Arguments
Does CO2 always correlate with temperature (and if not, why not?)
What the science says...
| Select a level... |
Basic
|
Intermediate
| |||
|
Surface temperature measurements are affected by short-term climate variability, and recent warming of deep oceans |
|||||
Climate Myth...
There's no correlation between CO2 and temperature
"Twentieth century global warming did not start until 1910. By that time CO2 emissions had already risen from the expanded use of coal that had powered the industrial revolution, and emissions only increased slowly from 3.5gigatonnes in 1910 to under 4gigatonnes by the end of the Second World War.
It was the post war industrialization that caused the rapid rise in global CO2 emissions, but by 1945 when this began, the Earth was already in a cooling phase that started around 1942 and continued until 1975. With 32 years of rapidly increasing global temperatures and only a minor increase in global CO2 emissions, followed by 33 years of slowly cooling global temperatures with rapid increases in global CO2 emissions, it was deceitful for the IPCC to make any claim that CO2 emissions were primarily responsible for observed 20th century global warming." (Norm Kalmanovitch).
At a glance
If you happen to be reading something about climate change in the popular media, be sure to keep an eye out for certain words. The one in this case is 'deceitful'. Why? Because it's an emotive word. It's a good sign that the writer is not a scientist but someone with a political axe to grind.
The heat-trapping properties of carbon dioxide, water vapour and other greenhouse gases were identified over 160 years ago. After that, climate research continued unhindered for many decades. However, by the second half of the 20th century the seriousness of the threat of climate change was well-understood. That led in due course to the involvement of bodies such as the United Nations. Treaties such as the Kyoto Protocol of 1997 followed.
In response, the fossil fuels sector and their political and media associates, perceiving threats to profitability, turned climate science into a political football. With climate science thus politicised, the arena within which research and outreach were conducted had changed. This was no longer a quiet backwater.
That's the historical context. Now we can get to the meat of the myth. The quote above this piece dates from September 2009. Apart from anything else, it's 14 years out of date now. Globally, the ten warmest years since 1880 have all occurred since the statement was made. According to NASA’s Goddard Institute for Space Studies, the average global temperature has increased by 1.4° Celsius (2.5° Fahrenheit) since 1880.
However, global temperature does not correlate exactly with CO2 emissions on a year in, year out basis.There are other well-understood factors that can warm or cool the climate over such short-term periods. You may have heard of El Nino and La Nina. These phenomena involve above- or below-average sea surface temperatures respectively, in the central and eastern Pacific Ocean. Their effects are global.
A strong El Nino can produce a massive global temperature-spike. Such very warm years once led to people making the claim of, "no warming since 1998". Briefly sounding plausible for a few years, it soon became self-evidently incorrect.
Instead, the correct way to look at temperature trends is to examine them over multiple decades - 30 years is standard in climate science. So to answer the question, "where are we now?", one would look at the temperature record from 1992-2022. Doing so takes out the noise, the ups and downs due to El Nino, La Nina and other factors. And the trend is most certainly upwards.
To the newcomer to climate science, it can be difficult to spot misinformation. However, opinion-pieces that accuse bodies such as the Intergovernmental Panel on Climate Change (IPCC) of intentions like deceit should instantly ring alarm-bells.
It is important to point out that the motive for such political misinformation is to spread confusion and doubt. The organisations behind it simply seek delaying any meaningful action. In kicking the can down the road, they try to deflect the pressure to get their own houses in order, and to hell with the consequences.
Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!
Further details
The amount of CO2 in our atmosphere is increasing all the time. On February 26th 2024, according to the monitoring resource Daily CO2, it had exceeded 425 parts per million (ppm). That's up by 3.96 ppm since the same time last year - but more importantly, up from around 280 ppm before the industrial revolution - a 50% plus increase.
Pre-industrial levels of CO2 and other greenhouse gases, like methane and water vapour, were sufficient to keep the Earth’s surface 30°Celsius (54°F) warmer than it would have been without them. Since then, we have added 50% more CO2 - but that doesn't mean the temperature will go up by 50% too.
