This is a good example of chart junk -- where the visuals overwhelm the data.   The link supporting that chart says:

This image is a comparison of 10 different published reconstructions of mean temperature changes during the last 2000 years. More recent reconstructions are plotted towards the front and in redder colors, older reconstructions appear towards the back and in bluer colors. An instrumental history of temperature is also shown in black. The medieval warm period and little ice age are labeled at roughly the times when they are historically believed to occur, though it is still disputed whether these were truly global or only regional events. The single, unsmoothed annual value for 2004 is also shown for comparison. (Image:Instrumental Temperature Record.png shows how 2004 relates to other recent years).

It is unknown which, if any, of these reconstructions is an accurate representation of climate history; however, these curves are a fair representation of the range of results appearing in the published scientific literature.

So, first of all, it says that this chart may be inaccurate and yet, we're still going to run off and make policy decisions using it!

Second, look at the scale.   Even the black line goes no higher than a 0.4C ( .5 to .7 degrees Fahrenheit ) anomaly.    All of the others fall within statistical range of the Medieval Warm Period.

This chart shows clearly that global warming is naturogenic, not anthrogenic.

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It's hard to extrapolate data from more than 100 years ago, when the records began to be kept. That's why there's uncertainty in the past. However, the range of uncertainty in the past is far below the certainty of the present both in terms of range and directionality: notice how the lines converge and all go up???

Jeez, way to be a troll.

In the Pacific Northwest one finds Douglas-fir trees 600-800 years old at higher elevations than their natural range today.  They date from the medievel warm period.  In Alaska and in some of those Douglas-fir stands are found yellow cedars that are declining or dying because of early soil warming and late frosts.  Many of these trees date from the little ice age.

Douglas-fir expanded its range when things were warmer and yellow cedar when it was colder.

Evidence of past fluctuations and current change is very visible if you know what you are looking at.