ncreaseHow much global warming comes from man made increased atomospheric carbon dioxide?

Question

Little doubt that increased CO2 is causing some global warming resulting from human activities, but are there any global modeling showing how much global warming is being caused by man? Seems like that is an important question to be addressed, given that the costs that would be demanded to control CO2 emissions. Any links showing a cost/benefits anlaysis?

Hey, Dr Jello, if the oxygen was decreased by the same % as the % of CO2 has increased, you would be knocked out on your a s s.

That would be dropping the O2 levels from 21 to 14%.

Answer 1

Hi Stewie,

To answer you question it's necessary to add a bit more information - namely, the timescale involved. The reason being that there are natural cycles that cause warming and cooling and these change quickly.

If we look at a short time scale such as the last few years then the amount of warming caused by man is in the order of 110%. The reason being that, if left to it's own devices, the natural mechanisms would have caused a slight cooling. So, at the moment, not only are we warming the planet but we're also compensating for the slight cooling that should be occurring - hence it's 110%.

In climatology it's unreliable to look at just a few years because there's so many short term factors that can skew the data. Ordinarily a base period or control period of 30 years or more is used, this is long enough to smooth out any anomalies.

The trouble is, when we start looking at longer time scales there's many variables involved, we can assign maxima and minima to the variables and thus we have values within a range. Some of these ranges (or forcings) overlap each other, some are coupled in feedback mechanisms, it all gets very complex. As a result, it's not possible to say precisely how much of the total warming is caused by human activities but what we can say is that since the earliest signs of anthropogenic global warming (AGW), somewhere upwards of 80% of the total warming that has occurred can be attributed to humans. It could be as high as 95%, it's probably closer to 90%.

If we separate natural global warming from AGW, it's much easier to be specific about the roles played by the different greenhouse gases. In terms of AGW only then CO2 emissions are responsible for 72% of the warming.

72% is the CONTRIBUTION that CO2 makes, the contribution is very different to the change in atmospheric concentration or quantity released.

Over 99% of all the greenhouse gases humans have produced is CO2 but it's a weak greenhouse gas in comparison to others such as methane and nitrous oxide, this is why it's contribution is considerably lower than the amount of emissions. One unit of methane for example causes 21 times as much warming as one unit of CO2, one unit of nitrous oxide causes 296 times as much warming. Many of the ozone depleting substances (ODS's) such as CFC's (chlorofluorocarbons) cause thousands of times as much warming per unit volume as CO2 does.*

* The potential of a gas to contribute to global warming is defined by assignation a value relative to the warming potential of CO2. CO2 has a fixed value of 1, all other gases are measured relative to this but because their 'potency' changes over time it's also necessary to specify the time period. The scale is called Global Warming Potential or GWP and the values I have quoted above are the 100 year GWP's.

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You mentioned a cost/benefit analysis and again, I'm sorry but it's hard to give a specific answer. The reason being that there are different schemes under consideration for addressing levels of atmospheric greenhouse gases and they have widely ranging price tags. Many ideas are in their infancy and no costs have yet been worked out. Of those that have got price tags the cheapest comes in at a few billion dollars, the most expensive at an amazing $452 trillion (although that is a cost based on current technology, if we were to develop electromagnetic propulsion systems it would drop significantly, it would still be a phenomenal amount, just not quite so much).

There is one scheme, currently being developed, that could actually return a profit. In this process, carbon dioxide is sequestered from the atmosphere using sodium hydroxide. After undergoing a chemical reaction the resultant by-product is synthetic gasoline and diesel which could be sold to offset the capital and maintenance costs.

Answer 2

Jello- How does going from 260 ppm to 340 ppm equate to a 0.008 % increase? Your numbers show a 24% increase. (That's (340 ppm - 260 ppm)/340 ppm = 24%)

Your concentration numbers are also wrong. Current average concentrations are 375 ppm by volume. The CO2 concentration has increased about 35% from before the industrial age.

Answer 3

75-95% is caused by increased greenhouse gases, mostly CO2. Scientists agree with you that this is important, and many studies have been done. There are several models (hence the range of percentages above), they all show that that's the main factor. Here's one good one, with an online summary:

Meehl, G.A., W.M. Washington, C.A. Ammann, J.M. Arblaster, T.M.L. Wigleym and C. Tebaldi (2004). "Combinations of Natural and Anthropogenic Forcings in Twentieth-Century Climate". Journal of Climate 17: 3721-3727

summarized at:

http://www.globalwarmingart.com/wiki/Image:Climate_Change_Attribution.png

Here's a plan to address it, with cost/benefit analysis. It was developed by hundreds of scientists and economists working together.

http://www.spiegel.de/international/world/0,1518,481085,00.html
http://www.ipcc.ch/SPM040507.pdf

Good websites for more info:

http://profend.com/global-warming/
http://www.ucsusa.org/global_warming/science/
http://www.realclimate.org
"climate science from climate scientists"
http://environment.newscientist.com/channel/earth/dn11462

Answer 4

Because the human experience on the planet is so short in geological time, I do not think there is indisputable evidence one way or the other. What I do think is that the human population is too large to be supported by the resources left on Earth. Good crop land and water sacristy will make the economic problems of today insignificant for your grandchildren. They will die of hunger or thirst. The only thing "under water" will be their mortgage.

Answer 5

First off, please ignore Jello's wrong answer. Atmospheric CO2 concentraton has increased from 280 ppm to over 380 ppm since the Industrial Revoltion, which any junior high math student can tell you is a 37% increase.

http://tamino.files.wordpress.com/2007/01/stomata1.jpg

Scientists have determined that 80-90% of the warming over the past 30 years has been due to human greenhouse gas emissions. You can read the IPCC report to see the details:

http://ipcc-wg1.ucar.edu/wg1/wg1-report.html

Or see it here graphically:

http://en.wikipedia.org/wiki/Image:Climate_Change_Attribution.png

And here are some nice plots from the IPCC report of the warming due to just natural causes (blue) vs. natural + human causes (pink). Black line is the actual measured temperature change.

http://environment.newscientist.com/data/images/ns/cms/dn11649/dn11649-1_688.jpg

Answer 6

I don't think Global warming is caused from CO2 but it is from all humans. Like smoking destroy's the O-zone and the O-zone protects us from the sun. that is one way.

Answer 7

co2 has increased from 260ppm (parts per million) to 340ppm, or just 80ppm - a scant 0.008%.

That's the width of a shoelace on a football field.
A $6.67/month pay raise to a guy making $100,000/yr.

Co2 has very little impact on the current climate. The Sun's output has increased 0.1%