Everyone’s going on about “The Earth is warming! The Earth is warming!” … and it is, you know. Overall, it has been warming since the depth of the “Little Ice Age” in about 1700. During the Little Ice Age, the Thames River in London regularly froze, and glaciers expanded to unheard of sizes, a few even over-running long settled villages.
Since then, the globe has been slowly warming, with a gradually reducing ice mass and a gradually increasing temperature.
Now, it is very likely that human actions were not responsible for both the Earth going into the Little Ice Age, and the Earth coming out of the Little Ice Age, because we’d have to blow hot and cold to do that.
And it is probable that human actions were not responsible for much of either cooling or warming from 1700-1900, since it was decades before a significant rise in CO2. So a majority of this three century rise (and the fall before it) is not due to humans, but is a natural temperature variation. What is causing it, then?
Most scientists agree that it is not a coincidence that the Sun was in what’s called the “Maunder Minimum” in the years around 1700. This was a time when there were no sunspots for a number of years. This time of solar magnetic quietness is thought to be associated with the cold temperatures, by means of a curious intermediary. This is the fact that cosmic rays, by striking molecules in the atmosphere, encourage cloud formation. When the sun is magnetically quiet, the cosmic rays are free to stream into the atmosphere, making the clouds that cool the planet. More cosmic rays means more clouds. More clouds reflect more sun, and the earth cools …
Since then, the solar magnetic field has strengthened, and at present is stronger than it has been in 1,000 years.
This stronger magnetism deflects the cosmic rays from the earth, causing less clouds, and allowing the sun to heat the earth. Thus, over time, the changes in the suns magnetic field have gradually increased the Earth’s temperature.
Now a current theory, called “AGW” for Anthropogenic (human caused) Global Warming, holds that in addition to the solar-caused warming, the earth is also being warmed by the increase in atmospheric CO2. Accordingly, the following questions arise
a) is it true that the increasing CO2 level is affecting the global mean temperature?, and
b) if so, how much?
People have made lots of claims about this, claiming that yes, this human caused warming is happening, at different numbers up to 4°C per CO2 doubling. But to my eye, there has been a great dearth of evidence on both sides, as to whether this is actually happening or not happening.
So my question is … what is the evidence that this is, or is not, happening?
Some notes and requests, with the aim of keeping the discussion focused on scientific evidence:
Please, no ad hominem attacks. I don’t care who paid for the grant, Greenpeace or Mobil, don’t go there. I don’t care if the scientist has made mistakes in the past. Scientific evidence must be either corroborated or contradicted by other scientific evidence, not by an attack on the scientist’s motives, previous work, or associations. AD HOMINEM ATTACKS ARE NOT EVIDENCE!
No derogatory name calling, no “Mr. Oil”, no “Greensheep”. No “denialists”, no “warmers”. There are three camps here, which I will call Human GW, Natural GW, and Agnostic GW. Human GW means those people who believe human caused warming exists and is measurable at the present time. Natural GW means those people who think the variations are mostly natural, with human caused variations being minimal. Agnostic GW means those who think there is not enough evidence to decide. I invite people to identify their position in their posts – do you think the warming is human caused or natural warming, or are you agnostic? Me, I’m an agnostic regarding GW, because of the scarcity of evidence on either side, and the tiny size of the signal.
I have called the categories Human, Natural, and Agnostic GW to avoid insult, because these terms have little emotional baggage. Please use these terms rather than “sceptic”, “deniers”, “warmers”, “those brain-dead fools on the other side”, etc. NO NAME CALLING, PLEASE BE POLITE!
The Earth’s climate is an externally driven, chaotic, buffered, multi-stable, tera-watt scale, fully developed constructal heat engine running at optimal turbulence. It has both known and unknown internal and external forcings, feedbacks, interactions, teleconnections, natural periodicities, and resonances. It has five major systems (ocean, atmosphere, lithosphere, cryosphere, and biosphere), each of which interacts with all of the other systems and with itself, at all scales, and each of which has its own internal subsystems. Current crude computer models of this maddeningly complex heat engine are very, very far from being evidence. All they can tell us are the beliefs of the programmers. CLIMATE COMPUTER MODEL RESULTS ARE NOT EVIDENCE! (Actually, computer models of any kind are not evidence, but that’s a subject for its own thread …)
Because of the aforementioned complexity of the climate system, theoretical formulations are not evidence. Yes, Arrhenius calculated that CO2 will raise the temperature of a theoretical thermally quiescent earth with a theoretical stable amosphere by an amount logarithmically related to CO2 increase … but that means nothing about what might happen in response to such a forcing change in an optimally turbulent terawatt scale planetary heat engine with unknown feedbacks.
For example, moonshine studies have shown that from 1985 to 1997, the albedo increased significantly. As a result, the solar forcing (sunlinght hitting the earth) dropped about by ten watts/m2. Calculations using IPCC forcing numbers say that this should have caused a 5° - 10° temperature drop. Obviously, this didn’t occur, that’s a huge temperature drop, ice age size.
Why didn’t the temperature fall from the drop in forcing? That change in forcing is the absolute size of almost three doublings of CO2. Why didn’t the temperature drop radically?
