The Intergovernmental Panel on Climate Change (IPCC) often expresses uncertainty in terms of the following confidence levels:

__2020 IPCC Confidence Levels.png

Per the IPCC (2013), here are a few of the “key uncertainties” (reflecting low or very low confidence) regarding the effects of climate change:

  • Global-scale trends in drought

  • Changes in tropical cyclone activity

  • Global-scale trends in cloud cover (as well as cloud-climate feedback effects)

  • Global-scale ocean sub-surface temperature trends and variability

  • Global-scale and regional changes in precipitation levels

  • Regional climate change

  • Global mean sea level rise

A huge uncertainty is how much warmer the planet will actually get over this century. Climate scientists develop different global warming scenarios associated with “Representative Concentration Pathways” (RCPs), which are hypothetical trajectories of greenhouse gas concentrations in the upper atmosphere. Problem is, there are multiple RCPs and multiple warming scenarios for each RCP. Check it out.

__2020 RCP Trajectories and Temp Range in F.png

Per the above chart, the global climate may warm anywhere from less than 2°F to over 8°F by 2100. How about the projected rise in sea level? According to various RCP-based global warming scenarios, sea levels could rise anywhere from less than a foot to around three feet over the next 80 years:

_2019 Global Sea Level Rise and RCPs.png

So, how does one plan for climate change when climate scientists are so uncertain about how the climate will change? Next

References:

Intergovernmental Panel on Climate Change Guidance Notes for Lead Authors of the IPCC Fourth Assessment Report on Addressing Uncertainties (2005) https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-uncertaintyguidancenote-1.pdf

Stocker, T.F., D. Qin, G.-K. Plattner, L.V. Alexander, S.K. Allen, N.L. Bindoff, F.-M. Bréon, J.A. Church, U. Cubasch, S. Emori, P. Forster, P. Friedlingstein, N. Gillett, J.M. Gregory, D.L. Hartmann, E. Jansen, B. Kirtman, R. Knutti, K. Krishna Kumar, P. Lemke, J. Marotzke, V. Masson-Delmotte, G.A. Meehl, I.I. Mokhov, S. Piao, V. Ramaswamy, D. Randall, M. Rhein, M. Rojas, C. Sabine, D. Shindell, L.D. Talley, D.G. Vaughan and S.-P. Xie, 2013: Technical Sum­mary. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assess­ment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.  https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_TS_FINAL.pdf