Saturday, March 15, 2008

I'm not supposed to be blogging but...

...Muriel Newman is quacking and it's hard to resist.

A conservative friend of the family recently sent me an email that was more or less a cut and paste of this post from Ms Newman's website.

I replied as follows:

That's an interesting email. It's also rather misleading. I'm not a climatologist and when I can spot elementary errors it leaves me inclined to think that the person who wrote it probably isn't qualified to comment on climate science.

Here's a couple of problems with the email.

1. They write: "Scientists have shown that in the earth’s geological past, concentrations of carbon dioxide have been up to 20 times higher than they are at present and temperatures have been considerably warmer."

Personally, I doubt the 20 times higher figure but it's possible, the Earth has a long history. Humans have only been around for a very short part of it; human civilisation for even less. And that's the point: it's true that temperatures have been considerably warmer in the distant past. So warm, in fact, that Crocodile like creatures lived close to the arctic circle. Which is good news for crocodile like creatures but rather disastrous for us humans - do you really think that we could endure this level of climate change (rendering most of the world's temperate zones uninhabitable) without huge suffering. The other point that the author is trying to make, of course, is that because the historical climate variations have been greater than those observed at present, then current variation may not be natural. This is incorrect. We know, thanks to basic atmospheric physics that - everything else being equal - more CO2 in the atmosphere will lead to higher temperatures. We know CO2 levels are rising (thanks to undisputed measurements). We know thanks to Carbon Isotope measures that human activity is causing this rise. We also know that temperature is rising. And, no known combination of known climate forcings which excludes the input of CO2 can explain this observed rise. In other words: the Earth has warmed naturally in the past; it is warming now - this is not natural.

2. They then write: "The two most recent warming periods occurred during Roman Times from 200BC to 600 AD and Medieval Times from 900AD to 1300AD, when Greenland was green and grapes grew in England. The Little Ice Age followed." This is simply not true. In some climate reconstructions the medieval warm period is close to being as warm in present (in most it's not even close); however, in no reconstruction is it warmer than present. Grapes, I might add, still grow in England. And Greenland was never green. Leif Erikson (or Eric the red - I get the two mixed up) named it Greenland to attract other settlers to the continent - one of history's oldest real estate swindles.

3. They then write: "Current temperature trends show a warm period between 1920 and 1940, followed by a cooling phase. There was a sudden warming surge from 1976 to 1978 and another in 1998. Since then the weather has been cooler." The cooling phase was caused by aerosol pollution - as countries tightened up on this (through clean air acts and the like) temperatures began to warm again. The 'surge' up to 1998 was caused by abnormally high temperatures in that year - a result of El Nino. All of this is common knowledge. That no one at the conference bothered to mention it makes me wonder about the credibility of the experts present.

4. They then write: "The year 1934 has emerged as the warmest of the 20th century." This, if I recall correctly, is also false. 1934 was the warmest year on record *in the United States*. It's called global warming for a reason - and the United States is not the globe.

5. I could go on, but dinner awaits. I will note on thing though - the IPPC does not run its own research. It assesses all the peer-reviewed research currently available. Its conclusions reflect the state of the science - not one conference run by an organisation that gets a bundle of money from Exxon Mobil and which has its own ideological bone to pick.

Anyhow, it was an interesting email, so thanks for that. Speaking of a warm climate, lovely weather today no?


They then posted my reply on Ms Newman's website. And she replied (and I received the reply via email from the family friend).

Here's my reply:
Thanks for your reply. I take it that the message is actually from Muriel Newman and that she has replied on a forum where you pasted the contents of myf first email?

Also I need to apologise in advance for two things:
1. My reply will be brief.
2. This is going to be my last reply on this subject matter.

As I'm sure you can appreciate, I have quite a lot on my plate at present and I could do with relaxing at least some of this weekend (1 day is already liekly lost to work), and while debating climate change can be enjoyable, it isn't relaxing.

Ms Newman is right: medieval Norse settlers in the sourthen coastal regions of Greenland did indeed graze cattle and grow crops. Grazing and agriculture - and the Norse settlers - were put paid by the Little Ice Age, where temperatures were significantly cooler than during either the Medieval Warm Period or the present day. Does this mean that the Medieval Warm Period was warmer than today? No. First Greenland is only 1 country (and remember we're talking about *global warming* here). Second, my understanding is that the current climate in southern Greenland is once again warm enough to support such agriculture. The reason it is not is because, thanks to the wonders of globalisation, it's far more efficient for Greenlanders to import such food (a good example of comparative advantage Ricardo style.)

