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