Every once in a while it is worth reviewing the basic physics behind the greenhouse effect and global warming. Sometimes all the debate about global warming in the media loses focus of the fact that the world really is governed by the laws of physics. Unfortunately, many internet explanations get dumbed down to the point of having an atmosphere that serves as a single “slab” between the ground and space, and has a bunch of colorful arrows coming out of it and bouncing off it, etc. This is a useless explanation, and gives no justice to understanding what is happening. Two encounters in the outside world recently prompted me to do another post just to have a reference handy, and I’m using this to replace an older post which I entitled “just a few more molecules.” There’s also been an interesting episode with Dr. Andy Lacis from NASA GISS over at Dot Earth which I’d like to elaborate on.
I thought that this article was interesting, discussing this recent paper in the Journal of Agricultural and Food chemistry. The analysis revealed that the relative amount of carbon-13 in maple syrup have gone down since the 1970s, which they attribute to changing isotopic signatures from fossil fuel burning in the atmosphere. Discussion and implications for the food industry in the article.
The webcast for Dr. Alley’s presentation is now up, so I recommend watching the video. It is concerning the role of CO2 on climate over geologic time.
As my own side note, Alley is one of my favorite scientists…he’s pretty much “the guy” when it comes to ice core work and has done a lot with paleoclimate (over the ice core record especially), abrupt climate change, glaciology, and sea level rise. He’s a very interesting character who always puts things in a nice perspective, and often humorous ways of teaching (e.g., his Johnny Cash geology lesson).
Professor Galen McKinley at the University of Wisconsin-Madison has recently put up a web page which discusses the global carbon cycle and its connection to climate change. Within, is an applet in which the user can play around with various inputs of carbon sources and sinks, and see how this determines future CO2 concentration and global mean temperature. It might be worth playing around with for a while to see how various future scenarios might look.
Recently, the world celebrated an International Day of Climate Action, called “350”, which is based on lifting public awareness on the need for an international climate treaty to reach a 350 parts per million CO2 level as a target threshold. I didn’t really join in on the fun or follow it in any detail, but from what I understand it was a pretty big deal, and I hope that they had some success in raising awareness.
I haven’t been able to post much lately, so I just want to put in this post which outlines some of the basic radiative forcing and feedback physics which climatologists use to assess climate change. This is fairly standard material which should be understood by anyone with a deep interest in climate. This article is a bit lengthy so hopefully you have the patience to go through it (or put it on your favorites and come back). Also, a lot of discussion has come up recently over Richard Lindzen’s ERBE analysis in which he purports to show that global climate sensitivity is small, and that the net effect of climate feedbacks is to dampen the so-called Planck response. That basically provoked this post. I’m going to define all these terms below, so don’t worry if I’ve already lost you, and while I am going to do some math in this post, it should be accessible to most people who know a bit of algebra. Skipping over a few calculus steps won’t be detrimental and I’ve tried not to assume much climate background (although I do link to some side references for clarification on some matters). My focus is not on Lindzen’s analysis here, which I don’t feel to be robust at all, but rather building up simple mathematical models for understanding climate change. This will not be new to anyone who has followed the climate literature or discussions for some time, but hopefully it can be helpful to some, or at the very least, serve as a useful reference.
Yesterday, I had the opportunity to attend a colloquium seminar where Zhengyu Liu of University of Wisconsin-Madison gave a presentation on a couple of topics. One was on his recent paper which I discussed not too long ago concerning transient simulations of the the deglacial climate evolution. He also discussed the stability issues of the Thermohaline circulation and how intermediate models of AMOC tend to exhibit hysteresis behavior while fully-coupled AOGCM’s do not. I won’t touch on that but I’ll touch briefly on a few key points concerning the time period of roughly LGM to Bolling Allerod and some background. The regional and global-scale responses of atmospheric warming and their causes are explained better in my first post which is linked above. I also discuss the time period of LGM-BA in a bit more detail in case readers are unfamiliar with these events.:
Hopefully people interested in the blog wars have been alerted to the ongoing climate change “debate” between George Monbiot and Ian Plimer. If not, the best place to start is probably Monbiot’s blog itself (with several posts on the topic already). Greenfrye and Tamino also have some ongoing commentary, so have fun catching up on what’s going on.
Unfortunately, round 1 consisted of Plimer dodging Monbiot’s questions which ask Plimer to defend certain indefensible statements in his book “Heaven and Earth.” Maybe Plimer just “wanted to go first” so I’ll give him the benefit of the doubt, but his own set of questions intended for Monbiot are quite revealing about his intentions.
One of the most interesting parts of the paleoclimate record over the last 100,000 years, is the series of abrupt climate changes prior to the Holocene that have occurred on very rapid timescales, ranging from years to decades (Alley et al, 2003). These changes were large, fast, and occurred when the climate was pushed across certain thresholds.
Of particular note, is the well over 20 Dansgaard-Oeschger events since the last interglacial. Typically, a rapid warming on timescales of decades was followed by slower cooling, rapid cooling, and then a brief period of little temperature change. A value near 1500 years between these events is common, although sometimes there are skips and so the spacing could be a scalar multiple of near 1500 years. Successive D-O oscillations become progressively cooler as the cold-based ice sheet grows in Hudson Bay, and when the base of the ice thaws, you get a Heinrich event surge that dumps large number of icebergs that calved from the Laurentide ice sheet into the North Atlantic, via the Hudson Straight (or perhaps other sources such as the Icelandic and British Isles ice sheet). This succession of progressively cooler D-O events, punctuated by a Heinrich event (until the next cycle begins or the climate becomes too warm for an ice sheet to grow) is a Bond cycle. These events are common before the Holocene which led to a climate punctuated by high-frequency variations and a much more variable situation than that which humans have enjoyed over the past 10,000 years.