The Hockey Stick
Mann et al's 'Hockey Stick' climate reconstruction has most certainly not been "well and truly discredited". It has been challenged, but these challenges themselves are of questionable merit. If you are interested you can read about the errors in McIntyre & McKitrick's putative refutation of the hockey stick here:

Let us, for argument's a sake, assume that the Mann et al's reconstruction was wrong, however. Would that disprove the theory that current climate change stems from predominantly human sources? In a word: no. For a start Mann is not the only person working on historical climate records. If you go to the following link you can look at the various credible climate reconstructions of the last 2000 years super imposed on the same graph:

Some of these are Mann's work but the majority are not. You will notice, of course, that in none of the reconstructions does the Medieval Warm Period come close to being as warm as current temperatures. Even if Mann's hockey stick graph was to be discredited this would do nothing to change this fact.

It is also worth noting that, even if all these reconstructions were wrong, this still wouldn't prove that current warming was not human generated. As I said in my last email, we know from basic physics that, everything else being equal, if CO2 levels in the atmosphere rise, temperatures will follow. We know that CO2 levels are rising. We know from Carbon Isotope measures that we are the source of this CO2. And we know that temperatures are also rising. This alone is reason for considerable concern.

The Relationship Between CO2 and Temperature in the Paleoclimate Record
Ms Newman is broadly correct when she says that CO2 lags behind temperature through much of the paleoclimate record. She misses the point here though. Prior to technology providing humans with the means to alter the Earth's climate, changes in the Earths climate were probably - in the first instance - primarily driven by orbital variations or fluctuations in solar activity. These initial temperature variations are likely to have then triggered a feedback process through which CO2 was released into the atmosphere (possibly from warming oceans). This then exacerbated the initial warming trends leading to the large variations in temperature visible in the paleoclimate record. This is is interesting but does nothing to disprove the theory of AGW. Recent observed solar fluctuations do not correspond to global temperature trends (the graph Ms Newman shows is long refuted and only tracks the US temperature record, anyhow). And, as I noted above, we have definitive proof of the fact that the rise in CO2 in the atmosphere is caused by human activity (i.e. it's not part of some feedback loop).

The Impact of Human CO2 Emissions verses Natural Quantities of CO2 in the Atmosphere
I have not had time to check the numbers that Ms Newman quotes from Robinson et al and it would not surprise me if they are wrong. Nevertheless, the basic point stands. Compared to quantities of CO2 to be found naturally in the atmosphere and biosphere, human emission levels are not large. But the important point is that naturally, over a period of broadly stable temperatures, naturally occurring CO2 is in balance. Sources of emission are countered by sources of absorption. The criticical thing here is that we humans are disrupting this balance. That is all that is required to trigger climate change.

I hope that this is of some help to you.



Anonymous said...

Hi Terence,

About the "CO2 rise is natural" myth, I retrieved the original stance, quoted from the Oregon petition man:

"The concentration of CO2 in Earth’s atmosphere has in creased during the past century. The magnitude of this atmospheric increase is currently about 4 gigatons (Gt C) of carbon per year. Total human industrial CO2 production, primarily from use of coal, oil, and natural gas and the production of cement, is currently about 8 Gt C per year (7,56,57). Humans also exhale about 0.6 Gt C per year, which has been sequestered by plants from at mospheric CO2. Office air concentrations often exceed 1,000 ppm CO2. To put these figures in perspective, it is estimated that the atmosphere contains 780 Gt C; the surface ocean contains 1,000 Gt C; vegetation, soils, and detritus contain 2,000 Gt C; and the intermediate and deep oceans contain 38,000 Gt C, as CO2 or CO2 hydration products. Each year, the surface ocean and atmosphere exchange an estimated 90 Gt C; vegetation and the atmosphere, 100 Gt C; marine biota and the surface ocean, 50 Gt C; and the surface ocean and the intermediate and deep oceans, 40 Gt C.

"So great are the magnitudes of these reservoirs, the rates of exchange between them, and the uncertainties of these es timated numbers that the sources of the recent rise in atmospheric CO2 have not been determined with certainty. Atmospheric concentrations of CO2 are reported to have varied widely over geological time, with peaks, according to some estimates, some 20-fold higher than at present and lows at approximately 200 ppm."