There are several reasons why. Doubling the amount of CO2 does not double the greenhouse effect. The way the climate reacts is also complex and it can be difficult to separate the effects of natural changes from man-made ones over short periods of time.
As the amount of man-made CO2 goes up, temperatures rise but not at the same rate. Estimates vary - climate sensitivity is a hot topic in climate science, if you’ll forgive the pun. Based on multiple lines of evidence, according to the IPCC Sixth Assessment Report (2021), the "very likely range [for climate sensitivity to doubling of CO2] is 2°C to 5°C".
So far, the average global temperature has gone up by about 1.4 degrees C (2.5 F).
"In 2023, hundreds of millions of people around the world experienced extreme heat, and each month from June through December set a global record for the respective month. July was the hottest month ever recorded. Overall, Earth was about 2.5 degrees Fahrenheit (or about 1.4 degrees Celsius) warmer in 2023 than the late 19th-century average, when modern record-keeping began."
Source: NASA.
The speed of the increase is worth noting too. Unfortunately, as this quote from NASA demonstrates, anthropogenic climate change is happening very quickly compared to changes that occurred in the past (text in bold for emphasis):
"As the Earth moved out of ice ages over the past million years, the global temperature rose a total of 4 to 7 degrees Celsius over about 5,000 years. In the past century alone, the temperature has climbed 0.7 degrees Celsius, roughly ten times faster than the average rate of ice-age-recovery warming."
Source: NASA Earth Observatory.
Small increases in temperature can be hard to measure over short periods, because they can be masked by natural variation. For example, cycles of warming and cooling in the oceans such as the El Niño-Southern Oscillation (ENSO) cause temperature changes that can mask small changes in temperature caused by CO2 emissions that occur at the same time. That's why scientists measure changes over long periods so that the effects of short natural variations can be distinguished from the effects of man-made CO2.
The rate of surface warming varies year by year, yet the physical properties of CO2 and other greenhouse gases do not change. Neither has the amount of energy arriving from the sun changed significantly in recent decades. But if that’s true, where is this heat going?
The answer is into the oceans. Fig. 1 is a graphic showing where the heat is currently going:
Figure 1: Global Energy Inventory: observed changes in the global energy inventory for 1971–2018 (shaded time series) with component contributions as indicated in the figure legend. Cross-Chapter Box 9.1 Figure 1 (part a) - From IPCC AR6 WGI Chapter 9.
The way heat moves in the deep oceans was poorly understood up until around the turn of the millennium. Since then, vast improvements in measurement techniques, such as the Argo float system, have allowed scientists to far more accurately gauge the amount of energy the oceans are absorbing. Argo floats, numbering several thousands, weigh 20-30 kilograms and are packed with instruments. They typically travel through the oceans around a kilometre below the surface. But they can rise up to the surface or dive down to 2 km. That makes it possible to collect profiles in terms of temperature, salinity and other parameters. So far, over two million such data-profiles have been collected.
Argo data have shown the upper 2,000 metres of the oceans has captured roughly 90% of the anthropogenic change in ocean heat content since the programme started in 1999. Temperatures in the upper 600 metres have been seen to fluctuate with shorter-term climate events like El Niño-Southern Oscillation. In deeper waters, however, there is a more consistent warming trend. In summary, the 700–2,000 metres ocean layer accounts for approximately one-third of the warming of the whole 0–2000 m layer of the World Ocean being mapped by the Argo floats.
So we know that the energy added to the climate system by man-made CO2 is not only apportioned into surface warming, because a large part of the heat goes into the oceans. The rate at which surface temperatures go up is not proportional to the rate of CO2 emissions but to the cumulative total amount of atmospheric CO2. Only by looking at long-term trends - 30 years is the standard period in climate science - can we measure surface temperature increases accurately, and distinguish them from short-term natural variation.
Last updated on 10 March 2024 by John Mason. View Archives
Ive been debating a climate change denier for a while on a website, and he stated this and I was looking for a fair rebuttal:
"
I return to the fact that you should not make the assumption that I know nothing about climate warming - and you would learn more if you asked questions about what my beliefts are.
