Thread by @JoeriRogelj

Explainer:
what are #NetZero targets?
why do they matter?
and why do vague targets lull the world in missing its climate goals?

A (long) thread with scientific and policy background on our recent @nature commentary

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#ClimateScience @NatureNews
nature.com/articles/d4158…

What are #NetZero targets?

#NetZero targets are key benchmarks towards a world where we avoid the worst of climate change. But if defined vaguely, they leave a lot of wiggle room and can compromise achievement of the #ParisAgreement

We provide guidelines to avoid this.

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First, why are there #NetZero targets?

Global warming is proportional to the total cumulative amount of CO2 we emit. Halting global warming thus means we have to stop adding CO2 to the atmosphere.
Rigorous net-zero CO2 targets achieve at least that, but also more...

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The #ParisAgreement says that we should go beyond net-zero CO2. It states that all greenhouse gases (GHG) should be taken into account, and global #NetZero GHG emissions (referred to as "a balance" in its Article 4) have to be achieved in the second half of the century.

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The #NetZero target of the #ParisAgreement achieves more than simply stabilising warming. Because of the way in which governments have chosen to define #NetZero it achieves a peak and then gradual decline in global warming.

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(On a technical note: governments have decided to aggregate emissions and removals of different greenhouse gases under the #ParisAgreement by using a specific greenhouse gas metric called the Global Warming Potential of a specific greenhouse gas over 100 years, GWP-100)

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#NetzZero targets thus need to define clearly which gases are included & how they are compared.

Change the gases covered, change the way in which they are compared, and the #NetZero target can be significantly less ambitious than what is needed to meet the #ParisAgreement

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If #NetZero targets cover CO2 only, or they re-define #NetZero by adding up greenhouse gases with a method or metric that differs from the one decided under the #ParisAgreement, this typically weakens their ambition.

Global warming might not peak & decline.

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#NetZero targets can thus include important pitfalls or even loopholes.

Depending on how they are defined, they can contribute to solutions to the #ClimateEmergency or undermine progress towards it.

Setting rigorous goals following our new guidelines can avoid this.

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We provide both a simple checklist (below) and an extended set of guidelines (follow the link) to set rigorous #NetZero targets.

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nature.com/magazine-asset…

What's the issue with #NetZero and "real zero"?

All Paris-compatible pathways combine 3 strategies: rapid large reductions in CO2; additional deep reductions in non-CO2 gases; and ramping removal of CO2.

But how much we reduce versus remove matters a lot!
@GretaThunberg
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CO2 removal is necessary, but can have important side-effects and there's only a limited potential available.

It should only be used as a means to draw down CO2 from those sources that we can really not eliminate, not as a reason to continue pollution.

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If CO2 removal and offsets are used by #NetZero targets to continue emitting, they undermine global ambition, often export sustainability problems to other, more vulnerable countries, and present a high risk that the #ParisAgreement climate goals are never met.

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How can this be avoided?

By prioritising:
- emissions reductions over emissions removals
- direct emissions removals under one's own control over offsets

In other words, aiming to limit the reliance on removals and offsets makes #NetZero as rigorous as possible.

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A key part of setting rigorous #NetZero targets is to make clear how a target is fair and adequate.

What does this mean?

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Anyone setting a #NetZero target generally assumes, and often claims, that it will meet the global #ParisAgreement goal. This assumes what a fair contribution would be & what others should contribute.

Ethical judgments are unavoidable, even if unvoiced

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#NetZero targets should clarify why they consider their targets to be fair.

Key questions to ask are:
- would the world still hit #NetZero and meet the #ParisAgreement if everyone applied your fairness logic?
- would it be fair to apply the same logic to all countries?

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Finally, #NetZero targets are benchmarks on a longer global journey and in the long-term we also need to consider going beyond and reach global net-negative emissions.

This would further accelerate the reversal of global warming (see figure below).

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Possibilities to reduce and remove emissions are not distributed equally across the globe. For some countries or sectors, it will be easy to reach #NetZero emissions, for others it still looks daunting at present.

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Countries that have the possibility to do so, should aim to go beyond #NetZero and aim for net negative CO2 and greenhouse gas emissions - not as a courtesy but as a necessity to reach net zero emissions and climate change mitigation globally.

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For more, read our piece @nature,
co-authored with @Oliver_Geden, @CowieAnnette and @ReisingerAndy

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nature.com/articles/d4158…