The IPCC report has been out for a while now, though still only in “final draft” form and I’ve just finished reading the summary for policy makers (WGIAR5-SPM_Approved27Sep2013.pdf (MD5sum: 5177839cc4f679dff4e035ebae96503b)). That this isn’t the final version is quite apparent from the number of diagrams labelled “Subject to final copy edit”, however it’s the version we’ve got and it’s what everyone’s been working with so may as well go with it. I’ve not read the full report and at 2,216 pages I suspect neither have many people. I’m not a scientist, and other people are doing much better jobs of analyzing this than I will. Before I start my ill informed delve into this report I’ll observe a few things, for all the claims that we must listen to the experts in doing so us non-experts need to evaluate the differing opinions of those experts. The report doesn’t offer just one scenario, so which is more likely, how good do we think the science is and more importantly as the report doesn’t touch on the matter what is the correct course of action. We’ll have to vote for politicians with differing stances on the matter, so we do actually need to have an opinion we have to weigh the evidence presented. The ramifications of this scientific report will affect more than just obscure corners of quantum dynamics and if the universe is expanding at 2 yonks a year or 3. Reading the report and looking at the variation in the possible scenarios considered the science is clearly not settled and there really isn’t that much of a consensus, so if voices like mine appear to be picking at nits, well that’s how science works. Science works best when the theories and evidence are put up for scrutiny and tested against real world observations and holes looked for – unfortunately there’s not many grants to be had in proving man made climate change won’t be catastrophic.
Before I go off delving into my bugbears about this report, it’s worth noting that the report is based almost entirely on what computer models say. Now computer models can prove pretty much anything you like even that climate change is caused by Dragons and unicorns, unless they’re tested against observation and the predictions they make validated they’re just posh computer games. This is also how science usually works, you get a theory it predicts something then you check if the prediction matches reality and if it doesn’t you get a better theory. So as we’re looking at computer models there are quite a few very good questions that need answering before we can trust them on anything, and I don’t think most of those questions have been answered let alone answered well.
I would really suggest reading the policy makers summary as it’s only 36 pages and about 10 of them are diagrams and tables. So after all that waffling on here’s what I most noticed about it from my first reading.
The first thing I noticed was that when they give time intervals they include the start and end years, as the box at the top of section B.1 on page 3 states:
“1983–2012 was likely the warmest 30-year period of the last 1400 years”
So that period includes 1983 and 2012, I know this is a minor point but it does actually make a difference. At the bottom of the page they state that:
“Due to natural variability,trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends. As one example, the rate of warming over the past 15 years(1998–2012; 0.05 [–0.05 to +0.15] °C per decade), which begins with a strong El Niño, is smaller than the rate calculated since 1951 (1951–2012; 0.12 [0.08 to 0.14] °C per decade)”
(emphasis mine) So from this we know that 15 years is considered a short and not indicative period, again this is worth remembering.
Detouring slightly it’s worth noting this note for figure SPM.2
“[FIGURE TO BE COPYEDITED AND MADE CONSISTENT WITH FIGURE SPM.1b]”
So there’s a change due to happen there that we’ve not seen yet, so anything citing either figure probably needs at this point to be taken with some apprehension. Below figure SPM.1 we discover that the models they use are apparently trust worthy over 20 year periods:
“Extreme weather and climate events: Global-scale assessment of recent observed changes, human contribution to the changes, and projected further changes for the early (2016–2035) and late (2081–2100) 21st century.”
So given that short periods are sensitive to start date and aren’t useful for predicting trends but their models can predict at the 20 year range either :
1) 20 years is the very smallest scale they can model and consider significant
or
2) They’ve left a bit of leeway and the smallest they can manage lies between 15 and 20 years, say about 17.5 years?
That being the case unless the temperature plays catch up very quickly we’re not far off the current anomaly being a trend.
Now talking about that sensitivity to start and end points this is a longer period, but am I the only one that finds an interval of 53 years just a tad odd?
