Natural Variability, Attribution and Climate Models #10 - More on Droughts
Western USA over 1000+ years
In #1 we saw an example of natural variability in floods in Europe over 500 years. Clearly the large ups and downs prior to the 1900s can’t be explained by “climate change”, i.e. from burning fossil fuels.
If you learnt about climate change via the media then you’ve probably heard very little about natural variability, but it’s at the top of climate scientists’ minds when they look at the past, even if it doesn’t get mentioned much in press releases.
Here’s another example, this time of droughts in the western USA. This is a reconstruction of the pre-instrument period.
The timescale is back to front, with today being on the left, and 1200 years ago being on the right. The top two graphs are the ones of interest:
We see that there has been huge variability in droughts in this region. Lots of climate change before we had “climate change”.
A couple of important points:
For people new to this blog/newsletter, I’m not saying that there is no effect from burning fossil fuels which puts more CO2 into the atmosphere. There is - more CO2 increases the surface temperature of the earth, this is certain (see The Greenhouse Effect).
The fact that past droughts have been much worse than current droughts doesn’t mean that rising temperature isn’t making current droughts worse than they would otherwise have been. That is (removing the double negatives), it’s entirely possible that current droughts are worse due to the increased temperatures from 100 years ago.
This article is just a tiny counterweight to the tsunami of media articles painting every drought, flood and storm as the worst ever in history.
References
ENSO, sun and megadroughts in SW USA during the last 11,000 years, Gonzalo Jiménez-Moreno, R. Scott Anderson & Jacqueline J. Shinker, Earth and Planetary Science Letters 2021
Here's the 6th assessment report of the IPCC making a useful comment on this, p449:
"Furthermore, Williams et al. (2020) used a combination of hydrological modelling and tree-ring reconstructions to show that the period from 2000 to 2018 was the driest 19-year span in south- western North America since the late 1500s.
Nonetheless, tree rings also indicate the presence of prolonged megadroughts in western North America throughout the last millennium that were more severe than 20th and 21st century events (high confidence) (Cook et al., 2004, 2010, 2015).
These were associated with internal variability (Coats et al., 2016; Cook et al., 2016b) and indicate that large-magnitude changes in the water cycle may occur irrespective of anthropogenic influence (see also McKitrick and Christy, 2019)."