Not to put too fine a point on it, we don’t know … but obviously, it’s something in my aforementioned “known and unknown internal and external forcings, feedbacks, interactions, teleconnections, natural periodicities, and resonances” that has counteracted this huge change in solar forcing. Simplistic linear theories don’t work to analyse a giant, chaotic, turbulent heat engine like the Earth. THEORY IS NOT EVIDENCE!
- There are three main global mean temperature calculations, done by different groups of scientists, called GHCN, GISS, and HadCRUT. Since there are only a certain number of meteorological ground stations in the world, or in any given country or area, these three global mean temperatures are calculated from the same raw data.
Unfortunately … the GHCN, GISS, and HacCRUT temperatures don’t agree with each other. They disagree on trend, mean, and year-to-year variation. Which one is closest to the real world? We don’t know.
In part, this scientific disagreement is based on the bad quality of the raw data. Temperature stations are often poorly sited, and get moved. Quality of equipment varies wildly, from a glass thermometer read three times a day most days, to digital constant recording thermometers. Times of observation change. Missing data is the rule and not the exception. Dust and spiderwebs clog up the louvres of the Stephenson Screens. Elevations are not consistent. Cities grow up around the ground stations. A paved parking lot goes in upwind, and temperatures soar. The new observer always rounds down and not up. Because of these and many other factors, the quality of the ground station temperature record is very spotty, and is subject to human-created “heat islands”.
These local heat islands add an upward bias to temperature measurements. The effect of these heat islands has been “adjusted for” in the GISS, GHCN, and perhaps slightly in the HadCRUT temperature measurements. Unfortunately, it has been adjusted for in different ways in each case, yielding different results, and there is no general agreement on the proper way to deal with the heat island problem.
Finally, on average there is only one thermometer for every 85,000 square kilometres on land, and less at sea. This leaves vast areas totally unsampled, and degrades the overall accuracy of the mean temperature calculation. The three different groups account for this in different ways, and thus give differing results.
A rigorous independent review of the surface record is clearly overdue.
IF YOU ARE USING SURFACE TEMPS, CITE WHICH ONE (GISS, GHCN, or HadCRUT), AND BEAR IN MIND THE DATA PROBLEMS.
Evidence is scientific studies, measurements, and logical and mathematical analyses of the real world. It is not a study of a virtual world. It is not a press release about a study. It is not someone’s comment about a study. It is the study itself. Please cite the study, with a link if it is available online, and where possible provide the abstract. Explain briefly and clearly what the study means, and whether it supports Human or Natural GW. PLEASE CITE, QUOTE, AND EXPLAIN.
Logical arguments which are based on evidence, while not evidence themselves, can explore the implications of the situation. To do so, they need to be firmly grounded in the evidence, and be evidently true. BE CLEAR ABOUT YOUR LOGIC.
Avoid words like “could”, “might”, “may”, and the like wherever possible. Yes, we could see 11°C warming in the next century, and we might see a new ice age starting next week, and pigs may fly … if you wish to explore uncertainty, please provide numbers. Weather forecasts are a good example. Rather than saying “it could rain today”, which means very little, they’ll say “A 30% chance of showers”. PUT NUMBERS ON UNCERTAINTY, AND ERROR BARS ON NUMBERS, WHEREVER POSSIBLE.
Since I’m the OP, guess I’ll start.
An Example of Scientific Evidence
Science Magazine, 11 November 2005:
Vol. 310. no. 5750, pp. 1013 - 1016
*Recent Ice-Sheet Growth in the Interior of Greenland
*Ola M. Johannessen, Kirill Khvorostovsky, Martin W. Miles, Leonid P. Bobylev
Recent Ice-Sheet Growth in the Interior of Greenland (must be a subscriber to Science)
What This Study Means
After this study came out in November, another study of recent glacier surging around the coast of Greenland was reported last week. That other new study received a lot of hype, saying that it shows that the ice cap is melting, sea levels will soon be up around our ears, and the rest of the usual “the world is melting” nonsense.
That study, however, needs to be read in conjunction with this one I reference above, which shows that despite the surging, the Greenland Ice Cap has been getting thicker over the same period.
Regardless of surging, since the ice cap is getting thicker, the Greenland Ice Cap must be gaining ice overall, not losing ice. Of course, the usual caveat applies, this is only a short record. But it does indicate that during the time of the recent surging, the amount of ice was constantly increasing. We can cancel the sea level alert, because at the moment, with the snow piling up on top, Greenland is actually lowering the sea level.
Does this support Human or Natural GW? Neither, directly. It is in fact what we would expect in a warming world, because more heat brings more evaporation, and more evaporation brings more snow and rain. It does indicate, however, that there is no “runaway” heating going on, as the Greenland Ice Cap is increasing, not melting.
An Example of a Logical Argument
I argue that the maximum size of any possible human-caused change to the climate must be small, near the limit of resolution. The reason is that if the change were large, we would have already found it in the record. The fact that it has not been found, despite fifteen years of extensive searching, indicates that it must be small.
To review: I’m not looking for evidence of global warming. The globe has been warming for 300 years.
I’m looking for evidence that humans have caused some part of that warming.