A recent paper by Oreskes et al. in the journal Philosophy of Science asserts that “there is a gap between the scale on which models produce consistent information and the scale on which humans act”. While the large scales, such as the global mean, provide the best indicators of the state of earth’s climate, it is on the local scales we feel a climate change, such as floods and extreme weather events. Extreme rainfall is usually local. So how is it possible then, as two new papers in Nature by Min et al. and Pall et al. (discussed here) have done, to attribute extreme precipitation and extreme UK floods to climate change?
First of all, Oreskes et al. emphasize that the reality of mean global warming is essentially undisputed, but that the future impacts on the scale for which humans would have to prepare are still the subject of considerable research, inquiry, and debate. Moreover, they argue that climate models do not give us the information we would need to accurately estimate the costs of adaptation and effectively prepare for the consequences of climate change – successful adaptation to future climate changes depends on whether the models produce realistic projections for regional and local scales.
We have already discussed why climate models are not well suited for providing detailed information about local climate on RC (here and here). It is important to keep in mind that models are only approximate representation of the real world, and that they are only meant to capture the essence of our climate – i.e. the larger picture. There will always be a limit to the degree of detail for which the models fail to produce reliable and useful information, and the interesting question is where this limit is. It’s a question of limitation rather than flaw.
There is a difference between the spatial scales associated with a local point measurement and statistics based on many local values. When looking at the statistics for a large region, one could argue that these studies do not rely on local scales. In fact, Min et al. used leading empirical orthogonal functions (EOFs; a type of principal component analysis) in their attribution analysis for extreme precipitation, implying large spatial scales. Hence, the points raised by Oreskes et al. may perhaps not be directly applicable to the attribution study done by Min et al.
Pall et al., however, involved statistical downscaling to bridge the scaling gap between model and real world. Oreskes et al. paper argues that even with downscaling, our information about local scales is incomplete. Hence, the points raised by Oreskes et al. may be more relevant for the study of Pall et al. – and indeed for several of my own papers (e.g. local temperature scenarios available for viewing in GoogleEarth described in a forthcoming publication).
So, does that mean that downscaling is worthless? No! We already know that the local climate is systematically influenced by many factors, such as latitude, distance from the coast, and altitude. This information can also be utilized in the making of local climate projections – and this is exactly what is done in most downscaling exercises. The question is whether the additional information, such as that provided by the GCMs about future trends, is reliable. If the downscaling involves more than just getting a number for the future, but also evaluation over the past and other diagnostics, then I think there is some value in the downscaling.
I will argue that the uncertainties make it necessary to look at many different methods for downscaling (regional climate models and statistical downscaling) as well as the largest possible range of (sensible) GCMs. Nevertheless, the problems raised by Oreskes et al. are deeper than just looking at more models and more methods. Downscaling future climate involves uncertainties from a range of sources, some better known than others.
Another issue is the attribution of extremes to climate change, and the difficulties associated with these. We have already said that it is impossible to prove that one event is due to a climate change (here). A climate change involves a changing weather pattern, and if one event is part of an emerging new pattern – a trend – then one may with hindsight say that it fits the picture. Time will show.
Obviously, care must be taken, and downscaling studies that do not appropriately account for the real range of uncertainties may risk ‘over-selling’ the results. In the rekognition of the uncertainties, the IPCC Good-Practice-Guidance-Paper on using climate model results offers some wise advice (first bullet point under section 3.5 on p. 10): the local climate change scenarios should be based on (i) historical change, (ii) process change (e.g. changes in the driving circulation), (iii) global climate change projected by GCMs, and (iv) downscaled projected change. By putting the local climate into the context of the larger picture, analyzing the uncertainties, and evaluating the methods in terms of past changes, I think that local climate projections can provide useful information. However, applied inappropriately, downscaling can also be deceptive.
In any case, Oreskes et al. make a strong case for the need of curbing the emission of GHGs. But I also think it is important to increase our efforts in making further progress in terms of our ability to get a clearer picture of how a global warming may affect the local climate and what that may mean for adaptation.
Dan H.,
And yet, we are seeing food insecurity begin to become a fact of life again in much of the world. It was in fact one of the causes of the revolts in Tunisia and Egypt. Now why do you think that is? Oh, and what color is the sky on your world?
Ray
Given that world grain production is at all time highs and yields are too, how do you justify your belief that the current food price problems are supply driven?
And please leave out the useless snark.
Jack Ballard,
Well, that’s kind of the point, isn’t it? Despite production and yield being maximized, supply still isn’t meeting demand–and production and yeild are being propped up by unsustainable reliance on petroleum and aquifer depletion. And yet, guys like Dan H. and you repeatedly assume there’s nothing to worry about and everything’s fine. In reality, we are doing irreparable damage to the planet’s ability to support us every single day.
