Notes to Select Committee Considering the Zero Carbon Bill

Presentation on 26 August, 2019. The full submission is here.


1. Climate change and sea level rising is one of the greatest challenges the world faces.

2. New Zealand should play its part in the world’s effort to restrain greenhouse gas emissions.

3. I broadly endorse the intention of the Climate Change Response (Zero Carbon) Amendment Bill.

4. My recommendation is that all specific references to biogenic methane emissions should be removed and that methane should be treated on the same basis as all the other greenhouse gases.


5. Compared to carbon dioxide, methane is an especially burdensome greenhouse gas.

6. On the other hand, compared to most other greenhouse gases, it has a short half life – between 10 and 12 years. It is analytically important to distinguish between gross and net emissions in a way that is not as important for other  greenhouse gases. 

7. In the past New Zealand generated a substantial methane cloud, mainly from the past  expansion of its livestock industry.

8. However, the methane cloud is no longer increasing. That is because gross annual methane emissions have been (roughly) stagnant and are being offset by the breakdown of methane in the existing cloud. Thus while gross emissions are substantial, the net emissions are near enough to zero. 

9.Methane from the livestock industry is not adding to global warming as its current emissions are being offset by reductions in the effect from its past emissions.

The Proposed Legislation

10. The proposed legislation treats biogenic methane differently from other  greenhouse gases including thermogenic methane. It is not clear why it should be separated out.

11. In particular it is not obvious why biogenic methane, which is treated in gross terms, should be distinguished from thermogenic methane which is treated in net terms.

12. Nor is it obvious why emissions from fossil fuels may be netted off against carbon sinks (such as trees), while biogenic methane may not be netted off, especially against previous methane emissions.

14. Alternately it is not obvious why we should ignore the past emissions from fossil fuels which contribute to global warming but give the livestock industry no credit for the fact that its past contribution to global warming emissions is diminishing.

15. A further weakness of the bill is that it quantifies in statute precise targets for gross biogenic greenhouse emission based on experts’ best guesses about the technological possibilities of methane reduction thirty years on. That is bad law. (Also, what happens if they have underestimated the possible reductions? )

16. It is proposed that the new law treat biogenic methane the same as other greenhouse gases by removing all reference to it. Section 5O of the bill would now read

(1) The target for emissions reduction (the 2050 target) requires that-

(a) net emissions of greenhouse gases in a calendar year, are zero by the calendar year beginning on 1 January 2050 and for each subsequent calendar year;

The Effect of the Proposed Change

17 The proposed change would remove the anomalies and inconsistencies in the bill as it now stands.

18. It does not affect the intention of the bill, nor add to the challenges the proposed commission faces.

19. It does not reduce the urgency of the need to reduce gross biogenic methane  emissions nor of all greenhouse gas emissions.

In summary the references to methane in the bill are unnecessary, discriminatory, divisive and bad law.