Arguments
What ended the Little Ice Age?
What the science says...
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The main drivers of the Little Ice Age cooling were decreased solar activity and increased volcanic activity. These factors cannot account for the global warming observed over the past 50-100 years. Furthermore, it is physically incorrect to state that the planet is simply "recovering" from the Little Ice Age. |
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Climate Myth...
We're coming out of the Little Ice Age
The argument that we're simply "coming out of the Little Ice Age (LIA)" makes one of two assumptions:
- The planet oscillates around some natural equilibrium temperature such that after it cools, it must warm to return to this temperature, and vice-versa.
- Whatever caused the LIA cooling has reversed phase and is now causing global warming.
The first assumption demonstrates a lack of understanding regarding what causes planetary temperature changes. The second does not hold up under scrutiny of the empirical data.
Climate Change Causes
A long-term increase in the Earth's average temperature is caused by a change in the planetary energy balance (incoming vs. outgoing energy), also known as a 'radiative forcing.' If the amounts of incoming and outgoing energy are equal, the planet is in equilibrium and its temperature will not increase on average.
Note that over short periods of time, energy can be exchanged between the Earth's oceans and surface air through natural cycles such as the Pacific Decadal Oscillation, which can result in a short-term warming of the surface oceans and air at the expense of a cooling of the deeper oceans, or vice-versa. However, these cycles oscillate between positive and negative states, which over the long-term cancel each other out and do not cause significant temperature trends. These oscillations neither create nor retain heat; they simply move it around and thus physically cannot cause global warming or cooling. Further, if these cycles were causing the surface to warm, they would be causing the oceans to cool, which is the opposite of what we observe.
There are many different factors which can cause a planetary energy imbalance. Some of the most common examples are changes in solar activity, atmospheric greenhouse gases, volcanic activity, the Earth's overall reflectivity, and variations in the Earth's orbit around the Sun (also known as 'Milankovitch cycles'). However, the key point is that the planet will not warm or cool over the long-term unless there is a radiative forcing causing a planetary energy imbalance. Thus the planet will not warm simply because it had previously cooled, and the notion that the planet is just "recovering" from the LIA makes no physical sense.
Little Ice Age Causes
Therefore, the only way the current warming could be because "we're coming out of the LIA" would be if whatever caused the energy imbalance resulting in the LIA cooling had since changed state to cause a positive radiative forcing, thus resulting in the global warming we've observed over the past century. Climate scientists have proposed numerous factors which likely contributed to the global cooling of the LIA.
Decreased Solar Activity
The LIA occurred from approximately the 16th to 19th centuries. During this time frame, there were periods of significantly diminished solar activity known as the Spörer Minimum (1460-1550) and Maunder Minimum (1645-1715). These minima were discussed in a seminal study by Eddy (1976). Additionally, the Dalton Minimum was a less prominent period of diminished solar activity observed from 1790 to 1830.
Figure 1: Reconsructed total solar irradiance (Delaygue and Bard 2010)
These periods of diminished solar activity were likely significant contributors to the LIA cooling. And solar activity has increased since the end of the Dalton Minimum to the current 'Modern Maximum'. However, solar activity has not increased on average since the mid-20th century.
Figure 2: Total Solar Irradiance as measured by satellite from 1978 to 2010
Studies quantifying the contributions of various radiative forcings to the global temperature change have estimated that over the past century, the increase in solar irradiance is responsible for about 15-20% of global warming (Meehl 2004). However, it cannot explain the accelerated warming over the past 50 years.
Figure 3: Solar radiative forcing temperature change vs. observed global surface temperature increase (Meehl 2004)
Increased Volcanic Activity
The Earth experienced heightened volcanic activity throughout the LIA. Volcanic eruptions release aerosols into the atmosphere which diffuse sunlight, causing global dimming and cooling. According to Crowley et al. (2000),
"over the interval 1400–1850, the volcanic contribution [to the decadal-scale variance in global temperatures] increases to 41 to 49% (P < 0.01), thereby indicating a very important role for volcanism during the Little Ice Age."
However, volcanic activity has had a net negative forcing (cooling effect) over the past century, particularly since 1950, and thus cannot explain the global warming over this period.
Figure 4: Volcanic radiative forcing temperature change vs. observed global surface temperature increase (Meehl 2004)
Ocean Conveyor Slowdown
Another proposed contribution to the LIA cooling is a slowdown of the thermohaline circulation through an introduction of a large amount of freshwater into the North Atlantic Ocean, potentially as a result of melting ice from Greenland due to warming temperatures during the Medieval Warm Period. The Gulf Stream is part of the thermohaline circulation, and transports warm water from the equator polewards toward Europe. If the North Atlantic Ocean becomes diluted with fresh water, this current could potentially become slowed or even shut down entirely. Broecker (2000) proposed this mechanism as a contributor to the LIA cooling.
