Both shoes drop
Almost two years ago, the worthies at MIT tried to hire a rising star, Alla Karpova, only to have their house Noble Prize winner, Susemu Tonegawa, break out in a fit of I got mine and you ain't gonna get any of it, chasing the waif away to a life of penury on Janella Farms where she gets to spend a bunch of Howard Hughes' dollars. MIT appointed a bery bery important committee to investigate and they were not pleased with Tonegawa.
Tonegawa resigned as director of his pet institute in November 2006, and late last month revealed plans to return to Japan as director of the RIKEN brain science institute. For now, he retains his lab at MIT.
Tuesday, April 29, 2008
Both shoes drop
Thursday, April 24, 2008
Eli is stealing this from Daniel Davies. I start off by linking to something moronic. In this case it is Phil Chapman's claiming that an ice age is upon us because there was a large drop in global temperature between Jan 2007 and 2008. Deltoid is having fun with it.
Anyone can play by linking to something else that is dumber. Your link has to "follow suit" by being either on the same topic or author, so you would have to find something by Chapman or about a decrease in global temperature. You also have to "bid up", your's has to be dumber than mine, which may be hard as Chapman is pretty dumb, but it's a big internet out there. As d-squared says
The game is open to all and is scored in "King of the Hill" style; at any point, the poster of the last valid card is "King of the Hill". The winner is the person who is king of the hill at the point when we all get bored and stop playing.
Posted by EliRabett at 11:16 PM
Eli was teaching electrochemistry today. One of the hard things to do is to do is to show the bunnies that this is something they should care about, so I told them to count how many battery operated things they were carrying around with them. Eli got to five . .
- Cell phone
- Car opener
- Laser pointer
Posted by EliRabett at 11:08 PM
Lights, camera, emissions . . . . .
It had come to Eli's attention that some folk were finding fault with the IPCC Emission Scenarios. While everyone was arguing about the alphabet soup used in the IPCC Fourth Assessment Report, in September 2007, the IPCC convened a meeting of experts to draw up new scenarios for the fifth assessment report. The approach will be quite different. First there will be near (2035) and further (2100) and way out there (2300) term scenarios.
Major motivations for the near-term scenarios are understanding the effect of emissions on air quality, providing information on trends and extreme events, and providing high-resolution output for the Impacts, Adaptation and Vulnerability community. Near-term adaptation and mitigation analyses can be matched to conventional planning time scales, can explore opportunities and constraints given institutional and technological inertia, and can play an important role in integrating climate change considerations into other areas of management and policy. Key issues on this time scale include identifying immediate risks; developing corresponding adaptive capacity; reducing vulnerability; making efficient investments to cope with climate change; and implementing investments in low emission technologies, energy conservation, and sink preservation and/or enhancement.Models (both physical and economic and ecological) can be run at higher resolution for the near term and provide the finer grained information that policy makers need. On the other hand
The longer term policy focus shifts towards evaluating climate targets to avoid risks from climate change impacts, improving the understanding of risks of major geophysical and biogeochemical change and feedback effects, and adopting strategies for adaptation, mitigation, and development that are robust over the long term to remaining uncertainties.Unlike the previous scenarios, the new ones will be based on four representative concentration pathways (RCPs). One will be as disaster, where the radiative forcing reaches >8.5 W/m2 by 2100 (1370 ppm CO2 equivalent) and continues increase. There will be two intermediate “stabilization pathways” with radiative forcing stabilized at 6 W/m^2 (850 ppm CO2) or 4.5 W/m^2 (650 ppm CO2) after 2100; and the Goldilocks pathway with radiative forcing peaked at 3 W/m2 (490 ppm CO2) before 2100 and declining. The scenarios will include the effects of all known forcings
The RCPs will be used to run GCMs to calculate the effects of the forcings as well as social and economic models. All of the models will be run in parallel to speed up development of the scenarios. Let the carping begin.
Posted by EliRabett at 9:59 PM
Monday, April 21, 2008
In the trenches
Over at Deltoid, a commentator going by the handle of Schneb posts from the secondary school trenches about teaching current affairs (it's pretty long, but you need the entire comment to see the issues that are raised and that Rabett Run wants to consider)
I teach a current events-type course to 12th graders. We spent quite a bit of time on Global Warming. There were two bright, very nice, responsible young people who kept to themselves in the class--I can't blame them, the rest of the class, as 2nd semester seniors tend to be, were NOT the most focused, thoughtful people.