“It is likely that the ocean warmed between 700 and 2000 m from 1957 to 2009”
I’m sure that’s just down to the study stopping in 2009 or something, unless the ocean stopped warming in 2009? (page 5) A bit further down we come across this utter gem:
“It is about as likely as not that ocean heat content from 0–700 m increased more slowly during 2003–2010 than during 1993–2002″
Emphasis mine, but unless they’re really torturing language that means they don’t know, it’s 50/50 if it did or not – surely this is something they’re measuring to validate the models? Again for a lower limit of a time frame as to what counts as significant we have a 20 year period in the box at the top of section B.3
“Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent (high confidence)”
(Emphasis mine) Just below that box they give two periods of measurement for ice rate loss, which again I’m just sure are due to research funding but 39 years (1971−2009) and 17 years (1993−2009) are also odd time periods, and don’t forget that 15 years isn’t significant but here it seems that 17 years is – so we’re pushing that significance boundary lower. Or according to the next bullet point even 10 years is significant if it’s ice loss, but presumably still shouldn’t be counted as indicative of a trend? Sorry to go on about these time periods but it’s something that really struck me, given the early statements they made as on page 6 talking about figure SPM.3 we find that a 6 year mean is useful. Again I find 6 years a slightly odd length of time to pick, given how sensitive short time scales are to start and end dates. Before we leave page 6 we have another short period of measurement that we’re supposed to consider relevant, 18 years this time for the mean rate of sea level rise (emphasised)
“It is very likely that the mean rate of global averaged sea level rise was 1.7 [1.5 to 1.9] mm/yr between 1901 and 2010, 2.0 [1.7 to 2.3] mm/yr between 1971 and 2010 and 3.2 [2.8 to 3.6] mm/yr between 1993 and 2010.”
They return to that same 18 year period on page 7, having “high confidence” that it’s consistent with observed changes due to thermal expansion and glacier and ice sheet melt, so again we should be able to expect predictions and data verification at the 18 year level surely?
Sticking with small time scales, we’ve a 10 year mean here for CO2 emissions
“Annual CO2 emissions from fossil fuel combustion and cement production were 8.3 [7.6 to 9.0] GtC
12 yr–1 averaged over 2002–2011 (high confidence)”
Notice that bit about cement production, it’s worth considering the life expectancy of windfarms and the huge blocks of cement they have to be stood in.
A relevant bit on page 10 at the top of section D.1:
“There are, however, differences between simulated and observed trends over periods as short as 10 to 15 years (e.g., 1998 to 2012). {9.4, Box 9.2}”
Yet previously we saw them citing 10 year periods of observations in such a way as to at the very least suggest they supported their climate models. So I do wonder how they choose which short periods should or shouldn’t count as relevant.
Regardless of that we do have an admission here that the models don’t match the last 15 years, now as I said at the start generally that should lead one to re-examine the models not claim that the data is out. As a friend of mine is fond of saying “the data is the data”.
Talking of data there’s a lovely bullet point on page 11 which I reproduce in full with added emphasis:
“There is robust evidence that the downward trend in Arctic summer sea ice extent since 1979 is now reproduced by more models than at the time of the AR4, with about one-quarter of the models showing a trend as large as, or larger than, the trend in the observations. Most models simulate a small downward trend in Antarctic sea ice extent, albeit with large inter-model spread, in contrast to the small upward trend in observations. {9.4}”
Now I could be reading this wrong but this shows that 75% of the models still get the trend in artic summer sea ice wrong, this isn’t a terribly good success rate. But also they start of talking about a downward trend observed since 1979 and finish on talking about an upward trend in observations. This suggests surely that the trend has changed and as what 75% of the models don’t represent that, surely there is a serious problem with the models?
Skipping on a bit to page 15 and section E.1, we have them making predictions about temperature for 20 year periods, so there better be a serious up kick in temperature change in the next 5 years for the current “anomaly” to be erased, as this statement must mean that 20 year periods are significant?
“The global mean surface temperature change for the period 2016–2035 relative to 1986–2005 will likely be in the range of 0.3°C to 0.7°C (medium confidence).”
That’s about all from me, except to note that the observations for from Figure SPM.4 we see that dissolved CO2
are only based on three sets of observations that from the graph look to have been going a bit over 20 years. Fair enough that may be the best data we have, but again I wonder if 15 years can’t be a trend at what point can it be a little over 20, where’s the cut off point and is it a hard rule or a fuzzy one?
That’s about me done, there’s a lot in the report to pay attention to and as you’ve probably noticed it was mainly the time frames that stuck out to me. Climate change happens no doubt about it, and humanity can influence it and impact it – however how much of a problem the current changes are, if we’re certain about the direction they’re going in and how quickly and more importantly what to do about it – those are I think still important questions especially the last.
Anyway have some links to more coherent people than me:
An alarming headline from the spectator
Bishop Hill suamrises an article from the Guardian
Richard Lindzen is unconvinced
If you picked up on the bits about extreme weather in the summary report then you might want to take a squint at these book out” which says maybe the sun has something to do with the earths climate after all.
