What About Mid-Century Cooling?

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.


There was global cooling in the 40's, 50's and 60's even while human Greenhouse gas emissions were rising. Clearly, temperature is not being driven by CO2.


None of the advocates of the theory of Anthropogenic Global Warming claim that CO2 is the only factor controlling temperature in the ocean-atmosphere climate system. It is a large and complex system, responsive on many different timescales, and subject to numerous forcings. AGW only makes the claim that CO2 is the primary driver of the current warming trend, as in the rapid rising seen over the last 100 years. This rise has not been smooth and steady, nor would it be expected to be. 

If you look at the temperature record for the 1990's you'll notice a sharp drop in '92, '93 and '94. This is the effect of massive amounts of SO2 ejected into the stratosphere by Mount Pinatubo's eruption. That doesn't mean that CO2 took a holiday and stopped influencing global temperatures, it only means that this greenhouse gas forcing was temporarily overwhelmed by another opposite forcing.

The situation is similar to the cooling seen in the 40's and 50's. During this period the CO2 warming (a smaller forcing at the time) was temporarily overwhelmed by by other factors, perhaps foremost among them, an increase in human particulates and aerosol pollution. Pollution regulations and improved technology saw a decrease in this different kind of emissions over the 60's and 70's and as the air cleared, the CO2 signal again emerged and took over.  Below, courtesy of Global Warming Art, is an image of the current understanding of the factors and their influence for the climate of the past century.

As the graph shows, as well as aerosol pollution (the sulphate line), volcanic influences were increasingly negative during the period of global cooling as also solar forcing slightly declined.  All forcings taken together and run through the model are a very good match for the observations.  (Please see the source page for details of what model and what study this image is derived from.)

So rather than confounding the climate consensus, mid-century cooling is actually a good test for the climate models, one they are passing quite convincingly.

Addendum: The opposing effect of cooling from airborne pollutants is often referred to as "Global Dimming" and Real Climate has a couple of articles on that effect:

One emerging concern is that as the pollution causing this effect is gradually cleaned up, we may see even greater greenhouse gas warming.

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

"What About Mid-Century Cooling?" was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.

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Why haven't you updated the graph to show current temperatures?

[ I will do that ASAP, these articles were written two years ago, my apologies.]

As a skeptic, I would postulate that it is because current temperature anomalies are around zero, and have gone negative.

[The short term trend has stalled, yes, but the anomoly is still .4oC as of 2007 (see CRU)]

It's such an easy spot on any alarmist site. Just look at the right hand side of graphs, and see when they truncate them.

[No, no conspiracy here, just a stale web page! Thanks for pointing it out. - coby]

" but the anomoly is still .4oC as of 2007 (see CRU)]"

Down to 0.2C or less as of 2008.

2008 was cooler than 8 of the previous 10 years and no warmer than 1980.

First to Travis, you need to supply a link so Coby can pick the crap out of it, whilst at the same time use words like "perhaps" when stating his case.

Coby i have another theory as to why the temps went down from 1940 to 1970 and then up from 1970 to 1998 and now why they are going back down again.

It is called the "Pacific Decadal Oscillations" you will find it listed under "science" so do yourself a favour and look it up.

Hi Crakar,

The problem with your PDO theory is that internal variability can not explain a net gain in thermal energy. Ups and downs maybe, but a century of steady climbing requires some kind of change in the radiative balance, i.e. a forcing of some kind that is external to the system.


I thought i would mention the PDO bit because in the "answer" section of this topic you only mention man made pollutants as a cause for the cooling periods rather than the myriad of other non human factors that drive the planets climate. Therefore i found the "answer" section to be highly misleading. However i do understand for the need of simplicity and how hard it would be to cover all of the factors.

Having said that i believe you have come close to the heart of this issue, Lets assume that ONLY changing PDO and El Nino/La Nina cause a 30 year approx swing in planetary climate why has the temp been slowly rising?

As you state "but a century of steady climbing requires some kind of change in the radiative balance, i.e. a forcing of some kind that is external to the system."

What external forces could cause this? Well some beleive it is soley C02 others believe the Sun plays a large part as well, submerged volcanoes can also warm oceans and the list goes on...........

Travis is correct when he states the globe is cooling, yes it is above the anomoly but lets look at the big picture, and that shows the planet is cooling.

The question is will it continue to cool for another 20 years or so or will it get warmer in the short term as the IPCC etc state?

