October 20, 2009

Global Cooling Got You Down? I Have Just the Charts For You

Climate denialism is once again making headlines with the release of a followup book by Freakonomics authors Steven Levitt and Stephen Dubner. They even inscribe "Global Cooling" into the sequel's subtitle. No beating around the bush for those two wacky contrarians.

The global cooling myth has unfortunately gotten new energy from the weather over the past couple of years -- it's been so cool, global warming must be a hoax! But I have two charts from Skeptical Science (an anti-denier site) that put things into perspective. The first is similar to a chart on long-term temperature trends that's often used to dispel the cooling myth. But this one uses moving averages (just like stock market and unemployment charts) which are useful for smoothing out short-term variations. It's mostly government data and pretty hard to ignore.

Globally-averaged annual mean temperature anomalies in degrees Celsius, together with 11-year unweighted moving averages (solid lines). Blue circles from the Hadley Centre (British). Red diamonds from NASA GISS. Green squares from NOAA NCDC. NASA GISS and NOAA NCDC are offset in vertical direction by increments of 0.5°C for visual clarity.

Think about it this way: if that was a stock chart and you bought in 1910 and sold in 2008, you'd be rich! When the market shows us trends like that we cheer (or freak out if it's unemployment). Yet because it's temperatures, we're supposed to ignore all the increase as so much random "noise."

But for me, the companion chart is far more compelling. It turns out that land and atmospheric warming is only one itty bitty part of global warming -- which explains why it's so easy to miss the big picture. The ocean sucks up the vast majority of the heat that all our carbon is trapping -- and it's a lot of heat. The following chart demonstrates this phenomenon in spades. And note that this is purely observational data -- it's simply looking at heat levels in the ocean over the last 50 years and does not involve climate models or carbon levels.

Total Earth Heat Content from 1950 (Murphy 2009). Ocean data taken from Domingues et al 2008. Land + Atmosphere includes the heat absorbed to melt ice.

As Skeptical Science put it:
[R]elatively small exchanges of heat between the atmosphere and ocean can cause significant changes in surface temperature... This internal variation where heat is shuffled around our climate is the reason why surface temperature is such a noisy signal.
And keep in mind the fact that if the ocean starts pumping out its heat at a higher rate (as it does during El Nino years), watch out. Things will heat up in a hurry.

Photo by milan.boers used under a CC license

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