Carbon is only one of MANY forcing elements in climate. And the IPCC has been spectacularly wrong on many of them - and even admitted the same. Such as, for example the importance of aerosol formation on clouds. The importance of ionizing radiation for aerosol formation.
Finally, I return to a question I asked several weeks ago.
When the temperature of the ocean increases, the solubility of gasses decrease - something known as Henry's law or Boyles law. This causes the oceans - when they get warmer - to release massive quantities of CO2 (and O2 etc).
This is known fact.
The opposite is in fact, not proven. In other words given increased CO2, AGW says that ocean temperatures increase.
The observable fact is that increasing temperatures correlates with increased CO2 concentration. But it doesn't say a damn thing about causation.
Can you restate my point here so that I can confirm you understand it?"
[TD] See the post "CO2 is Not the Only Driver of Climate," noticing the relative contributions of various forcings. By "ionizing radiation" I'm guessing that he/she means cosmic ray influence on clouds; see "It's Cosmic Rays." Notice there are multiple tabs--Basic, Intermediate, and Advanced.
Regarding oceans: Of course climatologists know that the CO2 absorbing capacity of the oceans decreases as the oceans warm. However, oceans continue absorbing until they reach a fairly high temperature. And a counterforce is that the oceans also absorb more CO2 as the amount of CO2 in the atmosphere increases. Climatologists figure all that into their calculations. We know that currently the oceans continue to absorb, not emit, CO2, because (a) the oceans continue to acidify (i.e., become less alkaline) as a consequence of their CO2 absorption, and (b) the oceans absorb the bulk of CO2 from human activities, along with all the natural emissions of CO2: See here and here.
Causality of CO2 versus temperature was established when the mechanisms were understood (via experimentation) back in the 19th through mid 20th centuries. Observations of global temperatures confirming those theoretical projections were made decades later, when global observations were sufficiently capable. The exact mechanism by which CO2 warms the oceans was determined later, but again with experimentation.
The fact that temperature increase causes CO2 increase in no way undermines the fact that CO2 increase causes temperature increase; see "CO2 Lags Temperature" and also "Warming Causes CO2 Rise."
Also have another one I'd like answered:
"If you take an atom of CO2 in the lower atmosphere and it absorbs energy and reradiates it - molecules can be modelled as radiating energy in all 360 degrees. Part of that energy gets radiated back to the earth (around 36% in the lower troposphere) and part gets radiated to space. (I'm simplifying, ignoring the convective, conductive etc elements of energy transfer between atoms, reradiation etc).
As you ascend the atmospheric column ipast the troposphere, several things happen.
a). The arc of reradiation to the earths atmosphere decreases (to a very small number - less than 1%). And the amount reradiated to space increases. (Virtually all).
b). The contribution of convection, conduction decrease as well to almost zero, and the contribution by radiation dominates (due to concentration of molecules, primarily).
So, by the time you get to the outer atmospheres, CO2 is no longer acting to warm the planet. In fact in the outer atmosphere, the amount of energy absorbed from IR emitted from the eart is for all intents and purposes - zero. Instead, in the outer atmospher, CO2 is energized (and in fact is almost always a plasma in some strata) by much more energetic radiation. And CO2 serves to reradiate this energy back into outer space.
This is proven born out by the fact that the energy density of solar radiation at the outer edge of the atmosphere is roughtly 1347 per meter square. And the aereal density at the earth's surface is much less than a quarter - the rest of the energy (simplification) is reradiated to space.
So in fact, by the outer atmosphere, CO2 is acting to COOL the planet.
In the previous thread, I provided links to the study by Nasa that confirmed this finding, and confirmed that they would have to reconsider the NET effect of CO2 on global warming (warming in the low atmosphere, cooling in the high atmosphere)."
[TD] First, he needs to revisit his geometry; CO2 molecules would have be to pretty darn high for "nearly all" of their emitted radiation to go to space. Here is one explanation of how CO2 cools the stratosphere while warming the troposphere: "Stratospheric Cooling and Tropospheric Warming."
tkman0... It sounds like your denier-guy has a bunch of accurate facts but is interpreting entirely the wrong way.