But as time went by, I realized the two 'nice' students were not just different in behavior, but in outlook: to them, Global Warming is an invented scheme, and/or hysterical over-reaction. And like the young blogger profiled on NPR, they have news stories about various carbon reading techniques, or the growth of the polar bear population, etc. to back themselves up. They see the mass of scientists who agree that GW is real and caused by human behavior as self-serving careerists who somehow profit from adopting/promoting the GW party line.
This is as good a statement of the problem as Eli has ever seen, but it is also clear that there is not one problem but several.
But the two that I'm talking about really are nice people--so they don't do a Penn & Teller 'Bull&$#@'-type proclamation of their views. In fact, it wasn't clear that they were hardline in their views 'til we were most of the way through the unit (maybe they kept a low profile initially because, while they're sure they're right, they're used to the rest of the world seeing things otherwise and mocking or dismissing them?--just a guess). When I finally realized their 'take' on GW, I wanted to engage them and bring them around to what I see as the only legitimate view [GW is real/human-caused]--but a flat-out dissing of their view would only have put me on their long list of 'sheep who follow the self-serving GW deceivers'. So I tried a couple of ways to indirectly explore the issue so they'd see the error of their ways. They never said, 'gosh, maybe it IS real!'--more the opposite, actually--so I can't say that I had any success, but I hope they'll eventually come around and that I started opening their minds a bit.
I mention this because the problem isn't that a GW-denying teen-blogger was profiled on NPR. It's what she stands for (and that's what I saw the NPR piece as being about). There's a sub-culture of anti-GW folks out there. And like the blogger, they can sound knowledgeable. As all here seem to agree, this is the problem.
And as you all have noted, others, who see GW as real, don't always sound knowledgeable. As I remember the NPR story, the blogger's friend sees GW as real, but couldn't say why. Sit that friend in a room with 2-3 of the GW deniers, who bombard her with legitimate-sounding criticism of GW and there'll be 3-4 deniers in the room (instead of 2-3).
But it's not just that the deniers have somehow fallen prey to bad science. Those who takes this position, and particularly the young people who do so, gets quite a 'rush' of self-empowerment. Sorry if this seems extreme, but it's probably what fed the Hitler Youth, and the Red Guard, but in a less virulent form: a basis for flouting authority; instead of being a dependent, subservient 'youngster' you get to thumb your nose at the dusty old, wrong-headed, know-it-alls, and you get to do so by (in your own eyes, at least) being smarter than them.
I don't mean to say that the two very nice young people in my class are somehow comparable to the Hitler Youth. Far from it! They are not advocating violence or racism--I'm sure they are actively doing 'the opposite', whatever that would be--but I think they're getting a little of the same vibe that fed the HY, etc.
I mention this because understanding where they're coming from, is important.
It's not a question of science alone, but of psychology, as well.
Showing them that their graphs are wrong might be very satisfying--and might keep them from convincing their friends to join (if the friend witnesses your debunking of the debunkers)--but I don't think you're likely to set them straight. It's not about the graphs for them--its about how they see themselves, and that's based on how they see anyone who says GW is real/human-caused. This is about identity, as defined in terms of 'science'--not science.
And frankly, that same psychology underlies a large part of what the religious right (of which these two young women may be a part) is all about, in general, as far as I can see.
It helped me to lay this all out. Sorry if I'm didactically stating the obvious.
1. The first, let us call it modestly, the Eli/Mashey N3xus is to expose the bad science for what it is so that those with casual interests don't fall prey. At the extreme this means confronting the agents of denial publicly.
2. The second, we can call this the Schneb imperative, is to not further alienate the cultural denialists and, at best, to raise some doubts in their minds which may later have an effect.
3. Then again there is the question of how you correct a sympathetic, but wrong advocate. Simon Donner points out wrt Kristen Byrnes
Are we really having this discussion? This is a high school student. Seriously, this is exhibit A for all those who argue we do more harm than good attacking 'skeptics'.Those are the issues. The question is what is the proper order of concern, is putting out an answer more important than not further alienating the alienated, how should one avoid ticking off bystanders. In short, what should be done.
