Climate Science Myths And Misconceptions – Post #5 On Climate Predictions and Projections

In the 2007 post

Global Warming and Forecasts of Climate Change

posted by Olive Heffernan on behalf of Kevin Trenberth

Kevin wrote [emphasis added] as part of his weblog post

Given that human induced climate change is with us, a looming challenge is to predict just what the climate will be. To date, there are no such predictions although the projections given by the Intergovernmental Panel on Climate Change (IPCC) are often treated as such. The distinction is important. A paper presented at the International Forecasting Symposium in New York City in late June 2007 by J. Scott Armstrong and K. C. Green is highly critical of IPCC procedures and “forecasts” for not being based on “evidence based” procedures as outlined in an earlier 2001 book of his. It is true that IPCC does not refer to Armstrong’s work as it has dubious relevance.

In fact IPCC does not do forecasts, as explained in my earlier post. The IPCC instead proffers “what if” projections of future climate that correspond to certain emissions scenarios. Armstrong has evidently read only chapter 8 of the IPCC Working Group I report and has therefore overlooked the fact that the other chapters address many of the things he is critical of…..

The authors should recognize that IPCC does not make forecasts but rather makes projections to guide policy and decision makers. If those changes are considered undesirable, it can create efforts to change that outcome.……… As such it is not a forecast of what will actually happen.

Kevin E. Trenberth
Head of Climate Analysis

This is semantic word twisting. A projection is a prediction assuming a specified forcing [in the case of the IPCC “projections” it is the amount of  anthropogenically caused greenhouse gases and aerosols and emitted into the atmosphere].

Misconception #5:  Climate Projections are different than Climate Predictions

In reality, climate projections, as made by the IPCC, are climate predictions. Since the real world can be monitored for the actual emissions of greenhouse gases and aerosols, that is the actual prediction (projection) that needs to be compared with observations.

This subject was discussed in 2002 in

Pielke Sr., R.A., 2002: Overlooked issues in the U.S. National Climate and IPCC assessments. Climatic Change, 52, 1-11

where I wrote

” In discussions of climate change by policymakers and researchers alike, sensitivity studies and scenarios are often framed as predictions of the state of the future climate (e.g., Climate Impacts LINK 1997, their Figure 5; Atmosphere, 1999). These sensitivity studies and scenarios are often referred to as ‘projections’ by this community with the claim they are ‘plausible scenarios’ and not ‘predictions’. However, one of the definitions of ‘projection’ in Webster’s New World Dictionary (1988) is that a ‘projection’ is ‘a prediction or advance estimate based on known data or observations: extrapolation’.”

 Thus climate projections and climate predictions are the same thing. This means that the climate projections need to be compared with real world data in the same manner as any prediction. Kevin is not correct when he writes that the  “IPCC does not do forecasts“. They most certainly do.

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