension and cannot be resolved by any purely technical assessment.

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