For me, history shows the planet warming and cooling the latest warming started 300 odd years ago and there is not a shred of evidence that points to C02 being a major driver of the warming, having said that all the evidence and theories that points to other sources as a major climate driver are still in their infancy.

I am more inclined to beleive that as you state the PDO plays a major role but their are other factors at work and to me the sun plays a much larger role than we understand. How big i am not sure but i beleive it to be much more than C02. Of course i might be wrong and if the temp starts to go up soon again then i suppose i am.

My question to you is if the planet continues to cool (lets assume it does) at what point would you abandon the AGW line of thought? What anomoly number (0, -.2 etc) would you consider as the level where C02 goes from being a major player to a bit part player in climate drivers?

For me it matters little what the temperature readings say from year to year, even the global temperatures. There are so many variables (forcings) that go into the averages that in the short run the temps are almost irrelevant. The danger is the steady increase each year of greenhouse gases, especially CO2. Now if we were to see those start to decline then we would have to rethink the entire theory of anthropomorphic climate change. But until that happens, the CO2 levels in the atmosphere are like a loaded gun at our head waiting for the other forcings to align. That is when we will see runaway temperatures as the greenhouse gases magnify the effects of other forcings such as sun activity and deforestation.


"For me it matters little what the temperature readings say from year to year, even the global temperatures. There are so many variables (forcings) that go into the averages that in the short run the temps are almost irrelevant."


"The danger is the steady increase each year of greenhouse gases, especially CO2."

Doubling CO2 will have half the impact of the previous doubling which was half the previous doubling. (I'll leave aside my contention that the CO2 absorption band is already saturated).

The levels of CO2 have been far higher than double the current levels - and in those times the oceans teemed with life including the current corals and other of the older groups of sea life that still exist today - lowered Ph or not. (Reports from the less politically correct experts state that the coral like the Barrier Reef is NOT suffering but that's another argument).

Given what we know about atmospheric CO2 concentration, that it has been higher in the past without the world turning into a desert and in fact when it was higher the Earth seemed to flourish more, I don't see any danger in higher CO2. I am becoming less and less convinced by the hypothesis of AGW which depends on apocalypse to get 'action' which always appears to be higher taxes.


Strangely the more the histrionics from the proponents of AGW the more the doubt in what they are saying. So it was the Nobel and Oscar winning "An Inconvenient Truth" that convinced me that CO2 driven AGW was probably not real. If one has to tell untruths to support a hypothesis - then it cannot be correct.

So let us assume that the world was really going to come to an end in only 4 years (Hansen) with CO2 output as it is now. Is it responsible to reduce the number of temperature measuring stations and only keep those that are decrepit and known to be incorrect? Is it responsible to allow type approval to vehicles whose operation increases the CO2 in the atmosphere (locally or remotely)? Is it really responsible to allow the transoceanic and transcontinental transport of groceries? Is it responsible to allow China and India to carry on building coal fired power plants? etc etc

What we DO see is taxation taxation taxation just enough to get money but not enough to stop what is going on - and the AGW proponents crying crocodile tears as they fly off to the next tropical convention center where they cram 4 hours work into 2 weeks.

This is NOT a convincing case

The worst argument (and there are many) against human induced climate change is that greenhouse gases are not heating up the planet or they are not as bad as the scientists want us to believe. I don't know if doubling the CO2 levels in the atmosphere is going to have half the impact as in the past or twice as much. But neither do the GW deniers. And I'm not willing to bet everyone's future on the slim chance that they may be right.

Given the strength of the evidence that supports the global warming theory, the right thing to do is take action to reduce the amount of greenhouse gases we pump into the atmosphere each year. That is where the legitimate debate has shifted.


Every scientist worth his salt knows the logarithmic relationship between C02 and temp, ie the doubling effect, both AGW proponents and the "deniers".

And just what is this "strength of the evidence that supports the global warming theory"

The IPCC projections for C02 levels to 2100 are already way too high after only 8 years!! Therefore their predicted temp for 2100 is already completely wrong.

C02 levels have been much higher in the past they were about 6000ppm (as opposed to 385ppm now), before the last ice age (the reasons for the ice age are debatable) but the fact still remains C02 did not stop the advance of said ice age, why is this so?

I do not know any "denier" that will state C02 has nothing to do with temp etc, however there is much debate on how much C02 causes the temps to rise. You need to do a bit of research yourself on these things to get a balanced view as i am sure i cannot and do not wish to convince you either way.

But remember if you have a computer model written based on assumptions, data inputted based on assumptions then what would you expect to get out? Like the old saying "GIGO" which translates into garbage in, gods truth out.

