Too much of a good thing?
Primary production refers to the basis of the entire food chain in plant growth through photosynthesis (it's a little broader than this, but that's the main idea). The total level of primary production can be measured by instruments on satellites and NASA have just published a new report summarising long term trends (more commentary including a short video can be found here. While primary production was rising fairly rapidly during the 1980s and 1990s, the last ten years have a slight decline in the total productivity of the globe's plant growth, largely due to more droughts. The full significance of this finding is not yet apparent, but it may signal a shift that scientists have predicted and feared: that the benefits of more carbon dioxide in the atmosphere to plant growth are being overwhelmed by disruptions to the hydrological cycle. Carbon dioxide is not simply "plant food", but also changes the climate, including precipitation patterns. And while (in small doses) it is necessary for life as we know it, it is possible to have too much of a good thing.
Indeed, a recent NAS study confirmed that for each degree Celsius the temperature rises, global crop yields from major grains like wheat, rice and corn will fall 5-15%. The recent Russian heat wave is estimated to have destroyed around 30% of Russia's entire wheat harvest. The heat wave cannot itself be directly blamed on global warming, but events like it become more common and more severe.
In years to come, it might not be climate change in the headlines, but food prices and political instability.
Give us this day our daily bread.
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13 comments:
Don't over commit Byron.
Here is another view.
David, thanks for the link to a very interesting paper (and only one in a whole journal addressing the issue). Have you read the paper that you linked to? I now have and let me summarise a few of the things I noticed.
It (a) explicitly excludes the very consideration of the paper I was talking about (redistribution of precipitation patterns) due to the difficulty of modelling precipitation changes at a high resolution (and the paper I quoted doesn't use models, just measures total productivity), (b) acknowledges that the gap between optimal productivity and actual productivity would have to be closed (while also acknowledging that this gap has always existed and that in most of the cases mentioned in the paper it is constant or growing), (c) doesn't mention that other studies have found increasing CO2 also leads to a drop in nutritional value, (d) assumes that crop yield improvements from breeding programmes don't hit a yield ceiling in the next fifty years, an assumption which is only partially defended and which goes against a plateau in yields across a range of crop types in the last 10-15 years, (e) acknowledges that many areas are growing crops in ways that are "mining the nutrients" in a way that is unsustainable, and suggests that only the application of fertilisers can avoid soil exhaustion, yet doesn't mention either peak oil or peak phosphorus, which threaten the global supply of cheap fertilisers, (f) assumes significant increases in the application of chemical pesticides and the necessity of ongoing poverty in many areas to keep labour cheap enough to be economic for manual weed control, (g) uses assumptions about the deleterious effects of increasing ozone that the paper described as "this may be optimistic", (h) extrapolates trends from the difference two data points a year apart (2006-07) while ignoring any negative trends on the assumption that they could be stopped, (i) assumes zero growth in non-food uses of arable land (i.e. no more biofuels or cotton, etc.), (j) assumes constant improvements in technologies and their distribution (i.e. no large-scale disruptions to society) and (k) acknowledges that soil-born pests and diseases are likely to increase in a warming world and that chemical pesticides have not been effective against these in the past.
More crushingly, the study explicitly ignored (a) soil degradation (salination, erosion, desertification), which it warns is especially associated with extreme weather events that are likely to increase in frequency, (b) nutrient depletion through unsustainable practices, (c) the fairly rapid loss of productivity from lands recently cleared for farming (e.g. in the Amazon) and (d) inefficiencies in irrigation techniques and water shortages for irrigation (hmm, never heard of those being a problem anywhere...).
Even with all these assumptions, they acknowledge that while global yields may only improve by 50% between 2007 and 2050, yet demand for food may well grow by 70%. Furthermore, the paper noted that the yield increases may be least in Africa, where food pressure is likely to have one of the fastest growth rates.
The paper concludes that even the rises in yield it predicts "relies heavily on improved technology" and that their " assumptions about future possibilities are based on past performance and that they are therefore rather uncertain". And it's final sentences are positively chirpy with confidence: "it should be possible to produce yield increases that are large enough to meet some of the predictions of world food needs [...] whether that food will be available to and affordable by all those who need it is another question."
Reading this paper made me more pessimistic about the situation, not least because this paper was one of 23 papers in that journal (which was all about food sustainability to 2050) and from skimming the abstracts, it seems to be the most optimistic one. The ones on fisheries, livestock, price volatility, climate impacts, use of fossil fuels in agriculture and food and health all seemed to be decidedly more gloomy.
I don't doubt that there are all kinds of ways of continuing to increase yields and it is truly stunning that human ingenuity has increased yields by staggering amounts in the last fifty or sixty years (as global population has undergone an equally staggering rise, as has ecological degradation). I am very grateful to farmers and, having studied some agriculture for five years, have an inkling of just how complex it all is. But assuming this rate of improvement can be sustained indefinitely even in the absence of other large threats (such as shifts in the hydrological cycle) is wishful thinking. I don't know how the future is going to play out, but I think that food security (and political stability linked to it) is likely to only grow as a global (and regional) concern.
And so we pray, give us this day our daily bread, and need to think again about what we eat, from where, how it was grown, who wins and who loses as a result.
Of course, human food isn't the only issue. Declining primary production means less food for other creatures, and less carbon dioxide removed through photosynthesis.
FP: The coming food crisis:
"This year, we may be able to limit the damage to a single supply shock in Russia and Eastern Europe. But even in the best of times, our global food system is stretched to the breaking point by the ever-present challenges of population growth, increased demand from changing diets, higher energy costs, and more extreme weather. Experts at the U.N. Food and Agriculture Organization estimate global agricultural productivity must double by 2050 to keep pace with increased demand. Unless we take immediate action, we are destined to race from food crisis to food crisis for generations to come, with grim consequences for the world's poor and our own national security."
China crops hit limits of land and water.
Learning from Brazil in a food crisis.
Improvements in US wheat production have been slowing since the mid-80s and are have now basically peaked, short of significant new investments in land and water.
Original study here. Summary here.
Review of Climate Wars, which is not about debates in the media or science, but some imaginative exploration of possible geopolitical consequences of worsening food insecurity.
Guardian: Food prices can't be swept under the table and perhaps small scale farming is the future.
NASA: Video summarising the 2010 paper on net primary production decline.
Northern Arizona University: Climate change helps, then quickly stunts growth. A new ten-year study questions how significant (and lasting) theorised benefits from initial modest warming might be.
PNAS: Global human appropriation of net primary production doubled during the 21stC. We now appropriate ~25% of NPP.
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