Imagine a Spherical Earth<\/h4>\n
Climate sensitivity is a term that refers to more than one thing, but the basic idea is this. If CO2 concentrations in the atmosphere were to double, how much would global surface temperatures rise? It is usually considered from a “baseline” of 280 parts per million (ppm), which is the pre-industrial level. We are currently at 400 ppm and we are heading for 560, the doubling, with little apparent serious effort (in my opinion) to curtail the rise. Climate sensitivity is expressed in degrees Celsius. So if some one says “climate sensitive is 2” than they mean that we can expect global surface temperatures to reach 2 degrees above baseline given 560 ppm of CO2 in the atmosphere.<\/p>\n
Imagine a spherical earth. Imagine no water vapor in the atmosphere, and just to keep things simple, let’s have only land surface and no ocean. But the amount of air and its overall composition minus the water vapor is like our actual earth. On this imaginary earth, climate sensitivity is about 1.2. That’s apparently pretty easy to figure out because it is a matter of how CO2 operates as a greenhouse gas and how much energy the sun supplies, etc.<\/p>\n
However, there could be negative and positive feedbacks that would make this work out differently. This would be things that either make some of the sun’s energy have less of an effect or more of an effect. Aerosols (dust) in the atmosphere, such as volcanic dust, can reflect sunlight away before it hits the earth’s surface, so it will have less of a contribution to heating the planet (which sunlight mainly does at the surface where it converts to infrared radiation). Ice and snow also reflect sunlight away (that’s called albedo). Water vapor in the atmosphere will generally act like a greenhouse gas and cause more heat by, to oversimplify a bit, interfering with the process of infrared heat leaving the atmosphere. Increased CO2 ultimately leads to more water vapor in the atmosphere, thus significantly amplifying warming. Warming can cause the release of methane into the atmosphere, another greenhouse gas, which in turn causes more warming until it oxidizes into CO2 and water. Water vapor can also get organized as clouds distributed in such a way as to add to albedo, reflecting away sunlight and decreasing warming.<\/p>\n
With all these (and other) effects tugging this way and that on the temperature of the earth’s surface (by which we mean the atmosphere and the upper layer of the seas), how is one to figure out what actual climate sensitivity is?<\/p>\n
Well, it is hard, and there has been a lot of work on it. There are papers coming out all the time on this topic. The IPCC spent a lot of effort on it. And, there are two answers to the question “what is the sensitivity of the climate?”<\/p>\n
(Before giving you the answers, I want to point something out that is very important. The Earth’s surface does not warm up instantly as CO2 is added. It takes time. In fact, the changes that happen after CO2 is added to the atmosphere will continue for something like thousands of years. But the initial change, which involves the air heating up and weather systems changing and all that, would be observable over decades and reach a short term level of some stability in less time, measured in many decades or centuries. So there are two “climate sensitivities,” long term equilibrium and transient, the latter being what is generally talked about, with the idea of a mutli-decade time scale. So, the question we are asking is what will the earth be like at the end of the century, given a doubling of CO2 in the atmosphere?)<\/p>\n
So, back to the answers. One answer is the simple answer, and it is 3. This is the number that climate scientists seem to settle on when you hold them down and say “shut up with the mumbo jumbo, just give me a number.” The other answer is about 1.5 to 4.5 but possibly higher at the higher end.<\/p>\n
Some who wish to minimize the importance of climate change will say things like “1.5. That’s a small number, what are you worried about?” Those people are boneheaded idiots and they are hoping you are too. Is 1.5 a small number? A large number? It depends. If I take 1.5 pennies from you it is a small number. If I kill you 1.5 times, it is a large number. Suffice it to say that 1.5 is a big enough number that we should be worried about it. Also, it is a low ball estimate of climate sensitivity. Almost nobody believes it. By one reckoning, there is something like a 5% chance that the sensitivity is actually around 6. Holy crap. That would probably melt almost every single drop of glacial ice on the planet and the map of the United States would look like this, in a couple\/few centuries:<\/p>\n
It would matter if there was a 20% chance that this is the map of the US your great grand children get to live with. They would actually have to remove stars from the US flag. If there is a US.<\/p>\n Below I supply a list of web pages you can check out to learn all about climate sensitivity.<\/p>\n But what about this report? Well, it’s a doozy. First, it has a forward extolling the virtues of Lewis and Crok. That’s nice. But the foreword is written by Climate Science Denialist Judith Curry. That does not bode well. Following this, the report is mainly a journey through a cherry orchard.<\/p>\n The report cherry picks a subset of scientific results that show lower sensitivity estimates and does a poor job of ruling out the other results that give higher estimates. They criticize the IPCC report, which summarized sensitivity studies, for leaving out the “good news” that climate sensitivity is actually very very low, by reporting a wide range of research indicating that it is not low. In other words, and I know this seems confusing but I think this is the point, Lewis and Crok are saying that the IPCC report is wrong because it reported all of the relevant scientific findings rather than just the ones Lewis and Crok would like to have seen noted.<\/p>\n DOES THE IPCC NOT KNOW ABOUT CHERRY PICKING YOU MAY ASK???<\/p>\n Sorry for shouting.<\/p>\n The authors suggest that the teams of scientists working on the IPCC report did not understand basic statistics, and that this contributed to their alleged overestimate of climate sensitivity. That part made me laugh.<\/p>\n Lewis and Crok put a lot of weight on what they term the observational record, which as you might guess if you have been following the denialist’s literature is one of the best places to pick cherries. Also, astonishingly and, really, laughably, they rely on Lewis’ prior publications suggesting low ball estimates of climate sensitivity. Yes, some guys have been pushing a particular scientifically difficult to support position; the world’s scientists in a major international effort produced a summary of countless hours of research and dozens of peer reviewed papers that disagree with those guys; those guys write a report about how what they’ve been saying all along, which differs with the established science, must be right because they’ve been saying it all along!<\/p>\n Yes, that’s about what this report amounts to. It’s a bunch of hooey.<\/p>\n For further reading on climate sensitivity I recommend the following:<\/p>\n NEW: GWPF optimism on climate sensitivity is ill-founded<\/a><\/p>\n “On Sensitivity” at Real Climate <\/a><\/p>\n “A Bit More Sensitive” on Real Climate<\/a><\/p>\n Climate-Change Deniers Must Stop Distorting the Evidence<\/a><\/p>\n How sensitive is our climate? at Skeptical Science<\/a><\/p>\n Also of interest: In Search of Sungudogo:<\/strong> A novel of adventure and mystery<\/a>, which is also an alternative history of the Skeptics Movement.<\/p>\n","protected":false},"excerpt":{"rendered":" Who What When Where Nic Lewis, an unaffiliated self described climate scientist, and a journalist, Marcel Crok, also unaffiliated, are known climate science denialists. The two of them have an objection to the International Panel on Climate Change (IPCC) conclusions regarding an important thing called “Climate Sensitivity.” Perhaps unable to get their work in the … Continue reading A New Fake Report On Climate Change.<\/span> ![\"Extreme_Sea_Level_Rise_Scenario\"](\"https:\/\/i0.wp.com\/scienceblogs.com\/gregladen\/files\/2013\/06\/Extreme_Sea_Level_Rise_Scenario-640x541.jpg?resize=604%2C511\")
<\/a><\/p>\nThe adventures of Lewis and Crok<\/h3>\n
\nOther posts of interest:<\/h3>\n
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