Climate sensitivity - how much will the planet warm when carbon dioxide levels double?

Question

One global warming skeptic argument we see every so often is that the climate is not as sensitive as climate scientists think, so their predictions overestimate future global warming.

This theory is based on a paper written by Stephen Schwartz last year which found that a doubling of atmospheric CO2 would cause a ~1°C warming.

http://www.ecd.bnl.gov/steve/pubs/HeatCapacity.pdf

RealClimate said this about the paper:

"Even if his result is correct (which it isn’t), it by no means 'kills AGW theory.' It simply changes the numbers. In fact, Schwartz’s analysis implicitly assumes that the planet *is* warming, and that the primary cause is man-made greenhouse gases."

I came upon this website summarizing the various studies which have analyzed climate sensitivity.

http://members.aol.com/bpl1960/ClimateSensitivity.html

If you scroll to the bottom, you see that over time, the studies are converging around a sensitivity of ~3°C.

What do you think the correct value is?

Answer 1

Much (over 2/3) of the future warming in the IPCC forecast is based on assumed positive feedback effects that tend to be rare in stable systems, and none have been proven empirically. This is a bit unrealistic/unfounded because the majority of feedback effects found in nature are negative, i.e. tending towards a stable state. Warming from CO2 yields a diminishing return such that each 100 ppm of CO2 has less warming effect than the last 100 ppm. Once CO2’s ability to absorb infrared energy is saturated, incremental quantities have little effect. Ultimately CO2 warming is asymptotic, so the total warming from CO2 is effectively capped at around 1.5° C

Answer 2

A better question is how much will it cool when the Gorians have had their way with us. Your sites are bogus! their either environmentalist sites, BBC, or they say right in them that these scientists aren't sure. That large discrepancies exist in their findings. You probably should try to find a new major. You are not objective enough to be a scientist, and you let your emotions cloud your judgment. Even if we quit altogether, don't use any more petroleum products, the glaciers aren't coming back, the permafrost is not going to refreeze. The Methane is going to be released at an alarming rate until the job is done. The Sun is causing the warming and that pisses you off!

Answer 3

The incremental energy flux due to greenhouse gasses is estimated to be about 2.5 W/m^2.  I am confident that the time constant for radiative forcing is much shorter than the thermal time constant for the earth's oceans.  Energy is being added much faster by radiative forcing than it mixes through the water column.  The calculation of the short term response depends upon the effective depth of the oceans that is warmed.  The oceans 1.35e9 km^3 are an enormous heat sink.  With uniform mixing the warming would be about 0.003 C/yr and with heating confined to the top 100 m, the warming would be about 0.075 C/yr.  I don't know enough about ocean dynamics to make a scientific estimate.  My expectation is that with intact thermohaline circulation, the ocean will moderate the radiative inbalance for several centuries keeping the short term warming to about 2 C.

Answer 4

Then maybe you should come upon this website.

Answer 5

Factor in population growth, at the rate we have seen it (though it's actually an asymptotic function, now, not a linear one), since 1960... and... well, I have a traumatic brain injury, which cost me the ability to do higher maths (which SXCKXD!), so I cannot contribute meaningfully to the maths part of this discussion.

However, Thomas Malthus, a philosopher in 1798, predicted that the Earth could only sustain a certain level of human population, before the Earth would 'fight back', and the human population would drop by 90%.

The 1960 World population (one year before I was born) was 2.5 x 10^9 human beings.

Now, that's the joint population of China and the Indian Subcontinent... which are industrialising furiously.

There are now well over 7 x 10^9 human beings crawling the surface of our Planet.

The population has trebled, since I was born.  This is unprecedented, in itself.  Now, with industrialisation...

Malthus was right.  We are hurtling toward a Malthusian Catastrophe. http://en.wikipedia.org/wiki/Malthusian_...

I forsee a Malthusian Catastrophe, within 10-30 years.

The Earth will survive.  Homeostasis will be restored.  And, there will be 7+ x 10^8 human beings... probably scattered about, on landlocked high ground.

Answer 6

0°C.

Answer 7

Slightly less than half the effect of the last doubling.

Answer 8

First I would point out that the human contribution may or may not be about 100 parts per million.  The current concentration of CO2 is about 400 parts per million.  If it took us 200 years to add 100 parts per million (it wasn't a linear addition however), then how many centuries would it take to reach 800 ppmV.  It is interesting that the realclimate wasn't more adamant that the number was too low.

Answer 9

The Intergovernmental Panel on Climate Change

(who won a noble peace prize)

predict that:

it is probable that there will be a temperature rise of between 1.8 - 4 degrees Celsius by the end of the century

it is possible that there could be a temperature increase of between 1.1 - 6.4 degrees Celsius by the end of the century

the difference between probable and possible is statistical, probable is more likely as it has a smaller statistical range

check it out though, the IPCC reports are pretty much the mother of climate change publications at the moment

and given how many different scientists and academics conducted research on it (more than 600) its got to be reliable and not just made up...

Answer 10

What's interesting is that in 1896, Nobel Prize winning Chemist Svante Arrhenius calculated (no computer models back then) purely with known physics that a doubling of the CO2 level would result in a global mean temperature increase of about 5 C.  Not bad for the 19th century.

Answer 11

carbon dioxide will double and it will create smog but scientist have proven that they have no idea what is making the ozone thin. it is thinning and that is laying more sun on the earth heating it. but most don't now that the ozone layer just healed itself and no one knows why. basically stop worrying about it, the earth changes and the carbon dioxide is not causing it the only thing it is doing is making the air next to the earth covered with smog.

Answer 12

looks like even some skeptical scientists have produced studies that show doubling CO2 will have a fairly substantial effect. Interesting that Arrhenius got similar results as those who had access to computers(and modern physics) 100 years later.

Answer 13

I think for the most part the scientist know what they are talking about. I based off what I know about global warming and everything have to say that the scientist have a pretty good I idea about how much the temperature should rise over the comming years.

Answer 14

It will stay the same.

Answer 15

Well, Schwartz's number (λ = .3 KW^-1m^-2) is a bit low, but in the ballpark. My recent regressions put it at roughly λ = .47 ± .03 which gives a rise of 1.8 K for doubling CO2 since preindustrial times. This is very similar to (but more precise than) IPCC 2001, which put it at .5 ± .25

A 3 K rise implies λ = .8, which is, IMHO, way too high.

Thanks for the links, though, very useful.