In summary, after 20 years the IPCC has not reduced C02 emmission by one molecule, after all the talkfests at some of the worlds most beautiful locations all they have come up with is an agreement that lets the worlds largest producers to keep on producing. In my country legislation will soon be debated that will allow the big producers to get carbon credits for free!!!! FOR FREE!!!!!!!!!!!!!!!!!

But dont worry none because i will be required to pay a TAX, and we like the rest of the world will continue to produce C02.

Since we haven't reached the year 2100 yet it is impossible to know accuracy of the IPCC temperature projections. What we do know for sure is that CO2 is increasing each year, man is causing this rapid increase, and the effect of the additional CO2 is to warm up the planet, possibly above levels that can sustain human life.

And remember, the concern here is the effect of rapid warming on human life. Were the CO2 levels to rise again to 6000 ppm it would be the end of human life as we know it. The fact that we had runaway CO2 levels 500,000,000 years ago is a poor argument for not paying attention to 21st century warming. Human development has occurred over a relatively narrow range of atmospheric CO2 levels.

By mikatollah (not verified) on 05 Feb 2009 #permalink

Quote "Since we haven't reached the year 2100 yet it is impossible to know accuracy of the IPCC temperature projections."

There is a lot of irony in this statement as i thought the models were bullit proof?

Quote "What we do know for sure is that CO2 is increasing each year, man is causing this rapid increase, and the effect of the additional CO2 is to warm up the planet, possibly above levels that can sustain human life."

C02 comes from many sources, the oceans are the largest C02 deposit. C02 lags temp by at least 800 years so tell me how much C02 has man produced? And show me the proof it has caused all the warming from the past 60 to 70 years.

Co2 levels were well above 5000ppm or more when the dinosaurs were alive (could man survive these levels?)

The smoothed Co2 levels were about 307ppm in 1940 up to about 337ppm in 1980, then to a bit under 385 in 2007

How many thousands of years would it take to reach 6000? We need to keep this in perspective something the IPCC has failed to do, as i said after 8 years into a 100 year prediction they are already wrong, this effects the predicted temp as well dont forget.

Thanks for response


I don't believe anyone has ever made the argument that climate models are "bulletproof". That is a straw man, and does not advance your argument... the models are tools used to make predictions based on the physical evidence.

We have a good idea what the CO2 levels have been in the atmosphere for the past several hundred thousand years, thanks to the ice core research. We also can see what has happened to them since the mid 19th century, which is roughly the beginning of the industrial age. The correlation is so clear to me and I don't know why some of my friends can't see it. Well, actually I do know, but I try to be nice anyway.

Sadly Crakar, there will never be enough proof for people like you. By that I mean folks who are too ideologically blinded to see the evidence. Fortunately, we don't need you to take action to reduce greenhouse gases. But it is important to respond to this nonsense so that people do not become complacent.

Don't hate the science...


Oh but it does advance my argument, the AGW theory is based primarily on model predictions and very little empirical data, therefore it is essential that the models are accurate or bullit proof. Models are not proof etc.

I suggest you take another look at the correlation you speak of, C02 levels have been up to 20 times higher in the past and yet temps have remained vertually steady at around 22C. In fact there seems to be very little correlation up until recently (as in thousands of years). Even then the correlation shown shows C02 LAGGING temp by about 800 years.

Co2 does not drive temp it is the other way around and C02 has very little effect on the green house.

There are many climate drivers out there that actually drive the climate for example, ocean currents that switch evey 30 years or so, ENSO and of course the sun.

Now if you want to look at correlation take a look at sunspot activity and the temps on Earth.

C02 is the gas of life below 250ppm plants stop growing, at 150ppm plants die so just how low do you want C02 to go?

All of these arguments you make have been made and debunked on this and other sites many times over, so there is no need to rehash them here. Just for the record, my favorite is the one where plants need CO2 or they will die. Interesting variation (and by interesting I mean bizarre) on the "CO2 is good for us" argument.

AGW theory does not exist because of computer modeling. The theory existed long before computer modeling and it's fate will rest on empirical evidence, not computer generated predictions. This is a red herring that I see every day to try and confuse the American public into inaction. The war against the truth of climate change is not about the science, it is about a disinformation campaign conducted as a PR battle.

Deniers have no scientists... they have bloggers.