For one, the IPCC isn't getting things "spectaculary wrong." They're merely putting out a report on the current science. If he wants to claim the IPCC is misinterpreting the research, I would have to say, I don't hear a lot of climate researchers jumping up and down about these supposed errors.
Your denier-guy correctly states that there are many forcings that act on the climate system. I'd have him watch Richard Alley's lecture "The Biggest Control Knob" which explains the science of why CO2 is the biggest (but not only) factor controling global temperature.
Another weird one here: "This causes the oceans - when they get warmer - to release massive quantities of CO2 (and O2 etc)." Etc, etc.
He's getting his knickers in a knot merely because he doesn't understand that CO2 can act as a feedback (as with ocean warming/glacial-interglacial cycles) but can also act as a forcing (as with burning fossil fuels).
tkman0,
Your description seems about right to me. At the surface (where we live) CO2 causes warming. In addition to the angle of emission, energy emitted upward is usually reabsorbed by another CO2 molecule at a higher altitude. This enhances the warming. Since the troposphere is cooler the higher you go, the higher molecule emitts less energy. As CO2 concentration in the atmosphere increases, the hight in the troposphere where the energy can escape to space becomes cooler. This is the basis of the greenhouse effect. This post on hte greenhouse effect might help a little.
The stratosphere is also cooled as you describe. This is one of the key predictions of greenhouse theory and demonstrates that the warming is caused by increased greenhouse gases and not the sun. There is no significant transfer of energy from the stratosphere to the troposphere so the cooling effect in the stratosphere has no significant temperature effect at the surface of the Earth. This effect was predicted decades ago.
Most of the energy that reaches the outer edge of the atmosphere reaches the troposphere. Half of the difference between the 1347 and the about 270 w/m2 at the surface is caused by the fact that half the Earth is in darkness all the time (the night side) so you have to devide 1347 by 2. Much of the rest of the difference is due to the fact that the remaining 675 W/m2 is a square meter perpendicular to the sun and the surface of the Earth is round so most does not receive the light directly. About 1/3 of the light is reflected by clouds. Scientists studying climate (the IPCC) have measured all this. While some energy is emitted from the upper atmosphere by CO2, the net effect on the surface of the Earth is warming. Much of the reflected energy and the energy emitted from the stratosphere has always been emitted. It is the changes in energy flux casued by changes in CO2 that we are interested in. Those energy fluxes cause the surface warming.
tkman0 @30:
From what follows, the assumption seems well warranted.
Your interlocuter here refers to Svensmark's hypothesis that cosmic rays cause clouds. He is definitely wrong about the IPCC being mistaken about this hypothesis. In AR4 all they had to say was:
What the IPCC AR5 actually says on the effects of cosmic rays on climate is:
Now, either your interlocuter thinks Svensmark's hypothesis is falsified, and was falsified as of AR4 (in which case they have indeed corrected an "error"), or he is completely misrepresenting the IPCC, presenting a stronger rejection of the hypothesis as being a correction of prior rejection of the hypothesis (which does not exist).
Absolutely it is a known fact. What is uncertain is the exact ratio of increase in atmospheric CO2 per degree C increase in Global Mean Surface Temperature (GMST), as other factors are involved. We can quantify it approximately, however, by the 100 ppmv increase in CO2 for an approximately 5 degree C increase in GMST between the last glacial and the Holocene. That gives an expected increase of 20 ppmv in atmospheric CO2 per degree C. Alternatively we could quantify it from the 10 ppmv increase in atmospheric CO2 during the MWP, although a massive human cause deforestation may interfere with that calculation. In either case, it is clear that this effect is not adequate to explain even half of the increase in CO2. Deniers hide that fact by referring to Boyle's law, but never quantifying the details. It is as though they have something to hide, and know it.
