A lot of political discourse about dealing with the climate emergency lately, including that surrounding the COP26 in Glasgow in November of this year, centers on promises of 'net-zero' emissions by 2050. There are many problems with this, and one of the most glaring is that this target fails to take into account one of the fundamental characteristics of science: cautious conclusions. The recommended greenhouse gas reductions targets in the 2018 and 2021 IPCC reports (to give us a 66% chance of staying at a 'safe' level of heating) are the absolute bare minimum of what humanity should be aiming for, because they don't include things that cannot be reliably modeled or supported by the evidence, yet. It does not mean that the science is wrong, it just means that it takes time to do it. The following is a summary of why we must try much much harder to get to zero (NOT net-zero) emissions as soon as possible.
1) NEAR-TERM POSITIVE WARMING FEEDBACKS NOT INCLUDED. The IPCC recommendations for avoiding the ‘worst’ impacts of climate disruption do not include the onset of near-term positive warming feedbacks in the climate system that would already commit us to a further 1.1°C global average surface air temperature rise above pre-industrial levels (Romm, 2017):
· 0.83°C from the permafrost melt-methane feedback
· 0.28°C from phytoplankton die-off due to ocean acidification, so less dimethylsulfide (DMS) is produced, which is a cloud-condensation nucleus, so fewer clouds are formed which results in lower atmospheric albedo and thus higher average surface air temperature.
2) AEROSOL MASKING OF TEMPERATURE RISE IS NOT INCLUDED. The IPCC recommendations do not include allowances for ‘global dimming’ (Xu et al., 2018), the masking of human-caused global average surface air temperature rise by particulate air pollution from the combustion of fossil fuels and burning of forests (the particles reflect solar radiation back out into space). It is estimated that once fossil fuel burning stops, we will experience a 0.3°C to 0.7°C additional rise in surface air temperature, depending on location (Salzmann, 2016).
3) IPCC PREDICTIONS FOR NEAR-TERM WARMING ARE AN UNDERESTIMATE. Greenhouse gas emissions are still rising, faster than the rate used by the IPCC in its October 2018 report to model near-term surface air temperature warming. This will cause temperatures to rise between 0.25°C and 0.32°C every decade, instead of the 0.2°C used by the IPCC (Xu et al., 2018).
4) RAPID AND IRREVERSIBLE CLIMATE BREAKDOWN IS STILL CONTROLLABLE IF WE ACT QUICKLY. We are close to passing several ‘Tipping Points’ in Earth’s climate system that would result in the onset of series of chain reactions that accelerate and exacerbate the warming caused by human activity (Hansen et al., 2008). These positive warming feedbacks in the climate system have caused abrupt and irreversible climate change in Earth’s past, and they will happen again if certain atmospheric CO2 and temperature thresholds are passed. Even though uncertainty exists about when precisely certain tipping points could be passed, the risk of passing them is far too great to take the chance (Lenton et al., 2019), as they would result in things like:
· collapse of the West Antarctic ice sheet (centuries to millennia timescales) +sea level rise (SLR) of 3m
· collapse of the Wilkes Basin in East Antarctica (100+ years) + SLR of 3m – 4m
· the tipping point for the entire Greenland ice sheet passed by 2030; resulting 7m SLR (1000+ years)
*What is key here is that the rate of melting depends on the magnitude of warming above the tipping point. The timescale of these events is still controllable. Ex: ~10,000 years at 1.5°C vs. ~1,000 years at 2°C (Lenton et al., 2019).
· Amazon rainforest and northern Boreal forest dieback would equal another 90 Gt CO2 and 110 Gt CO2 emitted into the atmosphere through forest fires and loss of carbon sinks. Our global annual CO2 emissions today are about 40 Gt CO2. This means that our remaining IPCC carbon ‘budget’ could already be used up (Steffen, 2018).
5) NO ACCOUNTING FOR CLIMATE JUSTICE. The IPCC target of a 45% reduction of global emissions by 2030 from 2010 levels does not take into account climate justice- the fact that rich countries are more responsible for historical emissions and more capable of reducing those emissions quickly than developing countries.
6) OVER-RELIANCE ON FUTURE TECHNOLOGY THAT BARELY EXISTS, AND HAS ITS OWN PROBLEMS. The IPCC scenarios for achieving the target of 1.5°C all include a peak of CO2 emissions globally in 2020, and a substantial reliance on the ‘scaling up’ of costly atmospheric CO2- removal technology. This is very unlikely to happen. Presently, carbon capture & storage (CCS) removes 40 million tonnes of CO2 globally, annually at a minimum cost of ~$100 US/tonne (IEA, 2021). By comparison, Canada’s annual emissions in 2019 were 730 million tonnes, and global emissions in 2018 reached 41.5 billion tonnes of CO2 (Envir. Canada, 2021). BECCS (bio-energy CCS), what the IPCC recommends, is even less developed and has serious implications for biodiversity and ecosystem maintenance. Researchers have also found that BECCS could result in the addition of CO2 into the atmosphere from the land, and that protecting and expanding terrestrial ecosystems is more effective (Harper et al., 2018).
Intergovernmental Panel on Climate Change. Global Warming of 1.5 °C (IPCC, 2018).
Harper, A.B., Powell, T., Cox, P.M. et al. Land-use emissions play a critical role in land-based mitigation for Paris climate targets. Nat Commun 9, 2938 (2018) doi:10.1038/s41467-018-05340-z
Lenton, T.M., Rockstrom, J., Gaffney, O., Rahmstorf, S., Richardson, K., Steffen, W., & Schellnhuber, J., 2019. Climate tipping points- too risky to bet against. Nature 575, 592-595. doi: 10.1038/d41586-019-03595-0
Romm, Joseph J. 2016. Climate change: what everyone needs to know. http://www.AUT.eblib.com.au/EBLWeb/patron/?target=patron&extendedid=P_4083293_0.
Salzmann, M. Sci. Adv. 2, e1501572 (2016).
Steffen, W. et al. Proc. Natl Acad. Sci. USA 115, 8252–8259 (2018).