However, since the Greenland Ice Sheet has been declining due to the global warming over the past century, and the slowdown and potential shutdown of the thermohaline circulation has become a concern as a result, quite obviously the ocean conveyor has not had a warming effect over the past century.
Decline in Human Population
The Black Death caused a decrease in the human populations of Europe, East Asia, and the Middle East during the 14th century and a consequent decline in agricultural activity. A similar effect occurred in North America after European contact in the 16th century. Ruddiman (2003) suggests reforestation took place as a result of this reduced human population and agricultural activity, allowing more carbon dioxide uptake from the atmosphere to the biosphere, thus having a cooling effect. Ruddiman concluded as follows.
"If the 10-ppm CO2 decreases are caused by plague-induced reforestation events, they would cool northern hemisphere temperatures by ∼0.17°C, assuming a 2 × CO2 sensitivity of 2.5°C."
Of course, we've seen the exact opposite effect in recent centuries, as the human population has continued to grow, increasing deforestation, and of course anthropogenic CO2 emissions through burning fossil fuels. However, it's difficult to classify increased human greenhouse gas emissions as a "recovery from the LIA."
The Planet is not Recovering from the LIA
To sum up, with the exception of the human population, the factors which contributed to the LIA cannot account for the global warming of the past 50-100 years. Further, it is not physically accurate to claim that the planet is simply "recovering" from the LIA. This argument is akin to saying that when you drop a ball off a cliff, it falls because it used to be higher. There is a physical mechanism for these changes. In the case of the ball, it falls because of the gravitational pull at the Earth's surface. In the case of the global temperature, it is warming from the increased greenhouse effect due to human activities.
Advanced rebuttal written by dana1981
Update July 2015:
Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial
Additional videos from the MOOC
Expert interview with Tim Osborne
Expert interview with Mike Lockwood
Last updated on 6 July 2015 by pattimer. View Archives
I think the whole flaw in the climate change argument can be expressed examining the words you have just used when saying "What the science really says":
"The main driver of the warming from the Little Ice Age to 1940 was the warming sun with a small contribution from volcanic activity. However, solar activity leveled off after 1940 and the net influence from sun and volcano since 1940 has been slight cooling."
OK, fine. While I don't necessarily agree with the sun portion (see Reply to Lockwood and Fröhlich - The persistent role of the Sun in climate forcing here - http://www.spacecenter.dk/publications/scientific-report-series/Scient_No._3.pdf/view), let's say everything you have said there is true. Even so, that does NOT automatically mean:
"Greenhouse gases have been the main contributor of warming since 1970."
Do we have any direct proof of that? Do we know exactly how much radiative forcing the greenhouse gases we emit produce? And do we know how much they produce when within the extremely complex climate system, as opposed to within laboratory conditions? Or is it just an assumption, considering we have exhausted all the possible natural causes that we can think of?
I think that there may be other natural causes (maybe even ones we have not yet discovered) causing this kind of warming, at least to a certain extent. Syun-Ichi Akasofu here (http://people.iarc.uaf.edu/~sakasofu/little_ice_age.php) wrote about the possibility that much of the current warming could be simplified down to a natural 0.5 degrees C linear trend, with superimposed fluctuations and oscillations.
Most importantly, he also notices that global warming has essentially stopped since 2000. This lack of warming does not agree with IPCC predictions. Instead it gives more credibility to this theory, as it could be explained as the most recent oscillation winding down and continuing on the 0.5 degrees C linear trend.
Re Akasofu's assertion that "global warming has essentially stopped since 2000", presumably, this is based on the HadCRUT surface temperature record which omits areas of the globe of extreme warming in recent years. A more comprehensive analysis of the Earth's energy imbalance finds the planet continued to accumulate heat past 2000 right up to the end of 2008 (where the analysis ends). Global warming has not stopped.
At the very least, if global warming has not stopped, it has definitely slowed down quite a bit, against what the IPCC has predicted.
global warming didn't stop nor slowed down, at least if you mean the trend.
Maybe temperature did, but it has the bad habit of going up and down in the short run; it always did and presumably will continue to do so. And the neither the IPCC nor the climatologists ever said it will not.
