Fast international travel will, at least temporarily, have to be for urgent or emergency purposes only. A triage approach is needed to ensure that the reallocation of society’s small carbon budget, its labour and resources, are used wisely to provide for a thriving society.

Once decarbonisation is complete, then, if it is considered desirable, rampant inequality can again be pursued, as it clearly is today. But between now and then, inequality is the main obstacle to getting anywhere near our Paris commitments.

Ultra deep geothermal power

fertiliser, the challenge is more real, but there is still an important and obvious first step – eat less meat. A large part of the world’s agricultural system is dedicated to growing crops and vegetables to feed animals, which we then eat. Reduce the last part of this equation (i.e. eat less meat), and the huge inefficiencies in the system mean far less fertiliser is required.

However, CCS on a powerstation is not going to stop CO2 being released from burning kerosene in an aircraft. The only near-medium term answer for this sector is a rapid, massive and fair cut in aviation use – at least until zero-carbon aircraft have replaced most of the current fleet.

Objective To determine the effects of diets varying in carbohydrate to fat ratio on total energy expenditure.Design Randomized trial.Setting Multicenter collaboration at US two sites, August 2014 to May 2017.Participants 164 adults aged 18-65 years with a body mass index of 25 or more.Interventions After 12% (within 2%) weight loss on a run-in diet, participants were randomly assigned to one of three test diets according to carbohydrate content (high, 60%, n=54; moderate, 40%, n=53; or low, 20%, n=57) for 20 weeks. Test diets were controlled for protein and were energy adjusted to maintain weight loss within 2 kg. To test for effect modification predicted by the carbohydrate-insulin model, the sample was divided into thirds of pre-weight loss insulin secretion (insulin concentration 30 minutes after oral glucose).Main outcome measures The primary outcome was total energy expenditure, measured with doubly labeled water, by intention-to-treat analysis. Per protocol analysis included participants who maintained target weight loss, potentially providing a more precise effect estimate. Secondary outcomes were resting energy expenditure, measures of physical activity, and levels of the metabolic hormones leptin and ghrelin.Results Total energy expenditure differed by diet in the intention-to-treat analysis (n=162, P=0.002), with a linear trend of 52 kcal/d (95% confidence interval 23 to 82) for every 10% decrease in the contribution of carbohydrate to total energy intake (1 kcal=4.18 kJ=0.00418 MJ). Change in total energy expenditure was 91 kcal/d (95% confidence interval −29 to 210) greater in participants assigned to the moderate carbohydrate diet and 209 kcal/d (91 to 326) greater in those assigned to the low carbohydrate diet compared with the high carbohydrate diet. In the per protocol analysis (n=120, P<0.001), the respective differences were 131 kcal/d (−6 to 267) and 278 kcal/d (144 to 411). Among participants in the highest third of pre-weight loss insulin secretion, the difference between the low and high carbohydrate diet was 308 kcal/d in the intention-to-treat analysis and 478 kcal/d in the per protocol analysis (P<0.004). Ghrelin was significantly lower in participants assigned to the low carbohydrate diet compared with those assigned to the high carbohydrate diet (both analyses). Leptin was also significantly lower in participants assigned to the low carbohydrate diet (per protocol).Conclusions Consistent with the carbohydrate-insulin model, lowering dietary carbohydrate increased energy expenditure during weight loss maintenance. This metabolic effect may improve the success of obesity treatment, especially among those with high insulin secretion