AGW Observer

Observations of anthropogenic global warming

Archive for January, 2010

Papers on natural variability

Posted by Ari Jokimäki on January 29, 2010

This is a list of papers on natural variability of Earth’s climate. This subject was suggested by PeterPan here. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (July 13, 2010): Lo & Hsu (2010) added.
UPDATE (June 12, 2010): Ghil & Vautard (1991) and Chao et al. (2000) added.

Change in the dominant decadal patterns and the late 1980s abrupt warming in the extratropical Northern Hemisphere – Lo & Hsu (2010) “Widespread abrupt warming in the extratropical Northern Hemisphere (NH) occurred in the late 1980s. This warming was associated with a change in the relative influence of the Pacific Decadal Oscillation (PDO)-like pattern and the Arctic Oscillation (AO)-like pattern. The AO-like pattern has had a dominant influence on the NH-mean temperature since the late 1980s, whereas the influence of the PDO has weakened. The AO-like mode appears as part of natural variability in the pre-industrial simulations of the CMIP3/IPCC climate models. However, its emergence in the late 1980s was not simulated by most models with or without the observed increasing greenhouse effect in the 20th century.”

Long-term natural variability and 20th century climate change – Swanson et al. (2009) “Here we present a technique that objectively identifies the component of inter-decadal global mean surface temperature attributable to natural long-term climate variability. Removal of that hidden variability from the actual observed global mean surface temperature record delineates the externally forced climate signal, which is monotonic, accelerating warming during the 20th century.” [Full text]

Changes in the phase of the annual cycle of surface temperature – Stine et al. (2009) “Here we show that the phase of the annual cycle of surface temperature over extratropical land shifted towards earlier seasons by 1.7 days between 1954 and 2007; this change is highly anomalous with respect to earlier variations, which we interpret as being indicative of the natural range. Significant changes in the amplitude of the annual cycle are also observed between 1954 and 2007. These shifts in the annual cycles appear to be related, in part, to changes in the northern annular mode of climate variability, although the land phase shift is significantly larger than that predicted by trends in the northern annular mode alone.” [Full text]

What is causing the variability in global mean land temperature? – Hoerling et al. (2008) “Diagnosis of climate models reveals that most of the observed variability of global mean land temperature during 1880–2007 is caused by variations in global sea surface temperatures (SSTs). Further, most of the variability in global SSTs have themselves resulted from external radiative forcing due to greenhouse gas, aerosol, solar and volcanic variations, especially on multidecadal time scales. Our results indicate that natural variations internal to the Earth’s climate system have had a relatively small impact on the low frequency variations in global mean land temperature. It is therefore extremely unlikely that the recent trajectory of terrestrial warming can be overwhelmed (and become colder than normal) as a consequence of natural variability.” [Full text]

Multidecadal Climate Variability in Observed and Modeled Surface Temperatures – Kravtsov & Spannagle (2008) “This study identifies interdecadal natural climate variability in global surface temperatures by subtracting, from the observed temperature evolution, multimodel ensemble mean based on the World Climate Research Programme’s (WCRP) Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset. The resulting signal resembles the so-called Atlantic multidecadal oscillation (AMO) and is presumably associated with intrinsic dynamics of the oceanic thermohaline circulation (THC). … Evidence suggests that the AMO influence on secular trends in the global-mean surface temperature can arise via direct, regional contribution to the surface temperature evolution, as well as via an indirect route linked to variability of the oceanic uptake of CO2 associated with AMO-related THC changes.” [Full text]

How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006 – Lean & Rind (2008) “To distinguish between simultaneous natural and anthropogenic impacts on surface temperature, regionally as well as globally, we perform a robust multivariate analysis using the best available estimates of each together with the observed surface temperature record from 1889 to 2006. The results enable us to compare, for the first time from observations, the geographical distributions of responses to individual influences consistent with their global impacts. We find a response to solar forcing quite different from that reported in several papers published recently in this journal, and zonally averaged responses to both natural and anthropogenic forcings that differ distinctly from those indicated by the Intergovernmental Panel on Climate Change, whose conclusions depended on model simulations.” [Full text]

A signature of persistent natural thermohaline circulation cycles in observed climate – Knight et al. (2005) “Using a 1400 year climate model calculation, we are able to simulate the observed pattern and amplitude of the AMO. The results imply the AMO is a genuine quasi-periodic cycle of internal climate variability persisting for many centuries, and is related to variability in the oceanic thermohaline circulation (THC). This relationship suggests we can attempt to reconstruct past THC changes, and we infer an increase in THC strength over the last 25 years. Potential predictability associated with the mode implies natural THC and AMO decreases over the next few decades independent of anthropogenic climate change.” [Full text]

Pacific interdecadal variability in this century’s sea surface temperatures – Chao et al. (2000) “Analysis of this century’s sea surface temperatures over the Pacific Ocean reveals an interdecadal oscillation with a period of 15–20 years. Our results show that the well‐known 1976–77 climate regime shift is not unique, but represents one of several phase transitions associated with this interdecadal oscillation, also found around 1924–25, 1941–42, and 1957–58. The oscillation’s striking north‐south symmetry across the equator implies strong interactions between tropics and extratropics. A mode with a period of approximately 70 years and an apparently different spatial pattern is also identified tentatively but has to be evaluated further using longer time series.” [Full text]

A Comparison of Surface Air Temperature Variability in Three 1000-Yr Coupled Ocean–Atmosphere Model Integrations – Stouffer et al. (2000) “This study compares the variability of surface air temperature in three long coupled ocean–atmosphere general circulation model integrations. It is shown that the annual mean climatology of the surface air temperatures (SAT) in all three models is realistic and the linear trends over the 1000-yr integrations are small over most areas of the globe. … Assuming that the simulation of variability of the global mean SAT is as realistic on longer timescales as it is for the shorter timescales, then the observed warming of more than 0.5 K of the SAT in the last 110 yr is not likely to be due to internally generated variability of the coupled atmosphere–ocean–sea ice system. Instead, the warming is likely to be due to changes in the radiative forcing of the climate system, such as the forcing associated with increases in greenhouse gases.” [Full text]

ENSO-like Interdecadal Variability: 1900–93 – Zhang et al. (1997) “A number of recent studies have reported an ENSO-like EOF mode in the global sea surface temperature (SST) field, whose time variability is marked by an abrupt change toward a warmer tropical eastern Pacific and a colder extratropical central North Pacific in 1976–77. The present study compares this pattern with the structure of the interannual variability associated with the ENSO cycle and documents its time history back to 1900. … By means of several different analysis techniques, the time variability of the leading EOF of the global SST field is separated into two components: one identified with the “ENSO cycle-related” variability on the interannual timescale, and the other a linearly independent “residual” comprising all the interdecadal variability in the record.” [Full text]

Global and regional variability in a coupled AOGCM – Tett et al. (1997) “The variability of near surface temperature on global and regional spatial scales and interannual time scales from a 1000 year control integration of the Hadley Centre coupled model (HADCM2-CTL) are compared with the observational record of surface temperature. The model succeeds in reproducing the observed patterns of natural variability, with high variability over the northern continents and low variability over much of the tropics. The model global mean variability has similar strength to observed global mean variability on time scales less than 20 years. The warming seen in the historical record is outside the range of natural variability as simulated in HADCM2-CTL.”

Robust estimation of background noise and signal detection in climatic time series – Mann & Lees (1996) “We present a new technique for isolating climate signals in time series with a characteristic red noise background which arises from temporal persistence. … We apply our methodology to historical climate and paleoclimate time series examples. Analysis of a ~ 3 million year sediment core reveals significant periodic components at known astronomical forcing periodicities and a significant quasiperiodic 100 year peak.”

Model assessment of the role of natural variability in recent global warming – Stouffer et al. (1994) “Here we evaluate the observed warming trend using a 1,000-year time series of global temperature obtained from a mathematical model of the coupled ocean–atmosphere–land system. We find that the model approximately reproduces the magnitude of the annual to interdecadal variation in global mean surface air temperature. But throughout the simulated time series no temperature change as large as 0.5 °C per century is sustained for more than a few decades. Assuming that the model is realistic, these results suggest that the observed trend is not a natural feature of the interaction between the atmosphere and oceans.”

An oscillation in the global climate system of period 65–70 years – Schlesinger & Ramankutty (1994) “Here we apply singular spectrum analysis to four global-mean temperature records, and identify a temperature oscillation with a period of 65–70 years. Singular spectrum analysis of the surface temperature records for 11 geographical regions shows that the 65–70-year oscillation is the statistical result of 50–88-year oscillations for the North Atlantic Ocean and its bounding Northern Hemisphere continents. These oscillations have obscured the greenhouse warming signal in the North Atlantic and North America. Comparison with previous observations and model simulations suggests that the oscillation arises from predictable internal variability of the ocean–atmosphere system.”

Interdecadal oscillations and the warming trend in global temperature time series – Ghil & Vautard (1991) “THE ability to distinguish a warming trend from natural variability is critical for an understanding of the climatic response to increasing greenhouse-gas concentrations. Here we use singular spectrum analysis1 to analyse the time series of global surface air temperatures for the past 135 years, allowing a secular warming trend and a small number of oscillatory modes to be separated from the noise. The trend is flat until 1910, with an increase of 0.4 °C since then. The oscillations exhibit interdecadal periods of 21 and 16 years, and interannual periods of 6 and 5 years. The interannual oscillations are probably related to global aspects of the El Niño-Southern Oscillation (ENSO) phenomenon. The interdecadal oscillations could be associated with changes in the extratropical ocean circulation. The oscillatory components have combined (peak-to-peak) amplitudes of >0.2 °C, and therefore limit our ability to predict whether the inferred secular warming trend of 0.005 °Cyr-1 will continue. This could postpone incontrovertible detection of the greenhouse warming signal for one or two decades.” [Full text]

Natural variability of the climate system and detection of the greenhouse effect – Wigley & Raper (1990) “Here we show how the ocean may produce low-frequency climate variability by passive modulation of natural forcing, to produce substantial trends in global mean temperature on the century timescale. Simulations with a simple climate model are used to determine the main controls on internally generated low-frequency variability, and show that natural trends of up to 0.3 °C may occur over intervals of up to 100 years. Although the magnitude of such trends is unexpectedly large, it is insufficient to explain the observed global warming during the twentieth century.”

Internally and Externally Caused Climate Change – Robock (1978) “A numerical climate model is used to simulate climate change forced only by random fluctuations of the atmospheric heat transport. This short-term natural variability of the atmosphere is shown to be a possible “cause” not only of the variability of the annual world average temperature about its mean, but also long-term excursions from the mean.” [Full text]

Posted in AGW evidence | 2 Comments »

Comments on Schwartz et al. (2010), version 2

Posted by Ari Jokimäki on January 27, 2010

I first wrote about Schwartz et al. (2010) here but as some of it was based on my misunderstandings I wrote it again, resulting text below. I mistakenly thought that ocean thermal lag would cause 0.5 K cooling to the observed temperature at all climate sensitivity values and then interpreted their results based on that mistake, which lead me to believe that they had forgot to include the ocean thermal lag to their final analysis. Also, my calculated value of 0.5 K was wrong (0.3 K would have been correct), see the comment section of the first version. So here’s the second, and hopefully more correct version:

Newly published paper by Schwartz et al. (2010) (abstract, full text) has been claimed to show that theory of AGW is false or that “global warming has been cancelled”, etc. The claims are based on this statement in the paper’s introduction:

However, the observed increase of GMST over the industrial period is less than 40% of what would be expected from present best estimates of Earth’s climate sensitivity and the forcing (imposed change in energy balance, W m-2) by the observed increases in GHGs.

(GMST = global mean surface temperature, GHG = greenhouse gases).

In other words, they determine expected temperature rise from greenhouse gas forcing and the climate sensitivity, then look at the observed temperature rise and compare the two. Not surprisingly, they found that the two are different. I said “not surprisingly” because they only looked at greenhouse gas forcing and I know that there are other forcings at play and I’m also quite sure that some of those forcings work in different direction than greenhouse gases, aerosols for example. Just a simple example of the situation would be that if GHG’s would cause a warming of 2K and aerosols would cause cooling of 1K, then the resulting warming from these two would be 1K meaning that the observed warming would be only 50 % of the expected warming from GHG’s.

