Climate Sensitivity to a Change in Forcing

[William]

From a scientific standpoint, there is agreement that increases in atmospheric CO2 causes the planet to warm.

The science is not settled as to how much the planet will warm due to a doubling of CO2 as there is not scientific agreement as to how sensitive the planet is to a change in forcing.

If the planet does not amplify a change in forcing the planetary temperature will increase 1.2C for a doubling of atmospheric CO2 from 0.028% to 0.056%.

The data and analysis in this study significantly reduces the maximum expected temperature for a doubling of CO2.

Schmittner, A., et al., 2011. Climate sensitivity estimated from temperature reconstructions of the Last Glacial Maximum, Science, in press*,

http://www.princeton.edu/%7Enurban/pubs/lgm-cs-uvic.pdf

Climate Sensitivity Estimated From Temperature Reconstructions of the Last Glacial Maximum

Assessing impacts of future anthropogenic carbon emissions is currently impeded by uncertainties in our knowledge of equilibrium climate sensitivity to atmospheric carbon dioxide doubling. Previous studies suggest 3 K as best estimate, 2–4.5 K as the 66% probability range, and non-zero probabilities for much higher values, the latter implying a small but significant chance of high-impact climate changes that would be difficult to avoid.

Here, combining extensive sea and land surface temperature reconstructions from the Last Glacial Maximum with climate model simulations we estimate a lower median (2.3 K) and reduced uncertainty (1.7–2.6 K 66% probability). Assuming paleoclimatic constraints apply to the future as predicted by our model, these results imply lower probability of imminent extreme climatic change than previously thought.

[William]

This graph shows how planetary temperature would change if atmospheric carbon dioxide where to increase based on two different assumed sensitivities.

http://wattsupwiththat.files.wordpre...idley_pic3.png

[PraedSt]

How long till we double? 100 years? Less?

[Ronald Brak]

Roughly 75 years at the current rate of increase.

[MikeMcc]

Even then, the effect of the doubling won't be felt for a number of years because of the lag in the system.

[Squink]

Even then, the effect of the doubling won't be felt for a number of years because of the lag in the system.

Due to what exactly?
We feel the effect of insolation angle on temp with only a 1-2 month lag.
Amospheric CO₂ isn't going to wait around for a while before it starts absorbing photons from the sun.

[Swift]

Even then, the effect of the doubling won't be felt for a number of years because of the lag in the system.

And of course that will mean the effects will last that much longer even once we begin to stabilize or reduce the amount of CO2 in the atmosphere.

[William]

For those of you who like to follow along looking at the past planetary temperature data in addition to recent temperature data this site provides an easily assessable summary and appears to be neutral.

http://climate4you.com/index.htm

http://climate4you.com/images/MSU%20...ingAverage.gif

http://climate4you.com/images/GISP2%...CA%20DomeC.gif

http://climate4you.com/images/Vostok...20000%20BP.gif

There have been six papers written trying to explain the recent lack of warming. Some papers appeal to a greater length of time being required to determine planetary sensitivity to a change in forcing. The specific time period to determine the climate`s sensitivity to a change in forcing was 17 years.

The CO2 forcing is logarithmic which means the first increase in CO2 has the greatest affect.

[Trakar]

From a scientific standpoint, there is agreement that increases in atmospheric CO2 causes the planet to warm.

The science is not settled as to how much the planet will warm due to a doubling of CO2 as there is not scientific agreement as to how sensitive the planet is to a change in forcing.

If the planet does not amplify a change in forcing the planetary temperature will increase 1.2C for a doubling of atmospheric CO2 from 0.028% to 0.056%.

The data and analysis in this study significantly reduces the maximum expected temperature for a doubling of CO2.

Schmittner, A., et al., 2011. Climate sensitivity estimated from temperature reconstructions of the Last Glacial Maximum, Science, in press*,

http://www.princeton.edu/%7Enurban/pubs/lgm-cs-uvic.pdf

Are they talking about short-term sensitivity or long-term sensitivity?

The last interglacial epoch isn't a very good match for this one in terms of total forcing agencies or magnitudes. I consider their study to be useful in helping to establish an evidenced and supported range of potential sensitivities.

It isn't too practical at this point to lock on too strongly to any one point along that range as "definitive." Beyond this we start talking about fat-tails and the dangers of ignoring them.

[Trakar]

...The CO2 forcing is logarithmic which means the first increase in CO2 has the greatest affect.

