A little warming goes a long way…

8 05 2013

Another guest post from Mark Cochrane

Putting climate change in perspective can be difficult. People argue back and forth over a

Mark Cochrane

Mark Cochrane

few degrees Celsius but it warmed more than that since you got up this morning. So what is the big deal?

The heating of the planet is not happening evenly, and the importance of the changes are not the same everywhere. A recent paper in Nature Climate Change (Xu et al. 2013 – link for paper) does a good job of explaining the magnitude of the climate change in the Arctic and Boreal regions.

The authors looked at the change in seasonal temperatures (depths of winter to height of summer) and how vegetation photosynthetic capability changed (translation – how much more time for growth the plants have gotten).  Specifically, they used historical temperature data (from CRUTEM4) to compare the climate being experienced by the vegetation across the entire 10 million square miles (26 million square kilometers) of northern vegetated lands for the early 80s, mid-90s and late 2000s.

What they found was that for the Arctic and Boreal regions, 34 -41% showed noticeable increases in growth (green and blue above), 51-62% had no change, and 3-5% had decreased growth. However, before anyone gets on the global warming is good bandwagon consider the following. The vegetation in these regions are experiencing climate conditions that they are not designed by nature to deal with. In short they are out of place.

Just how far off are they from where they should ‘climatically’ be?

“Arctic plant growth during the early-1980s reference period equaled that of lands north of 64 degrees north. Today, just 30 years later, it equals that of lands above 57 degrees north — a reduction in vegetation seasonality of about seven degrees south in latitude,” says co-author Prof. Terry Chapin, Professor Emeritus, University of Alaska, Fairbanks. ” (link)

For those who do not think in degrees of latitude, that is over 480 miles (780km). In other words, the low Arctic is now experiencing seasonal cycles that would have been almost 500 miles to the south just 30 years ago. That’s a lot!

The Arctic is greening at an increasing rate as shrubs and trees invade the tundra but the boreal region is experiencing change at a decelerating rate due to the effects of thawing permafrost, bug kill and fire. The authors also used an ensemble of 17 global climate models with the Business as Usual scenario to estimate how much more change these regions would experience by 2100. The effects would be the equivalent of moving another 20 degrees of latitude south – 1,380 miles (2,200 km).

In terms of temperature seasonality, being at 64 degrees north in 1980 could be like what was 37 degrees latitude at the time by 2100. That’s like moving from Iceland to the middle of the Mediterranean. What do you think it is going to be like in the current Mediterranean by then? See that big brown area in North Africa…

These are just temperature changes. The day length wouldn’t change in the Arctic and soils wouldn’t magically appear in the Boreal region to grow our crops. We are not going to be untouched by these changes. We can’t make this stop but we can still minimize things before we put palm trees in the Arctic. We are out of time for dithering though.




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