Jack Ballard – Your references for your claim please, which would appear to contradict the World Grain Council figures
> grain production
He’s posting a talking point, same one was used at the hearing. No cites.
I posted links refuting the same handwaving assertion that everything is good and getting better as it gets warmer, in the live chat thread yesterday.
Here’s one:
“the history and hype surrounding corn yields has one staggering asterisk: The very best farms, blessed with the best weather and land, have posted the same yields for at least 20 years — suggesting they have reached the limit of what the corn plant can produce.” http://www.startribune.com/business/46495542.html?elr=KArks7PYDiaK7DUHPYDiaK7DUiD3aPc:_Yyc:aUUr MATT McKINNEY, Star Tribune June 3, 2009 – 10:44 AM”
Dr. Field, in the hearing, provided data on temperature thresholds already reached causing decline in several important grains, and several more have thresholds that are very close. That’s the peak temperatures that knock down the yield of the crop.
Or you could look here: http://maps.grida.no/library/files/evolution_of_the_world_grain_production_comparison_world_europe_china_africa.jpg
SA @ 50, Larry S @ 51, try to get Lisa McFadden’s @40 point. Of course no one is against resilient communities. What is cynical in her meaning is destroying the environment and saying future people should just be “resilient” instead of us destroying less.
lol
So that’s what passes as proper cites around here. Makes me think I may have come to the wrong place.
I tend to like numbers from authoritative sources, it also helps if they are current.
I’m not in the habit of providing cites for common known facts but then again maybe my common known facts may be more uncommon than I realise.
For those of you who like to play with numbers you can’t beat the department of Ag web site. It is handy for us folks who find the need to dabble in such things
a search around their website turned up these numbers that back my statement about world production.
Feed grains
http://www.ers.usda.gov/Data/FeedGrains/Yearbook/FGYearbookTable02-Full.htm
Wheat
http://www.ers.usda.gov/data/wheat/YBtable04.asp
Rice
http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1229
> USDA
Same basic info as cited by others: the world year-ending stocks look like they have been decreasing for more than ten years. Do you suppose something has been changing?
That would require looking carefully site by site–as discussed in that Matt McKinney news story.
Done any statistics? Someone must have looked at the variability and figured out what it will take to say whether there’s a trend in the data.
Ray
Alternative theory, that has more legs
Look at that demand curve
http://www.indexmundi.com/agriculture/?country=cn&commodity=corn&graph=domestic-consumption
flxible
A three year trend? what does that prove?
Hank
Link 1 didn’t work and I don’t have time to go down to the county data but Iowa yields grew at a 2.2% anually averaged over the last 10 years.
http://www.extension.iastate.edu/agdm/crops/pdf/a1-12.pdf
But the point is important and there maybe a time when we reach the limits of technology. We run the greatest danger of this as we employ the latest tech. However there is a lot of the world that doesn’t use the latest and best and can see real gains in yields
As to your chart, it is 15 years out of date and irrelevent anyway.
At 55 Jack Ballard says “Given that world grain production is at all time highs and yields are too”
Miffed at being asked for his sources, at 60 he gives cites, which actually show that the most current harvest is in fact lower than the all time high on every measure including stocks on hand, both in the U.S. and world wide.
Try again Jack, we see your level of comprehension now concerning “playing with numbers”.
Wow.
http://www.pnas.org/content/107/46/19645.full
November 1, 2010, doi: 10.1073/pnas.1011078107
PNAS November 16, 2010 vol. 107 no. 46 19645-19648
Trading carbon for food: Global comparison of carbon stocks vs. crop yields on agricultural land
“… Here, we present a spatially explicit global analysis of tradeoffs between carbon stocks and current crop yields. The difference among regions is striking. For example, for each unit of land cleared, the tropics lose nearly two times as much carbon … and produce less than one-half the annual crop yield compared with temperate regions …”
flxible
I’m used to tastier troll bait than that Better work on your technique
Hank
That is well known amoung farming circles, of course they don’t talk about carbon, they put it in terms of organic matter.
and yeah land in the tropics don’t have much and it is gone fast. With out really careful stewardship tropical land can turn sterile in a short while. It is one of the reasons that we don’t list tropical areas among our major crop producers.
Rain leeches out the nutrients fast. with the increased water vapor in the air from global warming, leeching from excess rain fall may be more of a problem for the future of agriculture than the scary scary drought everywhere worries.
Well, Jack above is basically claiming what’s in the IPCC’s last report, but more recent work suggests the IPCC was optimistic.
