Climate Change Attribution

Earth’s climate system is extremely complex, chaotic and not particularly well understood. The factors which have caused climate change over the past millennia continue to cause climate change today and will likely continue to cause climate change in the future do not operate independently, but rather interact with each other over differing timescales to produce the effects we are able to detect and measure.

The consensed climate science community is focused on the anthropogenic factors which it believes cause or contribute to climate change, primarily the increased atmospheric concentrations of CO2 and other greenhouse gases. However, these anthropogenic factors operate against a background of numerous, pre-existing, complex natural factors which also cause or contribute to climate change. Therefore, as complex as detecting climate change might be, attributing climate change to the plethora of natural and anthropogenic causative or contributing factors is far more complex.

Anthropogenic factors are not generally believed to cause hurricanes, typhoons, tornadoes, severe storms, droughts, floods, heat or cold waves, heavy snowfalls, sea level rise, etc. because all these weather events existed prior to the period since ~1950 during which increased atmospheric CO2 concentrations are believed to affect climate. Rather, anthropogenic effects are typically alleged to make these events more frequent or more severe or more damaging.

Since there are no identified climate change effects which demonstrably have anthropogenic factors as their sole cause, there is growing interest in attribution studies intended to identify or estimate the relative impacts of the various natural and anthropogenic factors which contribute to climate change. However, the primary weakness of this approach is its reliance on unverified climate models and undefined climate sensitivities, forcing and feedbacks used as inputs to those models. It is not currently possible to measure or otherwise document anthropogenic impacts.

Attribution has been an issue recently regarding the extent to which anthropogenic climate change might have worsened the effects of Hurricanes Sandy, Harvey, Irma and Maria. Interestingly, no such issues were raised regarding the 12-year period with no landfalling strong hurricanes. Arguably, a 12-year period with no landfalling major hurricanes is at least as unusual as a year (2017) with 3 major landfalling hurricanes.

The weakness of the current state of attribution studies is highlighted by the range of estimates of anthropogenic impacts on various events studied. World Weather Attribution scientists have estimated that climate change made Hurricane Harvey 3 times more likely and its rainfalls 15% more intense. Other sources estimate that tropical cyclones might be 2-11% more intense by 2100.

Attribution studies attempt to evaluate the likelihood that anthropogenic climate change might impact the frequency or severity of natural weather events; and, the likely magnitude of the impacts. However, these studies are severely limited by their reliance on unverified climate models for their estimates. This again emphasizes the importance of improving and verifying climate models, to assure that they are actually modeling the real climate. Estimates of the potential impacts of anthropogenic effects on weather events in a make believe climate are worse than useless.