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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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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).

Why doesn’t the temperature rise at the same rate that CO2 increases?

The amount of CO2 is increasing all the time - we just passed a landmark 400 parts per million concentration of atmospheric CO2, up from around 280ppm before the industrial revolution. That’s a 42.8% increase.

A tiny amount of CO2 and other greenhouse gases, like methane and water vapour, keep the Earth’s surface 30°Celsius (54°F) warmer than it would be without them. We have added 42% more CO2 but that doesn't mean the temperature will go up by 42% 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 is 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 do not rise at the same rate. In fact, although estimates vary - climate sensitivity is a hot topic in climate science, if you’ll forgive the pun - the last IPCC report (AR4) described the likely range as between 2 and 4.5 degrees C, for double the amount of CO2 compared to pre-industrial levels.

So far, the average global temperature has gone up by about 0.8 degrees C (1.4 F).

"According to an ongoing temperature analysis conducted by scientists at NASA’s Goddard Institute for Space Studies (GISS)…the average global temperature on Earth has increased by about 0.8°Celsius (1.4°Fahrenheit) since 1880. Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade."

Source: NASA Earth Observatory

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 emboldened 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 cause temperature changes, but they are hard to separate from small changes in temperature caused by CO2 emissions which occur at the same time.

Tiny particle emissions from burning coal or wood are also being researched, because they may be having a cooling effect. Scientists like to 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 has slowed in the past decade. Yet the physical properties of CO2 and other greenhouse gases cannot change. The same energy they were re-radiating back to Earth during previous decades must be evident now, subject only to changes in the amount of energy arriving from the sun - and we know that has changed very little. But if that’s true, where is this heat going?

The answer is into the deep oceans. Here is a graphic showing where the heat is currently going:

From Nuccitelli (2012)

The way heat moves in the deep oceans is not well understood. Improvements in measurement techniques have allowed scientists to more accurately gauge the amount of energy the oceans are absorbing.

The Earth’s climate is a complex system, acting in ways we can’t always predict. The energy that man-made CO2 is adding to the climate is not currently showing up as surface warming, because most of the heat is going into the oceans. Currently, the heat is moving downwards from the ocean surface to deeper waters. The surface gets cooler, humidity reduces (water vapour is a powerful greenhouse gas), and air temperatures go down.

The rate at which surface temperatures go up is not proportional to the rate of CO2 emissions, but to the total amount of atmospheric CO2 added since the start of the industrial revolution. 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.

Basic rebuttal written by GPWayne

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Last updated on 17 July 2015 by MichaelK. View Archives

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Comments 176 to 182 out of 182:

  1. MA Rodger @175. 

    I didn't suggest there was a 0.6 increase 1880 to 1940's. My figure was 0.4 (Based on Global).

    Your "three quarters would perhaps have been closer to the mark" is not representative of the timeframes the NASA statement refers to. I'll assume you've added the 0.2 you referred to.

    Point was, NASA was talking about a portion of a total increase in a shorter timeframe than that overall gain was actually made, when looking at the total period.  They have done this to create a narrative and the OP has seized on that to further that narrative.

    There's no point selecting a short period to further a theory when the previous short period contradicts that theory.  Being selective with data to illustrate a point doesn't work and raises the question of objective credibility.

    There may have been some relevance to a rate of gain if a trend was always gaining.

  2. strop @176.

    You fail to describe this "theory" you mention @176. As it appears as a fundamental consideration of what you describe as "point was..." it does appear to be an important part of your comment. Can you describe what you mean by the "theory"?

    You did indeed set out @174 a 0.4 deg warming in the period 1880s-1940s, this 50% relative to the warming in the period 1880s-2010. And if your argument is made for you, the topic under discussion is the correlation between CO2 and global temperature (specifically here the Gistemp LOTI) and thus the comparison you suggest is not in principle unmerited. My apologies. I was paying little attention to your comment as it is somewhat banal.

    You still fail to explain properly your derivation of the numbers you set out and how you obtain the 50% result so I will do this analysis for you. To achieve a more fruitful outcome, I will not expend apples and oranges within this analysis. Rather than mix period-averages with cherry-picked period-maximims, I will use period-maximums throughout.

