I originally posted these comments in response to a complex series of questions in the netweather forum. Several people said they thought it was a decent effort, so I am repeating it here, with just a couple of tiny adjustments. I hope you, too, find it helpful.
“First; your comment about the pressures on scientists and presuppositions seems to get to the heart of the problem; you don’t know whether you can trust what they say, not only because there are doubts about the methods they use, but also because it isn’t clear to you that they are unbiased, or balanced, in their work.
There is no question that scientific academia has its own internal politicking and pressures for publication, etc., but against this, you have to balance the point that the journals will not normally publish ‘bad’ science, ie., work where the data is skewed or the conclusions do not follow from the evidence. You also need to remember that one ‘suspect’ paper can ruin a scientist’s reputation for life, so getting it right is the driving force behind most of the work that is done. Scientists are ordinary people with specialist jobs, so they have their own thoughts and opinions, but they also have a strong ethic of aspiration to truth. This is why fraudulent claims are so vilified, and why so much of what is published is couched in careful, ‘cover-my-ass’ language.
It is also important to remember that, for many years now, some organisations have expended millions in ‘grants’ to scientists to demonstrate that GW is not caused by fossil fuel burning, or, at least, to cast doubt on this assertion. Whilst there is still much to learn and debate in climate science, the failure to find an alternative explanation which stands up to scientific scrutiny, along with an ever increasing body of evidence for the claim of AGW, now puts us in a position where the doubt, where there is any at all, revolves around more esoteric issues, such as the relative role of land-use change, the mechanics of aerosol forcing and feedback, or the accuracy of estimates of climate sensitivity. Note, too, that the ‘IPCC-line’ is very much middle of the road; ‘sceptics’ and ‘alarmists’ alike exist, with perhaps more alarmists than sceptics, and there now seems to be an increasing body of concern that the estimates of GW and its impacts are too conservative, if anything.
Your next comment draws my attention to the need to be a bit more precise in what I say. Rather than talk of ‘greater’ or ‘lesser’ forcings, we should really be thinking in terms of forcings which have a strong positive or negative signal, and those which have a comparatively weak one, as well as considering the forcings where no clear conclusion has yet been reached due to insufficient data (generally, the timescale of many observations is too short, as most of them are based on satellite-era technology). As far as the climate models are concerned, the details of what is included vary from one run to another; even with supercomputers running at terahertz and almost petahertz speeds, a full 300 year run (1900-2200) using all the physics and all the forcings and feedbacks can take several weeks, if not months *[This might be wrong]. As a result, these are set up very carefully and a lot of work is done on the output; such an expensive procedure needs to be both as free from error as possible, and capable of extensive interpretation. But the full runs do include every known forcing and feedback, run at high resolutions, and including the best known physics and data available. So, the ‘lesser’ forcings (with weaker signals) are used, and analysed, extensively.
As far as I understand it (it gets a bit technical, here), there are formulae for most/all of the chemical and physical processes which affect the climate. Many of these have been derived from NWP models, others come from known physics or chemistry. Some of these formulae are known to be less than perfect, in that they don’t reproduce observed conditions precisely enough, but the principles on which they are based is sound. The process of working out which forcings and feedbacks are in play is known as detection and attribution; it is a whole subset of climate science on its own. Detection and attribution studies generally ‘play’ with the known variables in all sorts of ways, until the model runs replicate observations reasonably accurately. This can be a complex process, too, as other forcings need to be programmed to respond in as lifelike a way as possible, and feedbacks need to be fed back into the whole process.
There have been several major detection and attribution studies done in the past several years, and they have all come up with broadly comparable results; the detail is often interestingly different, but the strength of the forcings and their signal values fall within a measurable range. This is why the IPCC table of climate forcings and feedbacks gives a range of possible values for each element. It also seems to work on the assumption that a roughly ‘middle ground’ between extremes, or, better, an ensemble comparison, yield the (statistically) most likely results. As well as the model runs, there are also statistical models, which are almost purely mathematical procedures which attempt to establish values for these elements by a process of first principle, rather than observation. There has been a bit of a trend recently to suggest that the most accurate estimates come from a combination of both approaches, run in ensemble, though the veracity of this has yet to be fully tested.
The question you ask me directly next is a bit confusing. I think this answers it: of the 1800 scientists I asked, about 8% were identifiable as contributors or lead authors of the IPCC AR4 WG1 report. As far as I could, I tried to include representatives to cover ‘all climate scientists’. As the paper has been submitted and is awaiting approval for publication, I can’t say much more about it at the moment, but I promise to provide more information if it does get accepted and published. The sum of all the negative ‘forcings’ you previously mentioned, Solar and synoptic (though synoptics are not actually forcings), would certainly be strong enough to provide seasonal and interannual variations in the weather. But it does get a bit complicated dealing with both the AO, ENSO and GW; I think this is confusing matters somewhat, as we are dealing with two different beasts here. As I understand your question, the conclusion that positive forcings outweigh negative ones is the IPCC line.
