Climate Change

The IPCC AR4 report has concluded that atmospheric carbon dioxide has reached levels that are higher than anytime during the past 650,000 years. That was a recent update to the literature just several years ago which only went back 420,000 years. These results are supported by ice cores from Antarctica which trap bubbles of ancient atmosphere and allow for confident reconstructions of ancient climates. In the latest issue of Nature, members of the European Project for Ice Coring in Antarctica (EPICA) present the latest, and longest, record from ice cores which extend to 800,000 years. The glacial-interglacial, carbon dioxide, and methane cyclicity remain similar to the previous reconstructions, and the correlation of greenhouse gases to temperature also remains very firm. The latest graph on this is below, from Lüthi et al 2008 (click for enlarged image).

_{Roman numbers and Italic numbers represent glacial terminations and Marine Isotopic Stages}

Of interest here, is the unusually low levels of carbon dioxide during the two earliest glacial–interglacial cycles. The authors seem confident that they have the CO2 levels right, which extends the pre-industrial CO2 range from about 172–300 ppmv. There could be a long-term CO2 increase by about 25 ppmv from 800 to 400 kya BP, and a long-term decrease of 15 ppmv during the past four glacial cycles, which the authors suggest may be indicative of long-term variations in the carbon cycle on orders of hundreds of thousands of years. CO2 may have reached an absolute minima at 667 BP, though there is slight discrepancy between CO2 concentration measured at University of Bern (172 ppmv) and Grenoble (178 ppmv).

In the recent literature, as well as in the supplementary information in this paper, the infamous “CO2 lag” may be overestimated by some hundreds of years, so the 800 year lag at Termination V may be something like 300 years. In interesting case is during MIS 14.2 (~550 kyr BP), CO2 preceded temperature by about by a little over 1,000 years. Like many other of the ice core record papers which are blown out of context, the authors emphasize the role of CO2 as a positive feedback on temperatures supporting its greenhouse role.

Meanwhile, methane (See Loulergue et al) has fluctuated between around 350 and 800 parts per billion by volume (ppbv) over glacial-interglacial cycles, but over 1,770 ppbv during present day. Interestingly, methane seemed to follow the eccentricity signal more during the earlier cycles, but the methane levels appear more precession-paced since ~400 kya, which is likely due to changes in wetlands, monsoon systems, and ITCZ.

In other news, and going far away from the ice core record to the Paleocene-Eocene boundary around 55 million years ago, δ¹⁸O records show an abrupt spike when temperatures soared by 8° to 10°C in high-latitude sea surface temperatures, and 4° to 5°C in bottom water temperatures and tropical SST’s (Zachos et al., 2003). A major negative carbon-13 isotope bump also shows up in proxy records, signifying a massive release of isotopically light carbon, which gives clues to the cause of the dramatic temperature anomaly. Possible sources could have been from methane (decomposition of clathrates on the sea floor), CO2 outgassing from volcanoes, among other things. The mass extinction of benthic species at the time was probably a combination of thermal stress and ocean acidfication. In this latest paper by Panchuk, Ridwell, and Kump, the authors suggest that methane alone could not have caused the calcium carbonate dissolution in the oceans estimated from sediment layers, so a large external forcing from CO2 (perhaps a carbon pulse of ~6800 gigatons) helped out. This would enhance the greenhouse effect significantly, but a lot of that carbon would be removed by the oceans within a thousand years reducing the effect, but data suggests that the PETM lasted perhaps 200,000 years. A very large impulse of carbon would have been needed to sustain the warming over millennial timescales given that ~80% of it would be removed by the oceans in around 1,000 years.

Interesting week. Not too much to be excited about though as we keep burning fossil fuels, and nothing new for policy makers to hear.

So it appears that Florida has now decided to actually teach science in their science classrooms. After a February 19th vote, the United States science curriculum made the improvement from worse to bad, now allowing the young padawans to learn evolution in class. The infamous motto of “Teach the controversy” (like gravity and cell theory) won 4-3, but of course with the scientific caveat that “it’s just a theory.”; my guess is that lecture begins right after discussing “hypothesis,” “theory,” “law” definitions in chapter 1. Now, reading this new Nature article, it looks like the Institute for Creation Research wants to grant online master’s degrees in science education in Texas. But I loved the next line, which reads, “The ICR accepts the Bible as literal truth on all topics. According to its website, the palaeoclimatology class covers “climates before and after the Genesis Flood”". Maybe someone like Paul Reiter can moan about the IPCC not covering creation paleoclimates in the report…too bias I suppose.

Chris Colose even finds a book here. There you go, now we don’t need to hear about “CO2 lagging temperature” anymore. From our interpretation of the “young ice cores” the CO2 levels and temperatures fluctuated significantly over just a few thousand years…we’ve even gone through several ice ages since the global flood. Aside from the obvious climate pitfalls of a young ice sheet hypothesis, the other argument reads like “there were WW2 planes found deep in the ice sheet” so it must be a young ice sheet, but this discounts the fundamental fact that glaciers flow and so ice at the bottom is much more compacted than ice at the top. This means one meter of ice core at the bottom represents a much longer amount of time than one meter of core near the top.

So what about that global flood?

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Much noise has been made over the internets about “sea ice recovery” this year, along with a list of other noisy distractions, like “Global Warming stopped in January 2008″ (after it stopped in 1998).  But does that mean it has recovered? Most definitely not.  The ice covering the Arctic Ocean is much younger and thinner than normal, and 2008 might in fact be a new record low.  The previous record low was 2007 which beat out 2005 (lucky #2) by the size of California and Texas combined. 