    If we consider the maximum annual LOTI temperature within the start period (1880-1900, sometimes considered a measure of pre-industrial temperature) and the intermediate period (1940s) and the end periods (1) 1970s-2010 and (2) 1970s-2017:

    This yields a result of (1) 38%  and (2) 28% of the warming occuring by the 1940s (specifically in 1944), a time when the industrial-period CO2 forcing had reached (1) 34% and (2) 30% relative to the end periods. Thus the level of warming is reasonably reflective of the CO2 forcing (and indeed also if all positive forcings are included in the analysis). It should be noted that the 38% value relies solely on the 1944 annual anomaly. If multi-year averages are substituted for annual temperatures, something that should be done given the nature of the data, the percentage drops markedly.

  3. MA Rodger @ 177

    I am somewhat confused by the discussion between MA Rodger and strop regarding what the temperature rise has been since the 1880's.  My understanding is that MA Rodger suggests that it has increased from .8C to 1C as of now.

    But on Feb 4, MA Rodger on the "There is no empirical evidence" blog, he stated the following for 2016:

    "Using a modern global surface record to fill in recent decades (BEST was to hand) and aligning it with the tag end of the Loehle and McCulloch data (1850-1935), the temperature for 2016 would be plotted at +1.2ºC which is plainly off the graph."

    If the yearly temperature can jump up and down by .2C per year then do we not really have to use a minimum 10 year period in anything we talk about?  I appreciate that El Nino's and La Nina's, as well as volcanoes, complicates looking at what temperature rise we have had over this period.  But is even an average over a 10 year period relevant?  Look at the famous "hiatus". 

  4. NorrisM @178.

    You are famously confused, so you better concentrate.

    The recent BEST & GISS global temperature anomalies are in close agreement, their maximum annual values (2016) within 0.02ºC of each other. So the bulk of the 0.2ºC discrapency will likely be due to the other end of the record.

    There are a couple of other factors which cancel each other out. Here in this thread you will note I was using 'period-maximums' (which thus includes 2016) but the 'Empirical evidence that humans are causing global warming' comment was using BEST 'period-average' values (1850-1935) to align the BEST data with the Loehle & McCulloch data  (covering 11,700BC-1935AD with their zero equal to their full 'period-average'). Not using 'period-maximums' increases the measure of rise-in-temperature-since-pre-industrial by about 0.1ºC,  but this is canceled out by the re-basing to the Holocene 'period-average' which is warmer than pre-industrial by a similar amount.

    At the early end of the two temperature records, there is more of a discrepancy between BEST & GISS (with BEST -0.17ºC cooler than its GISS equivalent) which, coupled with BEST extending back to 1850 with even lower temperatures, this providing adjustments that tot-up to the bulk of the extra +0.2ºC above the zero to yield +1.2ºC on the Loehle & McCulloch graph.

  5. MA Rodger @ 179

    Thanks, I see the difference between the comparison of maximum annual values and average values.  I learn by asking questions but, as per strop's comment above,  I do not appreciate being insulted.  Take the edge off.

  6. @MA Rodge
    Now an atmosphere becomes formed around the hot body which is warmed by the hot body (this atmospheric warming you apparently have no problem with), the atmosphere reaching a chilly -18ºC = 255K at equilibrium. Being warmer than absolute zero, the atmosphere will radiate upward into space and downward back to the hot body. So will the extra energy flux back to the hot body not have a heating effect? Note - if it doesn't we will have to rewrite the laws of thermodynamics and we are not very keen on doing that.

    Pardon me, I am new here. And it has been 2 decades since I touched physics but doesn't thermodynamic equalibrim itself mean there will be no net energy transfers between the two objects?

    First you state that there is equalibirm then you suggest there will be a net heat transfer, how is that possible?

  7. ankit662003:

    You are confusing "no net transfer" with "no transfer at all".

    Adding $2000 to your bank account by depositing your paycheck, and then taking $2000 out to pay your bills results in no net change in your bank balance, but you still have $2000 as a "flux" in from your employer, and a $2000 "flux" out due to your withdrawal. Your bank account is in "equilibrium", but fluxes are not zero.

    Likewise for energy. Even at local thermodynamic equilibrium, two objects can be exchanging energy  it just has to be in equal quantities. And you need to consider all energy transfers - which in the atmosphere includes convection as well as IR radiation.

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