Even worse for your interlocuters argument is the fact that CO2 concentration in the ocean has been increasing. His theory predicts that it would be decreasing. Further, the decrease in proportion of C14 in the atmosphere indicates the source of the CO2 is C14 free, ie, like fossil fuels, and unlike oceanic CO2. Indeed, six out of 10 lines of empirical evidence preclude oceanic outgassing as being the source of the excess atmospheric CO2, with another two lines of evidence providing contrary evidence, but not decisively so.
tkman0 @31:
Your interlocuter is ignoring absorption and reradiation of emitted energy. Therefore his claim purports to be based purely on geometry. For only 36% of the sphere to be occupied by the Earth's surface, the angle from the closest point of the surface to the limb of the planet as seen from the point of emission must be 64.8 degrees. Given that the radius of the Earth is 6,371 km, it follows that the point of emission must be 670 km above the Earth's surface. Given that the troposphere only extends from 10-20 km above the Earths surface, your interlocuter's definition of the "lower atmosphere" is bizarre to say the least. Indeed, it only just avoids being in the exosphere, the layer of atmosphere from "700 km to the Moon's surface", a layer higher than most satellites.
The later 1% claim is even more outrageous. It requires an altitude of 196,458 km, approximately half way to the moon.
In fact, as you rise in the atmosphere, more and more radiation does escape to space - but that is entirely due to the decreasing atmospheric concentration rather than to changes in the subtended arc of the Earth's surface. Further, the proportions he quotes are pure fictions.
Does your interlocuter think the Earth has more than one atmosphere? Given the absurdity of some of their other errors, it is hard to be sure what is mistyped, and what is another fallacy.
What your interlocuter says from there on is reasonably close to true. It is only true of the Thermosphere, however, ie, the atmosphere from 50 to 800 km in altitude. At that altitude temperatures vary rapidly as the result of energy being dumped into the atmosphere from solar flares. That energy is then rapidly reradiated away, primarilly by CO2, with about 90% going to space and 10% to Earth. The effect is to buffer the Earth, reducing the increase in temperature at the Earth's surface from increased solar activity.
The effect has nothing to do with the greenhouse effect, which occurs in the first 30 km of the atmosphere. Above that, atmospheric concentration is to low to have much of an effect. It certainly does not falsify the greenhouse effect which has been experimentally observed and shown to exist in no uncertain terms.
Thank you very much for your assistance Tom, I'm an 2nd year Environmental Science major in university right now and while climate and resource management is my focus, it helps to have a seasoned researcher assist me in dealing with this denier.
tkman0 @36, de nada! I do need to correct a misapprehension. I am not a researcher, let alone a seasoned researcher.
tkman0... Don't let Tom fool you with his humility. He is probably the best informed non-researcher I've ever had the pleasure to come across. While actual researchers are likely to have a deeper understanding of their own area of the science, Tom probably has the broadest knowledge of climate of anyone I've seen.
When ever I look at the air temperature data, my eye always falls on the two upward trends, from 1910-1943 and 1970 to 2001. I keep finding myself thinking they have pretty much the same slope and the same duration. I cant help but thinking they may not have a common cause.
When I look at the modeling results of natural forcing only, like in the intermediate rebuttal of the 'models are unreliable page', niether period is modelled well. The man made forcing only model only captures the second increase. CO2 levels and increases are quite different in these two periods.
I realize that weather and climate data can be variable and can make one imagine things, but has there been any kind of study comparing these two periods?
Razo @39, yes there has been such a study. Many of them, which are summarized in the IPCC.
In summary the results are:
1) The early twentieth century warming was of a shorter duration, and with a lower trend than the late twentieth century warming;
2) Durring the early twentieth century warming, volcanic forcing, solar forcing and anthropogenic forcings were all positive relative to the preceding decades, and had similar magnitudes;
3) Durring the late twentieth century warming, volcanic forcing and solar forcing were both negative relative to preceding decades, while anthropogenic forcings were strongly positive.
Razo wrote "I cant help but thinking they may not have a common cause."
that is pretty irrational, given that we know that both anthropogenic and natural forcings have changed over the last century, and that neither can explain both sets of warming. So for that hypothesis to be correct, virtually everything we know ablut natural and anthropogenic forcings must be wrong. Personally I'd say the hypothesis was wrong.
"When I look at the modeling results of natural forcing only, like in the intermediate rebuttal of the 'models are unreliable page', niether period is modelled well."
