Climate Scientists Erring on the Side of Least Drama
by Dana Nuccitelli, via Skeptical Science
A paper recently published in Global Environmental Change by Brysse et al. (2012) examined a number of past predictions made by climate scientists, and found that that they have tended to be too conservative in their projections of the impacts of climate change. The authors thus suggest that climate scientists are biased toward overly cautious estimates, erring on the side of less rather than more alarming predictions, which they call “erring on the side of least drama” (ESLD).
In this paper, Brysse et al. examined research evaluating past climate projections, and considered the pressures which might cause climate scientists to ESLD.
Conservative Climate Projections
While we have recently shown that the Intergovernmental Panel on Climate Change (IPCC) temperature projections have been exceptionally accurate, several other projections in the IPCC reports have been far too conservative.
Sea Level Rise
For example, Rahmstorf (2007) and more recently Rahmstorf et al. (2012) showed that sea level is rising at a rate inconsistent with all but the highest IPCC scenarios (Figure 1). Rahmstorf et al. (2012) concluded,
“The satellite-based linear trend 1993–2011 is 3.2 ± 0.5 mm yr-1, which is 60% faster than the best IPCC estimate of 2.0 mm yr-1 for the same interval.”
Figure 1: Sea level measured by satellite altimeter (red with linear trend line; AVISO datafrom (Centre National d’Etudes Spatiales) and reconstructed from tide gauges (orange, monthly data from Church and White (2011)). Tide gauge data were aligned to give the same mean during 1993–2010 as the altimeter data. The scenarios of the IPCC are again shown in blue (third assessment) and green (fourth assessment); the former have been published starting in the year 1990 and the latter from 2000.
The main reason these sea level rise projections have been too low and that the IPCC almost certainly underestimates future sea level rise is that their models do not include the effects of dynamic ice processes from chunks of ice breaking off into the ocean (“calving”), then melting. The IPCC approach in attempting to account for these processes considers recent contributions to sea level rise from ice sheet melt, then “assume that this contribution will persist unchanged.” This is certainly a conservative approach, and the primary reason their sea level projections have been low.
Arctic Sea Ice Decline
Three years after the IPCC Fourth Assessment Report was drafted, the 2009 Copenhagen Diagnosis examined the latest climate research to effectively update the IPCC report. In addition to confirming the Rahmstorf finding that the IPCC has underestimated sea level rise, the Copenhagen Diagnosis also found that the IPCC has dramatically understimated the decline in Arctic sea ice extent (Figure 2).
Figure 2: Observed vs. IPCC modeled annual minimum Arctic sea ice extent
In 2012, Arctic sea ice melt shattered the previous record low, to levels unseen in millennia, increasing the margin by which IPCC projections have been too conservative.