Posted by EliRabett at 9:25 PM
It's not what you don't know that gets you,
it's what you think you know and is wrong
Eli was writing another thumb sucker which required that he calculate the CO2 forcing. He used the Mauna Loa and the Law Ice dome data. A bit of Googling found that the forcing is usually given as 6.3 ln (C/Co) where Co is the mixing ratio in ppm from 1880 and C the mixing ratio at any other time. The 6.3 is the IPCC recommendation (and indeed, you can find it in a forcing calculation used at Climate Audit). The 0.67 is a reasonable climate sensitivity given in K/(Watts/m^2), you might argue that 0.75 is a better current estimate, but it really doesn't make much difference
Some time ago Eli put up a bunch of graphs with different forcings, but didn't tie the forcings to temperature. He thought it would be a good idea to complete the circle, putting CO2 forcing and global temperatures on the same scale.
The changes in CO2 mixing ratios and calculated forcings can be seen in the graph to the right. The shape of the forcings follows the temperature curve quite well. It overestimates the temperature change by a bit, but, for a BOE calculation, it shows, especially in comparison with any multiple of the solar forcing, a good agreement with the observed global temperature increase.
The mixing ratios, of course are on a different scale so the so the comparison between the two is strained, but if you graph mixing ratio vs forcing you get the correct logarithmic dependence. For example, using this rough model the CO2 forcing at 2x CO2 is ~2.9 K, while at the current value of 380 ppm it is ~ 1.1 K.
Posted by EliRabett at 9:16 PM
Thursday, April 17, 2008
Given the dust-up (Deltoid, Islands of Doubt, Adventures in Ethics and Science, Pharyngula, Respectful Insolance, Quark Soup and Eli tires) about an NPR report on Kristen Byrnes and her opus, "Ponder the Maunder" Eli thought he would wander over and take a look again after the last two go rounds.
UPDATE: Michael Tobis has a great comment on the outbreak of precociousness with the coming of spring at Wired Science (also a few typos Mike)
It was quite painful. Eli is thinking of charging NPR for pain and suffering. Mostly what it was was an unending series of strawmen
According to the Wikipedia, a strawman can be wished into existence by
- Presenting a misrepresentation of the opponent's position and then refuting it,, thus giving the appearance that the opponent's actual position has been refuted.
- Quoting an opponent's words out of context -- i.e., choosing quotations that are not representative of the opponent's actual intentions (see contextomy and quote mining).
- Presenting someone who defends a position poorly as the defender and then refuting that person's arguments, thus giving the appearance that every upholder of that position, and thus the position itself, has been defeated.
- Inventing a fictitious persona with actions or beliefs that are criticized, such that the person represents a group of whom the speaker is critical.
- Oversimplifying an opponent's argument, then attacking the simplified version.
Woo hoo, teenager thinks she knows more than scientific experts … now that is news. I took a look; I'm unimpressed, even considering her age. Parroting right-wing think tanks is not evidence of independent, skeptical thought, I'm afraid.But Eli's approach to this sort of agitprop is to look at the arguments, one at a time. So Eli looked at some of Kristen's. UPDATE: (Temporary link to page in Google Cache, they are overlimit this month. )
The data that Dr. Keeling collected shows a steady increase in atmospheric CO2 levels to the current level of about 380 parts per million.True enough
Some scientists believe that CO2 increases are man made, other scientists have warned that past atmospheric CO2 levels calculated from studying ice cores are inaccurate and that present atmospheric CO2 level increases are a result of natural causes.Who would those other scientists be, why our old friends EG Beck and his running mate Jaworowski, who provide negative information content on the subject, but their existence allows the Kristen's of the world to build a strawman. Of course, she is not the only one. Fred Singer himself used exactly this tactic in his Heartland Institute Nonsensical Summary for Bad Climate Policy, including the half hearted fade out to another strawman
To me, this argument was put to rest by NASA’s Jet Propulsion Laboratory whose satellites and sensors have been able to track CO2 sources and have concluded that the current increases in atmospheric CO2 are coming from raw coal burning family home heaters in the third world, primarily in China. Dr. C. Miller of JPL, Director of the Carbon Observatory Project, stated on his web site that ½ of industrial CO2 has been cleansed by the atmosphere.Kristen appears to have missed a few things, but she is not big on useful references. It is clear that for atmospheric CO2 the rate of increase is being driven by the industrialization of China and India, but that US and European emissions contribute equal amounts to the absolute increase, it's just that our emissions are not growing as fast. The bit about home heaters almost certainly referred to black carbon emissions, not CO2 emissions, a whole other (Googlable) ball of buckeys. And then we get the classic
If man is responsible for a 100 part per million increase of atmospheric CO2 levels we must still keep in mind that 100 parts per million is a very tiny number. Said another way, man’s contribution to atmospheric CO2 is only one ten thousandth of total atmosphere.Yes kiddo, man is responsible for a 100 ppm increase of CO2, and given that 99% of the atmosphere does not absorb infrared light (oxygen and nitrogen), why yes that is an important increase. A venerable Type 1 strawman, but does the darling slow up, Sadly No
Greenhouse gases and the spectrum.Gadzooks, a veritable Type 5 (with an admixture of 3 rolled in) strawman, and we get then a repeat of the some scientists tactic.