So, the 40 % number they give doesn’t represent the total overall situation, but it only represents the situation if only greenhouse gases are considered and the rest forcings are ignored. Now, Schwartz et al. know this because it is the subject of their paper to study what causes the difference, so Schwartz et al. are not claiming that observed temperature is less than 40 % of the expected all-forcing-temperature. Yet, it is the 40 % number that is the one they are now parroting all over the Internet as if it would represent the total overall situation.

It would be the same as if I would calculate that aerosols in the air would cause cooling of certain amount and then I would note that global temperature has been rising instead of expected cooling from aerosols. I would then say that I will now consider why there is such a difference but somebody else would just quote me on the observed temperatures not showing the expected cooling and would then spread that word as a proof that the theory of aerosols has been now shown wrong.

Well, at this point we are only in the introduction section of the Schwartz et al. and we already have handled most of the false claims circulating in the Internet about this. But Schwartz et al. do have things to say even beyond the introduction.

Rest of the paper

Schwartz et al. are studying if the difference between the observed and expected greenhouse gas warming is due four main things:

- Natural variation in global temperature.
– Lack of attainment of equilibrium.
– Overestimate of climate sensitivity.
– Countervailing forcings over the industrial period.

They calculated that the expected warming from GHG’s would have been 2.1 K. They said that the observed temperature increase had been 0.8 K.

Natural variation in global temperature can cause up to 0.2 K of cooling according to them. This is how they found it out:

We use variation in preindustrial global temperature as inferred from proxy records, mainly tree rings, ice cores, corals, and varved sediments to estimate the likely magnitude of any natural cooling over the 150-year interval of the instrumental record.

Proxies? Tree-rings??? Surely any self-respecting climate denier at last now will dump this paper as a heretic production. Well, seriously, I think that’s reasonable approach to get a rough idea. However, it’s also bad news for those who think that the global warming is from natural variability. According to Schwartz et al. observed = 0.8 K and natural variability = 0.2 K. That means the observed warming is 400 % of the expected maximum warming from natural variability – a worse result than the observed versus expected from GHG’s.

Note that natural variability can work for both directions, it can cause cooling or warming.

Lack of attainment of equilibrium is a fancy way of saying that there might be delays in the climate system so that not all the warming from GHG’s has yet been realised in surface temperature but is instead hiding somewhere. Ocean is the most obvious and important place to hide the warming from GHG’s. They determine that 0.37 W/(m2) of the forcing could be hiding in the ocean, and they say that it corresponds to 22 % of the warming discrepancy.

Note that this effect works only to one direction, it has a cooling effect on global surface temperature.

Overestimate of climate sensitivity suggests that the climate sensitivity would be lower than the expected range. That would explain the discrepancy. They note that IPCC limit for very “unlikely” climate sensitivity is 1.5 K and they say that the observed warming would require the climate sensitivity to be even lower than that. The situation is presented in their Figure 2. There they present the observed warming as a horizontal line and they have added the natural variability as a horizontal band around the observed line. The expected warming from GHG’s is presented as an increasing line. One can see that when accounting for natural variability, the expected warming goes out of the band at climate sensitivity of about 1.7 K. That already is within IPCC very unlikely limits, and approaching the “likely” limit of 2.0 K.

Countervailing forcings over the industrial period also have an effect to the global temperature. They are discussing aerosol forcing here. In their Figure 2 they present also how aerosol forcing would effect the situation (however, see below for a minor error in the Figure 2 relating to this). The red lines in Figure 2 are with aerosol forcing; three lines for different amounts of assumed aerosol forcing. They say that with the IPCC best estimate aerosol forcing (1.2 W/m2) the warming “would be compatible with the lower end of the IPCC “likely” range of climate sensitivity”, but actually if we would consider the possible natural variability, we can see from their Figure 2 that resulting climate sensitivity would approach the nominal 3 K value, the climate sensitivity might in that case be about 2.8 K (but of course, as natural variation might work to other direction too, the resulting sensitivity might also be only about 1.6 K).

They then enter to a discussion about the methods of determining the climate sensitivity and possible actions for improving the aerosol forcing uncertainty.

Some notes

Their Figure 2 is not very clear, so it might be good to go explain some of the things in it. The yellow line there represents the GHG-forcing only. The black line represents the greenhouse forcing minus the ocean thermal lag of 0.37 W/m2. This is the expected forcing from the GHG’s without taking other forcings to consideration. The effect of aerosol forcing (and tropospheric ozone forcing) is then presented in three red lines. The highest line has aerosol forcing of 0.6 W/m2, the middle red line has aerosol forcing of 1.2 W/m2, and the lowest red line has aerosol forcing of 2.4 W/m2. The values of 0.6 and 2.4 are from the IPCC best estimate 5 % and 95 % range.

However, here is apparently a minor mistake (thanks to AJ for catching that, see the comment section of the first version), the highest and lowest red lines are drawn too high so that at the equilibrium climate sensitivity of 1 K/(W/m2) they are 0.15 K too high. The reason for this is unknown.

The equilibrium climate sensitivity of 1 K/(W/m2) (corresponding to CO2 doubling temperature of 3.7 K) is a good point to see how the numbers add because at that equilibrium sensitivity the forcing and temperature have numerically the same value (i.e. the ocean thermal lag forcing of 0.37 W/m2 is 0.37 K at that point). Let us check if the numbers add up. Here are the numbers as I have “measured” (based on the pixel amounts in the image) them from the Figure 2 (the difference from the yellow line is given in parentheses):

Yellow line:  2.63 K (0.00 K)
Black line:   2.26 K (0.38 K)
Red 0.6 line: 2.13 K (0.50 K)
Red 1.2 line: 1.36 K (1.28 K)
Red 2.4 line: 0.33 K (2.31 K)

As described above, the yellow line presents the GHG forcing which is said to be 2.6 W/m2, so at this point it would be expected to be 2.6 K. My measured value agrees very well with that.

The black line is expected to be 0.37 K below the yellow line at that point, and the measured difference from the figure is 0.38, so that agrees well.

The highest red line has the forcings of GHG’s, tropospheric ozone, ocean thermal lag, and aerosol forcing of 0.6 W/m2, so they would add up to (2.6 + 0.35 – 0.37 – 0.6) W/m2 = 1.98 W/m2. Here my measured value is 2.13 K, which is 0.15 K higher than it should be (this was discussed briefly above).

The middle red line has the same forcings as the highest red line, but now the aerosol forcing is 1.2 W/m2, so now all the forcings would add up to (2.6 + 0.35 – 0.37 – 1.2) W/m2 = 1.38 W/m2. Here my measured value is 1.36 K, a good agreement.

The lowest red line has the same forcings as the highest red line, but now the aerosol forcing is 2.4 W/m2, so now all the forcings would add up to (2.6 + 0.35 – 0.37 – 2.4) W/m2 = 0.18 W/m2. Here my measured value is 0.33 K, so here again is the 0.15 K discrepancy discussed above.

Note that solar and volcanic forcing have not been mentioned. They should be included in the natural variability, so there is no need to handle them separately here.

I’m little disappointed of the lack of references to the preceeding studies on the subject. For example, Lean & Rind (2008) determined the relative sizes on forcings, finding no such problems as Schwartz et al. are suggesting.

As I have been making my paperlists, I have read a lot of introduction sections of papers because there the existing research on the subject in question is given and also the references to the key papers on the subject. I was quite amazed when I had read the introduction section of this Schwartz et al. paper. There isn’t a single reference to peer-reviewed papers, but they only reference IPCC 4th assessment report once. I don’t recall seeing any other papers with so poor introduction section.

Note that James Annan has also made some comments on this (thanks to Paul Middents for pointing it out in the comment section of the first version).

Conclusion

Claims in the Internet about Schwartz et al. are largely based on misunderstanding and not reading the paper beyond the abstract and/or introduction chapter. However, there is an apparent actual point in Schwartz et al. that other factors contributing to the difference of observed and expected warming are not enough suggesting that we have some forcings wrong or that climate sensitivity is somewhat smaller than we have thought.

Schwartz et al. do make an important point about aerosol forcing, the fact that it has large uncertainty. But I’m not quite sure that’s exactly a new finding.

Posted in Climate claims, Climate science | Leave a Comment »

Comments on S c h w a r t z et al. (2010)

Posted by Ari Jokimäki on January 24, 2010

UPDATE: I misunderstood some points about this paper and made some false comments about it here. Therefore I wrote a new version. Use the new version because all the information in this version is not correct.

Newly published paper by Schwartz et al. (2010) (abstract) has been claimed to show that theory of AGW is false or that “global warming has been cancelled”, etc. The claims are based on this statement in the paper’s introduction:

However, the observed increase of GMST over the industrial period is less than 40% of what would be expected from present best estimates of Earth’s climate sensitivity and the forcing (imposed change in energy balance, W m-2) by the observed increases in GHGs.

(GMST = global mean surface temperature, GHG = greenhouse gases).

In other words, they determine expected temperature rise from greenhouse gas forcing and the climate sensitivity, then look at the observed temperature rise and compare the two. Not surprisingly, they found that the two are different. I said “not surprisingly” because they only looked at greenhouse gas forcing and I know that there are other forcings at play and I’m also quite sure that some of those forcings work in different direction than greenhouse gases, aerosols for example. Just a simple example of the situation would be that if GHG’s would cause a warming of 2K and aerosols would cause cooling of 1K, then the resulting warming from these two would be 1K meaning that the observed warming would be only 50 % of the expected warming from GHG’s.

So, the 40 % number they give doesn’t represent the total overall situation, but it only represents the situation if only greenhouse gases are considered and the rest forcings are ignored. Now, Schwartz et al. know this because it is the subject of their paper to study what causes the difference, so Schwartz et al. are not claiming that observed temperature is less than 40 % of the expected all-forcing-temperature. Yet, it is the 40 % number that is the one they are now parroting all over the Internet as if it would represent the total overall situation.

It would be the same as if I would calculate that aerosols in the air would cause cooling of certain amount and then I would note that global temperature has been rising instead of expected cooling from aerosols. I would then say that I will now consider why there is such a difference but somebody else would just quote me on the observed temperatures not showing the expected cooling and would then spread that word as a proof that the theory of aerosols has been now shown wrong.

Well, at this point we are only in the introduction section of the Schwartz et al. and we already have handled most of the false claims circulating in the Internet about this. But Schwartz et al. do have things to say even beyond the introduction.

Rest of the paper

Schwartz et al. are studying if the difference between the observed and expected greenhouse gas warming is due four main things:

- Natural variation in global temperature.
– Lack of attainment of equilibrium.
– Overestimate of climate sensitivity.
– Countervailing forcings over the industrial period.

They calculated that the expected warming from GHG’s would have been 2.1 K. They said that the observed temperature increase had been 0.8 K. That means that they are looking to find 2.1 K – 0.8 K = 1.3 K of cooling from the above mentioned four things.

Natural variation in global temperature can cause up to 0.2 K of cooling according to them. This is how they found it out:

We use variation in preindustrial global temperature as inferred from proxy records, mainly tree rings, ice cores, corals, and varved sediments to estimate the likely magnitude of any natural cooling over the 150-year interval of the instrumental record.

Proxies? Tree-rings??? Surely any self-respecting climate denier at last now will dump this paper as a heretic production. Well, seriously, I think that’s reasonable approach to get a rough idea. However, it’s also bad news for those who think that the global warming is from natural variability. According to Schwartz et al. observed = 0.8 K and natural variability = 0.2 K. That means the observed warming is 400 % of the expected maximum warming from natural variability – a worse result than the observed versus expected from GHG’s.

Note that natural variability can work for both directions, it can cause cooling or warming.

Lack of attainment of equilibrium is a fancy way of saying that there might be delays in the climate system so that not all the warming from GHG’s has yet been realised in surface temperature but is instead hiding somewhere. Ocean is the most obvious and important place to hide the warming from GHG’s. They determine that 0.37 W/(m2) of the forcing could be hiding in the ocean, and they say that it corresponds to 22 % of the warming discrepancy, which would give about 0.5 K of cooling (I might have misinterpreted that though, they don’t express it very clearly).

Note that this effect works only to one direction, it has a cooling effect on global surface temperature.