The colors are ice age, with green and purple being older ice, 5 and 6 years old. The older ice is rapidly being lost.

Meanwhile, Colorado researchers say there is a 3 in 5 chance that 2008 will have a new record low. Mr. Atmoz also has a post on this.

It is my non-quantified opinion that we’ve hit one of the first “tipping points” as far as global warming is concerned, or at least we will over the next few years– a commitment to seasonal loss of arctic sea ice regardless of what we do to CO2 emissions. We’ll be able to see by autumn if summer ice hit a new low, so stay tuned.

This was an interesting article.

Whether or not the oceans are net sources or sinks of CO2 is very important, since right now, atmospheric CO₂ increases at only about one half the rate of human-induced CO₂ emissions, because quite a bit is taken up by the oceans. The study back in 2007 by Le Quere et al on the decline of the Southern Ocean as a sink still looks like it is holding.

The planetary albedo (the percentage of the incoming solar radiation that is reflected back to space) plays a large role in the Earth’s radiative balance. The planet currently reflects about 30% of the incoming radiation back to space (clouds, particles in the atmosphere, ice sheets). If the albedo of the planet were 0 (all of it were absorbed) the planet would be over 20 degrees C hotter.

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The March 2008 temperature data is available now.  While some sources like Anthony Watts blog made a big deal out of anomalous January 2008 cooling (largely due to La Nina), and a DailyTech article went as far as to say that January 2008 cooling “cancelled out” a century of global warming. March 2008 recovered, but also jumped much higher than expected.

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Aside from the total solar irradiance changes, changes in cosmic rays might be the next skeptic alternative to increases in greenhouse gases and other anthropogenic activities as the cause of modern global warming. It is an idea being investiaged a lot, though some like Henrik Svensmark and Nir Shaviv are very confident that they have overturned the CO2 paradigm and found a link between cosmic rays and low level cloud cover.

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Modern climate science tells us that increased emissions of greenhouse gases, most notably carbon dioxide, will change the climate that we are used to and have consequences for ecosystems and societies worldwide. A rise of just several degrees can have large and widespread impacts that dramatically alter civilization, but there are worries aside from a slow and steady rise. Climatic records show that large, widespread, and abrupt climate changes have occurred repeatedly in the past. Dr. Richard Alley of Penn State University has lectured on this topic and has used an analogy of the climate being like a drunken college student– when you don’t do much to it then it will just sit there, but if you move it around a little bit then it will stagger about and maybe fall. The last ten thousand years or so (the Holocene) has been an unusual time of relative calmness, with little variation in the climate. However, for most of the last 100,000 years, and even before, this has not been the case. One of the potential threats that comes from altering the chemistry of the atmosphere, and changing the land around to suit or needs, is the ability to flip a “climate switch” and force it between different states. Other possibilities include crossing critical thresholds, such as melting the arctic sea ice, that will have large socio-economic and/or ecological consequences. Such events have been labeled “tipping points” and many scientists (notably James Hansen of NASA, Alley, and others) have started to issue many warmings that the Earth may not respond to a new climate is a nice and steady fashion.

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So Chris Colose says a few week ago that University of Albany’s professor and senior researcher Dr. Chris Walcek is to give a talk on global warming entitled “More Inconvenient and Convenient Aspects of Global Warming.” All went well, no one threw anything at Chris Walcek, although one irate chap did stand up in the Q&A and yell about the disservice he gave to the audience. That guy was a little strange, but what about Chris Walcek’s presentation??

I want to give justice to his points, so I can open up discussion to everyone. I also want to just bring up a lot of science so that even people who did not attend can discuss freely. According to Dr. Walcek, the “AGW consensus” vs. “skeptic” summary can be said as follows:

On Warming

Consensus– Yes it is

Skeptics– Yes, but trends very small compared to natural fluctuations

Causation

Consensus– Mostly anthropogenic (human-induced) factors in recent times

Skeptics– Possibly some anthropogenic, more solar variation, very low confidence for attribution

Is it bad ?

Consensus– Is bad

Skeptics– Maybe some bad, maybe some good

Can we slow it down?

Consensus– Can slow

Skeptics– Can’t stop global warming in any significant way

Additional points raised by Chris Walcek include– Sea level variability is not significant, cooling and ice accumulation in Antarctica interior, CO2 lagged (not led) temperature over the glacial-interglacial cycles, solar correlation to temperature is high over the 20th century, globe is warming but not outside the range of natural variation and within our understanding of the climate system, models not yet sufficient.

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In the preceding post, on the greenhouse effect, I investigated the role of the greenhouse effect and its play in radiative balance, and how the presence of an atmosphere acts to raise planetary temperatures. The take home points should be that for a planet with no infrared absorbing layer above the surface, the fourth power of the surface temperature always approximates a value determined by the incoming solar radiation. The only way the surface temperatures can exceed this value is if there is an atmosphere which acts to be a blanket to outgoing radiation. A planet can also be heated by internal processes such as radioactive decay or rigorous convections from the mantle, but these are rather negligible on the terrestrial planets. Adding greenhouse gases to an atmosphere whose temperature decreases with height must act to warm the surface by making the net downward emission greater than zero. In this post, I will elaborate on specific greenhouse gases, the runaway greenhouse effect, and an antigreenhouse effect.

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