Agree that these seem like useful links. The drought/food insecurity/instability route to mass death that my original comment discusses is addressed by both reports.
The first says there’s a “10% probability that by 2050 the incidence of drought would have increased by 150%, and the plausible worst case would be an increase of 300% by the latter half of the century”, and notes “the estimated future impacts on agriculture and society depend on changes in exposure to droughts and vulnerability to their effects. This will depend not only on population change, economic growth and the extent of croplands, but also on the degree to which drought mitigation measures (such as forecasting and warning, provision of supplementary water supplies or market interventions) are developed.”
The second seems most concerned about brief, year-long crop failures, as discussed in my original post: “probability of a synchronous, greater than 10 per cent crop failure across all the top four maize producing countries is currently near zero, but this rises to around 6.1 per cent each year in the 2040s. The probability of a synchronous crop failure of this order during the decade of the 2040s is just less than 50 per cent”.
On its own, this wouldn’t get anywhere near a GCR even if it happened. A ~10% drop in the yield of all agriculture, not just Maize, wouldn’t kill a remotely proportionate fraction of humanity, of course. Quick googling leads to a mention of a 40% drop in the availability of wheat in the UK in 1799/1800 (including imports), which led to riots and protests but didn’t cause Black Death levels of mass casualties. (Also, following the paper’s source, a loss of >20% is rated at 0.1% probability per year)
What would its effects be in that case (my original question)? This is where the report uses a combination of expert elicitation and graphical modelling, but can’t assign conditional probabilities to any specific events occurring, just point out possible pathways from non-catastrophic direct impacts to catastrophic consequences such as state collapse.
Yeah the IPCC seems to think that there is a lot of scope to use irrigation to adapt to increasing droughts. in Bangladesh >50% of agricultural land is irrigated and people in the fertile crescent at the dawn of agriculture made extensive use of irrigation. I’m still pretty worried about the potential effects on very poor agrarian countries. But this still falls well short of a GCR on any reasonable projection of future changes in agricultural technology. The effect outlined is more like—maybe the price of one staple crop increases by at most 50%. For example, the right hand pane shows the effect on food prices of climate change—up by on the order of 25% than the counterfactual, depending on the socioeconomic scenario.
Yeah, between the two papers, the Chatham house paper (and the PNAS paper it linked to, which Lynas also referred to in his interview) seemed like it provided a more plausible route to large scale disaster because it described the potential for sudden supply shocks (most plausibly 10-20% losses to the supply of staple crops, if we stay under 4 degrees of warming) that might only last a year or so but also arrive with under a year of warning.
The pessimist argument would be something like: due to the interacting risks and knock-on effects, even though there are mitigations that would deal easily with a supply shock on that scale, like just rapidly increasing irrigation, people won’t adopt them in time if the shock is sudden enough, so lots of regions will have to deal with shortfalls way bigger than 10-20% and have large scale hunger.
This particular paper has been cited several times by different climate pessimists (particularly ones who are most concerned about knock-on effects of small amounts of warming), so I figured it was worth a closer look. To try and get a sense of what a sudden 10-20% yield loss actually looks like, the paper notes ‘climate-induced yield losses of >10% only occur every 15 to 100 y (Table 1). Climate-induced yield losses of >20% are virtually unseen’.
The argument would then have to be ‘Yes the sudden food supply shocks of 10-20% that happened in the 20th century didn’t cause anything close to a GCR, but maybe if we have to deal with one or two each decade, or we hit one at the unprecedented >20% level the systemic shock becomes too big’. Which, again, is basically impossible to judge as an argument.
Also, the report finishes by seemingly agreeing with your perspective on what these risks actually consist of (i.e. just price rises and concerning effects on poorer countries): Our results portend rising instability in global grain trade and international grain prices, affecting especially the ∼800 million people living in extreme poverty who are most vulnerable to food price spikes. They also underscore the urgency of investments in breeding for heat tolerance.
Update: looks like we are getting a test run of sudden loss of supply of a single crop. The Russia-Ukraine war has led to a 33% drop in the global supply of wheat:
agree on the first one—it is very good. I hadn’t seen the second one thanks for sharing!
Agree that these seem like useful links. The drought/food insecurity/instability route to mass death that my original comment discusses is addressed by both reports.
The first says there’s a “10% probability that by 2050 the incidence of drought would have increased by 150%, and the plausible worst case would be an increase of 300% by the latter half of the century”, and notes “the estimated future impacts on agriculture and society depend on changes in exposure to droughts and vulnerability to their effects. This will depend not only on population change, economic growth and the extent of croplands, but also on the degree to which drought mitigation measures (such as forecasting and warning, provision of supplementary water supplies or market interventions) are developed.”
The second seems most concerned about brief, year-long crop failures, as discussed in my original post: “probability of a synchronous, greater than 10 per cent crop failure across all the top four maize producing countries is currently near zero, but this rises to around 6.1 per cent each year in the 2040s. The probability of a synchronous crop failure of this order during the decade of the 2040s is just less than 50 per cent”.
On its own, this wouldn’t get anywhere near a GCR even if it happened. A ~10% drop in the yield of all agriculture, not just Maize, wouldn’t kill a remotely proportionate fraction of humanity, of course. Quick googling leads to a mention of a 40% drop in the availability of wheat in the UK in 1799/1800 (including imports), which led to riots and protests but didn’t cause Black Death levels of mass casualties. (Also, following the paper’s source, a loss of >20% is rated at 0.1% probability per year)
What would its effects be in that case (my original question)? This is where the report uses a combination of expert elicitation and graphical modelling, but can’t assign conditional probabilities to any specific events occurring, just point out possible pathways from non-catastrophic direct impacts to catastrophic consequences such as state collapse.
Note that this isn’t a criticism—I’ve worked on a project with the same methodology (graphical modelling based on expert elicitation) assessing the causal pathways towards another potential X-risk that involves many interacting factors. These questions are just really hard, and the Chatham house report is at least explicit about how difficult modelling such interactions is.
Yeah the IPCC seems to think that there is a lot of scope to use irrigation to adapt to increasing droughts. in Bangladesh >50% of agricultural land is irrigated and people in the fertile crescent at the dawn of agriculture made extensive use of irrigation. I’m still pretty worried about the potential effects on very poor agrarian countries. But this still falls well short of a GCR on any reasonable projection of future changes in agricultural technology. The effect outlined is more like—maybe the price of one staple crop increases by at most 50%. For example, the right hand pane shows the effect on food prices of climate change—up by on the order of 25% than the counterfactual, depending on the socioeconomic scenario.
Yeah, between the two papers, the Chatham house paper (and the PNAS paper it linked to, which Lynas also referred to in his interview) seemed like it provided a more plausible route to large scale disaster because it described the potential for sudden supply shocks (most plausibly 10-20% losses to the supply of staple crops, if we stay under 4 degrees of warming) that might only last a year or so but also arrive with under a year of warning.
The pessimist argument would be something like: due to the interacting risks and knock-on effects, even though there are mitigations that would deal easily with a supply shock on that scale, like just rapidly increasing irrigation, people won’t adopt them in time if the shock is sudden enough, so lots of regions will have to deal with shortfalls way bigger than 10-20% and have large scale hunger.
This particular paper has been cited several times by different climate pessimists (particularly ones who are most concerned about knock-on effects of small amounts of warming), so I figured it was worth a closer look. To try and get a sense of what a sudden 10-20% yield loss actually looks like, the paper notes ‘climate-induced yield losses of >10% only occur every 15 to 100 y (Table 1). Climate-induced yield losses of >20% are virtually unseen’.
The argument would then have to be ‘Yes the sudden food supply shocks of 10-20% that happened in the 20th century didn’t cause anything close to a GCR, but maybe if we have to deal with one or two each decade, or we hit one at the unprecedented >20% level the systemic shock becomes too big’. Which, again, is basically impossible to judge as an argument.
Also, the report finishes by seemingly agreeing with your perspective on what these risks actually consist of (i.e. just price rises and concerning effects on poorer countries): Our results portend rising instability in global grain trade and international grain prices, affecting especially the ∼800 million people living in extreme poverty who are most vulnerable to food price spikes. They also underscore the urgency of investments in breeding for heat tolerance.
Update: looks like we are getting a test run of sudden loss of supply of a single crop. The Russia-Ukraine war has led to a 33% drop in the global supply of wheat:
https://www.economist.com/finance-and-economics/2022/03/12/war-in-ukraine-will-cripple-global-food-markets