Promises of net carbon reduction must be meaningful to avert climate catastrophe

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Biden administration climate envoy John Kerry reiterated the US commitment to net zero emissions by 2050, but has not yet specified which substances will be included in his pledge.Credit: Stefani Reynolds / Bloomberg / Getty

The administration of US President Joe Biden has pledged 2050 as the deadline for net zero greenhouse gas emissions. Earlier, China declared 2060 for its own net zero date. A debate is also ongoing in India, as in much of the rest of the world. In all, some 124 out of 202 countries polled in a report released last week made net zero pledges ahead of the November global climate summit in Glasgow, UK (see go.nature.com/2puuzmh). Activities leading up to the UN summit include a “race to zero” campaign for the remaining countries to participate by then.

But what does net zero really mean? In a 2018 special report, the Intergovernmental Panel on Climate Change said countries must reduce carbon dioxide emissions to ‘net zero’ by 2050 to keep global warming below 1 , 5 ° C from pre-industrial levels. But beyond that, there is less agreement on which substances net zero applies to. This creates serious ambiguity and countries and organizations define the term according to their own criteria. Agreeing on a definition is important for accountability but, above all, without it, the goal of the 2015 Paris climate agreement to limit warming to between 1.5 ° C and 2 ° C by mid-century might not be achieved.

Joeri Rogelj of Imperial College London and colleagues made it clear how different definitions and paths to net zero can have radically different results (J. Rogelj et al. Nature 591, 365–368; 2021). For example, reducing CO2 emissions stop warming, but CO2 that already exists in the atmosphere will remain for hundreds of years. At the same time, reductions in other greenhouse gases could affect warming more quickly. But removing these other gases is more complex than reducing carbon.

The researchers also warn that the relative amounts of these emission reductions will also affect the overall rates of gas decline. In some scenarios, temperatures might not start to drop, even with emission reductions. The team rightly asks for clarification on three policy areas: the scope of emission reductions; their adequacy and fairness; and concrete steps to achieve net zero. A 2050 or 2060 goal no longer makes sense without intermediate milestones.

The Paris climate agreement applies to all greenhouse gas emissions, but participating countries have not decided how emissions should be reduced, or how reductions will be measured. Agreeing on the two will be priorities for the Glasgow summit, but the information vacuum over the next six years has created space for multiple interpretations and options. So while the European Union’s commitment targets all of these gases, China’s plan focuses solely on CO2 emissions and does not include methane or nitrous oxide. And the US plan has not yet specified which gases are covered.

Companies that make net zero contribution pledges are also flexible in their definitions. For some, net zero means removing greenhouse gases from all their processes, including taking action to offset historical emissions. But others – like investment banks and fossil fuel companies – will continue to invest in fossil fuels while promising net zero policies in other areas of their business. And that rightly attracts criticism, especially from the movement inspiring climate strikes in schools, Fridays for the future.

Offset the risks

Controversy also continues around the word “net” – in the sense that net zero is the balance between emissions produced and emissions eliminated. Under previous emission reduction rules that expired in 2020 (under the 1997 Kyoto Climate Protocol), high-emission countries were allowed to offset their emissions with the help of low-emission countries. They could, for example, buy and sell carbon as a commodity on the many carbon exchanges that have been created around the world. Carbon trading allows high-emitting countries to reduce their net emissions without reducing the overall amount of carbon they release into the atmosphere. These countries could also claim carbon credits if they finance clean energy or plant trees in low-emission countries.

But if large emitters use such metrics more and more, the world could only reach net zero in a technical sense. The Paris goal of bringing global warming under control is less likely to be achieved if these countries do not drastically reduce their own emissions. The risk is that the world will heat up and a greater burden – for example, accelerated climate adaptation measures – will fall on climate-vulnerable countries. This is a real prospect and it is one of the reasons why countries most vulnerable to climate change, especially those in the south of the globe, are worried about the increasing use of offsets to achieve net zero.

While all decarbonization efforts have some value, the least that needs to be done is for there to be more transparency in how countries achieve their net zero ambitions – as this will allow researchers to determine more precisely what these commitments mean to achieve Paris. the purpose of the agreement. What the planet desperately needs are agreed rules and a reliable monitoring mechanism – which this review has already advocated in other areas of climate policy, such as funding climate mitigation and adaptation projects. (see Nature 589, 7; 2021).

Committing to net zero is not difficult – especially when the countries and organizations involved can set the parameters for that commitment themselves. But a commitment that does not include significant reductions – as opposed to more offsets – increases the risk that catastrophic climate change will become inevitable.

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