How overfed are we? (part 2)

How overfed are we? refers, in which I express some doubt about the problems of food production. But Battisti and Naylor (Science 9 January 2009: Vol. 323. no. 5911, pp. 240 – 244; DOI: 10.1126/science.1164363) Historical Warnings of Future Food Insecurity with Unprecedented Seasonal Heat re-raise these problems, and they do it in Science, so lets have another look. You can also read it direct.

They say:

Higher growing season temperatures can have dramatic impacts on agricultural productivity, farm incomes, and food security. We used observational data and output from 23 global climate models to show a high probability (>90%) that growing season temperatures in the tropics and subtropics by the end of the 21st century will exceed the most extreme seasonal temperatures recorded from 1900 to 2006. In temperate regions, the hottest seasons on record will represent the future norm in many locations. We used historical examples to illustrate the magnitude of damage to food systems caused by extreme seasonal heat and show that these short-run events could become long-term trends without sufficient investments in adaptation.

As far as I’m concerned, the predictions of temperature increases are non-controversial, so I won’t discuss them other than to note that the pix in their article are not temperature increases, but increases in exceedance, which is why the tropics looks more affected by the mid-latitudes. Its not clear to me whether crops care more about absolute temperature change, or about change relative to current variance.

B+N don’t make any predictions at all about future food supply. They note that in the past, exceptional heat has been linked to decreases in a years crops, and they note that in the future the temperature is going to go up, but thats it. So there is no way to know where they stand related to the 25% crop reduction as an extreme scenario. Perhaps, as physical scientists, they would rather stay out of that debate.

There are two obvious problems with / counters to their analysis. First, that crops are more sensitive to precipitation than temperatures; and second, that we will adapt crop varieties. There are other issues, such as the expected advances in tech, that JA mentions in the comments to my first post; but thats not too clocely connected to their analysis. And they rather quickly skate over the expected improvements in yields in areas that are currently too cold.

Taking the second first, their historical analysis is based around individual warm years leading to problems. Since no-one predicts these warm years in advance, the farmers then couldn’t adapt their crops, much less their techniques, to an expected warmer year. Thats obviosly not true not, when we expect a fairly smooth increase in temperature. Most parts of the world, in 100 years time, will remain cooler than the warmest cropped regions now; and its not clear to me that we won’t be able to adapt, by switching crops, over that timeframe.

As to the first… B+N note the european summer 2003 as an example of high temperatures (a) killing people and (b) reducing crops. But I recall (wrongly? could be. Anyone know?) that it was also a dry year; and indeed the dryness contributed substanitally to the heat (less water to evap so less cooling). Future warming will not necessarily be associated with dryness in this way. B+N make some effort to get around this. In their analysis of historical heat waves, they note that 1972 was hot and dry and lead to poor crops in the USSR; but that previous dry summers hadn’t. The Sahel is less convincing. Famine there was originally from drought; B+N note that in recent years the rains have returned but crops haven’t fully recovered; I wouldn’t be too surprised if politics was part of that.

I think this bit of their analysis needs more work. The obvious naive question is, why didn’t they run their GCMs scenarios for precip as well as temperature? One obvious answer might be that they don’t really trust the precip from the GCMs. Another, that they aren’t feeding the GCMs into any kind of mechanistic crop model (but why not?). So they do their best to work their analysis in terms of temperature, and to claim that precip is less important. I’m not convinced.

Summary: there isn’t much new in this paper. The dependancy of crops on ppn and/or temp needs to be clarified.

[Update: ICE isn’t impressed -W]

What we should do

Since I seem to be stating my position perhaps its time to clarify my position on CO2 taxes. I hear Obama is waiting to hear what I have to say on this burning issue 🙂

When I said that heavy, extremely painful carbon taxes weren’t going to happen, some people seem to have misinterpreted it to mean that I thought CO2 taxes were a bad idea. Far from it. But I also don’t think that we should be aiming at any particular number just yet (yes I agree we would need large cuts to stabalise CO2 levels in the atmosphere, but they just aren’t going to happen in the near (next decade or so) future, so for practical purposes we might just as well stop talking about them).

What we should do is…oh, hold on. By “we” I mean any given country. Could be the entire Cold West, could be the UK, could be the US. It doesn’t matter, which is good, because there is no need for that oh-so-difficult multi-national co-operation.

We should have a carbon tax (I don’t believe NN), and we should offset this against income taxes, and it should start at a fairly low and innocuous level and it should slowly ramp up. There should be no exceptions for heavily polluting industries. Having it start low and slowly ramp up gives everyone time to prepare, gives the government time to work out the offsetting-against-income-tax stuff, and should hopefully gain the trust of the citizenry who will see that the overall tax take doesn’t go up, and their income taxes go down. This is important, because at the moment no-one will trust the goverment not to just trouser the dosh. I think we should probably throw away the entire cap-and-trade stuff; but if we (the UK, obviously not the US) have to live with it because of EU rules then I suppose we can have that too: its hardly onerous. When it became high enough we could fold the fuel taxes into it.

