Foresight 13. Rapid climate change

Background

The rise in temperature associated with anthropogenic climate change does not seem to elicit a great deal of concern amongst the average citizen. Possibly this is because a person born 40 years ago would have experienced an average rise of + 0.7°C; barely noticeable given the average daily variation of ~ ± 10°C and seasonal variation of ~± 20°C. While the science has broadly been accepted, the urgency expressed by most scientists has produced only modest overall action. Here we consider what happens if co-ordinated action on climate change does not eventuate and the possibility that the rate of change is more variable or more extreme than most predictions.

Scenario

There are two scenarios that could see this relatively slow rise of 0.17°C decade-1 become more extreme. The first scenario is that the human population continues to rise and so does fossil fuel use. This possibility was simulated by the IPCC scenario RCP8.5.  Note current emissions are tracking at, or close to, this trajectory.  Also the IPCC model simulations that do not include climate –carbon feedbacks that have been shown to have a positive feedback on climate change.

Over the next 100 years, under the RCP8.5 scenario, the Arctic Ocean is up 9 to 13°C, continents are +3° at the coast and +6° inland, on average.  However, this warming is not occurring in isolation e.g. the oceans become more acidic, and sea levels continue to rise. The implications for water and food supply (both agriculture and fisheries), international stability and economic development are largely unknown but likely to be dire.

The second scenario is based on the empirical evidence that the rate of temperature increase is really highly variable.  We have recently seen the “pause” where modest changes to ocean circulation led to a ~5 year decline in the rate of warming (Meehl et al 2011)  This led some to claim that climate change was a hoax, or even over.  Well what about a jump in the rate of warming?  The best available record (above; NASA) shows periodic rapid rises with the strongest in ~ 1940 and 2017 (Friedrich et al. 2016). The mechanisms for this nonlinear variability are so poorly understood that we cannot predict them.

Both scenarios outlined above are much worse than the average scenario but they are reasonable expectations given the available data and existing IPPC models.  They are, however, not the most extreme predictions supported by both models and data. Some possible responses like the permafrost-methane positive feedback loop (Schuur et al. 2015) or the growing ice free Arctic (Pistone et al., 2014) have potential for positive feedback on global warming. Consider the climate of northwest Europe. For many thousands of years it has enjoyed a climate ~ 5°C above those found in other locations at the same latitude.  The explanation has been the Gulf Stream bringing heat northward. Recent observations suggest the fresher water from the increase in melting polar ice is blocking this flow and the subpolar North Atlantic is cooling very quickly (Sgubin et al., 2017). Of course the heat will go somewhere, we just don’t know where. This is just one example of the possible disruptions to our climate system with a range of others also predicted by models (Drijfhout et al., 2015).

Responses by nations to climate change should be expected to vary. 

For example, some high latitude nations may benefit from global warming while in low latitude and low altitude nations the negative consequences are likely to be extreme. Some nations may increase their efforts to reduce CO2 others may decide to put their nation first. Mass emigration, i.e. climate refugees, should be anticipated from the worst affected regions. Some nations may resort to large scale, and untested efforts to mitigate; possibly by injecting sulphur aerosols into the atmosphere. Australia will be a net loser with more droughts, fires, a reduced capacity to produce food, and reduced regional security. Perhaps the biggest unknown is how well societies will hold up as future prospects deteriorate potentially pushing some nations to respond aggressively.

Indicators: How would we know this is starting to happen?

  1. Global mean temperatures exceed 2C from the pre-industrial – i.e. exceed the Paris Agreement (COP21)
  2. Loss of coral reefs – more than 80% of coral reefs impacted annually
  3. Sustained decrease in food production impacting long-term food security at the regional/global scale
  4. Abandonment of coastal development due to prohibitive costs (e.g. insurance) – 80% major coastal cities impacted
  5. Permanent migration of climate refugees – larger than 50% of the population from individual countries e.g. the Pacific

Scoring of indicators

Project team only – “score” this scenario (requires login): Click to continue.

 

Additional reading

Drijfhout, S., Bathiany, S., Beaulieu, C., Brovkin, V., Claussen, M., Huntingford, C., Scheffer,M., Sgubin, G., Swingedouw, D., (2015) Catalogue of abrupt shifts in Intergovernmental Panel on Climate Change climate models. PNAS Plus – Physical Sciences – Earth, Atmospheric, and Planetary Sciences 2015 112 (43) E5777-E5786; doi:10.1073/pnas.1511451112.

Friedrich, T., Timmermann, A., Tigchelaar, M., Timm, O.E., Ganopolski, A., 2016. Nonlinear climate sensitivity and its implications for future greenhouse warming. Science Advances 2(11):e1501923 DOI: 10.1126/sciadv.1501923

Meehl, Gerald A.; Julie M. Arblaster; John T. Fasullo; Aixue Hu; Kevin E. Trenberth (2011). “Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods” (PDF). Nature Climate Change. 1: 360–364. doi:10.1038/nclimate1229

NASA Goddard Institute for Space Studies – http://data.giss.nasa.gov/gistemp/graphs/, Public Domain, https://commons.wikimedia.org/w/index.php?curid=24363898

Pistone, K., I. Eisenman, and V. Ramanathan (2014). Observational determination of albedo decrease caused by vanishing Arctic sea ice PNAS 2014 111 (9) 3322-3326; doi:10.1073/pnas.1318201111

Riahi, K., Rao, S., Krey, V. et al. Climatic Change (2011) 109: 33. doi:10.1007/s10584-011-0149-y

Schuur, E. A. G., McGuire, A. D., Schadel, C., Grosse, G., Harden, J. W., Hayes, D. J., … Vonk, J. E. (2015). Climate change and the permafrost carbon feedback. Nature, 520(7546), 171–179. Retrieved from http://dx.doi.org/10.1038/nature14338

Sgubin, G., Swingedouw, D., Drijfhout, S., Mary, Y., & Bennabi, A. (2017). Abrupt cooling over the North Atlantic in modern climate models. Retrieved from http://dx.doi.org/10.1038/ncomms14375