Thus, the problem is that all the IPCC looks at to make its predictions and recommendations and such is one 30 year trend from 1980-present. 30 years is not really enough to completely determine whether or not humans are having a sizable impact on the climate system in the first place, but if there is a possibility that last 10 years of that series do not conform to the predictions that the IPCC have made... it really throws the IPCC's predictions into doubt.
if 30 years are not enough to determine a trend i do not understand how 10 years can be enough. And it's not just 30 years, although smaller the contribution of ghg is sizeble even in the first half of the last century.
Also, that the models did not predict the last 10 years is a mith, not least because they never attempted to predict them. I'd suggest to read how meaningfull comparison should be done.
In response to "the models did not predict the last 10 years...because they never attempted to predict them", the link you gave actually shows the measurements not following the IPCC predictions.
if i got it right, 30 years are enough to establish a trend. If this is true, then the last 10 years are well inside the measured variability and cannot falsify the trend in any way.
But, given that you think that fig. 1 in the link i posted before "shows the measurements not following the IPCC predictions" you problably can say almost anything you like. The numbers tell a different story, though.
As for the IPCC predictions, maybe I'm making a mistake, but I thought that the black line was the IPCC trend, and the blue and red lines showing temperature have deviated from that line since 2005. That's at least 1/6th of the 30 year trend off course.
Michael, you are indeed making a mistake, as Riccardo tried to explain to you. The IPCC prediction is the entire gray area in that figure. The black line is merely the mean, which is merely the most probable point-by-point portion--the central tendency of the prediction, not the range of the prediction. The range is the gray area. Nobody, least of all the IPCC, expects the actual values to always fall exactly on the line. Nobody even expects the actual values to always fall within the gray area. Instead the expectation is that sometimes the actual values will be above the line and sometimes below the line, but on average they will fall more or less the same amount of time above as below the line, and almost all of the time they will fall within the gray area.
When you pick out the most recent four years as being below the black line, you are conveniently ignoring the several periods before that being above the line. Oh, but then you could point to the previous couple years being below the line. But then you'd be ignoring the years before that being far above the line.... And so on. If you play that game all the way back to the start of the graph, you see that on average the actual values spend nearly as much time above as below the line, and always inside the gray area.
There are formal, systematic ways of doing the above analysis. They were not invented for climatology. They have been used for many decades in many different fields of science and technology. They are being applied to climatology in exactly the same way. You can start to learn about them by reading Tamino's post "How Long?"
you can surely use just a few years to calculate a trend but you can not establish it this way; it would be just a mathematical exercise. Physics, and climate science as well, uses mathematics as a tool but they also give a meaning to the numbers.
When the data points have a "noise" of about 0.2 °C and a trend of about 0.17 °C/decade even common sense should convince you that it makes no sense at all to use just 7 years to calculate a meaningful trend.
If you really want to understand what is going on with our climate, it would be a good idea not to use "blind" google searches. You know, the internet is a great tool, but you can find almost anything you want. Given that we not always have the knowledge to state the credibility of a source by ourselves, an a priori reasoned choice is mandatory. Or anyone can fool you.
Read more, type less.
Oh my God! I didn't know I had to buy the analysis. Pardon me for having free thought.
Excuse me, but climatology is as much about trends as anything. We may not be able to completely explain them, but we see them and recognize them.
Heck, the analysis at the top pretty much says that the exact cause of the LIA is a bit of a mystery, but I guess they have everything else after that plumb figured out. :-)
They could have used this for the whole period.
You don't have to buy they analysis. But if you don't you should present some form of analysis of your own. Otherwise, 'free thought' is just opinion.
For example, what is the basis of the straight line in the figure you show in #14? For that matter, where does that graph come from? What is the cause of those wavy ups and downs that ride your straight line? There are temperature reconstructions going back to the LIA (some available in the articles below); yet your graph projects the same straight line backwards as well as forwards. What is the justification for that?
See Global warming and the unstoppable 1500 year cycle and The LIA and How we know the sun isn't causing global warming for starters.
In my former life in the oil business, we used to say 'a straight line trend is your best friend' at which point someone would reply 'until it stops being straight.'
Since Google is still our friend :D ...it's from here:
Two Natural Components of the Recent Climate Change (3/30/2009): (1) The Recovery from the Little Ice Age (A Possible Cause of Global Warming) and (2) The Multi-decadal Oscillation (The Recent Halting of the Warming)
Syun-Ichi Akasofu, International Arctic Research Center, Fairbanks, University of Alaska
http://www.webcommentary.com/docs/2natural.pdf
Agrees with: Ray Evans, Gerhard Gerlich, Roy Spencer, John Christy, Sarah Palin, Vincent R. Gray, Qing-Bin Lu, Denis Rancourt
Disagrees with: Martin Parry, IPCC, Al Gore, Svante Arrhenius, Rajendra Pachauri, Gavin Schmidt, RealClimate
Wow, a paper (published, when?) that sets out to fit straight lines to data and ends up with ... straight lines. And uses the fact that you can fit straight lines to data as proof that straight lines are appropriate:
"An intuitive approximation of the changes shown in Figure 1a (NASA:GISS). It is shown as the red line."