For CO2, in the shortest term, this approximates reality at average surface temperatures and pressures. The climate, however is more complex than CO2 forcing in isolate. Every additional watt of energy delayed in its exodus from the Earth's atmosphere warms our environment, this added energy increases the amount of water vapor our atmosphere can temporarily maintain, meaning an even larger greenhouse effect, meaning an even warmer environment where year-round ices disappear creating changes in albedo and releasing large amounts of methane from the thawing permafrosts, further warming the environment This doesn't even get into potentially catastrophic so-called "tipping point" feedback issues like massive shallow seafloor calthrate deposit decomposition (or exploitation for energy) potentially kicking off major global methane releases. On more natural scales of progression, life generally has a chance to migrate and adapt, at the scale and rate we are currently thumbing the scales,...

the arrogant irony of "homo sapiens sapiens," grows more apparent with each day that passes.

[Trakar]

Please pardon this transcription but there is a lot of material that deserves to be read in this section of this paper and I don’t want to misrepresent what I am quoting as anything other than landmarks to highlight this important section by the authors regarding their study: (please read in entirety and in full context at pdf)

…We propose three possible reasons why our study yields lower estimates of ECS2xC than previous work that also used LGM data. Firstly, the new reconstructions of LGM surface temperatures show less cooling than previous studies
…Tropical Atlantic SSTs between 20°S–20°N are estimated to be only 2.4 K colder during the LGM in the new reconstruction compared to 3 K used in (23), explaining most of the difference between their higher estimates of ECS2xC and TLGM (–5.9 K vs –3.5 K)
…The second reason is limited spatial data coverage
…Averaging over all grid points in our model leads to a higher global mean temperature (SST over ocean, SAT over land) change (–2.6 K) than using only grid points where paleo data are available (–2.2 K), suggesting that the existing dataset is still spatially biased towards low latitudes and/or oceans. Increased spatial coverage of climate reconstructions is therefore necessary in order to improve ECS2xC estimates.
…A third reason may be the neglect of dust radiative forcing in some previous LGM studies
…Our uncertainty analysis is not complete and does not explicitly consider uncertainties in radiative forcing due to ice sheet extent or different vegetation distributions. Our limited model ensemble does not scan the full parameter range, neglecting, for example, possible variations in shortwave radiation due to clouds. Non-linear cloud feedbacks in different complex models make the relation between LGM and 2CO2 derived climate sensitivity more ambiguous than apparent in our simplified model ensemble (27). More work, in which these and other uncertainties are considered, will be required for a more complete assessment…

Given these qualifications, and in, at the least, a preliminary examination of the character of their research, findings and considerations, I see nothing objectionable or out of line in their work. Furthermore, I see it as a potentially important piece of research and analysis in the furthering of our climate understandings. I don’t see this work as a defining break-through, but it does include some more recent datasets and forcing factor elements in its considerations. It will be interesting to see if these researchers pursue this line of research and follow-up with some more detailed and comprehensive studies including factors not present in this study’s consideration.

[starcanuck64]

If the planet does not amplify a change in forcing the planetary temperature will increase 1.2C for a doubling of atmospheric CO2 from 0.028% to 0.056%.

We're already at about a measured +0.8 C increase with a significant offset(masking) by human generated aerosols with a CO2 concentration of 0.039%, something tells me the much more common climate sensitivity calculation of about +3 C is closer to the mark.

[Ari Jokimaki]

The reason why this new study gives somewhat lower climate sensitivity (although the nominal value from this new study is also within the range of IPCC estimates) than some other studies is that they use temperature reconstruction for last glacial maximum that gives different (warmer) temperature than in previous similar studies.

[PraedSt]

The CO2 forcing is logarithmic which means the first increase in CO2 has the greatest affect.

It might be log function now, but will it always be that way? For example, if I converted all the carbon in all the sinks to CO², would T(CO²_max) still lie on the same graph?

[William]

It might be log function now, but will it always be that way? For example, if I converted all the carbon in all the sinks to CO², would T(CO²_max) still lie on the same graph?

Yes. The change in forcing as the concentration in CO2 increases continues to be logarithmic up to around 50000 ppm. The equation was determined by measuring the temperature of a long tube of gas as the concentration of CO2 has increased. The long tube does not of course simulate that entire atmosphere. Only the forcing change as the concentration of CO2 was increased.

The greenhouse effect is caused by carbon dioxide absorbing then remitting specific wave lengths. The mechanism starts to saturate as the concentration of CO2 in the atmosphere increases.

[William]

We're already at about a measured +0.8 C increase with a significant offset(masking) by human generated aerosols with a CO2 concentration of 0.039%, something tells me the much more common climate sensitivity calculation of about +3 C is closer to the mark.

Your comment is not correct.

A significant portion of the warming post little ice age occurred before the anthropogenic increase of carbon dioxide in the atmosphere. What caused the earlier warming?

Why has the warming abated? The warming as measured by satellite is significantly less than 0.8C. What temperature set is used to support the 0.8C assertion?

http://climate4you.com/images/MSU%20...ingAverage.gif

http://climate4you.com/images/GISP2%...CA%20DomeC.gif

This link compares all of the different temperature data sets.

http://climate4you.com/index.htm

[lomiller1]

Your comment is not correct.

A significant portion of the warming post little ice age occurred before the anthropogenic increase of carbon dioxide in the atmosphere. What caused the earlier warming?

Why has the warming abated? The warming as measured by satellite is significantly less than 0.8C. What temperature set is used to support the 0.8C assertion?

According to NASA the earth has warmed almost 1 deg C in the last 100 years. CO2 levels began rising some 50 years before that.

Most reconstructions of the "little ice age" show it half a degree C over ~300 years.

[PraedSt]

Yes. The change in forcing as the concentration in CO2 increases continues to be logarithmic up to around 50000 ppm. The equation was determined by measuring the temperature of a long tube of gas as the concentration of CO2 has increased. The long tube does not of course simulate that entire atmosphere. Only the forcing change as the concentration of CO2 was increased.

The greenhouse effect is caused by carbon dioxide absorbing then remitting specific wave lengths. The mechanism starts to saturate as the concentration of CO2 in the atmosphere increases.

Thanks William. That's good to know. Did the experiment continue beyond 50000 ppm? Because Venus has just under twice that.

[Trakar]

...The greenhouse effect is caused by carbon dioxide absorbing then remitting specific wave lengths. The mechanism starts to saturate as the concentration of CO2 in the atmosphere increases.

The greenhouse effect, is due to all of the GHGs in the atmosphere, not just CO2.

[Trakar]

http://climate4you.com/images/MSU%20...ingAverage.gif

http://climate4you.com/images/GISP2%...CA%20DomeC.gif

This link compares all of the different temperature data sets.

http://climate4you.com/index.htm

Do you have any source for this information other than the distortions presented from this denialist pseudo-science site?

[Trakar]

Thanks William. That's good to know. Did the experiment continue beyond 50000 ppm? Because Venus has just under twice that.

Venus also has a 90+ Bar atmosphere.

[PraedSt]

Venus also has a 90+ Bar atmosphere.

Excuse the analogy, but basically a thicker blanket?

[Trakar]

Excuse the analogy, but basically a thicker blanket?

Certainly, but my main point was that we aren't just talking about higher percentages of CO2, we are talking many magnitudes of higher absolute volume/mass.

[PraedSt]

Yeah, that makes sense. Thanks.

[starcanuck64]

Your comment is not correct.

A significant portion of the warming post little ice age occurred before the anthropogenic increase of carbon dioxide in the atmosphere. What caused the earlier warming?

Why has the warming abated? The warming as measured by satellite is significantly less than 0.8C. What temperature set is used to support the 0.8C assertion?

http://climate4you.com/images/MSU%20...ingAverage.gif

http://climate4you.com/images/GISP2%...CA%20DomeC.gif

This link compares all of the different temperature data sets.

http://climate4you.com/index.htm

The +0.8C warming is since the mid 1800s and is well documented as is the increase in concentration of atmospheric CO2.

As for the satellite measurements there was problems with coordinating the different satellite readings and the tendency of the satellites to read upper atmosphere temperatures, when corrected satellite measurements agree closely with ground, ocean and atmospheric readings.

Refer to the IPCC 2007 Physical Report, it's one of many mainstream sources on recent anthropogenic climate change.

[Trakar]

The +0.8C warming is since the mid 1800s and is well documented as is the increase in concentration of atmospheric CO2.

As for the satellite measurements there was problems with coordinating the different satellite readings and the tendency of the satellites to read upper atmosphere temperatures, when corrected satellite measurements agree closely with ground, ocean and atmospheric readings.

Refer to the IPCC 2007 Physical Report, it's one of many mainstream sources on recent anthropogenic climate change.

Still 1.5 - 2 years out from the fifth assessment report.
(unless you're registered to download an expert review copy -)

Working Group I (WGI) of the Intergovernmental Panel on Climate Change (IPCC) is pleased to announce that the First Order Draft of the WGI contribution to the IPCC Fifth Assessment Report (AR5) Climate Change 2013: The Physical Science Basis is available for Expert Review from 16 December 2011 to 10 February 2012. The WGI Bureau invites all experts with expertise and/or publications in the specific areas covered by the WGI Report to assist in the IPCC assessment process by registering to review here.