My opinion:

1) AFAIK the numbers in the first paragraph are correct and can be found in any standard carbon cycle diagram, with the exception of the sentence on human respiration (Humans also exhale about 0.6 Gt C per year, which has been sequestered by plants from atmospheric CO2) which is at best misleading. The carbon is not "sequestered by plants" but rather recycled through the biosphere and the human respiration does participate to the mechanism. IMO it is difficult to estimate the net impact of human metabolism because it is integrated in the carbon cycle but may contribute to its alteration via land use change, and as such be a net source of anthro CO2 (see an interesting post from Atmoz dated Dec. 2007),

2) The second paragraph smells typical contrarian stance:

"So great are the magnitudes of these reservoirs"
Man, small. Earth, big!

"the uncertainties of these estimated numbers"
Uncertainties, sacred cows. Don't quantify them, rely on our stance: they are huge!

"that the sources of the recent rise in atmospheric CO2 have not been determined with certainty"
Trust us: those taxpayer money fed whackos pretend they know everything, in reality they know nothing!

"Atmospheric concentrations of CO2 are reported to have varied widely over geological time, with peaks, according to some estimates, some 20-fold higher than at present and lows at approximately 200 ppm"
CO2 varied naturally in huge proportions in the past, and puny man definitely can't do it!

3) Your comment:
"Compared to quantities of CO2 to be found naturally in the atmosphere and biosphere, human emission levels are not large. But the important point is that naturally, over a period of broadly stable temperatures, naturally occurring CO2 is in balance. Sources of emission are countered by sources of absorption. The criticical thing here is that we humans are disrupting this balance. That is all that is required to trigger climate change."

I think the invocation of "balance" is misleading and rather gives fuel to pseudoskeptic countering like "Balance is the favorite argument of the climate scientology" seen in Coby Beck's blog (How to talk to a climate skeptic, version 1). Indeed CO2 is never exactly in balance and there were variations of atmospheric CO2 levels before the industrial revolution, around +/- 5 ppm during the 2nd millennium (see the ice core data). The problem, the difficulty, is to estimate and compare correctly the imbalances.

I would rather use the argument of recycling: the 7 GTC emitted annually have a residence time around 3 years only in the atmosphere but they recycle rapidly through biosphere and surface oceans, which are reservoirs of the same size as the atmosphere (ca 500 GTC for biosphere, 1000 for surface oceans), so that much of the carbon from past anthro emissions is brought back to the atmosphere, contributing to a sizeable part of the gross flux of 210 GTC to/from atmosphere. Therefore, we cannot just make the comparison of that flux to puny man's 7 GTC and conclude to 3% anthro as J. d'Aleo does. This value, though constantly recycled through the denialosphere, is bogus. A good carbon cycle illustration is given in (the site of John Cook) under the topic "CO2 rise is natural". OTOH, the oft-cited 50-200 years residence time correspond to the time constants of transfer of the excess carbon to the whole ocean and ocean homogeneisation. AFAIK I recently read of 2 time constants (30 years for most of the excess and ca 300 years for ca 20% of the excess).

Nevertheless, note that the above consideration is not a proof that CO2 rise is anthro, only a proof that the oft-cited 3% is false and that the real figure (of anthro contribution of recent rise) is much higher. In order to fully make the case one has to consider the fingerprints of "anthro CO2" source vs "natural" one : the isotope ratios (C13 but also C14, in the atmosphere but also biosphere and oceans), the latitudinal distribution (higher CO2 levels in northern hemisphere), the distribution of the carbon in the oceans (increase of dissolved carbon concentrations, pH decrease, mostly in the upper layers), the historical coincidence of the CO2 rise and of the anthro emissions from land use change + fossil fuels/cements (there is a nice diagram in Stephen Schwartz site), the temporal resolution of ice cores which prove, considering the carbon cycle fluxes, that the CO2 levels are highest for the last 20000 years (the oft-cited 650000 years has a lower level of certainty since the oldest ice cores mix up CO2 on time intervals up to 1500 years, and as such can smooth centennial spikes, and thus cannot disprove levels higher than 300 ppm, which could have occurred in short periods, for instance around the Eemian maximum).

So, the anthro case has overwhelming evidence, while the possible existence of a sizeble natural contribution in the recent CO2 rise is at best speculative. I would guess there is one, of a few ppm, because of thermal-induced net CO2 emission (ocean degassing, permafrost melting) due to natural warming since the LIA. But, this contribution might be equal or smaller than ... that from ocean degassing and permafrost melting due to the present "AGW" (positive feedback on the carbon cycle).

Hoping having been clear in my explanations.



Terence said...

Thanks Yves,

That's a really interesting post. I actually need some time to mull it over. Basically, I think, I take your point though.