Flirting with Dangerous Anthropogenic Climate Change – are we closer than we think?

Jeff Obbard, Ph.D.
Professor of Environmental Science

Twenty-five years ago, at the 1992 United Nations Framework Convention on Climate Change (UNFCCC) a bold and prophetic statement was issued i.e. that humanity must achieve “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system”1. The UNFCCC entered into force on 21 March 1994 with near-universal membership, where 197 countries ratified and become parties to the Convention.

In its Fifth Assessment Report (AR5) in 2013-2014), the Intergovernmental Panel on Climate Change (IPCC) stated that evidence for the warming of the Earth’s atmosphere and ocean system is now unequivocal, where it is extremely likely that human influence has been the dominant cause of observed global warming since 1950 due to atmospheric greenhouse gas (GHG) emissions2.

Although the term ‘dangerous’ was not scientifically defined at the time of the UNFCC, it has now become synonymous with a global average temperature increase of no more than 2 0C relative to a pre-industrial baseline. This climate goal represents a ‘guardrail’ of average temperature increase that will supposedly maintain the relatively stable climate conditions that human civilisation has adapted to over the last 12,000 years since the end of the last ice age and the onset of the Holocene interglacial period. The 2 0C limit is intended to minimize some of the worst impacts of climate change, including drought, heat waves, flooding, and sea level rise. In terms of the likelihood of not exceeding the 2 0C limit, Working Group 2 of the IPCC, at the time of the of the 2013-2014 AR5 report, stated that without new policies to mitigate climate change, an increase in global mean temperature by 2100 of 3.7 to 4.8 °C compared to pre-industrial levels can be expected (note these are median values within a range of 2.5 to 7.8 °C when accounting for climate uncertainty)3.

Embraced as an aspirational goal in the Copenhagen Accord at the 15th Conference of Parties (COP 15) in 20094, the 2 0C limit now forms the foundation of the Paris Climate Agreement (PCA)5. On 12 December 2015, at COP 21, the PCA committed the world to “holding the increase

in the global average temperature to well below 2 °C above preindustrial levels, and to pursue efforts to limit the temperature increase to 1.5 °C”. The lower guiderail limit of 1.5 °C is intended to lessen climate impacts even further, and was adopted in response evidence of enhanced global climate sensitivity due to ongoing GHG emissions.

The PCA requires countries that are parties to the UNFCCC to adopt nationally determined contributions (NDCs) to limit GHG emissions in accord with the 2 °C and 1.5 °C climate guiderail limits. Additionally, the agreement aims to strengthen the ability of vulnerable countries to deal with the impacts of climate change, where an appropriate flow of finances and technology to facilitate enhanced capacity building to mitigate and adapt to predicted impacts is planned. The PCA also provides for enhanced transparency of action and support through a robust framework of regulation, auditing and reporting of GHG emission inventories.

Although the PCA is to be commended as a landmark achievement in the world’s attempt to avoid dangerous anthropogenic interference with the climate system, it must also be acknowledged that there is a significant disparity between the scale of GHG reductions actually pledged within the NDCs. According to an evaluation by the International Energy Agency (IEA), the current NDCs will result in temperature increases of up to 2.7 0C by 2100, and above 3 OC thereafter6. In short, the current trajectory of global GHG emissions is not consistent with limiting global warming to below 2 0C, relative to pre-industrial levels – let alone 1.5 0C, and still commits the world to dangerous anthropogenic climate change. This position has been further denigrated by the unilateral decision of the United States of America, the world’s second largest GHG emitter after China, to withdraw from the PCA in June 2017. Continued emissions of greenhouse gases into the 21st century will result in further atmospheric warming, and will therefore risk inducement of long-term change in all components of the global climate, increasing the risk of severe, pervasive and irreversible impacts for both humanity and ecosystems.

