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.