"The red straight line was drawn by the JMA."
And once 0.5C/century is established as the slope of all these lines (with the explanation in Fig 2a that it is "caused by natural cause" -- I didn't make that up), said line is projected back to 1500.
Very insightful work. I enjoyed this quote from p. 7: "Although the global average temperature (T) changes can be approximated by a linear relation as a fraction of time (t) (T = at), CO2 changes are more like T= bt^2, suggesting that the T-CO2 relation is not simple."
But temperature itself is a simple straight line +/- some decadal ups and downs?
I found the graph on watts up, doc, where the word was ... it's all good.
The line is simply placed there by the man who made the chart. Fits pretty good.
For that matter, where does that graph come from?
My, you get your shorts in a wad when something contrary comes up.
What is the cause of those wavy ups and downs that ride your straight line?
Decadal shifts in the NAO and PDO most likely. It's an accurate temperature record so what does it matter?
"There are temperature reconstructions going back to the LIA (some available in the articles below); yet your graph projects the same straight line backwards as well as forwards."
It's not an important part of the graph. He is just trying to show warming from 1880 through 200. God, i see so many graphs from the pro folks that start in 1980, what is the problem with this?
What is the justification for that?
Kevin Trenberth offers up some perspective on Akasofu.
Speaks for itself.
The Yooper
I couldn't resist commenting on this. Are we in equilibrium? Is it possible to be in equilibrium? Think about it folks.
Do we know exactly what output from the sun produces this state?
I truly doubt we are ever in equilibrium. It's just such a hard thing to achieve in any system, much less an extremely complicated one like ours.
Then naturally we should be heating or cooling. Right?
Which one should we be doing now?
"@cruzn246: I don't think you understand what equilibrium means in this context."
Archie, explain it to me.
Why should I? You'll only ignore what I say and/or change the subject yet again. You've proved time and time again you're not interested in learning.
Here's a hint for you, though: equilibrium is not a "hard thing to achieve" in a system, it's what a system naturally tends to. Also, a thermal equilibrium isn't necessarily livable. Venus is in a thermal equilibrium (i.e. it's temperature is stable), but it's the closest thing we have to Hell.
"Why should I? You'll only ignore what I say and/or change the subject yet again. You've proved time and time again you're not interested in learning.
Here's a hint for you, though: equilibrium is not a "hard thing to achieve" in a system, it's what a system naturally tends to. Also, a thermal equilibrium isn't necessarily livable. Venus is in a thermal equilibrium (i.e. it's temperature is stable), but it's the closest thing we have to Hell."
Well, with Venus you have a completely different situation. It's like comparing apples and oranges. That type of equilibrium, static, is next to impossible in our atmosphere system . We have what is called a dynamic equilibrium.
I'll ask you the question that Tom doesn't seem to want to answer. Naturally, without anthropogenic influence, should we be heating up or cooling now?
It makes a difference, you know.
"Eliminating anthropogenic influence is the first issue. Do you mean all the changes since the land use changed by the introduction of agriculture, or the whole of the industrial revolution, or just the last 60 odd years of accelerated industry, land use and population changes?
It makes a difference, you know."
Of course it does. Lay a number on it.
So you think we should have stayed in about the same climate patterns we were having from the the 40s to the mid 70s?
Perhaps such a comment would better fit in the topic of models, however.
Next question?
Note another thing. The LAST part of that carbon chart shows the highest levels of carbon 14! The funny thing is it really took off in the latter part of the 19th century. that pretty much coincides with the warm-up from that time till the mid 40s. It says the graph stops in 1950. WHY? Are they afraid to show what happened with carbon 14 after that? I would say yes. they then go to a lame sunspot cycle. This is not the same as a carbon measurement. Why the switch? Because if they would have continued with a carbon graph you would have seen something like this.
I know this is not a carbon 14 measure, but this closely follows the same of pattern carbon 14 readings. If someone finds the chart for carbon 14 readings since 1950 I would sure like to see them.
Okay, now it's obvious you have no idea what you're talking about.