It has already been explained to you that this is likely an artefact of the baselining. The fact that both periods are reasonably well modelled by including both natural and anthropogenic forcings kind of suggests that the two periods do not have a common cause.
"but has there been any kind of study comparing these two periods?"
Try the IPCC report, the chapter where the figure was taken from is a good start.
Linear 'fit' to the last 38 years of ocean data yields 0.3 watts/m^2. Essentially the same as the Livitus et al results. This is ~93% of global warming power with a decent average time. Note this is only about 1/10 of the global warming power claimed by IPCC to reach 3C in a century.
Hi from Spain. I have a question:
"How much of the thermal radiation energy from the Earth in the band centered on the 14.77micron wavelength that is resonant with the vibrational mode of CO2 has already been affected by the current atmospheric CO2 concentration, and how much energy remains to be affected?”
A greeting and thanks in advance
SOMMERSWERD - See CO2 is saturated for a discussion of this. The real effects of greenhouse gases take place in the upper atmosphere when the concentrations drop to the level that IR can escape to space, and increased levels of CO2 just raise that altitude. There is no 'saturation' issue.
[PS] Fixed link
KR
My question was simple but you have not responded. No discussion; just a question that you do not respond directly.
[PS] KR pointed you to a more appropriate thread for discussion of question. It is off-topic here. Please take the discussion there. Offtopic discussion will be deleted from this thread.
SOMMERSWERD - Actually, I did answer your question. Atmospheric absorption is concentration and hence pressure/altitude dependent, with sea level pressure and concentrations of CO2 absorbing all CO2 frequencies in a matter of meters.
What matters for the greenhouse effect is at what temperature (and hence rate) IR is emitted to space - that occurs at altitude, when there is insufficient CO2 above the effective emission altitude to absorb the majority of the outgoing IR.
Increasing CO2 simply raises the effective emission altitude - and there is in fact solid data showing that over the last 50 years the tropopause where the effective emission occurs has risen a few hundred meters. Given the lapse rate relationship, that altitude change accounts for the observed rise in temps over that period.
So in detail the answer is "it depends on what you're asking". All CO2 frequencies get fully absorbed at the surface (with corresponding thermal emission), the strongest absorption lines continue to absorb a majority of the IR at those frequencies until pressure drops enough to allow >50% through to space, and changes in CO2 concentration simply change that altitude - where again >50% of the emitted IR at those wavelengths escapes the atmosphere. Your question "...how much energy remains to be affected?" is therefore somewhat meaningless without more context.
SOMMERSWERD - ...And your question is in fact a query about CO2 absorption saturation, which is more appropriately dealt with on the appropriate thread.
[PS] Fixed link
The global temperature did not increase from 1940 to 1970.
How do you explain this?
[PS] Read the article. (Net forcings, see figures 5 and 6 on the intermediate version of the article). Warning: Asking questions without any interest in the answers is simply sloganeering and forbidden by the comments policy.
I had read the article and still I did not understand why the global temperature did not increase
from 1940 to 1970. Could you tell me what is the main cause of it?
[PS] From the article, "If CO2 causes warming, why isn't global temperature rising over this period? To answer this, one needs to recognise that CO2 is not the only driver of climate. There are a number of factors which affect the net energy flow into our climate. Stratospheric aerosols (eg - from volcanic eruptions) reflect sunlight back into space, causing cooling. When solar activity increases, the amount of energy flowing into our climate increases. Figure 5 shows a composite of the various radiative forcings that affect climate."
Figure 5 shows all the factors other than CO2 affecting climate of the period and Fig 6 sums all them, positive and negative, to show little net forcing till 1970. Please take some time to study actually study and understand the figures.
Ken @49, your question is answered in the thread "CO2 is not the only driver of climate".
Quickest to go to the comments column there, and see Bozzza's (@20) laconic quote: "aerosols" ~ which is the short story . . . that could be expanded slightly to: "increasing industrialization produced reflective aerosols which counterbalanced the rising CO2, until the ever-higher CO2 levels overpowered the aerosol effect by around 1970 [combined with some clean-up of aerosol emissions].
You will note Tom Curtis's (@21) longer explanation of additional factors which contributed to a "flat" 1940-1970 record.