I will start this section with a very important point. CO2 in the atmosphere does not reflect radiation back to the earth as some have tried to state.
Some scientists have warned that when sun light strikes the surface of the Earth it is absorbed then re-emitted as infrared radiation. This infrared radiation is then absorbed by atmospheric CO2 and re-emitted back to the Earth’s surface thus causing the lower atmosphere to remain warmer.True. For a good technical explanation of this see Arthur Smith's article on arXiv, otherwise read the Dot.Earth deaththread. This is a basic result which is discussed in all textbooks on atmospheric physics,
Other scientists say that CO2 can only absorb infrared at very limited wavelengths and that those wavelengths are already saturated.It would be nice to know who these are, but Kristen doesn't tell, might embarrass the dears. Looks like a Type 4, but if that is not sufficient, she goes on
A simple example of this is that when you are watching television and someone is standing in your way, it does not matter if another person stands between you and the television. The light from the television cannot make it through the extra body when the first body is there. CO2 absorbs infrared radiation in very narrow bandwidths.A Type 5 and Type 1 combo. The girl is good. Kristen, how bout you try this one. You (a 16 year old photon) are trying to get out of a building (the atmosphere), but there is a big guy in front of you blocking your path, so you go around him and escape. OTOH, if there are 20 big guys in front of you it might be a bit more difficult.
Not if they know any spectroscopy, or for that matter exist. The first statement about re-emission is just a little bit off and that about no measurements is wrong. Anybunny with access to a cooled or heated cell, a vacuum pump and an FTIR can do this in her own burrow. What we know happens is that the wavelength range emitted by carbon dioxide lower in the atmosphere is from a hotter gas, at a higher pressure. Both mean that some of the radiation cannot be absorbed by CO2 higher in the atmosphere. Then, of course, the higher you go, the lower the relative concentration of water vapor to CO2, as well. Eli did a whole series on these effects a while back. Kristen has hit the five-fecta, all five types of strawmen in one short paragraph. Depressing
When confronted with this problem, the greenhouse theorists claimed that the CO2 re-emits the energy at a slightly different wavelength, but no measurements of this energy has ever been made and water vapor absorbs in the same wavelengths. Just how much of this re-radiated energy is absorbed by CO2 and how much is absorbed by water vapor is the key sticking point for many scientists who remain undecided about the greenhouse theory.
Posted by EliRabett at 1:48 AM
Monday, April 14, 2008
The public-service announcement - apparently Gore was directing - is meant to show that people who don't agree on much can still agree that the environment is important.UPDATE: Rabett Run is now showing this ad in the upper left corner.
Posted by EliRabett at 11:02 PM
Saturday, April 12, 2008
A hallmark of the modern punditocracy is that those who were wrong are taken to be the great and worthy, invited to pontificate in all venues and called on by the mighty for advice. In fact, they should be clothed in sackcloth and ashes and either sent into the wilderness to repent, or, given the damage they have done, have a final professional Roman bathtub sitdown, but that does not appear to be an option, which accounts for Eli's general outlook.
Rabett Run linked to recent papers on how we got into the climate science corner of the mess. Oreskes, Conway and Shindell (OCS) describe how William Nierenberg, led and distorted a 1983 National Research Council report on the consequences of man made climate change. Here we emphasize the corrosive role that Gary Yohe and William Nordhaus and a later Nobel Economist, Thomas Schelling played in the process and the consequences thereof. Nierenberg was the Director of the Scripps Institute of Oceanography, a member of the National Academy and soon to be a founder of the Marshall Institute, a position from which he, Fred Seitz and William Jastrow threw sand in the face of science till their deaths.