“… the relative rates of yield increase for all of the major cereal crops are already declining ….”
Hey, it’s an important area, there’s a good bit of research to read, and sometimes we only do get into talking about it here because somebody like wossname the advocacy scienceist, or Jack above, post talking points that someone bothers to check into.
Plenty to read. Poking around …
http://www.plantphysiol.org/content/154/2/526.full
© 2010 American Society of Plant Biologists
doi: 10.1104/pp.110.161349
Plant Physiology October 2010 vol. 154 no. 2 526-530
How Do We Improve Crop Production in a Warming World?
“… The IPCC projections assume that yield improvements from the latter half of the 20th century will continue into the future; however, based on historical temperature-crop yield relationships, potential ceilings to crop yields, and limitations to expansion of agricultural lands, that assumption may not be sound (Long and Ort, 2010). In fact, the relative rates of yield increase for all of the major cereal crops are already declining (Fischer and Edmeades, 2010).
In a global analysis of crop yields from 1981 to 2002, there was a negative response of wheat, maize, and barley (Hordeum vulgare) yields to rising temperature, costing an estimated $5 billion per year (Lobell and Field, 2007). An analysis of maize and soybean (Glycine max) production in the northern Corn Belt region of the United States found that productivity was adversely affected by rising growing season temperatures from 1976 to 2006 (Kucharik and Serbin, 2008). The response of maize and soybean to temperature is also nonlinear, and the decline in yields above the temperature optimum is significantly steeper than the incline below it (Schlenker and Roberts, 2009). Based on the nonlinearity of the temperature response, U.S. maize and soybean yields were predicted to decrease by 30% to 46% before the end of the century under the IPCC scenario with the slowest warming trend (Schlenker and Roberts, 2009). In addition to these historical trends, record crop yield losses were reported in 2003, when Europe experienced a heat wave with July temperatures up to 6°C above average and annual precipitation 50% below average (Ciais et al., 2005). Such extreme events are not well characterized in the IPCC assessment simulations (Easterling et al., 2007). Therefore, increased global temperatures and more frequent temperature extremes will greatly challenge agriculture in this century. Here, we identify regional priorities and biological targets for adaptation of agriculture to rising temperature. …”
So Hank, where are the charts showing this yield curve going down.
If it is happening we should be seeing it.
Yeah, heat and drought affect yields. And you can cherry pick all you want. But lets see that chart with numbers.
From all the data presented, it is apparent that grain production has increased over the past several decades. All this has occurred during a time of increasing atmospheric CO2, mostly increasing temperatures, and slightly increased precipitation (on average). Of course, there are technological advancements which are difficult to factor into the equation. But based on this data, why are some people predicting a huge future decrease in agricultural production? These conclusions are not supported by the data. In fact, they are contrary to the data. One would expect a continued increase in agricultural output as a result of an increase in CO2, temperature, and precipitation.
Hank Roberts quotes an abstract, containing:” In fact, the relative rates of yield increase for all of the major cereal crops are already declining (Fischer and Edmeades, 2010).”
Two people say where is the data? Are they really this clueless?
Jack Ballard and Dan H.,
Yields have been increasing becuase of increased use of fertilizers and irrigation (much of the water coming from nonrenewable aquifers). This is not sustainable–especially as temperatures increase, as petroleum is depleted and as growing population continues to make ever greater demands. Look at fisheries–declining across the board. Rice-one of the more temperature sensitie grains–has already shown decreasing yields with temparature.
http://www.fao.org/news/story/en/item/44618/icode/
Why not try science?
Ray,
Snide comments aside, your link references a report in PNAS by Welch, et. al. Their conclusions for rice are that “higher minimum temperature reduced yield, whereas higher maximum temperature raised it.” The temperature correlation was confounded by the changes in solar irradiance (clouds). The study also concluded that yields had grown during both the high- and low-yielding seasons, contradicting your statement that rice yields have decreased. Irrigation have have affected these yields as all the studied fields were in “intensely managed irrigated rice farms.”
Granted irrigation, fertilization, and other technological advances have probably resulted in significant yield increases. Possibly so much that any recent temperature effects are masked. However, recent data shows increasing crop yields during the time of greatest temperature increase. On average, global food prices have also decreased during this time. Funny that all crops have increased significantly except for cereals, and yet, t_p_hamilton focuses on this trend.
Recently read an article on African maize production and increasing temperatures. It stated that yield is affected by temperatures in excess of 30C. 30-31C, -1%/day. 32C, -2%/day. Drought, -2%/day. Yields are anticipated to be reduced 20% by 2050 in 2/3 of African growing regions.
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