Overestimate of climate sensitivity suggests that the climate sensitivity would be lower than the expected range. That would explain the discrepancy. They note that IPCC limit for very “unlikely” climate sensitivity is 1.5 K and they say that the observed warming would require the climate sensitivity to be even lower than that. That, however ignores the other factors causing the cooling mentioned above. The situation is presented in their Figure 2. There they present the observed warming as a horizontal line and they have added the natural variability as a horizontal band around the observed line. The expected warming from GHG’s is presented as an increasing line. One can see that when accounting for natural variability, the expected warming goes out of the band at climate sensitivity of about 1.7 K. That already is within IPCC very unlikely limits, and approaching the “likely” limit of 2.0 K.

However, they haven’t included the “Lack of attainment of equilibrium” value of 0.5 K discussed above. If we would include that, we would get a possible climate sensitivity of 2.2 K, well within the IPCC “likely” limits. This wouldn’t even include the aerosol forcing, which is likely to be substantially negative. With aerosol forcing of the size IPCC has determined to be the best estimate we would get even higher possible climate sensitivity (one that would agree quite well with IPCC limits), approaching 4 K. I have reconstructed some relevant parts of their Figure 2 and I have added the 0.5 K lines there as well. See the Figure 1 below.


Figure 1. Reconstruction of the relevant parts of Schwartz et al. Figure 2 – the warming of Earth’s surface (X-axis) as a function of climate sensitivity (Y-axis). Expected increase of global mean surface temperature for GHG’s only (black), expected increase of global mean surface temperature for GHG’s and aerosol’s based on IPCC’s best estimate (green), observed increase of global mean surface temperature (blue thick line) and the possible effect of natural variability to that (blue thin lines), and observed increase of global mean surface temperature when ocean thermal sink has been accounted for (red thick line) and the possible effect of natural variability to that (red thin lines).

Countervailing forcings over the industrial period also have an effect to the global temperature. Aerosol forcing we already discussed briefly above and it is the only forcing they are discussing here. Here too they discuss Figure 2 in a manner that is ignoring other factors. They say that with the IPCC best estimate aerosol forcing the warming “would be compatible with the lower end of the IPCC “likely” range of climate sensitivity”, but actually if we consider the natural variability and the warming wasted to the ocean, we can see from their Figure 2 that resulting climate sensitivity could easily be 4 K. Here are my estimates for the climate sensitivity (values in Kelvins) based on their reconstructed Figure 2 presented above as Figure 1:

                      GHG      GHG + aero
Observed              1.3         2.2
Obs & natural      1.0 - 1.6   1.7 - 2.7
Obs + ocean           2.1         3.5
Obs + ocean & nat  1.8 - 2.4   3.0 - 4.0

Schwartz et al. do make an important point about aerosol forcing, the fact that it has large uncertainty. But I’m not quite sure that’s exactly a new finding.

So, at this point it seems I’m disagreeing with them a little. In my opinion they are stressing the low end of their results and not considering the high end much. In fact the warming that goes to the ocean is quite certain component, so they definitely should have considered that in their Figure 2.

They then enter to a discussion about the methods of determining the climate sensitivity and possible actions for improving the aerosol forcing uncertainty.

Conclusion

Claims in the Internet about Schwartz et al. are largely based on misunderstanding and not reading the paper beyond the abstract and/or introduction chapter. However, there is an apparent actual point in Schwartz et al. that other factors contributing to the difference of observed and expected warming are not enough suggesting that we have some forcings wrong or that climate sensitivity is somewhat smaller than we have thought.

To me it seems that Schwartz et al. are mistaken and their point seems to rise from the fact that they didn’t consider ocean thermal lag when they determined the whole situation. They considered the ocean thermal lag separately but did not include it to their discussion of Figure 2 describing the overall situation. When the ocean thermal lag is included, the results seem to agree well with the IPCC values and the best estimate of the climate sensitivity would be 3-4 K.

I’m also little disappointed of the lack of references to the preceeding studies on the matter. For example, Lean & Rind (2008) determined the relative sizes on forcings, finding no such problems as Schwartz et al. are suggesting.

UPDATE (January 25, 2010):
I’ll add one note. As I have been making my paperlists, I have read a lot of introduction sections of papers because there the existing research on the subject in question is given and also the references to the key papers on the subject. I was quite amazed when I had read the introduction section of this Schwartz et al. paper. There isn’t a single reference to peer-reviewed papers, but they only reference IPCC 4th assessment report once. I don’t recall seeing any other papers with so poor introduction section. Also note that Schwartz had problems before with the ocean’s role in his 2007 paper, see the comment section below (thanks to Paul Middents for pointing that out).

Posted in Climate claims, Climate science | 13 Comments »

Papers on methane emissions

Posted by Ari Jokimäki on January 23, 2010

This is a list of papers on methane emissions from a variety of different sources. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (August 15, 2013): Nisbet (2002) and Brook et al. (2000) added.
UPDATE (April 1, 2011): Thom et al. (1993) and Eisma et al. (1994) added.
UPDATE (August 7, 2010): Shakhova et al. (2010) added.

Geochemical and geophysical evidence of methane release over the East Siberian Arctic Shelf – Shakhova et al. (2010) “The East Siberian Arctic Shelf (ESAS), which includes the Laptev Sea, the East Siberian Sea, and the Russian part of the Chukchi Sea, has not been considered to be a methane (CH4) source to hydrosphere or atmosphere because subsea permafrost, which underlies most of the ESAS, was believed, first, not to be conducive to methanogenesis and, second, to act as an impermeable lid, preventing CH4 escape through the seabed. Here recent observational data obtained during summer (2005–2006) and winter (2007) expeditions indicate the ubiquitous presence of elevated dissolved CH4 and an elevated atmospheric CH4 mixing ratio. The CH4 data were also analyzed together with high resolution seismic (HRS) data obtained by means of a “Sonic M-141” system consisting of a high-resolution profiler and side-scan sonar mounted in a towed fish during the Transdrift-X Expedition (2004) onboard the R/V Yakov Smirnitskiy. Results show anomalously high concentrations of dissolved CH4 (up to 5 μM) and an episodically (nongradually) increasing atmospheric mixing ratio of CH4 (up to 8.2 ppm) in some areas of the ESAS. A most likely source is year-round CH4 release through taliks (columns of thawed sediments within permafrost) from seabed CH4 reservoirs such as shallow hydrates and geological sources. Such releases occur not only within the areas underlain by fault zones but also outside of them. This points to permafrost’s failure to further preserve CH4 deposits in the ESAS. The total amount of carbon preserved within the ESAS as organic matter and ready to release CH4 from seabed deposits is predicted to be ∼1400 Gt. Release of only a small fraction of this reservoir, which was sealed with impermeable permafrost for thousands of years, would significantly alter the annual CH4 budget and have global implications, because the shallowness of the ESAS allows the majority of CH4 to pass through the water column and escape to the atmosphere.” N. Shakhova, I. Semiletov, I. Leifer, A. Salyuk, P. Rekant, D. Kosmach, Journal of Geophysical Research: Oceans (1978–2012), Volume 115, Issue C8, August 2010, DOI: 10.1029/2009JC005602.

Escape of methane gas from the seabed along the West Spitsbergen continental margin – Westbrook et al. (2009) “More than 250 plumes of gas bubbles have been discovered emanating from the seabed of the West Spitsbergen continental margin, in a depth range of 150–400 m, at and above the present upper limit of the gas hydrate stability zone (GHSZ). Some of the plumes extend upward to within 50 m of the sea surface. The gas is predominantly methane. Warming of the northward-flowing West Spitsbergen current by 1°C over the last thirty years is likely to have increased the release of methane from the seabed by reducing the extent of the GHSZ, causing the liberation of methane from decomposing hydrate. If this process becomes widespread along Arctic continental margins, tens of Teragrams of methane per year could be released into the ocean.” [Full text]

Tropical methane emissions: A revised view from SCIAMACHY onboard ENVISAT – Frankenberg et al. (2008) “Methane retrievals from near-infrared spectra recorded by the SCIAMACHY instrument onboard ENVISAT hitherto suggested unexpectedly large tropical emissions. Even though recent studies confirm substantial tropical emissions, there were indications for an unresolved error in the satellite retrievals. Here we identify a retrieval error related to inaccuracies in water vapor spectroscopic parameters, causing a substantial overestimation of methane correlated with high water vapor abundances. We report on the overall implications of an update in water spectroscopy on methane retrievals with special focus on the tropics where the impact is largest. The new retrievals are applied in a four-dimensional variational (4D-VAR) data assimilation system to derive a first estimate of the impact on tropical CH4 sources. Compared to inversions based on previous SCIAMACHY retrievals, annual tropical emission estimates are reduced from 260 to about 201 Tg CH4 but still remain higher than previously anticipated.” [Full text]

Anomalies of methane in the atmosphere over the East Siberian shelf: Is there any sign of methane leakage from shallow shelf hydrates? – Shakhova et al. (2008) “Extremely high concentrations of methane (up to 8 ppm) in the atmospheric layer above the sea surface along with anomalously high concentrations of dissolved methane in the water column (up to 560 nM, or 12000% of super saturation), registered during a summertime cruise over the ESS in September 2005, were analyzed together with available data obtained during previous and subsequent expeditions to distinguish between possible methane sources of different origin, potential, and mobility. Using indirect evidence it was shown that one such source may be highly potential and extremely mobile shallow methane hydrates, whose stability zone is seabed permafrost-related and could be disturbed upon permafrost development, degradation, and thawing. … …we consider release of up to 50 Gt of predicted amount of hydrate storage as highly possible for abrupt release at any time. That may cause ~12-times increase of modern atmospheric methane burden with consequent catastrophic greenhouse warming.”

Early anthropogenic CH4 emissions and the variation of CH4 and 13CH4 over the last millennium – Houweling et al. (2008) “The main idea is that emissions of isotopically depleted CH4, from, for example, rice cultivation, domestic ruminants, and waste treatment started increasing earlier than the isotopically enriched emissions from fossil fuel, which started with the start of industrialization. However, because the observed increase of atmospheric methane only started around 1750 A.D., these preindustrial anthropogenic emissions must have been accompanied by a net reduction of natural CH4 sources during the Little Ice Age (LIA) compensating for the increase of anthropogenic emissions during that period. Results of transient box model simulations for the last millennium show that under the new hypothesis a close agreement can be obtained between model and measurements.” [Full text]

Methane hydrate stability and anthropogenic climate change – Archer (2007) “The hydrate reservoir is so large that if 10% of the methane were released to the atmosphere within a few years, it would have an impact on the Earth’s radiation budget equivalent to a factor of 10 increase in atmospheric CO2. … Hydrates are releasing methane to the atmosphere today in response to anthropogenic warming, for example along the Arctic coastline of Siberia. However most of the hydrates are located at depths in soils and ocean sediments where anthropogenic warming and any possible methane release will take place over time scales of millennia. Individual catastrophic releases like landslides and pockmark explosions are too small to reach a sizable fraction of the hydrates. The carbon isotopic excursion at the end of the Paleocene has been interpreted as the release of thousands of Gton C, possibly from hydrates, but the time scale of the release appears to have been thousands of years, chronic rather than catastrophic.” [Full text]

Methane emissions from terrestrial plants under aerobic conditions – Keppler et al. (2006) “Here we demonstrate using stable carbon isotopes that methane is readily formed in situ in terrestrial plants under oxic conditions by a hitherto unrecognized process. Significant methane emissions from both intact plants and detached leaves were observed during incubation experiments in the laboratory and in the field. If our measurements are typical for short-lived biomass and scaled on a global basis, we estimate a methane source strength of 62–236 Tg yr-1 for living plants and 1–7 Tg yr-1 for plant litter (1 Tg = 1012 g).” [Full text]

Late Quaternary Atmospheric CH4 Isotope Record Suggests Marine Clathrates Are Stable – Sowers (2006) “One explanation for the abrupt increases in atmospheric CH4, that occurred repeatedly during the last glacial cycle involves clathrate destabalization events. Because marine clathrates have a distinct deuterium/hydrogen (D/H) isotope ratio, any such destabilization event should cause the D/H ratio of atmospheric CH4 (δDCH4) to increase. Analyses of air trapped in the ice from the second Greenland ice sheet project show stable and/or decreasing δDCH4 values during the end of the Younger and Older Dryas periods and one stadial period, suggesting that marine clathrates were stable during these abrupt warming episodes. Elevated glacial δDCH4 values may be the result of a lower ratio of net to gross wetland CH4 emissions and an increase in petroleum-based emissions.”

Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming – Walter et al. (2006) “Thaw lakes in North Siberia are known to emit methane, but the magnitude of these emissions remains uncertain because most methane is released through ebullition (bubbling), which is spatially and temporally variable. Here we report a new method of measuring ebullition and use it to quantify methane emissions from two thaw lakes in North Siberia. … We find that thawing permafrost along lake margins accounts for most of the methane released from the lakes, and estimate that an expansion of thaw lakes between 1974 and 2000, which was concurrent with regional warming, increased methane emissions in our study region by 58 per cent. Furthermore, the Pleistocene age (35,260–42,900 years) of methane emitted from hotspots along thawing lake margins indicates that this positive feedback to climate warming has led to the release of old carbon stocks previously stored in permafrost.” [Full text]

Assessing Methane Emissions from Global Space-Borne Observations – Frankenberg et al. (2005) “In the past two centuries, atmospheric methane has more than doubled and now constitutes 20% of the anthropogenic climate forcing by greenhouse gases. Yet its sources are not well quantified, introducing uncertainties in its global budget. We retrieved the global methane distribution by using spaceborne near-infrared absorption spectroscopy. In addition to the expected latitudinal gradient, we detected large-scale patterns of anthropogenic and natural methane emissions. Furthermore, we observed unexpectedly high methane concentrations over tropical rainforests, revealing that emission inventories considerably underestimated methane sources in these regions during the time period of investigation (August through November 2003).” [Full text]

The distribution of methane on the Siberian Arctic shelves: Implications for the marine methane cycle – Shakhova et al. (2005) “We present two years of data obtained during the late summer period (September 2003 and September 2004) for both the ESS and LS shelves. According to our data, the surface layer of shelf water was supersaturated up to 2500% relative to the present average atmospheric methane content of 1.85 ppm. Anomalously high concentrations (up to 154 nM or 4400% supersaturation) of dissolved methane in the bottom layer of shelf water suggest that the bottom layer is somehow affected by near-bottom sources. Considering the possible formation mechanisms of such plumes, we favor thermo-abrasion and the effects of shallow gas or gas hydrates release.” [Full text]

Global inventory of methane clathrate: sensitivity to changes in the deep ocean – Buffett & Archer (2004) “We present a mechanistic model for the distribution of methane clathrate in marine sediments, and use it to predict the sensitivity of the steady-state methane inventory to changes in the deep ocean. … Preferred values for these parameters are taken from previous studies of both passive and active margins, yielding a global estimate of 3×1018 g of carbon (3000 Gton C) in clathrate and 2×1018 g (2000 Gton C) in methane bubbles. The predicted methane inventory decreases by 85% in response to 3 °C of warming.” [Full text]

Have sudden large releases of methane from geological reservoirs occurred since the Last Glacial Maximum, and could such releases occur again? – Nisbet (2002) “Methane emissions from geological reservoirs may have played a major role in the sudden events terminating glaciation, both at the start of the Bølling/Allerød and also at the end of the Younger Dryas. These reservoirs include Arctic methane hydrates and also methane hydrate stored in offshore marine sediments in tropical and temperate latitudes. Emissions from hydrate stores may have resonated with tropical wetland emissions, each reinforcing the other. Because methane is such a powerful greenhouse gas, much smaller emissions of methane, compared with carbon dioxide, are required in order to have the same short–term impact by climate forcing. The methane–linked hypothesis has much geological support from sea–floor evidence of emission. However, Greenland ice–core records have been interpreted as showing methane as a consequential factor, rather than the leader, of change. This interpretation can be challenged on the grounds that temperature gradients in Greenland ice record local changes and local timing of a step–like shift in weather fronts, while methane concentrations record changes on a hemispheric and global scale. There are large remaining hydrate reservoirs in the Arctic and in shelf sediments globally, and there is substantial risk of further emissions.” Euan G. Nisbet, Phil. Trans. R. Soc. Lond. A 15 April 2002 vol. 360 no. 1793 581-607, doi: 10.1098/rsta.2001.0958.

Measurements of an anomalous global methane increase during 1998 – Dlugokencky et al. (2001) “The increased growth rate during 1998 corresponds to an increase in the imbalance between CH4 sources and sinks equal to ∼24 Tg CH4, the largest perturbation observed in 16 years of measurements. We suggest that wetland and boreal biomass burning sources may have contributed to the anomaly.”

On the origin and timing of rapid changes in atmospheric methane during the Last Glacial Period – Brook et al. (2000) “We present high resolution records of atmospheric methane from the GISP2 (Greenland Ice Sheet Project 2) ice core for four rapid climate transitions that occurred during the past 50 ka: the end of the Younger Dryas at 11.8 ka, the beginning of the Bølling-Allerød period at 14.8 ka, the beginning of interstadial 8 at 38.2 ka, and the beginning of interstadial 12 at 45.5 ka. During these events, atmospheric methane concentrations increased by 200–300 ppb over time periods of 100–300 years, significantly more slowly than associated temperature and snow accumulation changes recorded in the ice core record. We suggest that the slower rise in methane concentration may reflect the timescale of terrestrial ecosystem response to rapid climate change. We find no evidence for rapid, massive methane emissions that might be associated with large-scale decomposition of methane hydrates in sediments. With additional results from the Taylor Dome Ice Core (Antarctica) we also reconstruct changes in the interpolar methane gradient (an indicator of the geographical distribution of methane sources) associated with some of the rapid changes in atmospheric methane. The results indicate that the rise in methane at the beginning of the Bølling-Allerød period and the later rise at the end of the Younger Dryas were driven by increases in both tropical and boreal methane sources. During the Younger Dryas (a 1.3 ka cold period during the last deglaciation) the relative contribution from boreal sources was reduced relative to the early and middle Holocene periods.” Edward J. Brook, Susan Harder, Jeff Severinghaus, Eric J. Steig, Cara M. Sucher, Global Biogeochemical Cycles, Volume 14, Issue 2, pages 559–572, June 2000, DOI: 10.1029/1999GB001182. [Full text]

Continuing decline in the growth rate of the atmospheric methane burden – Dlugokencky et al. (1998) “Measurements have revealed that although the global atmospheric methane burden continues to increase with significant interannual variability, the overall rate of increase has slowed. Here we present an analysis of methane measurements from a global air sampling network that suggests that, assuming constant OH concentration, global annual methane emissions have remained nearly constant during the period 1984–96, and that the decreasing growth rate in atmospheric methane reflects the approach to a steady state on a timescale comparable to methane’s atmospheric lifetime.”

Changing concentration, lifetime and climate forcing of atmospheric methane – Lelieveld et al. (1998) “Here, we review sources and sink estimates and we present global 3D model calculations, showing that the main features of the global CH4 distribution are well represented. The model has been used to derive the total CH4 emission source, being about 600 Tg yr-1. Based on published results of isotope measurements the total contribution of fossil fuel related CH4 emissions has been estimated to be about 110 Tg yr-1.”

Methane emissions from cattle – Johnson & Johnson (1995) “Ruminant livestock can produce 250 to 500 L of methane per day. This level of production results in estimates of the contribution by cattle to global warming that may occur in the next 50 to 100 yr to be a little less than 2%.” [Full text]

A dramatic decrease in the growth rate of atmospheric methane in the northern hemisphere during 1992 – Dlugokencky et al. (1994) “Global measurements of atmospheric methane have revealed a sharp decrease in the growth rate in the Northern Hemisphere during 1992. The average trend for the Northern Hemisphere during 1983–1991 was (11.6±0.2) ppbv yr−1, but the increase in 1992 was only (1.8±1.6) ppbv. In the Southern Hemisphere, the average increase (1983–1991) was (11.1±0.2) ppbv yr−1, and the 1992 increase was (7.7±1.0) ppbv. Various possibilities for a change in methane sources or sinks are discussed, but the most likely explanation is a change in an anthropogenic source such as fossil fuel exploitation, which can be rapidly and easily affected by man’s activities.”

Determination of European methane emissions, using concentration and isotope measurements – Eisma et al. (1994) “The determination of methane emissions on a regional scale is needed in order to reduce some of the uncertainties in the global methane budget. Our measurements of the concentration and the Carbon-13 isotope composition (δ13C) of atmospheric methane are, combined with trajectories, used to get insight in the type and size of the methane emissions of a large area.” Roos Eisma, Alex T. Vermeulen and W. M. Kieskamp, Environmental Monitoring and Assessment, Volume 31, Numbers 1-2, 197-202, DOI: 10.1007/BF00547197.

The regional budget of atmospheric methane of a highly populated area – Thom et al. (1993) “A regional methane budget for the catchment area of Heidelberg has been established, using quasi-continuous measurements of the atmospheric methane concentration and its stable isotope ratios (13C/12C, D/H). Methane in Heidelberg shows a mean concentration offset of 155 ppbv relative to background air. This concentration offset is due to a direct influence from – mainly anthropogenic – continental European methane sources. Using parallel atmospheric 222Radon observations, and the observed CH4 concentration offset, we estimated the mean CH4 flux density within the catchment area to be (12±6) gCH4 m-2 yr-1. This is three times the global average for continental surfaces. From the stable isotope observations we derived the isotopic composition of the mean methane source to be δ13Csource(PDB) = (−54.3±1.7)‰ and δDsource(SMOW) = (−270±41)‰. In an independent approach we evaluated the distribution of methane sources from source statistics within a catchment area of ca. 500 km radius around Heidelberg. With help of a simple dispersion model we then calculated their contributions to the concentration offset at the sampling site. Using the isotopic composition of the mean source as constraint to adjust the specific emissions of individual sources it turned out that the major contributions to the observed concentration offset in Heidelberg are from cattle (37%), landfills (27%), coal mining (12%), agricultural wastes (11%), burning of fuels (8%), and gas leakages (5%). This source mix is more or less the same as in the whole catchment area (e.g. Central Europe).” Marcus Thom, Rainer Bösinger, Martina Schmidt and Ingeborg Levin, The regional budget of atmospheric methane of a highly populated area, Chemosphere, Volume 26, Issues 1-4, January-February 1993, Pages 143-160, doi:10.1016/0045-6535(93)90418-5.

Role of methane clathrates in past and future climates – MacDonald (1990) “Methane occurrences and the organic carbon content of sediments are the bases used to estimate the amount of carbon currently stored as clathrates. The estimate of about 11,000 Gt of carbon for ocean sediments, and about 400 Gt for sediments under permafrost regions is in rough accord with an independent estimate by Kvenvolden of 10,000 Gt. … The sensitivity of clathrates to surface change, the time scales involved, and the large quantities of carbon stored as clathrate indicate that clathrates may have played a significant role in modifying the composition of the atmosphere during the ice ages. The release of methane and its subsequent oxidation to carbon dioxide may be responsible for the observed swings in atmospheric methane and carbon dioxide concentrations during glacial times.”

Methane Emission From Natural Wetlands: Global Distribution, Area, and Environmental Characteristics of Sources – Matthews & Fung (1987) “A global data base of wetlands at 1º resolution has been developed from the integration of three independent global, digital sources: (1) vegetation, (2) soil properties and (3) fractional inundation in each 1º cell. … The annual methane emission from wetlands is ∽110 Tg, well within the range of previous estimates (11-300 Tg).”

Posted in AGW evidence | 3 Comments »

Viewing Angle on ISCCP Problems

Posted by Ari Jokimäki on January 20, 2010

International Satellite Cloud Climatology Project (ISCCP) provides measurements of global cloud cover. See the project website for the introduction (see also Rossow & Schiffer, 1991, for basic description of ISCCP cloud data products). They offer the longest satellite dataseries for global cloud cover. ISCCP data has been widely used to study trends in global cloud cover. For example, Pallé et al. (2004) have used ISCCP data to determine a decrease in Earth’s reflectance. Figure 1 shows the global cloud cover trends in ISCCP data, and there we can see that the global cloud cover has apparently decreased rather strongly between about 1987 and 2000.


Figure 1. The global cloud cover from ISCCP data. (Image is loaded from ISCCP website.)

