Reducing the greenhouse gas emissions that are driving climate change will involve answering difficult questions about our lifestyles, and the signs are ambivalent about whether the world , write Professor Hoesung Lee, chair of the Intergovernmental Panel on Climate Change, and Professor Jim Skea, co-chair of IPCC Working Group III.

All reasonable doubts about climate change have now been dispelled by both climate science and everyday experience of unusual weather. The world’s attention is now turning to solutions that could reduce and ultimately eliminate emissions of carbon dioxide (CO2), the most important greenhouse gas. But CO2 emissions are deeply embedded in the activities and social practices of a modern economy. Power stations, industry, cars, aeroplanes, heating buildings, food production and land management are all major sources of emissions worldwide.

In 2018, a special report by the Intergovernmental Panel on Climate Change (IPCC) provided a stark warning about the consequences of allowing the world to warm by more than 1.5 degrees Celsius.

The report noted that it was possible, within the laws of physics and chemistry, to limit global warming to 1.5C. But it concluded that this would require “rapid and far-reaching transitions in energy, land, urban and infrastructure” that would be “unprecedented in terms of scale”.

Emissions of CO2 would need to fall by roughly 45 per cent by 2030 from present-day levels to keep us on track towards 1.5C. Are governments, and are citizens, up for that?

The signs are ambivalent. Under the Paris Agreement, governments set an aim of removing as much CO2 from the atmosphere as we put in by the second half of the 21st century – “net zero” or “carbon neutrality” in other words. And some countries have indeed started to set “net zero” targets.

The Climate Change Bill, which has just started its journey through the Scottish Parliament, allows for exactly that.

But, at the same time, as governments are formulating lofty long-term goals, there has been less progress in terms of immediate actions.

Globally, emissions are still rising. And the pledges that governments have made under the Paris Agreement set the world on a path to global warming of 3C or more.

The recent IPCC report concluded that limiting the rise to 1.5C could be achieved through a range of different emission pathways. Policymakers would need to balance the option of very rapid emissions reductions in the short term against a second option of slower emission reductions, followed by the removal of large quantities of CO2 from the atmosphere in the second half of the 21st century.

Large-scale CO2 removal is currently assumed to be achieved by combining the use of bioenergy with carbon capture and storage. Growing biomass draws CO2 from the atmosphere. When the biomass is burned, the resulting CO2 would be captured and stored geologically, for example in depleted oil and gas fields.

At scale, this option is unproven. There are only a few dozen carbon-capture plants operating globally, and only one is linked to biomass. Converting large tracts of land to bioenergy has become an issue of concern because of the implications for food security, if land is taken out of food production, and threats to biodiversity.

But “net zero” cannot be achieved unless some CO2 is removed from the atmosphere. There are sectors, such as heavy industry or aviation where mitigation options are currently lacking. Emissions from these would need to be balanced by CO2 removal.

There is a growing interest in “nature-based” solutions that can remove CO2 from the atmosphere at a more modest scale and which may yield wider benefits. These include re-building stocks of carbon in soils through agricultural practices or by re-wetting peatlands.

There are concerns about the feasibility of the alternative option of making rapid emissions reductions in the short term. Some countries – and Scotland is a leading example – have been able to reduce CO2 emissions by two to three per cent per year at best. Reducing emissions by 45 per cent by 2030 and hitting net zero by around 2050 is a major step up in terms of effort. Addressing the electricity sector alone will not be enough. We would need to reduce radically emissions from heating and transport as well. Technical fixes – whether through the energy supply side or through energy efficiency – are unlikely to be enough. The difficult question of how lifestyles and consumption patterns influence emissions would need to be addressed.

This is not to say the task of moving emissions in the right direction is impossible. There are grounds for cautious optimism. In particular, the cost of renewable energy – wind and solar – has fallen dramatically in recent years.

This has been driven by a combination of government policies and economies of scale. Deployment is expanding in many parts of the world. Renewables now meet two thirds of Scottish demand for electricity. Several countries have set target dates for phasing out sales of petrol or diesel cars. Vehicles powered by electricity derived from renewable sources can have a big impact on emissions from private transport. And in many parts of the world, this will also deliver improved air quality and health benefits. These are areas in which the current pace of development matches what might be needed to limit global warming in line with the Paris Agreement.

Scientists from the IPCC are meeting in Edinburgh this week to grapple with these issues. In particular, they have been invited by governments to consider for the first time the social as well as the technical aspects of emissions reduction. Last year’s report on global warming of 1.5C identified that system change that is “rapid, large-scale and unprecedented” would be needed. The challenge now is for scientists to offer policymakers a range of possible solutions that could bring about these required system changes.

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