The Nierenberg report followed reports on climate research by a committee headed by Jule Chaney and from the JASON group which established (see papers by Oreskes and Myanna Lahsen) [link updated - thanks to Stoat], even then a consensus that increasing greenhouse gas concentrations were known to be a serious threat. Nierenberg built a jury rigged sandwich with moldy bread.
The physical sciences, in the middle, were pretty much along the lines later filled in by the IPCC process. There was more uncertainty, less was known then, but the broad outlines conformed to the current scientific consensus, however the bread that held the sandwich (and the bottom line conclusions) were from Nierenberg and his band of merry economists, singing don't worry, be happy we can take care of any problems later at lower cost, a song they are still singing as things get worse. Sadly, many are listening.
As OCS point out, they did so by accepting the conclusions of the physical scientists, but then only considering the least threatening of the range of possibilities.
Nierenberg’s principal tactic was to rely on the arguments provided by the two economists. At the first full discussion of the issues facing the committee, both Schelling and Nordhaus introduced the idea that climate change was not necessarily bad, that most likely it would have both negative and positive effects. Nordhaus wanted to evaluate costs and benefits, suggesting that although he “suspected that the impacts of increasing carbon dioxide would be negative,” they might not be, and it would be hard to prove either way, given the complexity of social and economic systems.The economists provided the necessary cover and continue to do so for the Marshall Institute types, indeed it is the same economists.
Chapter 1, written by Nordhaus, Ausubel, and Gary Yohe, an economics professor at Wesleyan University brought in mid-stream as a consultant, focused on future energy use and carbon dioxide emissions. The long and detailed chapter was perhaps the first serious study of the problem that looked at many variables, and did not assume linear extrapolations. It began by acknowledging the “widespread agreement that anthropogenic carbon dioxide emissions have been rising steadily, primarily driven by the combustion of fossil fuels.” The emphasis here, however, was not so much on what was known, but on what was not known: the “enormous uncertainty” beyond 2000, and the “even greater uncertainty” about the “social and economic impacts of possible future trajectories of carbon dioxide.” This uncertainty provided the basis for an argument that no meaningful action could be taken now. They used the uncertainty to hide the pea, acknowledging the possibility of rapid and damaging changes, but then only considering far off and lesser threats from climate change. Moving the danger far enough in the future meant that it did not have to be confronted, which is what Nierenberg wanted as a conclusion Nor did Nierenberg attempt to deny the legitimacy of the existing science. Rather, he accepted the scientific facts while adopting a conceptual framework in which those facts were irrelevant. The essence of the report is the reframing of climate change as something that policymakers and politicians should ignore, which in the United States at least, for the next two decades, they largely did The actions of William Nierenberg belie that assumption. Nierenberg did not engage his scientific colleagues over the technical basis of their scientific views. He did not produce new or competing claims about how the Earth would respond to increased CO2. In short, he did not try to construct knowledge about the Earth. Rather, while accepting his colleagues’ technical conclusions, he dismissed the interferences that they (and others) had drawn from those conclusions, substituting an alternative framework that insisted that those inferences were wrong. Rather than constructing knowledge, William Nierenberg de-constructed it.This fits well with current threads on grist and inkstain, where the protagonists walk right past what could have been done ten and twenty years ago if clear scientific conclusions had been honestly accepted and well into the postmodernist framing debate. Indeed OCS write 70+ pages on how Nierenberg was able to reframe the question of what was happening to climate, to that of should we bother doing anything about it. Which leads to the serious question of why Nordhaus and Yohe have any remaining credibility given that they played a knowing and crucial role in making us miss the opportunity to deal with climate change at low cost, at a crucial time. You and your children will pay the price.
Posted by EliRabett at 10:46 AM
Thursday, April 10, 2008
The third way
Eli and Ethon have been doing professional stuff, and are actually gonna be in the barrel for a couple of more days, but we have been following this and that.
There is lots of discussion about adaptation or mitigation or both, or maybe, as Ethons favorite pecked would put it, adaptation in the first 23 paragraphs, and then a swift mention that mitigation can't do nothing for fifty years, but it would be a good thing, maybe followed by claims that he, poor dear, has been misquoted.
