For these last two cases, "reaching the greenhouse-gas intensity targets with product modifications alone will be challenging, and therefore structural changes in consumption patterns might be needed," wrote the scientists in Environmental Research Letters (ERL) .

As population rises and consumption levels increase, the greenhouse emissions of goods and services are set to grow. The team projected that the share of animal-derived calories will increase, transport will become faster and more energy intensive, and buildings will demand more cooling. This increase in consumption will mean reducing greenhouse-gas emissions by a factor of five rather than a factor of three, in order to meet the 2° target.

"With the developed approach the requirement for the 2° target can be translated from an abstract international level to the level of actual products and consumption categories," Bastien Girod of the Swiss Federal Institute of Technology Zurich told environmentalresearchweb. "This work brings together the global and household perspectives."

Girod, along with colleagues from Utrecht University in the Netherlands, PBL-Netherlands Environment Assessment Agency and the Norwegian University of Science and Technology, calculated the permitted greenhouse-gas intensities compatible with a 2° target on a per-calorie basis for food, per square metre for shelter, per person kilometre for transport, per kilogram for goods and per US dollar for services.

The team used an IPAT approach, in which the Impact (in terms of greenhouse-gas emissions) depends on Population, Affluence (consumption per head) and Technology.

For many of the products and services, the reduction in emissions required is already possible through existing technologies. When it comes to food, the researchers said that animal calories could be replaced by vegetables processed to resemble animal-based food, for example, tofu and wheat gluten. People could eat poultry, fowl and pork rather than cattle and sheep, or turn to in vitro meat production.

For air travel the required greenhouse-gas intensity seems unattainable, they added, as electrification is not possible, and hydrogen power would be costly because of the required storage volume and safety concerns. The only realistic solution for 2050 is blending biofuels with conventional aviation fuels, said the researchers, but biofuels have limited potential, and the issues of non-energy-related greenhouse-gas emissions as well as embodied emissions from biofuels remain to be solved.

According to Girod, the greenhouse-gas target intensities give guidance for product developers and consumers. "But this approach could also inform policy makers regarding emission targets on a product level," he said. "This is especially relevant in the absence of an international climate-policy regime, because climate policy focusing on consumption in contrast to production does not impact on competitiveness or lead to carbon leakage."

Now Girod plans to investigate barriers to the diffusion of products and services consistent with a 2° world. "My co-author Detlef van Vuuren is using integrated assessment models focusing on the effectiveness of concrete measures in relation to long-term emission pathways towards 2 °C," he said, "while Edgar Hertwich is working on an integrated life-cycle assessment model that can address the interaction between technology change on the energy-supply side and measures on the energy-demand side to assess whether specific solutions meet the targets defined in our paper."

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