Friday, 14 February 2014

Climate change: What they said, and what happened

Some people may have the misconcieved notion that scientists saw some global warming and started looking for something to blame. 

In fact, as these graphs show (taken from the excellent webtool produced by Dr Kevin Cowtan, which can be found at, while there certainly had been warming in the 20th century when the IPCC was formed in 1988, warming over the preceding 30 years was actually pretty slow, and uncertain.

So while looking at this picture might alarm you (you in 1988, that is)

HADCRUT4 data series, 1900 to 1987

your 1988 self might be a lot more sanguine when you saw this

"No warming over the last 30 years", you might say.  "Nothing to worry about here."

So, if a bunch of climate scientists at the IPCC then said "We are certain of the following: there is a natural greenhouse effect...; emissions resulting from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases: CO2, methane, CFCs and nitrous oxide. These increases will enhance the greenhouse effect, resulting on average in an additional warming of the Earth's surface. The main greenhouse gas, water vapour, will increase in response to global warming and further enhance it." would you be worried, or not?

I'd suggest that if, following that statement, you saw temperatures do this

you might come to the conclusion that the climate scientists knew something afterall.

OK, there are major limitations with this post.  You ideally like more than 24 years to extract a meaningful trend, and the trend over the last 24 years has been lower that the trend the IPCC estimated (though it's clearly within the error bars - the said 0.2 deg to 0.5 deg per decade) but I think the message is pretty clear.

If scientists tell you something bad is going to happen if you don't change your behaviour, and you ignore them, and then what they said happens, continuing to ignore them is not rational.

This is also good.

And, finally, has global temperature rise slowed since 1998?  You might be surprised to see the answer.

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