With reference to the lower guiderail limit of 1.5 0C, it is worth noting that the average global surface temperature in 2016 was the highest in the period of instrumental measurements, and was 1.24 0C above the 1880-1920 pre-industrial baseline7,8. Although the 2016 temperature was partially boosted by the 2015-16 El Niño, warming in the Arctic is was about 3 °C above average in 2016, and the tropics about 1 °C warmer7. Global average temperatures in 2017 to date have

lessened, but as of end-June, measurements indicate that 2017 is on track to become the second warmest year on the instrumental record9.

In a new publication in July 2017 by the leading climate scientist, James Hansen et al., in the scientific journal, ‘Earth System Dynamics’ it is reported that global warming in the past 50 years has raised average temperatures well above the prior range of the Holocene, and now matches the level of the previous interglacial period i.e. the Eemian period (130,000 to 115,000 years ago) when sea level was 6-9 meters higher than today10. Based on the findings of Hansen et. al, the rate of GHG climate forcing has accelerated markedly in the past several years – a finding that contrasts with the perception that the world has started to mitigate climate change by ratifying the PCA, and which further commits the planet to an ongoing radiative energy imbalance with associated climate impacts.

It is now beyond doubt that the world will have to dramatically accelerate GHG reduction efforts if it wants to meet the goals of the Paris Agreement. But by how much? In the new publication, Hansen et al. examine the level of GHG emission reductions required to achieve temperatures that are compatible with the current post-glacial Holocene period of the Earth’s climate system10. Basically, global warming can now only be held at below the 1.5 °C guiderail limit if rapid reductions of global CO2 emissions begin no later than 2021, by at least 3% per year onwards – and, critically, by assuming there is no net growth in other climate GHG forcings such as methane gas emissions from natural carbon reservoirs including permafrost and/or ocean methane clathrates due to induced positive feedbacks in the climate system. This scale of GHG reduction can be considered as ambitious, but still achievable although the authors emphasize that 1.5 0C of global warming still exceeds Eemian temperatures, and is not an appropriate climate goal (let alone the 2 0C target).

References

1. United Nations Framework Convention on Climate Change. http://unfccc.int/essential_background/convention/items/6036.php. Accessed 06 August 2017.
2. Intergovernmental Panel on Climate Change, Fifth Assessment Report. https://www.ipcc.ch/report/ar5/. Accessed on 06 August 2017.
3. IPCC Working Group II – Impacts, Adaptation, and Vulnerability. http://www.ipcc- wg2.awi.de/index.html. Accessed on 06 August 2017.

4. U.N. Framework Convention on Climate Change. United Nations. 18 December 2009. http://unfccc.int/resource/docs/2009/cop15/eng/l07.pdf. Accessed on 06 August 2017.
5. Paris Climate Agreement. United Nations Treaty Collection. 8 July 2016. https://treaties.un.org/pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XXVII-7- d&chapter=27&clang=_en. Accessed on 06 August 2017.
6. Energy, Climate Change and Environment. International Energy Agency, 2016.http://www.iea.org/publications/freepublications/publication/ECCE2016.pdf. Accessed on 06 August 2017.
7. Global Temperature in 2016. Hansen J., Satoa M., Ruedy R., Schmidt G.A, Lob K., Persin A. Climate Science, Awareness and Solutions (CSAS), Columbia University Earth Institute . http://www.columbia.edu/~mhs119/Temperature/. Accessed on 06 August 2017.
8. Hansen, J., Ruedy R., Sato M., and Lo K., 2010. Global surface temperature change. Rev. Geophys., 48, 1-29.
9. GISTEMP Team, 2017: GISS Surface Temperature Analysis (GISTEMP). NASA Goddard Institute for Space Studies. https://data.giss.nasa.gov/gistemp/. Accessed on 06 August 2017.
10. Hansen J. et. al (July, 2017). Young people’s burden: requirement of negative CO2 emissions. Earth System Dynamics, 8, 577-616, 2017.
11. Energy Technology Perspectives 2017 (ETP 2017). International Energy Agency, June 2017. https://www.iea.org/etp2017/summary/. Accessed on 06 August, 2017.

12. Renewables Global Status Report (2017). Renewable Energy Policy Network for the 21st Century (REN21). http://www.ren21.net/status-of-renewables/global-status-report. Accessed on 06 August 2017.