Your argument is very well reasoned but I do not think it is supportable. Hansen at Climate Change Congress in Copenhagen stated that:

Even if we accept the IPCC aerosol estimate, which was pretty much pulled out of a hat, it leaves the net forcing almost anywhere between zero and 3 watts.

We do not have measurements of aerosols going back to the 1800s â we donât even have global measurements today.

Any measurements that exist incorporate both forcing and feedback.

Aerosol effects on clouds are very uncertain.

As I under stand what Hansen is saying, there is no evidence to back up you position. Further, if what I read is correct, and I am not a statistian, on lucia's site, the acutal temperature falls outside the 95% confidence interval for the multi-model mean for GCM's that do incorporate volcanic forcings.

I think that you may be right, but there is no evidence to prove it. We just had a studies that show that aerosols are responsible for cooling the Atlantic and yet another study shows that aerosols are responsible for 1/3 to 2/3 of the warming in the Arctic.

I have two critiques of the main article:

First, it appears to me that what has been done with the back-correction of the model for Volcanic and Aerosol effects is somewhat problematic. The key question is how do they know that they have the correct climate sensitivities for these effects? It appears that the authors of this study have assumed that the AGW models are correct and have used the offset between the AGW model results and the temperature record to calibrate the sensitivities of the Volcanic and Aerosol effects. That is fine, but it means they cannot then use those same sensitivities with the same data set to prove that the AGW models are correct!

The sensitivities they have gotten may be correct, but we will only be able to verify that is the case in the future when we have new data showing that the combined model including all effects correctly predicts the temperature trends.

My second critique is just a minor quibble about the last line:

"One emerging concern is that as the pollution causing this effect is gradually cleaned up, we may see even greater greenhouse gas warming."

If pollution-derived cooling is removed it may lead to additional global warming, but not to additional "greenhouse gas" warming, unless you are saying that the pollution somehow inhibits the ability of CO2 or other gases to behave as greenhouse gases.

By SemiChemE (not verified) on 19 Jun 2009 #permalink

Hi SemiChemE,

Point taken for your second quibble. I hope readers will understand what I meant.

For your first point, climate sensitivities to various forcing are not inputs to the models, they are derived outputs. There surely are many estimates of factors that are poorly constrained by observational data, this will always be the case. And a certain amount of back and forth between model adjustments and data improvements is going to be an ongoing process. But I don't think it is as simple as tweaking the expected effects of sulphates so that CO2 is seen to have a large role.

All of these factors combine and all have various observational data and physical derivations to constrain there possible importance, in the end the validation comes from hind casting, the time scales involved don't really allow for us to wait for predictions.

A while back it was suggested that a change in data collection methods could have resulted in an apparent spike in ocean temperatures (especially the North Atlantic) during and just after World War II. Have the data been corrected for this and does it make any noticeable difference?

By Richard Simons (not verified) on 20 Jun 2009 #permalink


You are probably talking about this...?

I would assume that the current temperature records that incorporated that data have incorporated the corrections. I have not seen any before-after comparisons with the exception of the schematic guesstimate from the Guardian (you can see it at the link above.

Yes, Coby, that's the one (I looked for it but couldn't find it). I see that the graphic you used is based on 2004 data so it obviously won't include the 2008 correction. I haven't seen anything that explicitly included it but, if the Independent's graphic is any guide, the 1940s peak and dip might be a lot less conspicuous.

By Richard Simons (not verified) on 20 Jun 2009 #permalink

Temperatures seem to have been higher in the past, if the graphs created from the Vostok data are to be believed, with much lower levels of CO2. How do we know that what caused THOSE warmer climates isn't causing THIS warmer climate?

It also appears that the temperature increases PRECEDE the CO2 increases (which makes sense to me in that warmer climates are more conducive to life), so how do we know "how much" of this (or any other) warmer period is caused by CO2?

Anthony: it's called Milankovitch cycles. We know we're not in part of a cycle that should give warming. We're in part of the cycle that should give colder temperatures.

Moreover, we know that in the past(!) temperature increases *started* before CO2 increases, but for most of the time the two then increase in parallel. I don't see the "sense to me" in increasing CO2 levels at higher temperature related to life. Life doesn't just exist of CO2 emitting species. In fact, you need plants in larger amounts to be able to sustain the food chain. And plants *use* CO2.

Regarding your last question: physics.


Re post 26

You delight yourself in ridiculing me at every opportunity but i will refrain from returning the favour this time as i know you can do better. The next time you type such rubbish i will not be so lenient.

The "source page" for the Climate Change Attribution graph does not come up.