...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.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 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?
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: http://tamino.wordpress.com/2008/03/06/pca-part-4-non-centered-hockey-sticks/
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.