Eli would suggest looking at the dictionary
adaptation: adjustment to environmental conditions specifically in the sense of improving the chances of survivalThere are nasty implications in this that the Boys in Boulder have missed, or more likely are hoping you have missed, as in not everyone will survive, the changes needed to survive will have very negative consequences in other areas, it ain't gonna be cheap and they are obligated to pay for it. In the UN Framework Convention on Climate Change the developed countries clearly have accepted that burden (of course some of US probably lied)
Article 4.4 “The developed country Parties and other developed Parties included in Annex II shall also assist the developing country Parties that are particularly vulnerable to the adverse effects of climate change in meeting costs of adaptation to those adverse effects.”The conventional other side is
mitigation: steps taken to avoid or minimize negative environmental impacts. Mitigation can include: avoiding the impact by not taking a certain action; minimizing impacts by limiting the degree or of the action; rectifying the impact by repairing or restoring the affected environment; reducing the impact by protective steps required with the action; and compensating for the impact by replacing or providing substitute resources.The principle differences between mitigation and adaptation is that adaptation passive while being more expensive in the long and short run. Sometimes, if you mess up enough, all you can do is adapt. For sure those who push adaptation are members of the lie back and enjoy it club. Having brought us to this point by resisting action on climate change in the 90s, they are now claiming that, gee it's too late to do anything, and anything we do will take a while to have an effect. In short, they are the first we should throw overboard and the last we should listen to.
Let your humble hare suggest a third word which encompasses both mitigation and an active attempt to improve the situation.
amelioration: amelioration is synonymous with improvement.
If a patient's condition shows amelioration, the patient is clearly better -- there is some improvement in her or his condition.
Amelioration infers that an effort is being made to correct or at least make more acceptable conditions that are difficult to endure.
The word "amelioration" is compounded from the Latin "ad",-", to or toward + ""melior", better = toward better = improvement.
When someone says that we have to ADAPT to climate change, tell them that they are wrong. Adaptation is what dumb animals do (Ethon demurrs). Humans work together to improve the world. We need to correct what climate change is making increasingly difficult and dangerous to endure. We need amelioration, right now.
Posted by EliRabett at 8:56 PM
Wednesday, April 02, 2008
With the coming of spring, the moles have sprung up and the godly tire of 24/7 mole whacking duties. Some say, this stuff is so dumb no one could believe it, but, there are many sacks of hammers on two legs, and a lot of them are in state legislatures. Back in November, Rod Bembry, Head of the Kansas Department of Health and the Environment rejected an application by Sunflower Electric Power to build two coal fired plants on health and emissions grounds.
Sunflower Electric Power threatened to sue, sued and then attempted to buy the Kansas Leg to overturn the decision. Interestingly they were outspent 4 to 1 by a natural gas giant, Chesapeake Energy, still, the legislature easily passed a bill which would have overturned the decision, only for it to be vetoed by Gov. Kathleen Sebelius. As a friend in KS told Eli yesterday, there are enough votes in the lower house to sustain the veto, but what brings out the need for mole whacking is a comment in the KS Star article by Karen Dillon and David Klepper,
Not that it would help, but maybe we need to send Avery and Singer, Unstoppable Hot Air to our friends in Kansas?
Count Rep. Larry Powell as a skeptic. This year, the Garden City Republican offered lawmakers copies of a book that asserted there was no scientific consensus on global warming. Titled Unstoppable Global Warming: Every 1,500 Years, the book was sent to Powell by the Heartland Institute, a free-market think tank based in Chicago that has received funding from foundations associated with the owners of Wichita-based energy giant Koch Industries and Exxon Mobil.
After state rejection of the Sunflower project, Powell wrote to the state's newspapers, saying carbon emissions likely would boost agricultural output by 50 percent.
Many lawmakers say climate change may end up being much ado about nothing.
And those scientists who say climate change could have a catastrophic impact?
"Hysterics who claim the sky is falling," said Rep. Mike Kiegerl, an Olathe Republican.
During four days of legislative hearings on the coal plant, only one climate scientist spoke. And he got only seven minutes to explain the work of the International Panel on Climate Change, a consortium of 2,000 scientists.
Posted by EliRabett at 11:12 PM