Twenty years ago back in 1998 an article was published in Nature in which climate scientists presented data that confirmed that the observed warming was unprecedented in at least six centuries…
Global-scale temperature patterns and climate forcing over the past six centuries
This year those same scientists have published an article in Nature that admits that the 1998 article was quite wrong.
That’s a cue for a climate denialist to pop up with “Michael Mann admits he was wrong, therefore human-caused climate change is a hoax“. Ah but hang on, let’s take a quick peek at the 2018 study.
Reconciling divergent trends and millennial variations in Holocene temperatures
…Here we show that temperatures reconstructed from sub-fossil pollen from 642 sites across North America and Europe closely match simulations, and that long-term warming, not cooling, defined the Holocene until around 2,000 years ago …
…amplified warming in recent decades increased temperatures above the mean of any century during the past 11,000 years.
So there you go then. It’s not just warming that is unprecedented over the last six centuries, but warming that is unprecedented in at least eleven millennia.
But Science is always changing, how can we have any confidence in it?
This very much comes down to asking the question “How do we know what we know?”.
OK, let’s very briefly cover a few quick basics.
Science is not simply a body of information, instead it is a process, a methodology, for working out what is and is not wrong. To keep it really very simple, it works like this. We make observations. We then form an idea to explain those observations. We then test the idea to see if it is not wrong. If the test fails, then the idea is wrong. No matter how profound the idea is, or how beautiful it might be, regardless of who proclaimed it, if the test fails, it’s wrong and we need a better idea.
Never Right – Just not wrong
Another related key point here is that conclusions are never right, they are simply not wrong. In other words we hold conclusions provisionally. If better more subtle observations are made then we may need a better more refined explanation.
Newtonian mechanics is perhaps an ideal example. Newton’s algorithms work well, and still do. You can calculate orbits quite successfully using his maths. As we then built better ways of measuring things, it was clear that what we had was incomplete and that there was something more subtle going on. We needed a better idea and so General Relativity has emerged to handle the more subtle cases at the observational extremes.
Back to the Climate Change example
The 1998 nature article is in reality still correct. The observed warming is unprecedented in at least six centuries. That is still true.
The 2018 Nature article makes use of better observations because we now have smarter ways of looking further back. In order to work out what the climate has been like over the last 11,000 years they used fossil pollen from 642 sites across North America and Europe. To then test this they ran climate models and compared the results – they matched.
With a new way of making observations that look further back in time the 2018 paper is now able to make the robust evidence-based conclusion that the observed warming is unprecedented in at least eleven millennia.
If in another 20 years somebody comes up with a new idea for looking even further back, then that “at least” number will be once again revised, and so the boundary of our understanding will have expanded a little bit further.
Climate Denialism
A simplistic rejection of tested ideas that explain the observations does not cut it, you need to come up with an even better explanation, one that can be tested. So far there is nothing on offer, and until there is, the most honest best possible evidence-based conclusion is that our greenhouse gas emissions are warming the planet at an unprecedented rate, and that if we do not address this, then we face the certainty of catastrophic change.