Couple of other examples of papers using ISCCP data in cloud cover research:

Pinker et al. (2005):

Long-term variations in solar radiation at Earth’s surface (S) can affect our climate, the hydrological cycle, plant photosynthesis, and solar power. … Here we present an estimate of global temporal variations in S by using the longest available satellite record. We observed an overall increase in S from 1983 to 2001 at a rate of 0.16 watts per square meter (0.10%) per year; this change is a combination of a decrease until about 1990, followed by a sustained increase. The global-scale findings are consistent with recent independent satellite observations but differ in sign and magnitude from previously reported ground observations. Unlike ground stations, satellites can uniformly sample the entire globe.

Hatzianastassiou et al. (2005):

The monthly mean shortwave (SW) radiation budget at the Earth’s surface (SRB) was computed on 2.5-degree longitude-latitude resolution for the 17-year period from 1984 to 2000, using a radiative transfer model accounting for the key physical parameters that determine the surface SRB, and long-term climatological data from the International Satellite Cloud Climatology Project (ISCCP-D2). … Significant increasing trends in DSR and net DSR fluxes were found, equal to 4.1 and 3.7 Wm−2, respectively, over the 1984–2000 period (equivalent to 2.4 and 2.2 Wm−2 per decade), indicating an increasing surface solar radiative heating. … The surface solar heating occurs mainly in the period starting from the early 1990s, in contrast to the commonly reported decreasing trend in DSR through the late 1980s, found also in our study.

The apparent decrease in global cloud cover has also been used as an argument against anthropogenic warming (but mainly outside of scientific literature). But when the sources of these arguments are consulted, almost without exception we run into ISCCP cloud cover data being used as the source. In the following, I will show you why it is false to claim global cloud cover trends based on ISCCP data.

Problematic satellite viewing angle

Norris (2000) searched for suspicious spatial patterns from ISCCP cloud data, and found some:

The most striking feature of Figure 2 is the circular patch of positive correlation centered on 0°N, 0°E. It seems unlikely that a natural process would produce such a regular pattern, but it is interesting to note that the pattern almost exactly resembles the footprint of Meteosat data incorporated into ISCCP (Meteosat is the European geostationary satellite).

Norris concluded:

Accordingly, the ISCCP time series presented in Figure 1 is probably spurious, and any resemblance to time series of other parameters (e.g., Marsh and Svensmark, 2000) is merely coincidental.

Campbell (2004) showed images of the same problem. Campbell showed simply the cloudiness on the map of the world in certain time period and pointed out that there were clear “seams” showing in the maps. Campbell noted:

Qualitatively one suspects that different view angles are affecting the products.

Campbell then showed a graph that had cloudiness plotted for one latitude band, and the satellite positions were marked to the graph. The cloudiness clearly increased further from the satellite positions, so the cloudiness seemed to be increasing with satellite viewing angle. Campbell also made an effort of quantifying the apparent effect; the cloudiness data was divided to different bins by viewing angle, and average cloudiness was calculated for the bins. The resulting graph shows almost linear increase in cloudiness with the increase in viewing angle. Campbell presented the finding also in the form of an equation that describes the viewing angle dependence of cloudiness in ISCCP data.

So Campbell had established that the amount of measured cloudiness in ISCCP data is larger when the satellite viewing angle is larger. Next Campbell entered into a discussion of trends. Campbell noted an important thing:

As the ISCCP project progressed, different numbers of geo satellites were available. This had the unforeseen effect of changing the average view angle as the data set has been accumulated.

And it turns out that the number of satellites increased, and that then decreased the average viewing angle. As higher viewing angle was associated with higher cloudiness, decreasing average viewing angle decreases the amount of measured clouds. Campbell showed that it has indeed happened in the ISCCP data and the result is that the long decreasing trend in ISCCP cloud data seems to be an artifact of satellite viewing angle. Campbell then applied a correction based on the equation for the viewing angle dependency. The result still shows a decreasing trend but clearly smaller than without the correction. However, the corrected map still showed some “seams” so the correction was only rough one, and there were some calibration issues Campbell suspected might still be at play. Campbell concluded:

A substantial part of the ISCCP trend is due to systematic changes in the view angle over the 18 years of the data analysis. From an analysis of the AVHRR data alone, increasing cloudiness at steeper view angles is obvious.

Pallé (2005) also noted that there possibly is viewing angle problems with ISCCP data. Campbell (2006) continued to define a correction to the ISCCP viewing angle problem among some other problems (some diurnal corrections). After corrections, not much cloud trends were left. However, Campbell noted that there still were a discontinuity in the data:

But there is a very distinct discontinuity in all the cloud amount time series in October 2001 when NOAA 16 AVHRR data replaced NOAA 14 data.

Evan et al. (2007) also studied the viewing angle issue. They first noted how the ISCCP data had been used, including most of the above mentioned studies, and they then said:

However, these trends in total cloudiness have not been observed in surface [Norris, 2005] and other satellite [Jacobowitz et al., 2003; Wylie et al., 2005] cloud records.

In their figure 2 they showed similar map as Norris and Campbell did previously of the cloud variability, showing the circular features suggestive of the viewing angle problem. They said:

These circles correspond to so-called geostationary ‘‘footprints’’ that describe the area observed by each satellite. At the center of these footprints a satellite sensor’s viewing angle is perpendicular to the surface, corresponding to a satellite zenith angle of 0 degrees. At the footprint edges the satellite zenith angle is much higher, corresponding to a longer path length through the atmosphere that light must travel before it is detected by the sensor.

They then performed a test where they created two dataseries from ISCCP data; one from large satellite viewing angles and one from small viewing angles. It turned out that the dataseries with large viewing angles (black solid line in their figure 3) showed far stronger decrease in clouds than the one with small viewing angle (black dashed line in their figure 3). They also showed how changes in viewing angle over time from large viewing angle areas (grey solid line in figure 3) matched very well the step changes in the change in cloudiness (compare grey and black solid lines in figure 3). They also listed some events in the satellite network (launches of new satellites, repositioning of satellites, etc.) that might have affected the data, and the listed events matched the step changes in tha data rather well. One such event was a shift that occurred in 2001. That shift seems to be related to a change in reference satellite (Knapp, 2008).

Evan et al. then showed an example of one location which had large satellite viewing angle where there was a known satellite network event, and showed how the cloud data clearly jumped at the event (see their figure 4), while a nearby region that had small viewing angle showed trendless line at the same time. To finish the paper, Evan et al. suggested some actions that could be done to correct the problem.

Berthier et al. (2008) also found some potential problems with ISCCP data:

Comparisons of CTH developed from LITE, for 2 weeks of data in 1994, with ISCCP (International Satellite Cloud Climatology Project) cloud products show that the cloud fraction observed from spaceborne lidar is much higher than that from ISCCP. Another key result is that ISCCP products tend to underestimate the CTH of optically thin cirrus clouds.

They considered the viewing angle problem to be one possible source for the differences they found. The viewing angle problem was also briefly touched in Norris (2008).

Conclusion

It seems that the finding of Norris, Campbell, and Evan et al. about ISCCP satellite viewing angle (by changes in satellite network that affect the viewing angles) creating a spurious trend is a real problem. I think they have shown it beyond reasonable doubt. ISCCP website lists known and fixed errors in ISCCP data but there doesn’t seem to be any mention of this problem.

Many studies have made conclusions relating to clouds based on the apparent long term decrease in ISCCP data, but all that research is in doubt because the trend at least partly is not real. Furthermore, ISCCP cloud data is the longest satellite record we have on the subject, so it would be important to issue an official correction to this problem. When the trend is corrected, interesting things might be found, as shown by Clement et al. (2009) who corrected for the problem and found that cloud feedback is positive. As a long record, ISCCP data would be suitable to that kind of studies.

References

Berthier, S., Chazette, P., Pelon, J., Baum, B., 2008, “Comparison of cloud statistics from spaceborne lidar systems”, Atmos. Chem. Phys., 8, 6965-6977, 2008, [Full text]

Campbell, G. Garrett, 2004, “View angle dependence of cloudiness and the trend in ISCCP cloudiness”, 13th Conference on Satellite Meteorology and Oceanography, [Full text]

Campbell, G. Garrett, 2006, “Diurnal and Angular Variability of Cloud Detection: Consistency Between Polar and Geosynchronous ISCCP Products”, 14th Conference on Satellite Meteorology and Oceanography, [Full text]

Clement, Amy C., Burgman, Robert, Norris, Joel R., 2009, “Observational and Model Evidence for Positive Low-Level Cloud Feedback”, Science 24 July 2009, Vol. 325. no. 5939, pp. 460 – 464, DOI: 10.1126/science.1171255, [Full text]

Evan, Amato T., Heidinger, Andrew K., Vimont, Daniel J., 2007, “Arguments against a physical long-term trend in global ISCCP cloud amounts”, Geophys. Res. Lett., 34, L04701, doi:10.1029/2006GL028083, [Full text]

Hatzianastassiou, N., Matsoukas, C., Fotiadi, A. Pavlakis, K. G., Drakakis, E., Hatzidimitriou, D., Vardavas, I., 2005, “Global distribution of Earth’s surface shortwave radiation budget”, Atmos. Chem. Phys. Discuss., 5, 4545-4597, [Full text]

Knapp, Kenneth R., 2008, “Calibration Assessment of ISCCP Geostationary Infrared Observations Using HIRS”, Journal of Atmospheric and Oceanic Technology, Volume 25, Issue 2 (February 2008), DOI: 10.1175/2007JTECHA910.1, [Full text]

Norris, Joel R., 2000, “What Can Cloud Observations Tell Us About Climate Variability?”, Space Science Reviews, Volume 94, Numbers 1-2 / November, 2000, DOI 10.1023/A:1026704314326, [Full text]

Norris, J. R., 2008, “Observed Interdecadal Changes in Cloudiness: Real or Spurious?”, Advances in Global Change Research, 33, DOI 10.1007/978-1-4020-6766-2, [Full text]

Pallé, E., Goode, P. R., Montañés-Rodríguez, P., Koonin, S. E., 2004, “Changes in Earth’s Reflectance over the Past Two Decades”, Science 28 May 2004, Vol. 304. no. 5675, pp. 1299 – 1301, DOI: 10.1126/science.1094070, [Full text]

Pallé, E., 2005, “Possible satellite perspective effects on the reported correlations between solar activity and clouds”, Geophys. Res. Lett., 32, L03802, doi:10.1029/2004GL021167, [Full text]

Pinker, R. T., Zhang, B., Dutton, E. G., 2005, “Do Satellites Detect Trends in Surface Solar Radiation?”, Science 6 May 2005, Vol. 308. no. 5723, pp. 850 – 854, DOI: 10.1126/science.1103159

Rossow, William B., Schiffer, Robert A., 1991, “ISCCP Cloud Data Products”, Bulletin of the American Meteorological Society, Volume 72, Issue 1 (January 1991), DOI: 10.1175/1520-0477(1991)0722.0.CO;2, [Full text]

Posted in Climate claims, Climate science | 1 Comment »

Papers on solar cycle length

Posted by Ari Jokimäki on January 18, 2010

This is a list of papers on the solar cycle length, and especially on its effect to the climate. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative. Thanks to John Cook for notifying me about this subject, and doing lot of preliminary paper searching as shown here.

Transition of solar cycle length in association with the occurrence of grand solar minima indicated by radiocarbon content in tree-rings – Miyahara et al. (2008) “In this paper, we review the variation of the 11-year solar cycle since the 15th century revealed by the measurement of radiocarbon content in single-year tree-rings of Japanese cedar trees. … As a result, slight stretching of the “11-year” and the “22-year” solar cycles was found during these two grand solar activity minima; continuously during the Maunder Minimum and only intermittently during the Spoerer Minimum. On the contrary, normal or slightly shortened 11-year cycles were detected during the interval period of these two minima.”

A Note on Solar Cycle Length Estimates – Vaquero et al. (2006) “In this short contribution, we show estimates of the solar cycle length using the RFC-method and the Group Sunspot Number (RG) instead the RZ. Several authors have showed the advantages of RG for the analysis of sunspot activity before 1850. The use of RG solves some doubtful solar cycle length estimates obtained around 1800 using RZ.”

A review of the solar cycle length estimates – Benestad (2005) “New estimates of the solar cycle length are calculated from an up-to-date monthly sunspot record using a novel but mathematically rigorous method involving multiple regression, Fourier approximation, and analytical expressions for the first derivative based on calculus techniques. … There have been speculations about an association between the solar cycle length and Earth’s climate, however, the solar cycle length analysis does not follow Earth’s global mean surface temperature. A further comparison with the monthly sunspot number, cosmic galactic rays and 10.7 cm absolute radio flux since 1950 gives no indication of a systematic trend in the level of solar activity that can explain the most recent global warming.”

