16 May 2019

PhD research

Strategies for reducing non-carbon dioxide emissions

Carbon dioxide is not the only emission that must be reduced in order to meet global climate targets. Around a quarter of emissions come from other sources, including methane, nitrous oxide, fluorinated gases and various aerosols. So what are attractive strategies for integrating the reduction of non-CO2 emissions into long term climate policy?

There’s a lot of talk about carbon dioxide. But what about the other emissions? Nitrous oxide is produced during various processes including wastewater management. Human activities emitting methane include livestock farming and leaks from oil and natural gas systems. And fluorinated gases are used as substitutes for ozone-depleting substances (e.g. as refrigerants) and are emitted through a variety of industrial processes such as aluminum and semiconductor manufacturing.

Cattle are a large source of methane emissions. Image: Cally Lawson

There are many possible low cost mitigation strategies to reduce non-CO2 emissions. Mathijs Harmsen is researcher at the Netherlands Environmental Assessment Agency (PBL) and PhD candidate at the Copernicus Institute of Sustainable Development, Utrecht University. In his PhD thesis he investigated how such strategies could reinforce climate policy, and contribute to the goals set out in global climate agreements.

Reduction of emissions with short atmospheric lifetime has advantageous short term effects

Using multimodel comparisons including PBL’s IMAGE model, Harmsen’s research suggests that a strong focus on non-CO2 emissions with a short atmospheric lifetime would be a good short term solution to global temperature increases, resulting in a marked reduction in global temperatures. These emissions include methane, HFCs and soot (or ‘black carbon’). 

However, in an ambitious future climate scenario (like reaching the goals set out in the Paris Agreement), this effect would disappear towards the end of the century. With atmospheric levels of non-CO2 greenhouse gases greatly reduced, the mitigation focus would have to shift back to carbon dioxide emissions.

Image: Olga Oginskaya

Added health benefits

Timely reduction of non-CO2 emissions will also offer permanent global health benefits. Improved air quality from combining climate and air quality policy would avoid an estimated 11 million deaths worldwide between now and 2030.

Although a cost-effective measure with considerable health benefits, black carbon emission reduction is a less suitable climate policy measure. It likely leads to negligible or even negative climate benefits.

Livestock farming a major challenge

Harmsen’s research suggests it is not possible to bring non-CO2 emissions down to zero. The biggest challenge is posed by the methane produced by digestion in cattle and sheep, with emissions linked to continued large scale intensive livestock farming.

GWP an efficient mechanism in climate policy

There is much of criticism of the current level of ambition in climate policy. It is generally understood to be far from sufficient to reach the stringent long-term targets as set during the Paris climate accords. Harmsen’s thesis shows that one mechanism used today in climate policy works quite well, namely the Global Warming Potential (GWP).

Mathijs Harmsen will defend his PhD thesis at 11am on Friday 21st June at the Utrecht University Hall.

Further reading

Harmsen, J.H.M., Nayak, D., Van Vuuren, D.P., Lucas, P., Stehfest, E., Nielsen, J., Höglund Isaksson, J. (in press) Long-term emission reduction potential of non-CO2 greenhouse gases, Environmental Science & Policy

Harmsen, J.H.M., Fricko, O., Hilaire, J., Vuuren, D.P.v., Drouet, L., Durand-Lasserve, O., Fujimori, S., Keramidas, K., Luderer, G., Reis, L.A., Riahi, K., Sano, F., Smith, S.J. (in press) Taking some heat off the NDCs? The limited potential of additional short-lived climate forcers’ mitigation. Climatic Change

Harmsen, J.H.M., Vuuren, D.P.v., Bodirsky, B.L., Chateau, J., Durand-Lasserve, O., Drouet, L., Fricko, O., Fujimori, S., Gernaat, D.E.H.J., Hanaoka, T., Hilaire, J., Keramidas, K., Luderer, G., Moura, M.C.P., Sano, F., Smith, S.J., Wada, K. (in press) The role of methane in future climate strategies: Mitigation potentials and climate impacts. Climatic Change

Harmsen, J.H.M., Van den Berg, M., Luderer, G., Marcucci, A., Strefler, J., Vuuren, D.P.V. (2016) How climate metrics affect global mitigation strategies and costs: a multi-model study. Climatic Change 136, 203–216. doi.org/10.1007/s10584-016-1603-7

Harmsen, J.H.M., Vuuren, D.P.v., Van den Berg, M., Hof, A., Hope, C., Krey, V., Lamarque, J.-F., Marcucci, A., Shindell, D.T., Schaeffer, M. (2015) How well do integrated assessment models represent non-CO2 radiative forcing? Climatic Change 133, 565–582. doi.org/10.1007/s10584-015-1485-0