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

July 24, 2013

This is a repost from Skeptical Science of a new ‘basic’ level rebuttal of the myth “ There’s no correlation between CO2 and temperature

What The Science Says:

Surface temperature measurements are affected by short-term climate variability, and recent warming of deep oceans.

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 33°Celsius (59.4°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:

Nuccitelli_OHC_Data_med

From Nuccitelli et.al (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.

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3 Comments leave one →
  1. achuara permalink
    March 24, 2016 12:53 am

    Dr. Sherwood Idso (1998 and 2000) calculated based on eight natural experiments an increase of 0.1 °C/(Wm−2) resulting in a climate sensitivity of only 0.4 °C for a doubling of the concentration of CO2 in the atmosphere. Idso’s paper has never been refuted by anyone. Try to refute it if you can…

    http://www.int-res.com/articles/cr/10/c010p069.pdf

  2. Graham Wayne permalink*
    March 24, 2016 7:23 am

    Ah, the Idso family. We’ll just skip over all their connections to the fossil fuel industry, and their organisation’s funding by Heartland, and the fact that the NIPCC reports they contribute to are some of the most staggeringly inept, deceitful and incompetent cod-scientific publications ever put out by climate change deniers – put out by anybody, really. You can read my deconstruction of the exec summary here, but I suspect you will not like it.

    We’ll just ignore all that, and address the facts. I don’t need to refute this very outdated work, for the empirical evidence has already done that. How can you take seriously a claim that the planet will heat up by only 0.4 °C for a doubling of CO2, when it has already warmed up by 1 °C for an increase of just 40%? Do you think perhaps that the next 60% of CO2 will produce a cooling effect?

    Idso was wrong, and what’s more you could have worked this out for yourself since it’s really blindingly obvious. Except to deniers, of course.

  3. achuara permalink
    March 24, 2016 7:51 pm

    “Of course, I was expecting the usual…” (SNIP)

    [Small Ephiphanies] An ironic start to your attempted post, considering I was expecting the usual load of crap from a climate denier, and you certainly didn’t disappoint.

    So, a few things: everything you wrote is monumental rubbish, regurgitated from denier blogs about subjects clearly neither you or they understand. Of particular note is your use of the most widely debunked denier cliche in the playbook: ‘it’s the sun’. NO IT ISN’T, YOU IDIOT! And like your references to old science, your position itself now strikes me as antiquated, and so out of date it’s like reading something from a time capsule buried in 1995.

    The level of irrationality in your post is quite disturbing. All I see is another strange and frightened member of a rapidly shrinking cult, desperately clinging to a life-raft of victimhood and conspiracy. My advice: get help.

    Meanwhile, take your madness elsewhere. You are now banned (if you don’t understand why, read the comment policy). Don’t bother coming back as you’re not welcome here.

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