Pattern of Strange Errors Plagues Solar Activity and Terrestrial Climate Data – Damon & Laut (2004) “The last decade has seen a revival of various hypotheses claiming a strong correlation between solar activity and a number of terrestrial climate parameters. Links have been made between cosmic rays and cloud cover, first total cloud cover and then only low clouds, and between solar cycle lengths and northern hemisphere land temperatures. These hypotheses play an important role in the scientific debate as well as in the public debate about the possibility or reality of a man-made global climate change. Analysis of a number of published graphs that have played a major role in these debates and that have been claimed to support solar hypotheses shows that the apparent strong correlations displayed on these graphs have been obtained by incorrect handling of the physical data.” [Full text]

Solar activity and terrestrial climate: an analysis of some purported correlations – Laut (2003) “I have analyzed a number of published graphs which have played a major role in these debates and which have been claimed to support solar hypotheses. My analyses show that the apparent strong correlations displayed on these graphs have been obtained by an incorrect handling of the physical data. … In 1991 Friis-Christensen and Lassen published an article claiming a ‘strikingly goodagreement ’ between solar cycle lengths (SCLs) and Northern Hemisphere land air temperatures. … The apparent agreement with the recent global warming is obtained artificially by combining the 20 points of the smoothed curve with the most recent of several ‘upward swings’ of the oscillating non-filtered data, i.e., by combining two incongruous sets of physical data.” [Full text]

Persistence of the Gleissberg 88-year solar cycle over the last ∼12,000years: Evidence from cosmogenic isotopes – Peristykh & Damon (2003) “For that perspective,we examined the longest detailed cosmogenic isotope record—INTCAL98 calibration record of atmospheric 14C abundance. The most detailed precisely dated part of the record extends back to ∼11,854 years B.P. During this whole period, the Gleissberg cycle in 14C concentration has a period of 87.8 years and an average amplitude of ∼1‰(in Δ14C units). Spectral analysis indicates in frequency domain by sidebands of the combination tones at periods of ≈91.5 ±0.1 and ≈84.6 ± 0.1 years that the amplitude of the Gleissberg cycle appears to be modulated by other long-term quasiperiodic process of timescale∼2000 years. … Attempts have been made to explain 20th century global warming exclusively by the component of irradiance variation associated with the Gleissberg cycle. These attempts fail, because they require unacceptably great solar forcing and are incompatible with the paleoclimatic records.” [Full text]

On the length of the solar cycle and the Earth’s climate – Kristjánsson (2001) Reviews the situation briefly. [Full text]

Solar forcing of the Northern hemisphere land air temperature: New data – Thejll & Lassen (2000) “Adding new temperature data for the 1990s and expected values for the next sunspot extrema we test whether the solar cycle length model is still adequate. We find that the residuals are now inconsistent with the pure solar model. We conclude that since around 1990 the type of Solar forcing that is described by the solar cycle length model no longer dominates the long-term variation of the Northern hemisphere land air temperature.” [Full text]

Is There a Correlation between Solar Cycle Lengths and Terrestrial Temperatures? Old Claims and New Results – Laut & Gundermann (2000) Analyses the work of Friis-Christensen & Lassen (1991) “Our present work demonstrates that an alternative analysis of the underlying physical data leads to figures which do not support the claims mentioned above.” [Full text]

Solar cycle lengths and climate: A reference revisited – Laut & Gundermann (2000) “An article published by Friis-Christensen and Lassen [1991] appeared to indicate an association between solar cycle lengths (SCLs) and climate. … We here present an updated analysis using a recent temperature reconstruction with the time period of comparison considerably expanded. The correlation is found to be weak. In the light of this new result we analyze the question how the article by Friis-Christensen and Lassen was able to create the impression of a ‘strikingly good agreement’, as the authors described it. We show that the main reason is an unacceptable mixing of filtered and nonfiltered data in the graphical representation. Hereby, an artificial agreement of the solar data with the global warming since 1970 was established. The article by Friis-Christensen and Lassen has created and still creates confusion both in scientific and public discussions on climate change.”

Solar cycle length and 20th Century northern hemisphere warming: Revisited – Damon & Peristykh (1999) “It has been suggested that the length of the solar cycle (SCL) is related to solar forcing of global climate change [Friis‐Christensen and Lassen, 1991]. Although no physical mechanism had been proposed, the relation seemed to be supported by interesting correlations with several paleoclimate records and, separately, with the 20th century Northern Hemisphere instrumental record. Actually, what has been correlated is the quasi‐sinusoidal Gleissberg cycle which is slightly greater in the 18th century than in the 20th century. Using the pre‐industrial record as a boundary condition, the SCL‐temperature correlation corresponds to an estimated 25% of global warming to 1980 and 15% to 1997.”

Determination of solar cycle length variations using the continuous wavelet transform -Fligge et al. (1999) “The length of the sunspot cycle determined by Friis-Christensen & Lassen (1991) correlates well with indicators of terrestrial climate, but has been criticized as being subjective. In the present paper we present a more objective and general cycle-length determination. Objectivity is achieved by using the continuous wavelet transform based on Morlet wavelets and carrying out a careful error analysis. … All activity indicators give cycle length records which agree with each other within the error bars, whereby the signal due to the solar cycle is weaker within (10) Be than in the other indicators. In addition, all records exhibit cycle length variations which are, within the error bars, in accordance with the record originally proposed by Friis-Christensen & Lassen (1991).” [Full text]

Solar cycle length hypothesis appears to support the ipcc on global warming – Laut & Gundermann (1998) “We analyse the period 1579–1987 and find that the solar hypothesis—instead of contradicting—appears to support the assumption of a significant warming due to human activities. We have tentatively corrected the historical northern hemisphere land air temperature anomalies by removing the assumed effects of human activities. … It turns out that the agreement of the filtered solar cycle lengths with the corrected temperature anomalies is substantially better than with the historical anomalies, with the mean square deviation reduced by 36% for a climate sensitivity of 2.5°C, the central value of the IPCC assessment, and by 43% for the best-fit value of 1.7°C. Therefore our findings support a total reversal of the common assumption that a verification of the solar hypothesis would challenge the IPCC assessment of man-made global warming.”

Seip & Fuglestvedt (1998, Cicerone 6/1998) As described by Kristjánsson (2001): “Already in Cicerone 6/98, Seip and Fuglestvedt pointed out that updated temperature and solar-cycle data showed that the correlation between solar cycle length and global temperature did not apply beyond the period that Friis-Christensen and Lassen were looking at. … As Seip and Fuglestvedt (Cicerone 6/98) pointed out, however, there was no physical mechanism that could explain the alleged correlation.”

A new method to determine the solar cycle length – Mursula & Ulich (1998) “Here we propose a new method to define the solar cycle length as a difference between the median activity times of two successive sunspot cycles. The great advantage of this method is that the median times are almost independent of how the sunspot minima are determined. Therefore the method allows the solar cycle lengths to be calculated with a very small inaccuracy of a few days only. We show that the individual cycle lengths calculated from the conventional and the median method may differ by nearly a year. However, the long‐term trend of cycle lengths remains roughly the same during modern times.” [Full text]

Variability of the solar cycle length during the past five centuries and the apparent association with terrestrial climate – Lassen & Friis-Christensen (1995) “Therefore, a critical assessment of existing and proxy solar data prior to 1750 is reported and tables of epochs of sunspot minima as well as sunspot cycle lengths covering the interval 1500–1990 are presented. The tabulated cycle lengths are compared with reconstructed and instrumental temperature series through four centuries. The correlation between solar activity and northern hemisphere land surface temperature is confirmed.”

Solar cycle length, greenhouse forcing and global climate – Kelly & Wigley (1992) “Here we model the effects of a combination of greenhouse and solar-cycle-length forcing and compare the results with observed temperatures. We find that this forcing combination can explain many features of the temperature record, although the results must be interpreted cautiously; even with optimized solar forcing, most of the recent warming trend is explained by greenhouse forcing.”

Length of the Solar Cycle: An Indicator of Solar Activity Closely Associated with Climate – Friis-Christensen & Lassen (1991) “It has recently been suggested that the solar irradiance has varied in phase with the 80- to 90-year period represented by the envelope of the 11-year sunspot cycle and that this variation is causing a significant part of the changes in the global temperature. This interpretation has been criticized for statistical reasons and because there are no observations that indicate significant changes in the solar irradiance. A set of data that supports the suggestion of a direct influence of solar activity on global climate is the variation of the solar cycle length. This record closely matches the long-term variations of the Northern Hemisphere land air temperature during the past 130 years.” [Full text]

Secularly smoothed data on the minima and maxima of sunspot frequency – Gleissberg (1967) “When I introduced the method of secular smoothing into the study of the variations of sunspot frequency (GLEISSBERG, 1944) I published a table containing the secularly smoothed epochs and ordinates od sunspot minima and maxima which I had deduced from the data published by BRUNNER in 1939. … Now, the table ought to be enlarged for two reasons: on the one side, two 11-year cycles more have elapsed in the meantime and, on the other side, the ordinates of five minima and four maxima between 1698 and 1745 were deduced (GLEISSBERG, 1960) from the annual means of sunspot-relative numbers 1700-1748 as published by WOLF (1868) and corrected by CHERNOSKY and HAGAN (1958).”

A table of secular variations of the solar cycle – Gleissberg (1944) “In Table 1 the secular variations of the solar cycle show themselves by systematic fluctuations of the intervals between two minima (m-m), between two maxima (M-M), from minimum to maximum (3I-m) or from maximum to minimum (m-M), and of the quantities r and R which characterize the depths of secularly smoothed minima and the heights of secularly smoothed maxima. … It would be of interest to learn whether the secular variations of the solar cycle are reproduced also in terrestrial phenomena”

Posted in AGW evidence, Climate claims | 3 Comments »

Papers on the ocean carbon dioxide sink

Posted by Ari Jokimäki on January 14, 2010

This is a list of papers on the measurements of ocean uptake of atmospheric carbon dioxide. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans – Takahashi et al. (2009) “A climatological mean distribution for the surface water pCO2 over the global oceans in non-El Niño conditions has been constructed with spatial resolution of 4° (latitude) ×5° (longitude) for a reference year 2000 based upon about 3 million measurements of surface water pCO2 obtained from 1970 to 2007. … The annual mean for the contemporary net CO2 uptake flux over the global oceans is estimated to be −1.6±0.9 Pg-C y−1, which includes an undersampling correction to the direct estimate of −1.4±0.7 Pg-C y−1. Taking the pre-industrial steady-state ocean source of 0.4±0.2 Pg-C y−1 into account, the total ocean uptake flux including the anthropogenic CO2 is estimated to be −2.0±1.0 Pg-C y−1 in 2000.”

Tracking the Variable North Atlantic Sink for Atmospheric CO2 – Watson et al. (2009) “Historically, observations have been too sparse to allow accurate tracking of changes in rates of CO2 uptake over ocean basins, so little is known about how these vary. Here, we show observations indicating substantial variability in the CO2 uptake by the North Atlantic on time scales of a few years. Further, we use measurements from a coordinated network of instrumented commercial ships to define the annual flux into the North Atlantic, for the year 2005, to a precision of about 10%.”

