Eddie:
Thankyou for your constructive continuation of our dialogue.
I write to try to answer your points to me and – hoping you do not mind – I also comment on a point you make to ‘Consanescerion’.
To begin, I am a climate change proclaimer and, therefore, I do not know why I am called a “climate change denier”. I proclaim that climate has always changed everywhere and it always will. The challenge to me and others who study climate is to discover how and why it changes.
On my explanation of the observable facts of climate history you say:
“So it’s cycles within cycles. That has a familiar ring. The major problem for this explanation is the weak evidence — much of it anecdotal — for the influence of cycles, at least in recent geologic times, whereas there is strong evidence for the current influence of CO2.”
However, there is no evidence (n.b. none, not any of any kind) for significant influence of recent increase of CO2 on climate. And the evidence for climate cycles (or oscillations if you prefer the term) is very, very strong.
There are many observed climate cycles. But, to date, few explanations exist for the true causes of any of them. The cycles include glacial to interglacial periods, El Nino Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), etc.. Their existence is well documented and their natures are studied.
At this point I hope you will forgive my inserting two asides.
The recent controversial paper by Keenleyside et al. uses model studies to attribute the present halt to rising global temperature to be a function of these oscillations.
Your being, as you say, “outside of your expertise” when assessing climate data puts you in good company because the oft-repeated assertions in this forum that only climatologists are qualified to assess climate data is denied by Milankovich. His analysis of the collective effect of changes in the Earth’s movements upon its climate is known as the ‘Milankovitch cycles’, and is the most accepted explanation of the changes to phases of the glacial to interglacial cycle. But – like you – Milankovich was not a climatologist. Milankovich was a Serbian civil engineer who specialised in cement engineering.
To return to the subject.
The lack of understanding of the causes of the oscillations is a problem for climatological prediction. This is clearly demonstrated by ENSO.
One of many major faults of the GCMs’ predictions of future climate is that they cannot predict the El Nino and La Nino phases of ENSO in future years and decades. These phases have global climatic effects, but they are governed by upwelling of cold ocean waters and nobody knows what governs that upwelling. (When Pacific Ocean temperatures are observed to change then GCMs are used to predict if that change is initiation of a new ENSO phase, but they get those predictions right about as often as tossing a coin would.)
Most of the popular explanations for the climate cycles assume that they are governed by variations of the Sun. This seems to make some sense. Almost all of the climate system’s energy is derived from the Sun, and the system is very stable. Over the last 2.5 billion years the Sun has increased its output ~30% but within each glacial and interglacial period the Earth’s temperature has remained similar throughout that time. This stability implies that the system has some negative feedbacks that operate to maintain stable global temperature. If so, then the observed oscillations are (to use control system terminology) observation of the climate system hunting its control temperature in response to solar variation.
Furthermore, isotope studies of past climates and solar activity correlate well over geological ages. Indeed, variations in global temperature correlate to solar variations much better than to variations in atmospheric carbon dioxide concentration.
But correlation proves nothing. For example, each year children return to school after their summer holidays and shortly after their return leaves start falling off trees, but this does not prove that the end of school holidays causes autumn.
What can be said with certainty is that variations in total solar irradiance are not sufficient to explain observed changes to global temperature. However, this is where the Svensmark Hypothesis becomes important.
There is not sufficient space here to fully explain the Svensmark Hypothesis but you should be able to find it on the web with ease. In essence, the hypothesis says the flux of cosmic rays into the atmosphere affects cloud cover over the Earth, and clouds reflect solar heat so they cool the Earth’s surface (as every sunbather has noticed). As I previously said to you:
“clouds reflect solar heat and a mere 2% increase to cloud cover would more than compensate for the maximum possible predicted warming due to a doubling of carbon dioxide in the air. Good records of cloud cover are very short because cloud cover is measured by satellites that were not launched until the mid 1980s. But it appears that cloudiness decreased markedly between the mid 1980s and late 1990s. Over that period, the Earth’s reflectivity decreased to the extent that if the Sun were constant then the reduced cloudiness provided an extra surface warming of 5 to 10 Watts/sq metre. This is a lot of warming. It is between two and four times the entire warming estimated to have been caused by the build-up of human-caused greenhouse gases in the atmosphere since the industrial revolution. (The IPCC says that since the industrial revolution, the build-up of human-caused greenhouse gases in the atmosphere has had a warming effect of only 2.4 W/sq metre).”
An experiment to check the Svensmark Hypothesis is to be conducted at CERNE and its results are eagerly awaited.
Until then, I caution against any certainty concerning climate mechanisms. None of the data is really reliable (not even the surface temperature data sets). AGW-advocates proclaim their cause with religious certainty, and some supporters of solar effects seem to have similar certainty.
As for me, I only know what the available data says, and the available data poses more questions than answers. As I said in my first posting here;
“One apparent cycle length is ~1500 years and since the time of Christ it has given us
the Roman Warm Period, then
the Dark Age Cool Period, then
the Medieval Climate Optimum, then
the Little Ice Age, and
the Present Warm Period.
Another apparent cycle length is ~60 years so globally there was
cooling to ~1910, then
warming to ~1940, then
cooling to ~1970, then
warming to 1998, followed by
no significant warming or cooling.
Is anthropogenic warming preventing the 30 years of global cooling that the 60-year cycle could be expected to provide from ~2000?
Or
Has the 1500 year cycle reached its peak so another long cooling trend is about to start?
Or
Is the apparent existence of the cycles an effect of randomness or of something else?
Or ….
Possible answers to these and similar questions deserve serious investigation.”
This brings us to your statement saying:
“The generally accepted view is among climate scientists, as reflected in IPCC reports, and as I said, this view is supported by the evidence. But this raises an interesting point. Like most people who have an interest in global warming I am not a climate scientist. I know the basics, but in the absence of becoming proficient in the relevant discipline, as a layperson I must settle for taking the word of people who I believe have the best case. ”
Well, no. As a Reviewer for the IPCC my job is to read every word of every draft of the IPCC reports and to comment on them. And I can tell you the following.
The Summaries for Policymakers (SPMs) of the IPCC reports agree with the published versions of the technical reports they “summarise”, but they have significant differences from those technical reports prior to their published form.
The SPMs are written after reviewers comments on the technical reports. And the SPMs are approved by all the participating governments (the IPCC is an interGOVERNMENTal panel) but before the final draft of the technical reports. Importantly, the technical reports are amended to agree with the SPMs prior to publication.
Simply, the IPCC reports are government (i.e. political) documents that publish selected scientific information to support a case.
Please try to be skeptical when considering all these matters. Just as few climate data are trustworthy, few of the most well-funded data sources can be trusted, either. I explain above about the IPCC, so also look at the alternative interpretation of the same data used by the IPCC at
I contributed to that but be skeptical of it as well. Simply, compare the IPCC and the NIPCC publications and be skeptical at all times when considering information concerning climate change.
Importantly, you cite the RealClimate blog as a source of information. That blog needs especial skepticism. It was established by the ‘hockey team’ when their infamous Hockey Stick temperature graph (that even the IPCC has dropped) was discredited. They still operate their blog as a method to present a front that might make them seem credible.
Richard
