Thursday, April 23, 2015

The view from Greenland's highest peak

It's amusing to me whenever a science denier cites the ice cores in Greenland as "proof" that global warming either a) isn't happening or b) isn't a big deal. It's a horrible argument for deniers to make. Here's why.

First, we're talking about ice cores taken from one location in Greenland. Not only is it one single location, but it just happens to be Greenland's highest point (10,660 feet/3,249 meters above sea level) and near the center of the continental glacier that covers Greenland. Guess what? It's going to be cold up there, just from the elevation alone, to say nothing of how all that ice affects the local temperature. Location matters. It's amusing that the same deniers who claim urban heat island when trying to explain away any warming trends seem to forget that when faced with factors that would decrease the rate of local temperature change.

Second, when we talk about global warming, we mean the entire planet, which is far larger than one single spot in the center of Greenland. While interesting and informative (hey, we need all the data we can get!), it ultimately says little to nothing about whether or not the entire planet is warming up and at what rate, just as readings from a thermometer in your backyard says little the change in the global average.

Third and most amusing is this: The research that at least one denier (and WUWT) tried to cite as proof that modern temperatures have yet to exceed historical temperatures (Kobashi et al. 2011) is...wait for it...a hockey stick paper! Take a look at Figure 1 from that paper:

Figure 1 from Kobashi et al. 2011

Now what does that show? Well, the top shows the past 170 years, the middle shows the last 1,110 years, and the bottom graph shows the last 4,010 years. What do you see? WUWT and other deniers focused on the fact that reconstructed temperatures were higher than the 2001-2010 average at multiple points in the past. But take a good look at the overall trend in the data, especially relative to the 2001-2010 average. What do you see? Yep. A gradual cooling trend, with a sudden reversal in the last 100 years. The same story found by Marcott et al., PAGES 2k, and other hockey stick papers.  Oops. I wonder if anyone at WUWT ever noticed that.

In short, WUWT is correct—the reconstruction does show that one location at the top of Greenland was warmer in the past. But it's a matter of trying so hard to win the battle that they end up losing the war by ignoring that the same study corroborates the warming of the past century and show that same cooling-until-the-20th-century pattern as many other studies.

Tuesday, April 21, 2015

Using NOAA's Climate-at-a-glance widget to fact-check James Taylor

Okay, I'm back.  Sorry for the lengthy gap between posts but work and losing my laptop intervened.  Now to get back in the saddle.

A reader by the pen name of cosmicomic asked several questions on my last post concerning James Taylor's claims about winter-time cooling in the US.  Since NOAA's climate-at-a-glance widget didn't work properly for him, I thought I'd post a video of what one should see as well as expound on the bogus method Taylor used.  Specifically, I'll examine Taylor claim that winters in the US have cooled, with the cooling trend dating back to 1930.

First, a very brief tutorial by yours truly on using NOAA's widget and what you should see when you do:


Now, Taylor's claim that US winters have cooled since 1930 is already in trouble. The simple linear regression model done by the widget shows that US winters have warmed by an average of +0.18ºF/decade since 1930. ARMA time series regression shows that the warming trend since 1930 is statistically significant (p = 0.03015). Dropping 2015 (since Taylor was writing about the 1930-2014 time period) only lowers the trend since 1930 to 0.17ºF/decade (p = 0.041), still a statistically significant increase.

So, what did Taylor do to come up with his "cooling since 1930" claim? Simple. He played "connect the dots." It's really easy to do (David Rose of the British tabloid The Daily Mail is a master of it). Just find a year that was warmer than the end year (in this case 2014), draw a line connecting that year to the end year, and claim "Cooling since _____!" In Taylor's case, just connect 1930 to 2014.

Voila! Instant cooling trend and you don't even have to bother with all that pesky time-series analysis, ARMA regression, and the like. All you need is what you learned in kindergarten. Of course that only works to climate deniers' favor  if the end point is lower than the starting point. And if you ignore everything except the beginning and end points. And if you ignore pretty much everything a beginning stats student learns in the first semester. get the idea.

In short, Taylor's "method" is utterly bogus. But he won't let such a trifling detail stop him.