Saturation of the Southern Ocean CO2 Sink Due to Recent Climate Change – Le Quéré et al. (2007) “Based on observed atmospheric carbon dioxide (CO2) concentration and an inverse method, we estimate that the Southern Ocean sink of CO2 has weakened between 1981 and 2004 by 0.08 petagrams of carbon per year per decade relative to the trend expected from the large increase in atmospheric CO2. We attribute this weakening to the observed increase in Southern Ocean winds resulting from human activities, which is projected to continue in the future.” [Full text]

An empirical estimate of the Southern Ocean air-sea CO2 flux – McNeil et al. (2007) “Here we employ an independent method to estimate the Southern Ocean air-sea flux of CO2 that exploits all available surface ocean measurements for dissolved inorganic carbon (DIC) and total alkalinity (ALK) beyond 1986. … Including the effects of sea ice, we estimate a Southern Ocean (>50°S) CO2 sink of 0.4 ± 0.25 Pg C/yr. Our analysis also indicates a substantial CO2 sink of 1.1 ± 0.6 Pg C/yr within the sub-Antarctic zone (40°S–50°S), associated with strong cooling and high winds. … This paper estimates for the first time basic seasonal carbon cycle parameters within the circumpolar Southern Ocean, which have up to now been extremely difficult to measure and sparse.” [Full text]

Inverse estimates of the oceanic sources and sinks of natural CO2 and the implied oceanic carbon transport – Mikaloff Fletcher et al. (2007) “We use an inverse method to estimate the global-scale pattern of the air-sea flux of natural CO2, i.e., the component of the CO2 flux due to the natural carbon cycle that already existed in preindustrial times, on the basis of ocean interior observations of dissolved inorganic carbon (DIC) and other tracers, from which we estimate ΔCgasex, i.e., the component of the observed DIC that is due to the gas exchange of natural CO2. … We find a pattern of air-sea flux of natural CO2 characterized by outgassing in the Southern Ocean between 44°S and 59°S, vigorous uptake at midlatitudes of both hemispheres, and strong outgassing in the tropics.” [Full text]

Decadal variability of the air-sea CO2 fluxes in the equatorial Pacific Ocean – Feely et al. (2006) “In order to determine the interannual and decadal changes in the air-sea carbon fluxes of the equatorial Pacific, we developed seasonal and interannual relationships between the fugacity of CO2 (fCO2) and sea surface temperature (SST) from shipboard data that were applied to high-resolution temperature fields deduced from satellite data to obtain high-resolution large-scale estimates of the regional fluxes. … On average, the surface water fCO2 in the equatorial region has been increasing at a rate similar to the atmospheric CO2 increase. In addition, there appears to be a slight increase (∼27%) in the outgassing flux of CO2 after the 1997–1998 Pacific Decadal Oscillation (PDO) regime shift.”

The Oceanic Sink for Anthropogenic CO2 – Sabine et al. (2004) “Using inorganic carbon measurements from an international survey effort in the 1990s and a tracer-based separation technique, we estimate a global oceanic anthropogenic carbon dioxide (CO2) sink for the period from 1800 to 1994 of 118 ± 19 petagrams of carbon. The oceanic sink accounts for 48% of the total fossil-fuel and cement-manufacturing emissions, implying that the terrestrial biosphere was a net source of CO2 to the atmosphere of about 39 ± 28 petagrams of carbon for this period. The current fraction of total anthropogenic CO2 emissions stored in the ocean appears to be about one-third of the long-term potential.” [Full text]

Global sea–air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects – Takahashi et al. (2002) “Based on about 940,000 measurements of surface-water pCO2 obtained since the International Geophysical Year of 1956–59, the climatological, monthly distribution of pCO2 in the global surface waters representing mean non-El Niño conditions has been obtained with a spatial resolution of 4°×5° for a reference year 1995. The monthly and annual net sea–air CO2 flux has been computed using the NCEP/NCAR 41-year mean monthly wind speeds. An annual net uptake flux of CO2 by the global oceans has been estimated to be 2.2 (+22% or −19%) Pg C yr−1 using the (wind speed)2 dependence of the CO2 gas transfer velocity of Wanninkhof (J. Geophys. Res. 97 (1992) 7373).” [Full text]

Interannual Variability in the North Atlantic Ocean Carbon Sink – Gruber et al. (2002) “We report an 18-year time series of upper-ocean inorganic carbon observations from the northwestern subtropical North Atlantic near Bermuda that indicates substantial variability in this sink. We deduce that the carbon variability at this site is largely driven by variations in winter mixed-layer depths and by sea surface temperature anomalies.” [Full text]

Uptake and Storage of Carbon Dioxide in the Ocean: The Global CO2 Survey – Feely et al. (2001) “In this paper, we summarize our present understanding of the exchange of CO2 across the air-sea interface and the storage of natural and anthropogenic CO2 in the ocean’s interior.” [Full text]

Low interannual variability in recent oceanic uptake of atmospheric carbon dioxide – Lee et al. (1998) “Here we estimate the interannual variability in global net air–sea CO2 flux using changes in the observed wind speeds and the partial pressure of CO2 (p CO2) in surface sea water and the overlying air. … The calculated interannual variability in oceanic CO2 uptake of 0.4 Gt C yr-1 (2σ) is much less than that inferred from the analysis of atmospheric measurements.”

Quantification of decadal anthropogenic CO2 uptake in the ocean based on dissolved inorganic carbon measurements – Peng et al. (1998) “Accurate estimates of CO2 uptake have been difficult to obtain, however, as the annual increase of dissolved inorganic carbon (DIC) concentration in surface water due to anthropogenic input is 0.05% of the total DIC, an order of magnitude lower than past measurement precision. … Here we use recent improvements in DIC measurement techniques to determine changes in DIC concentrations between 1978 and 1995 in the Indian Ocean.”

Global air-sea flux of CO2: An estimate based on measurements of sea–air pCO2 difference – Takahashi et al. (1997) “Approximately 250,000 measurements made for the pCO2 difference between surface water and the marine atmosphere, ΔpCO2, have been assembled for the global oceans. … The annual net uptake flux of CO2 by the global oceans thus estimated ranges from 0.60 to 1.34 Gt-C yr−1 depending on different formulations used for wind speed dependence on the gas transfer coefficient. … Temperate and polar oceans of the both hemispheres are the major sinks for atmospheric CO2, whereas the equatorial oceans are the major sources for CO2. The Atlantic Ocean is the most important CO2 sink, providing about 60% of the global ocean uptake, while the Pacific Ocean is neutral because of its equatorial source flux being balanced by the sink flux of the temperate oceans. The Indian and Southern Oceans take up about 20% each.” [Full text]

Atmospheric carbon dioxide and the ocean – Siegenthaler & Sarmiento (1993) “The ocean is a significant sink for anthropogenic carbon dioxide, taking up about a third of the emissions arising from fossil-fuel use and tropical deforestation. Increases in the atmospheric carbon dioxide concentration account for most of the remaining emissions, but there still appears to be a ‘missing sink’ which may be located in the terrestrial biosphere.” [Full text]

Posted in AGW evidence | Leave a Comment »

Anti-AGW papers debunked

Posted by Ari Jokimäki on January 12, 2010

I have added a new page: Anti-AGW papers debunked.

It is a resource that helps you to find debunkings of the papers that have been used to advance anti-AGW views. The list is sorted alphabetically by first author. The list doesn’t contain any explanations, just links to the relevant information as briefly as possible. There is only a handful of papers so far, but I will build the list as time goes by.

This is the thread for any feedback, suggestions, etc. for this resource.

Posted in General | 29 Comments »

Papers on glacial terminations

Posted by Ari Jokimäki on January 9, 2010

This is a list of papers on the terminations of glacial periods, with emphasis on the papers dealing with the causes and the sequence of events when coming out of glacial period and entering interglacial period. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative. I thank John Cook for discussing this matter with me and pointing out several papers that appear in this list.

UPDATE (April 17, 2012): Shakun et al. (2012) added. Thanks to Barry for pointing it out.

Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation – Shakun et al. (2012) “The covariation of carbon dioxide (CO2) concentration and temperature in Antarctic ice-core records suggests a close link between CO2 and climate during the Pleistocene ice ages. The role and relative importance of CO2 in producing these climate changes remains unclear, however, in part because the ice-core deuterium record reflects local rather than global temperature. Here we construct a record of global surface temperature from 80 proxy records and show that temperature is correlated with and generally lags CO2 during the last (that is, the most recent) deglaciation. Differences between the respective temperature changes of the Northern Hemisphere and Southern Hemisphere parallel variations in the strength of the Atlantic meridional overturning circulation recorded in marine sediments. These observations, together with transient global climate model simulations, support the conclusion that an antiphased hemispheric temperature response to ocean circulation changes superimposed on globally in-phase warming driven by increasing CO2 concentrations is an explanation for much of the temperature change at the end of the most recent ice age.” [Full text, Supplementary information]

Feedback between deglaciation, volcanism, and atmospheric CO2 – Huybers & Langmuir (2009) “An evaluation of the historical record of volcanic eruptions shows that subaerial volcanism increases globally by two to six times above background levels between 12 ka and 7 ka, during the last deglaciation. Increased volcanism occurs in deglaciating regions. … CO2 output from the increased subaerial volcanism appears large enough to influence glacial/interglacial CO2 variations. … After accounting for equilibration with the ocean, this additional CO2 flux is consistent in timing and magnitude with ice core observations of a 40 ppm increase in atmospheric CO2 concentration during the second half of the last deglaciation. … If such a large volcanic output of CO2 occurs, then volcanism forges a positive feedback between glacial variability and atmospheric CO2 concentrations: deglaciation increases volcanic eruptions, raises atmospheric CO2, and causes more deglaciation. Such a positive feedback may contribute to the rapid passage from glacial to interglacial periods.” [Full text]

The Roles of CO2 and Orbital Forcing in Driving Southern Hemispheric Temperature Variations during the Last 21 000 Yr – Timmermann et al. (2009) “Transient climate model simulations covering the last 21 000 yr reveal that orbitally driven insolation changes in the Southern Hemisphere, combined with a rise in atmospheric pCO2, were sufficient to jump-start the deglacial warming around Antarctica without direct Northern Hemispheric triggers. Analyses of sensitivity experiments forced with only one external forcing component (greenhouse gases, ice-sheet forcing, or orbital forcing) demonstrate that austral spring insolation changes triggered an early retreat of Southern Ocean sea ice starting around 19–18 ka BP. The associated sea ice–albedo feedback and the subsequent increase of atmospheric CO2 concentrations helped to further accelerate the deglacial warming in the Southern Hemisphere.” [Full text]

Modulation of the bipolar seesaw in the Southeast Pacific during Termination 1 – Lamy et al. (2007) “Our study is based on a well-dated and high-resolution alkenone-based sea surface temperature (SST) record from the SE-Pacific off southern Chile (Ocean Drilling Project Site 1233) showing that deglacial warming at the northern margin of the Antarctic Circumpolar Current system (ACC) began shortly after 19,000 years BP (19 kyr BP). The timing is largely consistent with Antarctic ice-core records but the initial warming in the SE-Pacific is more abrupt suggesting a direct and immediate response to the slowdown of the Atlantic thermohaline circulation through the bipolar seesaw mechanism. … In addition, modelling results suggest that insolation changes and the deglacial CO2 rise induced a substantial SST increase at our site location but with a gradual warming structure. The similarity of the two-step rise in our proxy SSTs and CO2 over T1 strongly demands for a forcing mechanism influencing both, temperature and CO2.” [Full text]

Southern Hemisphere and Deep-Sea Warming Led Deglacial Atmospheric CO2 Rise and Tropical Warming – Stott et al. (2007) “We determined the chronology of high- and low-latitude climate change at the last glacial termination by radiocarbon dating benthic and planktonic foraminiferal stable isotope and magnesium/calcium records from a marine core collected in the western tropical Pacific. Deep-sea temperatures warmed by 2°C between 19 and 17 thousand years before the present (ky B.P.), leading the rise in atmospheric CO2 and tropical–surface-ocean warming by 1000 years. The cause of this deglacial deep-water warming does not lie within the tropics, nor can its early onset between 19 and 17 ky B.P. be attributed to CO2 forcing. Increasing austral-spring insolation combined with sea-ice albedo feedbacks appear to be the key factors responsible for this warming.” [Full text]

Integration of ice-core, marine and terrestrial records for the Australian Last Glacial Maximum and Termination: a contribution from the OZ INTIMATE group – Turney et al. (2006) “Here we present climatic and environmental reconstructions from across Australia, a key region of the Southern Hemisphere because of the range of environments it covers and the potentially important role regional atmospheric and oceanic controls play in global climate change. We identify a general scheme of events for the end of the last glacial period and early Holocene but a detailed reconstruction proved problematic.” [Full text]

High resolution characterization of the Asian Monsoon between 146,000 and 99,000 years B.P. from Dongge Cave, China and global correlation of events surrounding Termination II – Kelly et al. (2006) “We have obtained higher resolution data in the interval between 99 and 146 ka B.P., providing a detailed account of δ18O variations over most of MIS 5 and the latter portion of MIS 6. … The most abrupt portion of the shift in δ18O values ( 1.1‰) marking the end of the Last Interglacial Asian Monsoon occurred in 120 years, the midpoint of which is 120.7 ± 1.0 ka B.P. … We demonstrate that monsoon intensity correlates well with atmospheric CH4 concentrations over the transition into the Bølling-Allerød, the Bølling-Allerød, and the Younger Dryas. In addition, we correlate an abrupt jump in CH4 concentration with Asian Monsoon Termination II. On the basis of this correlation, we conclude that the rise in atmospheric CO2, Antarctic warming, and the gradual portion of the rise in CH4 around Termination II occur within our “Weak Monsoon Interval” (WMI), an extended interval of heavy δ18O between 135.5 ± 1.0 and 129.0 ± 1.0 ka B.P., prior to Asian Monsoon Termination II and Northern Hemisphere warming. Antarctic warming over the millennia immediately preceding abrupt northern warming may result from the “bipolar seesaw” mechanism. As such warming (albeit to a smaller extent) also preceded Asian Monsoon Termination I, the “bipolar seesaw” mechanism may play a critical role in glacial terminations.”