That was easy, no?

Horrible English weather

Its all rather manky here: cold, thin snow semi-melted by rain and refrozen. Urgh.

Which brings up the obvious question: if I could suddenly make the world, or at least this little bit of it, 2 degrees warmer all year round, would I be better or worse off? I’m just thinking of direct response, mind you, so leaving out any ecological problems and assuming no change in precipitation. +2 oC would mean that we never had snow and hardly ever had frosts. That latter would make breaking up the soil each winter a bit harder (and would have lots of ecological repercussions, but I’m ignoring them, only thinking of me). But it would make the summers too hot. They already are a bit too hot, every other year has a week (ish) when its hot enough to make it unpleasant to sleep at night. But on balance, I think it would be an overall gain: there is more unpleasantly cold winter than there is unpleasantly hot summer.

Saying things like that inevitably makes me suspected of being an evil septic (even folks at work have started to comment) so I suppose I’ll take a stab at sketching out my position (again). My last go was I’d like us to slow down, step back and take a far longer term perspective on life and values. Vast swathes of things that we currently do simply don’t need to be done at all. I’d like us to do this because we could all be happier, and the environment less damaged. But I don’t see any real chance of this happening, absent some external shock, because sitting quietly tends to get overwhelmed by doing. On the CO2 front, my position is still that a “vast geophysical experiment” is a bad idea: we know enough to know that we don’t know what is going to happen to a sufficient degree of accuracy to know that we’re safe. I think that’s pretty clear. Its a slightly weaker version of what mt has been saying ever since the days when sci.env was worth reading (or posting to). But this is, obviously, a much weaker position than “we’re all going to die/become homeless/be flooded by refugees/become poor from rising sea levels real soon now” or somesuch. I’m sure I had a post somewhere looking at the top reasons why we should worry about climate change, but I can’t find it now, so you’ll have to be content with these ramblings (somewhere in the middle, about Bali).

[Update: (a) with thanks to Eli (b) it was quite beautiful comnig in this morning. But cold.

Also: http://www.dilbert.com/fast/2009-01-06/

Or: http://www.dilbert.com/fast/2009-01-05/ -W]

Climate scientists: it’s time for ‘Plan B’?

So says the Independent.

The substance seems to be Just over half – 54 per cent – of the 80 international specialists in climate science who took part in our survey agreed that the situation is now so dire that we need a backup plan that involves the artificial manipulation of the global climate to counter the effects of man-made emissions of greenhouse gases. About 35 per cent of respondents disagreed with the need for a “plan B”, arguing that it would distract from the main objective of cutting CO2 emissions, with the remaining 11 per cent saying that they did not know whether a geoengineering strategy is needed or not.

I’m ever so slightly dubious about their selection, since they asked me :-). I’m also unsure about their interpretation: Q4 (below) is somewhat ambiguous: you can answer yes to it if you only want more research. I answered no, because I thought they would probably interpret yes as clear-action-now, as indeed they have done, and I think thats wrong.

As far as I can see, they don’t say what the actual survey was, so here are the questions, with my responses:

1. Are you more, or less optimistic about the prospects of curbing CO2 levels to avoid dangerous climate change now compared to ten years ago when Kyoto was signed?

More optimistic………[ ]
Less optimistic ……….[X]
About the same………[ ]

2. Are you more, or less optimistic about the ability of the Earth’s climate system to cope with expected increases in atmospheric carbon levels now compared with 10 years ago given recent research on potential climate feedbacks and carbon sinks?

More optimistic………[X]
Less optimistic……….[ ]
About the same………[ ]

3. Do you believe that talk of geoengineering is a dangerous distraction and that on no account should it ever be considered as a viable option even if carbon dioxide levels continue to rise?

Agree…………………[ ]
Disagree………………[X]
Don’t know……………[ ]

4. Do you agree that we now need a “Plan B” whereby a geoengineering strategy – research, development and possible implementation – is drawn up in parallel to a treaty to reduce carbon emissions (subject to international agreements and a scientific assessment of risk)?

Agree…………………[ ]
Disagree………………[X]
Don’t know……………[ ]

Oh, and because they asked me, here is a link to Climate Ark. Which is perhaps an excuse to chatter to a snarky bunny: yes I know I haven’t updated my blogroll in ages; this is mostly because I never use anyone elses, and assume others don’t use mine. I do use “share” in google reader, though. And I may twitter a bit.

More detail here.

Why did Malthus assume linear increase in food?

JF comments on Malthus, which is my excuse for raising a question I’ve wondered about for a bit (without being sufficiently interested to actually read M, so for all I know I’m perpetuating common misreadings): M assumes exponential population growth (for which there is some basis) and linear food growth, for which there is no apparent basis at all. To first order (in an economy with little mech), it would seem to be natural to assume that food output is proportional to the number of people working the land. Or, if you assumed that land output and land area was fixed, you might assume that food output was fixed. What assumptions does M use to justify a linear increase in food production?

Refs

* [2018] CIP has a go at the subject.