I’m no expert on the AO or synoptics, but these are drivers of weather, are they not, rather than climate forcings? As such, they produce effects which can be global, but which tend to be regional. Whilst weather models need to factor the AO and other synoptics in (initial conditions !), climate models need to be checked to see whether they models such phenomena accurately; in other words, whether the trends in AO patterns result from the input into the models. I get the impression that climate models do some of the synoptic trends reasonably well, but not others (like ENSO); this is why Trenberth thinks they need to have initial conditions values incorporated. The ECMWF is currently working on a ‘combination’ model, which starts climate runs from NWP model data; the aim is to provide reliable forecast for a range from 15 days all the way out to about five or ten years. Like the NASA models, it is experimental, and its skill is not yet known.
Following what I have said above, I don’t know whether AO data is fed into climate models (though I can find out…), but I am sure that all solar variables, including the upcoming ‘Gliessberg minimum’, are intensely scrutinised, and invariably factored into the analyses; this is because the Sun is the source of almost all of the energy in the climate system, ans even small variations have an impact on climate. A models which did not include all known information about past and future solar variations would be of little use.
On the question of the ocean’s response to climate change, there is a great deal of uncertainty. there simply is not enough reliable historical data on which to reach firm conclusions. But it is important to understand that some of the concerns of the last decade, like a potential ‘shut down’ of the THC, have been studied a great deal, due to the likely consequences of such an event. As things stand, the general agreement is that a slow down of circulation is likely, eventually, but a complete shut down is quite unlikely. Hadley’s work on this (which is as good as any in the World) suggests that the most likely situation is that, if current trends continue, the UK and the North Atlantic may face a cooling effect in the latter part of the 21st century, but that, by then, the warming will have increased to such an extent that all this will do is ‘return’ our climate to current conditions, give or take, for a few years, after which, the underlying global warming will start heating us up again. This is not a strong projection: it is more like a ‘best guess’ (I hope this isn’t misunderstood). The truth is, we simply don’t know enough yet about the ocean systems or the freshening of NA water by Arctic influx, to be sure what might happen, or when. Again, this is a cause for concern; there is evidence that things in the Arctic are changing faster even than the models/scientists expected, and evidence that these changes are not likely to slow down, so almost anything is possible.
On your later comments, I’d remind you that the IPCC doesn’t do any of the science; it is more like a ‘summary’ of all the different work going on all around the world. I’ll not comment on its specific recommendations, as these are to do with policy and government, and are contentious, or whether their policyconclusions do, legitimately, follow from the science which they have in the WG1 report. I’d also point out that most of the debate pre-publication between the lead authors and governments was about the governments trying to ‘soften’ the language of the report, and the lead authors trying to hold on to the strength of the scientific data; the governments won, so the finsished report was negatively compromised, not an over-dramatisation.
At bottom, your doubts seem to be based on a belief that the scientific evidence is compromised by political interference, or pressure; is this correct? A small number of scientists might agree with you, but most would probably argue that their work is not about ‘desired results’, it is about getting to the truth of the matter, whoever or whatever this means in the bigger picture.
As far as rigour and thoroughness, the only thing I can suggest is that you read some of the open access papers in Atmospheric Chemistry and Physics, or Climate of the Past, or any one of a number of journals, and judge for yourself how careful and considered the vast majority of scientific work is.
I am not sure what to say about ‘trusting’ the climate models. They are not the final word, but they have been constructed with the greatest care and diligence. Their output is not absolutely reliable, but the trends and patterns of climate change they show are repeated time and time again, in a host of different experiments, and in a large number of studies. I do not suggest that we must ‘trust’ what they tell us without doubt or questioning, but I will say that, as far as whether or not it is likely to get warmer around the world over the next forty years is concerned, the case for this is very, very strong.
I know that I have only touched the surface on many of your intelligent and important observations, but look how much I have written already! Sorry for the oversights; they were coincidental. I don’t know what your feelings will be about what I have tried to say here, but I will only conclude with the observation that, about a year ago, I entered into research on the subject with a vast ignorance and a huge set of misguided assumptions, and it has only been through long and considered research and debate that I have reached a point where I can say with some confidence that I am convinced that we face a real problem in the long term, that much of that problem is of our own making, and that AGW is the single largest threat to our grandchildren and their way of life tht currently exists. If this is understood as hype or exaggeration, then so be it; I’ll continue to do my best to convince people that there really is a problem, and that they shouldn’t trust what they read in the media.