Chronology reconstruction for the disturbed bottom section of the GISP2 and the GRIP ice cores: Implications for Termination II in Greenland – Suwa et al. (2006) “We have reconstructed chronology for the disturbed bottom parts of the GRIP and GISP2 ice cores using the combined paleoatmospheric records of CH4 concentration and δ18Oatm in the trapped gases. … The climate history we derive suggests that the last interglacial at Summit, Greenland, around 127 ka was slightly warmer than the current interglacial period. Reduction of various ion concentrations in ice and thickening of the ice sheet during Termination II was similar to that in Termination I.” [Full text]

Quantitative interpretation of atmospheric carbon records over the last glacial termination – Köhler et al. (2005) “Forcing the coupled ocean-atmosphere-biosphere box model of the global carbon cycle BICYCLE with proxy data over the last glacial termination, we are able to quantitatively reproduce transient variations in pCO2 and its isotopic signatures (δ13C, Δ14C) observed in natural climate archives. … The processes considered here ranked by their contribution to the glacial/interglacial rise in pCO2 in decreasing order are: the rise in Southern Ocean vertical mixing rates (>30 ppmv), decreases in alkalinity and carbon inventories (>30 ppmv), the reduction of the biological pump (∼20 ppmv), the rise in ocean temperatures (15–20 ppmv), the resumption of ocean circulation (15–20 ppmv), and coral reef growth (<5 ppmv). The regrowth of the terrestrial biosphere, sea level rise and the increase in gas exchange through reduced sea ice cover operate in the opposite direction, decreasing pCO2 during Termination I by ∼30 ppmv. According to our model the sequence of events during Termination I might have been the following: a reduction of aeolian iron fertilization in the Southern Ocean together with a breakdown in Southern Ocean stratification, the latter caused by rapid sea ice retreat, trigger the onset of the pCO2 increase.” [Full text]

Deep Pacific CaCO3 compensation and glacial–interglacial atmospheric CO2 – Marchitto et al. (2005) “Here we reconstruct deep equatorial Pacific CO32− over the last glacial–interglacial cycle using benthic foraminiferal Zn/Ca, which is strongly affected by saturation state during calcite precipitation. Our data are in agreement with the CaCO3 compensation theory, including glacial CO32− concentrations similar to (or slightly lower than) today, and a Termination I CO32− peak of 25–30 μmol kg−1. The deglacial CO32− rise precedes ice sheet melting, consistent with the timing of the atmospheric CO2 rise. A later portion of the peak could reflect removal of CO2 from the atmosphere–ocean system due to boreal forest regrowth. CaCO3 compensation alone may explain more than one third of the atmospheric CO2 lowering during glacial times.” [Full text]

Climate evolution at the last deglaciation: the role of the Southern Ocean – Bianchi & Gersonde (2004) “Two sediment sequences recovered close to, and south of, the present Polar Front (50°, 53°S) in the Atlantic sector of the Southern Ocean were analysed in order to evaluate the environmental evolution of the Southern Ocean surface over the last deglaciation and the Holocene. … Time correspondence of Southern Ocean warming and Heinrich event 1 in the North Atlantic is compatible with the transmission of the climate signal from the Northern to the Southern Hemisphere through the “bipolar seesaw.” Our data support modeling results suggesting that the Northern Hemisphere Bølling warming and turn-on of the North Atlantic Deep Water formation are triggered by gradual warming and sea-ice retreat in the Southern Ocean. Meltwater shedding into the Southern Ocean associated with the ACR may maintain Northern Hemisphere warming during the Allerød. The development of sea surface warming and sea-ice retreat is compatible with a Southern Ocean control on the atmospheric CO2 increase during the deglaciation.”

Timing of Atmospheric CO2 and Antarctic Temperature Changes Across Termination III – Caillon et al. (2003) “The analysis of air bubbles from ice cores has yielded a precise record of atmospheric greenhouse gas concentrations, but the timing of changes in these gases with respect to temperature is not accurately known because of uncertainty in the gas age-ice age difference. We have measured the isotopic composition of argon in air bubbles in the Vostok core during Termination III (~240,000 years before the present). This record most likely reflects the temperature and accumulation change, although the mechanism remains unclear. The sequence of events during Termination III suggests that the CO2 increase lagged Antarctic deglacial warming by 800 ± 200 years and preceded the Northern Hemisphere deglaciation.”

Sequence of events during the last deglaciation in Southern Ocean sediments and Antarctic ice cores – Shemesh et al. (2002) “The last glacial to interglacial transition was studied using down core records of stable isotopes in diatoms and foraminifera as well as surface water temperature, sea ice extent, and ice-rafted debris (IRD) concentrations from a piston core retrieved from the Atlantic sector of the Southern Ocean. … our data suggest that sea ice and nutrient changes at about 19 ka B.P. lead the increase in atmospheric pCO2 by approximately 2000 years. Our diatom-based sea ice record is in phase with the sodium record of the Vostok ice core, which is related to sea ice cover and similarly leads the increase in atmospheric CO2. If gas exchange played a major role in determining glacial to interglacial CO2 variations, then a delay mechanism of a few thousand years is needed to explain the observed sequence of events. Otherwise, the main cause of atmospheric pCO2 change must be sought elsewhere, rather than in the Southern Ocean.” [online PDF exists but seems to be defective, at least for me]

The phase relations among atmospheric CO2 content, temperature and global ice volume over the past 420 ka – Mudelsee (2001) “Comparing the CO2 record with other proxy variables from the Vostok ice core and stacked marine oxygen isotope records, allows the phase relations among these variables, over the last four G–IG cycles, to be estimated. Lagged, generalized least-squares regression provides an efficient and precise technique for this estimation. Bootstrap resampling allows account to be taken of measurement and timescale errors. Over the full 420 ka of the Vostok record, CO2 variations lag behind atmospheric temperature changes in the Southern Hemisphere by 1.3±1.0 ka, and lead over global ice-volume variations by 2.7±1.3 ka. However, significant short-term changes in the lag of CO2 relative to temperature, subsequent to Terminations II and III, are also detected.” [Full text]

Atmospheric CO2 Concentrations over the Last Glacial Termination – Monnin et al. (2001) “A record of atmospheric carbon dioxide (CO2) concentration during the transition from the Last Glacial Maximum to the Holocene, obtained from the Dome Concordia, Antarctica, ice core, reveals that an increase of 76 parts per million by volume occurred over a period of 6000 years in four clearly distinguishable intervals. The close correlation between CO2 concentration and Antarctic temperature indicates that the Southern Ocean played an important role in causing the CO2 increase. However, the similarity of changes in CO2 concentration and variations of atmospheric methane concentration suggests that processes in the tropics and in the Northern Hemisphere, where the main sources for methane are located, also had substantial effects on atmospheric CO2 concentrations.”

Evidence against dust-mediated control of glacial–interglacial changes in atmospheric CO2 – Maher & Dennis (2001) “Here we examine the timing of dust fluxes to the North Atlantic Ocean, in relation to climate records from the Vostok ice core in Antarctica around the time of the penultimate deglaciation (about 130 kyr ago). Two main dust peaks occurred 155 kyr and 130 kyr ago, but neither was associated with the CO2 rise recorded in the Vostok ice core. This mismatch, together with the low dust flux supplied to the Southern Ocean, suggests that dust-mediated iron fertilization of the Southern Ocean did not significantly influence atmospheric CO2 at the termination of the penultimate glaciation.” [Full text]

The structure of Termination II (penultimate deglaciation and Eemian) in the North Atlantic – Lototskaya & Ganssen (1999) “A study of the 140–100 ka interval in core T90-9P from the North Atlantic (45° N, 25° W), based on analysis of oxygen and carbon isotope records from planktonic and benthonic foraminifera, and from the bulk sediment fine fraction facilitates a detailed paleoceanographic reconstruction of the penultimate deglaciation (Termination II), and of the Eemian interglacial (δ18O stage 5e). The first step of Termination II was characterised by low productivity and a mixed water column, which was a remnant of glacial conditions. A 3 ka period of relatively stable conditions, with a stratified water column (‘Termination II pause’), occurred half-way through Termination II, and preceeded a second and more rapid climatic shift. The end of the deglaciation (Eemian maximum, i.e. isotopic event 5.53) initiated the establishment of strong, seasonal, water column stratification. North Atlantic Deep Water (NADW) production remained low during the complete glacial–interglacial transition. After the Eemian maximum, NADW prodution was restored, and bottom waters remained quite stable during the course of the Eemian, while surface waters gradually cooled in the second half of the stage. A short surface water cooling event accompanied by a reduced seasonal water column stratification and nutrient instability occurred at approximately 117 ka BP.” [Full text]

Dual modes of the carbon cycle since the Last Glacial Maximum – Smith et al. (1999) “Here we present the stable-carbon-isotope composition (13CO2) of CO2 extracted from air trapped in ice at Taylor Dome, Antarctica, from the Last Glacial Maximum to the onset of Holocene times. The global carbon cycle is shown to have operated in two distinct primary modes on the timescale of thousands of years, one when climate was changing relatively slowly and another when warming was rapid, each with a characteristic average stable-carbon-isotope composition of the net CO2 exchanged by the atmosphere with the land and oceans.” [Full text]

Variation of atmospheric C02 by ventilation of the ocean’s deepest water – Toggweiler (1999) “A new box model for glacial-interglacial changes in atmospheric CO2 produces lower levels of atmospheric CO2 without changes in biological production or nutirent chemistry. … Atmospheric CO2 is reduced 21 ppm by reduced ventilation of the deep water below the divide. A further reduction of 36 ppm is due to CaCO3 compensation in response to lower CO3= below the divide. Colder surface temperatures account for an additional 23 ppm of CO2 reduction.” [Full text]

The Sequence of Events Surrounding Termination II and their Implications for the Cause of Glacial-Interglacial CO2 Changes – Broecker & Henderson (1998) “Events surrounding Termination II, as preserved in the Vostok ice core, provide a number of clues about the mechanisms controlling glacial to interglacial climate change. Antarctic temperature and the atmosphere’s CO2 content increased together over a period of ∼8000 years. This increase is bounded by a drop in dust flux at its onset and by a drop in the δ18O of trapped air at its finish. A similar lag between dust flux and foraminiferal δ18O is seen in a Southern Ocean marine record, suggesting that the δ18O in air trapped in Vostok ice is a valid proxy for ice volume. The synchronous change of atmospheric CO2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets.” [Full text]

Closely related

Papers on GHG role in historical climate changes

Posted in AGW evidence | 2 Comments »

Suggestions for paperlist subjects

Posted by Ari Jokimäki on January 7, 2010

Ok, that’s it, I’ve run out of paperlist subjects…

…well, seriously, I do have lot of ideas for new subjects for paperlists, but I thought that now would be a good time to ask you about the subjects you would like to see searched for papers. Post your suggestions here. I won’t make any promises, but I do like to keep my readers happy, so I imagine that most of the suggestions here will result in a list of papers in the future.

Some subjects I already have more or less in the works:
Glacial terminations
Theory of CO2 absorption properties
Lapse rate feedback
Ice-albedo feedback
Other feedbacks
CO2 emissions from mankind
laboratory measurements of other GHGs
Temperatures of other planets

Posted in General | 9 Comments »

 
Follow

Get every new post delivered to your Inbox.

Join 63 other followers

%d bloggers like this: