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When it is a Patagonian Toothfish - renamed into a Chilean Seabass for promotional purposes. The price and popularity of fish seems to have little to do with taste or nutritional content, and everything to do with marketing. To give just one example, Patagonian Toothfish was undesirable until a Californian fish merchant marketed it as the new-found delicacy of Chilean Seabass in the late 1970s29, pushing the price to over PS60/$85 per kilo. It isn't even a seabass! Sadly, the result of all the popularity is that stocks of this once-abundant fish, found in the deep (by which I mean anything from 300 m to over 3.5 km down) Southern Ocean, and able to grow to over 2 m in length and 100 kg in weight, are now threateningly low. And it takes 45 years to replace a 45-year-old fish.

The urgency of responding to climate change looks very different if you are a drowning island state than if you are a huge nation that stands to find its ports unfreezing in winter, its frozen wastelands becoming fertile and its abundant fossil fuel reserves more accessible.

Meat and dairy When animals are fed human-edible crops, this is the most inefficient part of the global food supply in terms of calories, protein and micro-nutrient terms. The inefficiency is also costly in greenhouse gas terms especially when the animals are ruminants (sheep and cattle) and typically double their impact through the belching of methane. Other problems include the two thirds of the world's antibiotics that are used in animal farming, and the welfare of the beasts themselves.

Over 1% of the world's total GHG footprint could be saved by simple improvements to the way rice is usually grown. This is a big untold story. It has nothing to do with the fossil fuel used by tractors, lorries, boats or any other parts of the supply chain. Specifically, what is needed is more judicious use of fertiliser and not flooding paddy fields22. Paddy field methane is about 6% of all greenhouse gas emissions from the food supply chain. I've seen photos of rivers in China that are bright green from so much excess fertiliser; the yield is probably actually suffering from over application.

it is a stark truth that the sum of all the world's climate action has so far made little or perhaps even zero detectable impact on rising global emissions.

Whilst more than two thirds of all farm animal food are grass and pasture, which cannot be eaten directly by us, the human-edible crops that we feed them amount to more than three quarters of the calorific needs of the entire human population.

Food transport only really becomes a big problem when things get put on an aeroplane. UK examples of this can include grapes and berries from California, fresh tuna from the Indian Ocean, baby vegetables from Africa and, perhaps worst of all, asparagus all the way from Peru. (You can't eat flowers, but many of them also travel on planes so the same rule applies.)

putting food on a boat, even from the other side of the world, can enable a relatively sustainable food supply. What turns out to be a fairly small transport energy demand comes in return for an important flow of nutrients from places with plenty of sun and fertile land to highly populated places that are unable to meet their own food needs. Nor are a few hundred road miles a disaster, although the fewer the better, especially when it comes to heavy stuff like beer.

How is the world's wealth distributed? America has 138 times more wealth per person than Africa. About half the world's wealth rests with 1% of the population, whilst the poorest 70% own just 2.7%

Sometimes it is better to do a bad job of measuring something important than a good job of measuring something irrelevant.

Animals contribute 590 kcal to the human food chain as meat and dairy. BUT they eat 1740 kcal per person per day of human-edible food as well as 3810 kcal of grass and pasture.

Roughly two thirds of the carbon footprint of driving an oil-powered car is down to the fuel and the rest comes from the emissions involved in manufacturing the car in the first place. So, unless they are very inefficient, cars should be looked after and kept on the road for a long time.

How can we produce enough food for 9.7 billion of us in 2050? As we have seen, the priorities are (1) to reduce human-edible food being fed to animals, (2) to cut waste, (3) to keep biofuels in check and (4) the sensitive application of new technologies.

Diesels became popular in the UK for their supposed carbon efficiencies. However, this benefit is marginal because whilst diesel cars do a few more miles to the gallon, a gallon of diesel also has about 20% more carbon in it.

The single most important change will be an amazingly simple dietary shift towards less meat and dairy consumption, with a particular focus on reducing beef.

An estimated two thirds of all antibiotics14, 63,151 tonnes per year in fact15, are gobbled up by animals - and some of that even makes it back to us through meat and milk.

Out of 1320 kcal wasted per person per day, 48% is cereals. That's enough calories to feed everyone in China and America. Nearly two thirds of all losses occur in harvest or just afterwards, in storage. After dietary change away from eating too much meat and dairy, cutting waste is probably the next most important way to ensure there is enough nutrition to go round.

What happens to the food we grow? Some 1320 kcal are lost or wasted, 810 kcal go to biofuels and a massive 1740 kcal are fed to animals.

It is also very possible, perhaps even likely, that at some point we trigger 'positive feedback mechanisms'; vicious circles in which temperature change causes things to happen that in turn trigger more temperature change. This would be likely to provoke a step change in the climate that would probably be unstoppable by human activity. A recent and credible paper looked at five of these positive feedbacks and estimated that the trigger point for a step change could well occur at around 2 degC3

A global temperature rise of 2 degC looks very risky but 1.5 degC much less so

When a measure directs our attention one way, it has to be taking it away from something else. All quantitative metrics are simplifications of the world and therefore need keeping in context. They have an important place alongside, but not instead of, our rich qualitative understanding of the world and the human experience within

In the UK 40,0007 people a year die prematurely from air pollution, and vehicles cause 8,900 of those deaths. That is five times more than the 1,775 who died in road traffic accidents.

At the global level, we grow 5940 kcals per person per day. That's nearly two and a half times as much as the 2350 kcals per day that the average person needs to eat to be healthy.

A person's inherent worth is independent of their circumstances or the choices they have made in their lives or have had made for them.

Gas (natural gas) The least carbon intensive fossil fuel in terms of energy per tonne of carbon dioxide. Emits about half the carbon dioxide per unit of energy that oil does, and is even better compared to coal. Sadly gas and oil extraction usually go together. The exception, fracking, is marred by other environmental concerns.

Methane In the phrase 'coal, oil and gas', methane is the gas we are talking about. As well as being commercially extracted, it is also produced by cows and sheep when they chew the cud (ruminate), by paddy fields if they are flooded, it pours out of permafrost if it melts, and is produced by rotting organic matter in landfill sites. When burned it releases a lot of heat energy (that's good) but produces carbon dioxide (that's bad). Much more problematic is that if it is released into the atmosphere without burning it is a much more powerful greenhouse gas than carbon dioxide. In fact if you compare the global warming impact of methane over 20 years to the same weight of carbon dioxide of that period you find it is 76 times worse. However, methane only has a half-life of about 12 years in the atmosphere, so over a 100-year period, the slow acting but long lasting carbon dioxide has caught up a bit and the methane is 'only' 25 times worse. There is an arbitrary convention to take a 100 years' timeframe, for most purposes. However, there is a very strong case for being interested in much shorter timescales than this, in which case methane needs to be considered as an even more powerful greenhouse

Biofuels Energy from plant matter. There is a limited place for this in a sustainable energy system; managed woodland for burning fuel, conversion of waste products to liquid fuels, and perhaps a small amount of cropland for biofuel to allow aviation in the low carbon world. If land is used for biofuel crops instead of food crops, the nutritional sacrifice is huge for just a small contribution to the world's energy supply. An explosion in biofuels as a replacement for oil would present a real threat to global nutrition. (See Are biofuels bonkers?,

Animal feed Here we are not talking about grass or pasture. We are talking about plant matter that is digestible by humans but is instead fed to animals. Globally, there is enough of this to provide about 1800 calories per day to every person on the planet; that's about three quarters of the global food requirement for human energy. In return, animals give us back about 10% in the form of meat and dairy products. Cutting out animal feed would hugely help us feed the world and preserve biodiversity.

Low carbon flying is a hard nut to crack, but solutions look possible. The most obvious one is use biofuel. Unfortunately, we saw on page 78 that the trade-off between fuel and food is incredibly steep. If the biofuel used was made from wheat, the amount of it required would be enough to meet the calorific needs of all the passengers for a whopping four years and would require 1.5 square miles of prime California land for a year to produce it13

Whatever its low carbon credentials, biodiesel should not be thought of as a major part of our energy solution. Going down this route would put huge strain on the global food system and risk widespread malnutrition.

If the biodiesel came from wheat grown on our square metre, even assuming 100% efficiency of conversion, you could get enough to drive about one mile. To look at in another way, enough wheat to provide a person's calorific needs for a day will only provide enough biodiesel to power car for 2.7 miles. That is a steep trade off!

What makes our values change? Our values move with the messages we receive and the things we think about.

Overall, tax doesn't make people poorer. That is just the direct impact that we can most clearly see. Tax does three key things. Firstly it disincentives some activities. Secondly it raises money that can fund things that make life better. Thirdly it can be used to change the way wealth is distributed.

Metrics are ways of simplifying our world view, sometimes for better and sometimes for worse. All metrics are harmful if you give them too much power. GDP is no different. It is not a measure of human progress. Its simplicity makes it a tempting crutch for any politician who is feeling freaked out by the complexities of running a country full of real sentient people and is looking for a way to reduce their anxiety.

GDP goes up if things we used to give and receive for free become chargeable. A country's GDP might well go up if the level of spontaneous kindness were to go down. If friends won't baby sit or look after a frail neighbour, then it becomes a commercial activity. To give another example, the laundered profits from drugs and other crimes show up as GDP.