"I'll ask you the question that Tom doesn't seem to want to answer. Naturally, without anthropogenic influence, should we be heating up or cooling now?"
Cooling, most probably. The fact temperatures are still increasing tells you how large the anthropogenic influence is.
"The funny thing is it really took off in the latter part of the 19th century. that pretty much coincides with the warm-up from that time till the mid 40s. It says the graph stops in 1950. WHY? Are they afraid to show what happened with carbon 14 after that? I would say yes."
Are we back to conspiracy theories, now? The evil scientists are hiding the data, is that it?
"I know this is not a carbon 14 measure"
In other words, it is completely irrelevant. You just wanted to add a graph to give your innocuous post some credibility.
Please try to stick to peer-reviewed science - that way you avoid the people who trying to fool you.
"The carbon data is all over the place clearly showing the Little ice age big time, but hockey stick Mann claims it wasn't a NA event. Please."
Mann doesn't say that the LIA was a non event. It is very clearly evident in the Mann 2008 reconstruction;
"WHY? Are they afraid to show what happened with carbon 14 after that? I would say yes."
Congratulations, your official wacky conspiracy theorist tin foil hat is in the mail.
Carbon 14 ratio was a reasonable proxy for solar irradiance prior to the point that we started putting tons of fossil carbon into the atmosphere and releasing bursts of radiation with atomic explosions.
Of course, we've been able to measure solar irradiance directly for decades so we don't need proxies any more. We've been in a pronounced solar minimum for a few decades now... while temperatures have been going through the roof.
"I know this is not a carbon 14 measure, but this closely follows the same of pattern carbon 14 readings."
Ummm... what? They aren't even close. Total atmospheric carbon levels barely changed at all between 1000 AD and 1800 AD while Carbon 14 ratio was going up and down like a roller coaster along with TSI. Since then total atmospheric CO2 has risen at a steadily increasing rate while Carbon 14 has continued to roller coaster.
Er, no. Not even remotely. Did you miss this graph?
Figure 1: Reconsructed total solar irradiance (Delaygue and Bard 2010)
Note the Y axis.
The running mean of solar irradiance (after smoothing out the 11-year cycle) has varied by less than 1 W/m2 over the past 1300 years.
If it had actually dropped by 30 W/m2 for "over 500 years" we'd have glaciers running amok all over the place.
I can see it. I meant 1365. The graph is mostly under 1365, on average from about 800 AD to almost 1900 AD. from During the LIA it was averaging about 1364.75. Even the minimum around 1975 was higher than anything the previous 100 years.
Did you miss the 2008 announcement that solar wind strength is decreasing?
The average pressure of the solar wind has dropped more than 20% since the mid-1990s. ... The change in pressure comes mainly from reductions in temperature and density. The solar wind is 13% cooler and 20% less dense.
And yet, we still see higher temperatures. Why would that be?
OK, so we're talking about an 0.25 W/m2 forcing in a plane perpendicular to the Earth-Sun axis. That's an 0.0625 W/m2 forcing when distributed over the spherical top of the atmosphere, and about 0.044 W/m2 after taking into account the Earth's albedo.
In comparison, the IPCC TAR gives the total current forcing from greenhouse gas emissions (relative to 1750) as 2.10 W/m2. (And of course this is increasing every year).
So, you think that a (natural) 0.044 W/m2 forcing might just have happened to push us over some kind of tipping point, but you're completely unconcerned about a (anthropogenic) forcing that's 48 times larger and growing?
This kind of thing makes it very hard to take "skeptics" seriously. It's like the old joke about lawyers straining at gnats and swallowing camels.
This sounds like a continued effort to explain warming from solar effects. Lets try the science approach. What would we predict to occur, from considerations of past solar warming and from basics physics? Warming more pronounced in tropics; warmer days rather than warmer nights; summers warming faster than winters; and the biggy - the stratosphere warming not cooling. Observation dont match these predictions but they do match the predictions for GHG-driven warming.
http://zacost.zamg.ac.at/phaeno_portal/was-so-los-ist.html
In the end of the page: "Kirschblüte in Japan"
In this chart there are dates of full-flowering of cherry trees in Kyoto of years 700 to 2000. No LIA, but the recent warming is visible.
http://tinyurl.com/39nqn7m
Flowering of cherry trees in Japan does no reveal any LIA:
https://www.cfa.harvard.edu/~wsoon/MiyaharaHiroko08-d/AonoKazui07-Aug23-KyotoSpring.pdf
http://www.envi.osakafu-u.ac.jp/atmenv/aono/KyoPhenoTemp4.html
Part 1
Part 2
Part 3 is still to come.