The only redeeming thing about long plane rides is the
chance to catch up on reading and movies. Alas, my flight to Japan had no
movies, and it was only eight hours, so I didn’t have time to finish reading
Sol’s last G-FEED post.
But I was able to catch up on various papers I’ve been
meaning to read, including a recent collection of short papers that Nature
Climate Change put together related to the recent hiatus, or pause, in global
warming since 1998. As readers of this blog will surely know, a lot of
attention has been given to the lack of significant warming trend since 1998,
aka “the pause”. (Not to be confused with an "awkward pause.”) I’ve normally
viewed the pause as much ado about nothing, or at least very little, since
you’d expect variation around the long-term trend and models have consistently
shown a non-small probability for flat trends over a 10 or even 15 year period,
even as longer-term trends are positive. So having not followed the
conversation too closely, I was interested to catch up with these papers. Here are a couple of interesting lessons:
First, Gavin Schmidt and co-authors explain how a lot of the
disparity between expected and observed trends is not necessarily due to
natural variability, but instead to the fact that short-term forcings since
2000 are not what models had assumed. As they say “the influence of volcanic
eruptions, aerosols in the atmosphere and solar activity all took unexpected
turns over the 2000s. The climate model simulations, effectively, were run with
the assumption that conditions were broadly going to continue along established
trajectories.” But instead, all of these factors deviated in a way that caused
climate to be cooler. In other words, the models weren’t the problem, but the
assumptions used to force them were. They also emphasize that none of these
factors should be expected to continue to cool climate much, and predict that “ENSO
will eventually move back into a positive phase and the simultaneous
coincidence of multiple cooling effects will cease. Further warming is very
likely to be the result.“
Second, an interesting piece led by Sonia Seneviratne shows
that trends in daytime extreme temperatures over land, arguably a more relevant
measure in terms of climate impacts, haven’t slowed down at all (red line in figure below). Essentially,
they object to the entire notion of a “pause.”
All of these papers on the pause also reminded me of a great book I recently
finished – “Thinking Fast and Slow” by Daniel Kahneman. He talks a lot about
loss aversion - how humans tend to dislike losses about twice as much as they
like gains - and how even small losses
can be very annoying. One consequence is that for an identical putt,
professional golfers will tend to try harder and make it more often if it’s for
par (to avoid loss) than if for birdie (to get a gain). I’m sure that explains
why I always miss birdie putts! Another consequence is that people are usually
risk averse when it comes to gains (i.e. prefer to take $100 than flip a coin
for a 50/50 chance of winning $200), but risk seeking when it comes to losses
(i.e. prefer to flip a coin for a 50/50 chance of losing $200 rather than give
$100, because $100 hurts almost as much as $200). This is compounded by another
tendency humans have - to way overweight events that have low probability in
their decisions. So even if there’s a very small chance of a “no loss” outcome,
people will tend to take a chance hoping that outcome will happen, because it
will be so much more pleasant than even a small loss, and because they think
it’s more likely than it actually is.
All this seems like a pretty good description of many people's reaction to climate
change. It might be a small deal or it could be really bad. We could maybe
guarantee a small loss if we paid for a lot of mitigation and adaptation. Or we
can roll the dice and hope for the best. After reading his book, it hardly
seems surprising that people would opt for the latter. They do in all walks of
life, and are worse off because of it. It is also hardly surprising that people
will latch onto anything that seemingly justifies overweighting the probability
of no loss, such as the pause. I'm not saying that either are the appropriate response to the problem, especially by institutions that should be less prone to these behavioral quirks, but it may help to partly explain people's fascination with the pause.
The pause has also highlighted for me how wide the full
distribution of potential trends over a 10 year period is, and that includes
the potential for very rapid warming. What will happen if warming rates in the
next 10 years are at the other end of the distribution – other than, of course,
people asking climate scientists why their models are too conservative? It’s a
question I’ve been looking at with Claudia Tebaldi in terms of crop
implications, which hopefully will be a paper in the not-so-distant future to
blog about.
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