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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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Archived Rebuttal

This is the archived Basic rebuttal to the climate myth "There's no correlation between CO2 and temperature". Click here to view the latest rebuttal.

What the science says...

How much the climate warms up depends on the total amount of CO2 emissions, not just the CO2 in a year, or a decade. The rate of heating is usually measured over long periods because short term measurements may be misleading.

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 270ppm before the industrial revolution. That’s a 48% increase.

A tiny amount of CO2 and other greenhouse gases, like methane and water vapour, keep the Earth’s surface 30 degrees warmer than it would be without them. 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’s only increases the temperature by a small amount. The ways the climate reacts is also complex, and it is difficult to separating 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 – it’s 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 twice the amount of CO2 compared to pre-industrial levels.

So far, the average global temperature has gone up by a small amount - about 0.8 degrees C (33.4 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

Small increases 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.

Yet the physical properties of CO2 and other greenhouse gases cannot change. The same heat they were re-radiating back to Earth during previous decades must be evident now, subject only to changes in the amount of heat 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:

The oceans absorb most of the heat from global warming

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 heat the oceans are absorbing. Recent research has found a surprising amount of heat below 700 metres:

Recent research (Balmaseda et. al, 2013) has found a surprising amount of heat below 700 metres:

“In the last decade, about 30% of the warming has occurred below 700 m, contributing significantly to an acceleration of the warming trend. The warming below 700 m remains even when the Argo observing system is withdrawn although the trends are reduced. Sensitivity experiments illustrate that surface wind variability is largely responsible for the changing ocean heat vertical distribution”.

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. When deep oceans warm, the heat moves downwards from the surface. The surface gets cooler, humidity reduces (water vapour is a powerful greenhouse gas), and air temperatures go down.

The effects of man-made CO2 on climate are complex. Natural variability will always play a part, and the rate at which surface temperatures go up will not always be in proportion to the amount of CO2 humans are adding to the atmosphere.

Updated on 2013-06-23 by gpwayne.

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